Electro Voice 250 User Manual

Nexus

1250 /1252

High Performance SCADA Monitor

Installation & Operation Manual

Version 1.25

November 13, 2006

Doc # E107706 V1.25

Electro Industries/GaugeTech

1800 Shames Drive

Westbury, New York 11590

Tel: 516-334-0870 ꢀ Fax: 516-338-4741

[email protected] ꢀ www.electroind.com

“The Leader in Web Accessed Power Monitoring and Control”

Nexus 1250/1252

Installation and Operation Manual

Revision 1.25

Published by:

Electro Industries/GaugeTech

1800 Shames Drive

Westbury, NY 11590

publication may be reproduced or

transmitted in any form or by any

means, electronic or mechanical,

including photocopying, recording,

or information storage or retrieval

systems or any future forms of

duplication, for any purpose other

than the purchaser’s use, without

the expressed written permission of

Electro Industries/GaugeTech.

Electro Industries/GaugeTech

Printed in the United States of

America.

Electro Industries/GaugeTech Doc # E107706 V1.25

Customer Service and Support

Customer support is available 9:00 am to 4:30 pm, eastern standard time, Monday through Friday.

Please have the model, serial number and a detailed problem description available. If the problem

concerns a particular reading, please have all meter readings available. When returning any merchandise

to EIG, a return materials authorization number is required. For customer or technical assistance, repair

or calibration, phone 516-334-0870 or fax 516-338-4741.

Product Warranty

Electro Industries/GaugeTech warrants all products to be free from defects in material and workmanship

for a period of four years from the date of shipment. During the warranty period, we will, at our option,

either repair or replace any product that proves to be defective.

To exercise this warranty, fax or call our customer-support department. You will receive prompt

assistance and return instructions. Send the instrument, transportation prepaid, to EIG at 1800 Shames

Drive, Westbury, NY 11590. Repairs will be made and the instrument will be returned.

Limitation of Warranty

This warranty does not apply to defects resulting from unauthorized modification, misuse, or use for any

reason other than electrical power monitoring. Nexus 1250/1252 is not a user-serviceable product.

OUR PRODUCTS ARE NOT TO BE USED FOR PRIMARY OVER-CURRENT PROTECTION. ANY

PROTECTION FEATURE IN OUR PRODUCTS IS TO BE USED FOR ALARM OR SECONDARY

PROTECTION ONLY.

THIS WARRANTY IS IN LIEU OF ALL OTHER WARRANTIES, EXPRESSED OR IMPLIED,

INCLUDING ANY IMPLIED WARRANTY OF MERCHANTABILITY OR FITNESS FOR A

PARTICULAR PURPOSE. ELECTRO INDUSTRIES/GAUGETECH SHALL NOT BE LIABLE FOR

ANY INDIRECT, SPECIAL OR CONSEQUENTIAL DAMAGES ARISING FROM ANY AUTHO-

RIZED OR UNAUTHORIZED USE OF ANY ELECTRO INDUSTRIES/GAUGETECH PRODUCT.

LIABILITY SHALL BE LIMITED TO THE ORIGINAL COST OF THE PRODUCT SOLD.

Statement of Calibration

Our instruments are inspected and tested in accordance with specifications published by Electro

Industries/GaugeTech. The accuracy and a calibration of our instruments are traceable to the National

Institute of Standards and Technology through equipment that is calibrated at planned intervals by

comparison to certified standards.

Disclaimer

The information presented in this publication has been carefully checked for reliability; however, no

responsibility is assumed for inaccuracies. The information contained in this document is subject to

change without notice.

This symbol indicates that the operator must refer to an explanation in the operating

instructions. Please see Chapter 3, Hardware Installation, for important safety

information regarding installation and hookup of the Nexus 1250/1252 Meter.

Electro Industries/GaugeTech Doc # E107706 V1.25

About Electro Industries/GaugeTech

Electro Industries/GaugeTech was founded in 1973 by Dr. Samuel Kagan. Dr. Kagan’s first innovation,

an affordable, easy-to-use AC power meter, revolutionized the power-monitoring field. In the 1980s Dr.

Kagan and his team at EIG developed a digital multifunction monitor capable of measuring every aspect

of power.

EIG further transformed AC power metering and power distribution with the Futura+ device, which

supplies all the functionality of a fault recorder, an event recorder and a data logger in one single meter.

Today, with the Nexus 1250/1252,1262/1272 and the Shark, EIG is a leader in the development and

production of power monitoring products. All EIG products are designed, manufactured, tested and

calibrated at our facility in Westbury, New York.

Applications:

Multifunction power monitoring

Single and multifunction power monitoring

Power quality monitoring

On board data logging for trending power usage and quality

Disturbance analysis

Futura+ Series Products:

Power quality monitoring

High-accuracy AC metering

On board data logging

On board fault and voltage recording

DM Series Products:

Three-phase multifunction monitoring

Wattage, VAR and amperage

Modbus, Modbus Plus, DNP 3.0 and Ethernet protocols

Analog retransmit signals (0–1 and 4–20mA)

Single-Function Meters:

AC voltage and amperage

DC voltage and amperage

AC wattage

Single-phase monitoring with maximum and minimum demands

Transducer readouts

Portable Analyzers:

Power quality analysis

Energy analysis

Electro Industries/GaugeTech Doc # E107706 V1.25

iii

Electro Industries/GaugeTech Doc # E107706 V1.25

Table of Contents

Chapter 1: Three-Phase Power Measurement

1.1: Three-Phase System Configurations . . . . . . . . . . . . . . . . . . . . . 1-1

1.1.1: Wye Connnection . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1

1.1.2: Delta Connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3

1.1.3: Blondell’s Theorem and Three Phase Measurement . . . . . . . . . . . . . 1-4

1.2: Power, Energy and Demand . . . . . . . . . . . . . . . . . . . . . . . . 1-6

1.3: Reactive Energy and Power Factor . . . . . . . . . . . . . . . . . . . . . 1-8

1.4: Harmonic Distortion . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-10

1.5: Power Quality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-13

Chapter 2: Nexus Overview

2.1: The Nexus System . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-1

2.2: DNP V3.00 Level 1 and Level 2 . . . . . . . . . . . . . . . . . . . . . . 2-2

2.3: Flicker . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-2

2.4: INP2 Internal Modem with Dial-In/Dial-Out Option . . . . . . . . . . . . . . 2-3

2.4.1: Hardware Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-3

2.4.2: Dial-In Function . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-3

2.4.3: Dial-Out Function . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-3

2.5: Total Web Solutions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-4

2.5.1: Hardware Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-4

2.5.2: Hardware Connection . . . . . . . . . . . . . . . . . . . . . . . . . . 2-4

2.6: Measurements and Calculations . . . . . . . . . . . . . . . . . . . . . . . 2-6

2.7: Demand Integrators . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-10

2.8: Nexus External I/O Modules (Optional) . . . . . . . . . . . . . . . . . . . 2-12

2.9: Nexus 1250/1252 Meter Specifications . . . . . . . . . . . . . . . . . . . 2-13

2.10: Nexus P40N, P41N, P43N External Display Specifications . . . . . . . . . . 2-14

2.11: Nexus P60N Touch Screen Display Specifications . . . . . . . . . . . . . . 2-14

Chapter 3: Hardware Installation

3.1: Mounting the Nexus 1259/1252 Meter . . . . . . . . . . . . . . . . . . . . 3-1

3.2: Mounting the Nexus P40N, P41N, P43N External Displays . . . . . . . . . . . 3-3

3.3: Mounting the Nexus P60N Touch Screen External Display . . . . . . . . . . . 3-4

3.4: Mounting the Nexus External I/O Modules . . . . . . . . . . . . . . . . . . 3-6

Chapter 4: Electrical Installation

4.1: Wiring the Monitored Inputs and Voltages . . . . . . . . . . . . . . . . . . 4-1

4.2: Fusing the Voltage Connections . . . . . . . . . . . . . . . . . . . . . . . 4-1

4.3: Wiring the Monitored Inputs -VRef . . . . . . . . . . . . . . . . . . . . . 4-1

4.4: Wiring the Monitored Inputs - VAux . . . . . . . . . . . . . . . . . . . . . 4-1

4.5: Wiring the Monitored Inputs - Currents . . . . . . . . . . . . . . . . . . . 4-1

4.6: Isolating a CT Connection Reversal . . . . . . . . . . . . . . . . . . . . . 4-2

4.7: Instrument Power Connections . . . . . . . . . . . . . . . . . . . . . . . 4-2

4.8: Wiring Diagrams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-3

Electro Industries/GaugeTech Doc # E107706 V1.25

Chapter 5: Communication Wiring

5.1: Communication Overview . . . . . . . . . . . . . . . . . . . . . . . . . 5-1

5.2: RS-232 Connection-Nexus Meter to a Computer . . . . . . . . . . . . . . . 5-5

5.3: RS-485 Wiring Fundamentals (with RT Explanation) . . . . . . . . . . . . . . 5-5

5.4: RS-485 Connection- Nexus Meter to a Computer or PLC . . . . . . . . . . . . 5-8

5.5: RJ-11 (Telephone Line) Connection- Nexus with Internal Modem Option to PC . . 5-8

5.6: RJ-45 Connection- Nexus with Internal Network Option to multiple PC’s . . . . . 5-8

5.7: RS-485 Connection- Nexus to an RS-485 Master (Unicom or Modem Manager) . . 5-9

5.7.1: Using the Unicom 2500 . . . . . . . . . . . . . . . . . . . . . . . . . 5-9

5.8: RS-485 Connectiion- Nexus Meter to P40N, P41N, P43N External Display . . . 5-11

5.9: RS-485 Connectiion- Nexus Meter to P60N External Display . . . . . . . . . 5-12

5.10: Communication Ports on the Nexus I/O Modules . . . . . . . . . . . . . . 5-13

5.11: RS-485 Connection—Nexus Meter to Nexus I/O Modules . . . . . . . . . . 5-14

5.12: Steps to Determine Power Needed . . . . . . . . . . . . . . . . . . . . . 5-15

5.13: I/O Modules’ Factory Settings and VA Ratings . . . . . . . . . . . . . . . 5-15

5.14: Linking Multiple Nexus Devices in Series . . . . . . . . . . . . . . . . . 5-16

5.15: Networking Groups of Nexus Meters . . . . . . . . . . . . . . . . . . . 5-17

5.16: Remote Communication Overview . . . . . . . . . . . . . . . . . . . . 5-18

5.17: Remote Communication- RS-232 . . . . . . . . . . . . . . . . . . . . . 5-21

5.18: Remote Communication- RS-485 . . . . . . . . . . . . . . . . . . . . . 5-21

5.19: Programming Modems for Remote Communication . . . . . . . . . . . . . 5-22

5.20: Selected Modem Strings . . . . . . . . . . . . . . . . . . . . . . . . . 5-23

5.21: High Speed Inputs Connection . . . . . . . . . . . . . . . . . . . . . . 5-23

5.22: Five Modes of Time Synchronization . . . . . . . . . . . . . . . . . . . 5-24

5.23: IRIG-B Connections . . . . . . . . . . . . . . . . . . . . . . . . . . 5-25

Chapter 6: Using the Nexus External Displays

6.1: Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-1

6.2: Nexus P40N, P41N, P43N LED External Display . . . . . . . . . . . . . . . 6-1

6.2.1: Connect Multiple Displays . . . . . . . . . . . . . . . . . . . . . . . . 6-2

6.2.2: Nexus P40N Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-2

6.3: Dynamic Readings Mode . . . . . . . . . . . . . . . . . . . . . . . . . 6-3

6.4: Navigational Map of Dynamic Readings Mode . . . . . . . . . . . . . . . . 6-5

6.5: Nexus Information Mode . . . . . . . . . . . . . . . . . . . . . . . . . . 6-6

6.6: Navigational Map of Nexus Information Mode . . . . . . . . . . . . . . . . 6-7

6.7: Display Features Mode . . . . . . . . . . . . . . . . . . . . . . . . . . 6-8

6.8: Navigational Map of Display Features Mode . . . . . . . . . . . . . . . . . 6-9

6.9: Nexus P60N Touch Screen External Display . . . . . . . . . . . . . . . . . 6-10

6.10: Navigational Map for P60N Touch Screen External Display . . . . . . . . . 6-18

Chapter 7: Transformer Loss Compensation

7.1: Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-1

7.2: Nexus 1250/1252 Transformer Loss Compensation . . . . . . . . . . . . . . 7-3

7.2.1: Loss Compensation in Three Element Installations . . . . . . . . . . . . . . 7-4

7.2.1.1: Three Element Loss Compensation Worksheet . . . . . . . . . . . . . . . 7-5

Chapter 8: Nexus Time-of-Use

8.1: Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-1

8.2: The Nexus TOU Calendar . . . . . . . . . . . . . . . . . . . . . . . . . 8-1

Electro Industries/GaugeTech Doc # E107706 V1.25

8.3: TOU Prior Season and Month . . . . . . . . . . . . . . . . . . . . . . . 8-2

8.4: Updating, Retrieving and Replacing TOU Calendars . . . . . . . . . . . . . . 8-2

8.5: Daylight Savings and Demand . . . . . . . . . . . . . . . . . . . . . . . 8-2

Chapter 9: Nexus External I/O Modules

9.1: Hardware Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-1

9.1.1: Port Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-2

9.2: Installing Nexus External I/O Modules . . . . . . . . . . . . . . . . . . . 9-3

9.2.1: Power Source for I/O Modules . . . . . . . . . . . . . . . . . . . . . . 9-4

9.3: Using PSIO with Multiple I/O Modules . . . . . . . . . . . . . . . . . . . 9-5

9.3.1: Steps for Attaching Multiple I/O Modules . . . . . . . . . . . . . . . . . 9-5

9.4: Factory Settings and Reset Button . . . . . . . . . . . . . . . . . . . . . 9-6

9.5: Analog Transducer Signal Output Modules . . . . . . . . . . . . . . . . . . 9-7

9.5.1: Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-7

9.5.2: Normal Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-8

9.6: Analog Input Modules . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-9

9.6.1: Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-9

9.6.2: Normal Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-10

9.7: Digital Dry Contact Relay Output (Form C) Module . . . . . . . . . . . . . 9-11

9.7.1: Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-11

9.7.2: Communication . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-12

9.7.3: Normal Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-12

9.8: Digital Solid State Pulse Output (KYZ) Module . . . . . . . . . . . . . . . 9-13

9.8.1: Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-13

9.8.2: Communication . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-14

9.8.3: Normal Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-14

9.9: Digital Status Input Module . . . . . . . . . . . . . . . . . . . . . . . . 9-15

9.9.1: Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-15

9.9.2: Communication . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-15

9.9.3: Normal Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-16

9.10: Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-16

Chapter 10: Nexus Monitor with INP2 - Internal Modem Option

10.1: Hardware Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 10-1

10.2: Hardware Connection . . . . . . . . . . . . . . . . . . . . . . . . . . 10-2

10.3: Dial-In Function . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-2

10.4: Dial-Out Function . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-2

Chapter 11: Nexus Monitor with Internal Network Option

11.1: Hardware Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-1

11.2: Hardware Connection . . . . . . . . . . . . . . . . . . . . . . . . . . 11-3

Chapter 12: Flicker

12.1: Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-1

12.2: Theory of Operation . . . . . . . . . . . . . . . . . . . . . . . . . . 12-1

12.3: Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-3

12.4: Software - User Interface . . . . . . . . . . . . . . . . . . . . . . . . 12-4

12.5: Logging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-7

12.6: Polling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-7

Electro Industries/GaugeTech Doc # E107706 V1.25

vii

12.7: Log Viewer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-7

12.8: Performance Notes . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-8

Appendix A: Transformer Loss Compensation Excel Spreadsheet with Examples

A.1: Calculating Values . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-1

A.2: Excel Spreadsheet with Example Numbers . . . . . . . . . . . . . . . . . A-1

Glossary of Terms

Electro Industries/GaugeTech Doc #: E107706 V1.25

VIII

Chapter 1

Three-Phase Power Measurement

This introduction to three-phase power and power measurement is intended to provide only a brief

overview of the subject. The professional meter engineer or meter technician should refer to more

advanced documents such as the EEI Handbook for Electricity Metering and the application standards

for more in-depth and technical coverage of the subject.

1.1: Three-Phase System Configurations

Three-phase power is most commonly used in situations where large amounts of power will be used

because it is a more effective way to transmit the power and because it provides a smoother delivery

of power to the end load. There are two commonly used connections for three-phase power, a wye

connection or a delta connection. Each connection has several different manifestations in actual use.

When attempting to determine the type of connection in use, it is a good practice to follow the

circuit back to the transformer that is serving the circuit. It is often not possible to conclusively

determine the correct circuit connection simply by counting the wires in the service or checking

voltages. Checking the transformer connection will provide conclusive evidence of the circuit

connection and the relationships between the phase voltages and ground.

1.1.1: Wye Connection

The wye connection is so called because when you look at the phase relationships and the winding

relationships between the phases it looks like a wye (Y). Figure 1.1 depicts the winding relationships

for a wye-connected service. In a wye service the neutral (or center point of the wye) is typically

grounded. This leads to common voltages of 208/120 and 480/277 (where the first number represents

the phase-to-phase voltage and the second number represents the phase-to-ground voltage).

Phase B

Phase C

Phase A

Figure 1.1: Three-Phase Wye Winding

The three voltages are separated by 120 electrically. Under balanced load conditions with unity

power factor the currents are also separated by 120 . However, unbalanced loads and other

conditions can cause the currents to depart from the ideal 120 separation.

Electro Industries/GaugeTech Doc # E107706 V1.25

1-1

Three-phase voltages and currents are usually represented with a phasor diagram. A phasor diagram

for the typical connected voltages and currents is shown in Figure 1.2.

Fig 1.2: Phasor Diagram Showing Three-phase Voltages and Currents

The phasor diagram shows the 120 angular separation between the phase voltages. The phase-to-

phase voltage in a balanced three-phase wye system is 1.732 times the phase-to-neutral voltage. The

center point of the wye is tied together and is typically grounded. Table 1.1 shows the common

voltages used in the United States for wye-connected systems.

Phase-to-Ground Voltage

120 volts

Phase-to-Phase Voltage

208 volts

277 volts

480 volts

2,400 volts

4,160 volts

7,200 volts

12,470 volts

13,200 volts

7,620 volts

Table 1.1: Common Phase Voltages on Wye Services

Usually a wye-connected service will have four wires; three wires for the phases and one for the

neutral. The three-phase wires connect to the three phases (as shown in Figure 1.1). The neutral wire

is typically tied to the ground or center point of the wye (refer to Figure 1.1).

In many industrial applications the facility will be fed with a four-wire wye service but only three

wires will be run to individual loads. The load is then often referred to as a delta-connected load but

the service to the facility is still a wye service; it contains four wires if you trace the circuit back

to its source (usually a transformer). In this type of connection the phase to ground voltage will be

the phase-to-ground voltage indicated in Table 1, even though a neutral or ground wire is not

physically present at the load. The transformer is the best place to determine the circuit connection

type because this is a location where the voltage reference to ground can be conclusively identified.

Electro Industries/GaugeTech Doc # E107706 V1.25

1-2

1.1.2: Delta Connection

Delta connected services may be fed with either three wires or four wires. In a three-phase delta

service the load windings are connected from phase-to-phase rather than from phase-to-ground.

Figure 1.3 shows the physical load connections for a delta service.

Phase C

Phase A

Phase B

Figure 1.3: Three-Phase Delta Winding Relationship

In this example of a delta service, three wires will transmit the power to the load. In a true delta

service, the phase-to-ground voltage will usually not be balanced because the ground is not at the

center of the delta.

Figure 1.4 shows the phasor relationships between voltage and current on a three-phase delta circuit.

In many delta services, one corner of the delta is grounded. This means the phase to ground voltage

will be zero for one phase and will be full phase-to-phase voltage for the other two phases. This is

done for protective purposes.

Vca

Vbc

Vab

Figure 1.4: Phasor Diagram, Three-Phase Voltages and Currents Delta Connected.

Another common delta connection is the four-wire, grounded delta used for lighting loads. In this

connection the center point of one winding is grounded. On a 120/240 volt, four-wire, grounded

delta service the phase-to-ground voltage would be 120 volts on two phases and 208 volts on the

third phase. Figure 1.5 shows the phasor diagram for the voltages in a three-phase, four-wire delta

system.

Electro Industries/GaugeTech Doc # E107706 V1.25

1-3

Fig 1.5: Phasor Diagram Showing Three-phase, Four-wire Delta Connected System

1.1.3: Blondell’s Theorem and Three Phase Measurement

In 1893 an engineer and mathematician named Andre E. Blondell set forth the first scientific basis

for poly phase metering. His theorem states:

If energy is supplied to any system of conductors through N wires, the total power in the system is

given by the algebraic sum of the readings of N wattmeters so arranged that each of the N wires

contains one current coil, the corresponding potential coil being connected between that wire and

some common point. If this common point is on one of the N wires, the measurement may be made

by the use of N-1 wattmeters.

The theorem may be stated more simply, in modern language:

In a system of N conductors, N-1 meter elements will measure the power or energy taken provided

that all the potential coils have a common tie to the conductor in which there is no current coil.

Three-phase power measurement is accomplished by measuring the three individual phases and

adding them together to obtain the total three phase value. In older analog meters, this

measurement was accomplished using up to three separate elements. Each element combined the

single-phase voltage and current to produce a torque on the meter disk. All three elements were

arranged around the disk so that the disk was subjected to the combined torque of the three elements.

As a result the disk would turn at a higher speed and register power supplied by each of the three

wires.

According to Blondell's Theorem, it was possible to reduce the number of elements under certain

conditions. For example, a three-phase, three-wire delta system could be correctly measured with

two elements (two potential coils and two current coils) if the potential coils were connected

between the three phases with one phase in common.

In a three-phase, four-wire wye system it is necessary to use three elements. Three voltage coils are

connected between the three phases and the common neutral conductor. A current coil is required in

each of the three phases.

In modern digital meters, Blondell's Theorem is still applied to obtain proper metering. The

difference in modern meters is that the digital meter measures each phase voltage and current and

calculates the single-phase power for each phase. The meter then sums the three phase powers to a

Electro Industries/GaugeTech Doc # E107706 V1.25

1-4

single three-phase reading.

Some digital meters calculate the individual phase power values one phase at a time. This means the

meter samples the voltage and current on one phase and calculates a power value. Then it samples the

second phase and calculates the power for the second phase. Finally, it samples the third phase and

calculates that phase power. After sampling all three phases, the meter combines the three readings to

create the equivalent three-phase power value. Using mathematical averaging techniques, this method

can derive a quite accurate measurement of three-phase power.

More advanced meters actually sample all three phases of voltage and current simultaneously and

calculate the individual phase and three-phase power values. The advantage of simultaneous sampling

is the reduction of error introduced due to the difference in time when the samples were taken.

Phase B

Phase C

Node “n”

Phase A

Figure 1.6:

Three-Phase Wye Load illustrating Kirchhoff’s Law

and Blondell’s Theorem

Blondell's Theorem is a derivation that results from Kirchhoff's Law. Kirchhoff's Law states that the

sum of the currents into a node is zero. Another way of stating the same thing is that the current into a

node (connection point) must equal the current out of the node. The law can be applied to measuring

three-phase loads. Figure 1.6 shows a typical connection of a three-phase load applied to a three-

phase, four-wire service. Krichhoff's Laws hold that the sum of currents A, B, C and N must equal zero

or that the sum of currents into Node "n" must equal zero.

If we measure the currents in wires A, B and C, we then know the current in wire N by Kirchhoff's

Law and it is not necessary to measure it. This fact leads us to the conclusion of Blondell's Theorem

that we only need to measure the power in three of the four wires if they are connected by a common

node. In the circuit of Figure 1.6 we must measure the power flow in three wires. This will require

three voltage coils and three current coils (a three element meter). Similar figures and conclusions

could be reached for other circuit configurations involving delta-connected loads.

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1.2: Power, Energy and Demand

It is quite common to exchange power, energy and demand without differentiating between the

three. Because this practice can lead to confusion, the differences between these three

measurements will be discussed.

Power is an instantaneous reading. The power reading provided by a meter is the present flow of

watts. Power is measured immediately just like current. In many digital meters, the power value is

actually measured and calculated over a one second interval because it takes some amount of time to

calculate the RMS values of voltage and current. But this time interval is kept small to preserve the

instantaneous nature of power.

Energy is always based on some time increment; it is the integration of power over a defined time

increment. Energy is an important value because almost all electric bills are based, in part, on the

amount of energy used.

Typically, electrical energy is measured in units of kilowatt-hours (kWh). A kilowatt-hour

represents a constant load of one thousand watts (one kilowatt) for one hour. Stated another way, if

the power delivered (instantaneous watts) is measured as 1,000 watts and the load was served for a

one hour time interval then the load would have absorbed one kilowatt-hour of energy. A different

load may have a constant power requirement of 4,000 watts. If the load were served for one hour it

would absorb four kWh. If the load were served for 15 minutes it would absorb ¼ of that total or

one kWh.

Figure 1.7 shows a graph of power and the resulting energy that would be transmitted as a result of

the illustrated power values. For this illustration, it is assumed that the power level is held constant

for each minute when a measurement is taken. Each bar in the graph will represent the power load

for the one-minute increment of time. In real life the power value moves almost constantly.

The data from Figure 1.7 is reproduced in Table 2 to illustrate the calculation of energy. Since the

time increment of the measurement is one minute and since we specified that the load is constant

over that minute, we can convert the power reading to an equivalent consumed energy reading by

multiplying the power reading times 1/60 (converting the time base from minutes to hours).

Kilowatts

100

Time (minutes) Æ

Figure 1.7: Power Use Over Time

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1-6

Time Interval

(Minute)

Accumulated

Energy (kWh)

Power (kW)

Energy (kWh)

0.50

0.83

0.67

0.92

1.00

1.17

1.00

1.17

1.33

0.83

1.17

1.33

0.50

1.33

2.00

2.92

3.92

4.92

6.09

7.26

8.26

9.43

10.76

12.42

13.59

14.92

Table 1.2: Power and Energy Relationship Over Time

As in Table 1.2, the accumulated energy for the power load profile of Figure 1.7 is 14.92 kWh.

Demand is also a time-based value. The demand is the average rate of energy use over time. The

actual label for demand is kilowatt-hours/hour but this is normally reduced to kilowatts. This makes

it easy to confuse demand with power. But demand is not an instantaneous value. To calculate

demand it is necessary to accumulate the energy readings (as illustrated in Figure 1.7) and adjust the

energy reading to an hourly value that constitutes the demand.

In the example, the accumulated energy is 14.92 kWh. But this measurement was made over a

15-minute interval. To convert the reading to a demand value, it must be normalized to a 60-minute

interval. If the pattern were repeated for an additional three 15-minute intervals the total energy

would be four times the measured value or 59.68 kWh. The same process is applied to calculate the

15-minute demand value. The demand value associated with the example load is 59.68 kWh/hr or

59.68 kWd. Note that the peak instantaneous value of power is 80 kW, significantly more than the

demand value.

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Figure 1.8 shows another example of energy and demand. In this case, each bar represents the

energy consumed in a 15-minute interval. The energy use in each interval typically falls between 50

and 70 kWh. However, during two intervals the energy rises sharply and peaks at 100 kWh in

interval number 7. This peak of usage will result in setting a high demand reading. For each interval

shown the demand value would be four times the indicated energy reading. So interval 1 would have

an associated demand of 240 kWh/hr. Interval 7 will have a demand value of 400 kWh/hr. In the

data shown, this is the peak demand value and would be the number that would set the demand

charge on the utility bill.

Kilowatt-hours

100

Intervals Æ

Figure 1.8: Energy Use and Demand

As can be seen from this example, it is important to recognize the relationships between power,

energy and demand in order to control loads effectively or to monitor use correctly.

1.3: Reactive Energy and Power Factor

The real power and energy measurements discussed in the previous section relate to the quantities

that are most used in electrical systems. But it is often not sufficient to only measure real power and

energy. Reactive power is a critical component of the total power picture because almost all real-life

applications have an impact on reactive power. Reactive power and power factor concepts relate to

both load and generation applications. However, this discussion will be limited to analysis of

reactive power and power factor as they relate to loads. To simplify the discussion, generation will

not be considered.

Real power (and energy) is the component of power that is the combination of the voltage and the

value of corresponding current that is directly in phase with the voltage. However, in actual practice

the total current is almost never in phase with the voltage. Since the current is not in phase with the

voltage, it is necessary to consider both the inphase component and the component that is at

quadrature (angularly rotated 90 or perpendicular) to the voltage. Figure 1.9 shows a single-phase

voltage and current and breaks the current into its in-phase and quadrature components.

Electro Industries/GaugeTech Doc # E107706 V1.25

1-8

I_R

Angle θ

I_X

Figure 1.9: Voltage and Complex

The voltage (V) and the total current (I) can be combined to calculate the apparent power or VA.

The voltage and the in-phase current (IR) are combined to produce the real power or watts. The volt-

age and the quadrature current (IX) are combined to calculate the reactive power.

The quadrature current may be lagging the voltage (as shown in Figure 1.9) or it may lead the

voltage. When the quadrature current lags the voltage the load is requiring both real power (watts)

and reactive power (VARs). When the quadrature current leads the voltage the load is requiring real

power (watts) but is delivering reactive power (VARs) back into the system; that is VARs are

flowing in the opposite direction of the real power flow.

Reactive power (VARs) is required in all power systems. Any equipment that uses magnetization to

operate requires VARs. Usually the magnitude of VARs is relatively low compared to the real power

quantities. Utilities have an interest in maintaining VAR requirements at the customer to a low value

in order to maximize the return on plant invested to deliver energy. When lines are carrying VARs,

they cannot carry as many watts. So keeping the VAR content low allows a line to carry its full

capacity of watts. In order to encourage customers to keep VAR requirements low, most utilities

impose a penalty if the VAR content of the load rises above a specified value.

A common method of measuring reactive power requirements is power factor. Power factor can be

defined in two different ways. The more common method of calculating power factor is the ratio of

the real power to the apparent power. This relationship is expressed in the following formula:

Total PF = real power / apparent power = watts/VA

This formula calculates a power factor quantity known as Total Power Factor. It is called Total PF

because it is based on the ratios of the power delivered. The delivered power quantities will include

the impacts of any existing harmonic content. If the voltage or current includes high levels of

harmonic distortion the power values will be affected. By calculating power factor from the power

values, the power factor will include the impact of harmonic distortion. In many cases this is the

preferred method of calculation because the entire impact of the actual voltage and current are

included.

A second type of power factor is Displacement Power Factor. Displacement PF is based on the

angular relationship between the voltage and current. Displacement power factor does not consider

the magnitudes of voltage, current or power. It is solely based on the phase angle differences. As a

Electro Industries/GaugeTech Doc # E107706 V1.25

1-9

result, it does not include the impact of harmonic distortion. Displacement power factor is calculated

using the following equation:

Displacement PF = cos θ, where θ is the angle between the voltage and the current (see Fig. 1.9).

In applications where the voltage and current are not distorted, the Total Power Factor will equal the

Displacement Power Factor. But if harmonic distortion is present, the two power factors will not be

equal.

1.4: Harmonic Distortion

Harmonic distortion is primarily the result of high concentrations of non-linear loads. Devices such

as computer power supplies, variable speed drives and fluorescent light ballasts make current

demands that do not match the sinusoidal waveform of AC electricity. As a result, the current

waveform feeding these loads is periodic but not sinusoidal. Figure 1.10 shows a normal, sinusoidal

current waveform. This example has no distortion.

A Phase Current

1500

1000

500

-500

-1000

-1500

Figure 1.10: Nondistorted Current Waveform

Figure 1.11 shows a current waveform with a slight amount of harmonic distortion. The waveform is

still periodic and is fluctuating at the normal 60 Hz frequency. However, the waveform is not a

smooth sinusoidal form as seen in Figure 1.10.

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1-10

Total A Phase Current with Harmonics

1500

1000

500

-500

-1000

-1500

Figure 1.11: Distorted Current Wave

The distortion observed in Figure 1.11 can be modeled as the sum of several sinusoidal waveforms

of frequencies that are multiples of the fundamental 60 Hz frequency. This modeling is performed

by mathematically disassembling the distorted waveform into a collection of higher frequency

waveforms. These higher frequency waveforms are referred to as harmonics. Figure 1.12 shows the

content of the harmonic frequencies that make up the distortion portion of the waveform in Figure

1.11.

Expanded Harmonic Currents

250

200

150

100

-50

-100

-150

-200

-250

2 Harmonic Current

7 Harmonic Current

3 Harmonic Current

ACurrent Total Hrm

5 Harmonic Current

Figure 1.12: Waveforms of the Harmonics

The waveforms shown in Figure 1.12 are not smoothed but do provide an indication of the impact of

combining multiple harmonic frequencies together.

When harmonics are present it is important to remember that these quantities are operating at higher

frequencies. Therefore, they do not always respond in the same manner as 60 Hz values.

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Inductive and capacitive impedance are present in all power systems. We are accustomed to thinking

about these impedances as they perform at 60 Hz. However, these impedances are subject to

frequency variation.

X_L= jωL and

X_C= 1/jωC

At 60 Hz, ω = 377; but at 300 Hz (5 harmonic) ω = 1,885. As frequency changes impedance

changes and system impedance characteristics that are normal at 60 Hz may behave entirely

different in presence of higher order harmonic waveforms.

Traditionally, the most common harmonics have been the low order, odd frequencies, such as the

rd th th

3 , 5 , 7 , and 9 . However newer, new-linear loads are introducing significant quantities of

higher order harmonics.

Since much voltage monitoring and almost all current monitoring is performed using instrument

transformers, the higher order harmonics are often not visible. Instrument transformers are designed

to pass 60 Hz quantities with high accuracy. These devices, when designed for accuracy at low

frequency, do not pass high frequencies with high accuracy; at frequencies above about 1200 Hz

they pass almost no information. So when instrument transformers are used, they effectively filter

out higher frequency harmonic distortion making it impossible to see.

However, when monitors can be connected directly to the measured circuit (such as direct

connection to 480 volt bus) the user may often see higher order harmonic distortion. An important

rule in any harmonics study is to evaluate the type of equipment and connections before drawing a

conclusion. Not being able to see harmonic distortion is not the same as not having harmonic

distortion.

It is common in advanced meters to perform a function commonly referred to as waveform capture.

Waveform capture is the ability of a meter to capture a present picture of the voltage or current

waveform for viewing and harmonic analysis. Typically a waveform capture will be one or two

cycles in duration and can be viewed as the actual waveform, as a spectral view of the harmonic

content, or a tabular view showing the magnitude and phase shift of each harmonic value. Data

collected with waveform capture is typically not saved to memory. Waveform capture is a real-time

data collection event.

Waveform capture should not be confused with waveform recording that is used to record multiple

cycles of all voltage and current waveforms in response to a transient condition.

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1.5: Power Quality

Power quality can mean several different things. The terms "power quality" and "power quality

problem" have been applied to all types of conditions. A simple definition of "power quality

problem" is any voltage, current or frequency deviation that results in mis-operation or failure of

customer equipment or systems. The causes of power quality problems vary widely and may

originate in the customer equipment, in an adjacent customer facility or with the utility.

In his book Power Quality Primer, Barry Kennedy provided information on different types of power

quality problems. Some of that information is summarized in Table 1.3 below.

Cause

Disturbance Type

Source

Lightning

Transient voltage disturbance,

sub-cycle duration

Electrostatic discharge

Load switching

Impulse Transient

Capacitor switching

Line/cable switching

Capacitor switching

Load switching

Oscillatory transient

with decay

Transient voltage, sub-cycle

duration

RMS voltage, multiple cycle

duration

Sag / swell

Remote system faults

System protection

RMS voltage, multiple second or Circuit breakers

Interruptions

longer duration

Fuses

Maintenance

RMS voltage, steady state,

multiple second or longer

duration

Motor starting

Load variations

Load dropping

Undervoltage /

Overvoltage

Intermittent loads

Motor starting

Arc furnaces

RMS voltage, steady state,

repetitive condition

Voltage flicker

Steady state current or voltage, Non-linear loads

long term duration System resonance

Harmonic distortion

Table 1.3: Typical Power Quality Problems and Sources

It is often assumed that power quality problems originate with the utility. While it is true that may

power quality problems can originate with the utility system, many problems originate with

customer equipment. Customer-caused problems may manifest themselves inside the customer

location or they may be transported by the utility system to another adjacent customer. Often,

equipment that is sensitive to power quality problems may in fact also be the cause of the problem.

If a power quality problem is suspected, it is generally wise to consult a power quality professional

for assistance in defining the cause and possible solutions to the problem.

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Chapter 2

Nexus Overview

2.1: The Nexus System

Electro Industries’ Nexus 1250/1252 combines high-end revenue metering with sophisticated power

quality analysis. Its advanced monitoring capabilities provide detailed and precise pictures of any

metered point within a distribution network. The P60N, P40N, P41N and P43N displays are detailed in

Chapter 6. Extensive I/O capability is available in conjunction with all metering functions. The optional

Communicator EXT software allows a user to poll and gather data from multiple Nexus meters installed

at local or remote locations (see the Communicator EXT User Manual for details). On board mass

memory enables the Nexus to retrieve and store multiple logs. The Nexus Meter with Internal Modem

(or Network) Option connects to a PC via standard phone line (or MODBUS/TCP) and a daisy chain of

Nexus Meters via an RS-485 connection. See Chapters 10 and 11 for details.

Modem/Ethernet

Option

Modem Gateway or

Ethernet Gateway

RS-485 Connection

Computer

or SCADA

System

Expandable I/O Modules

Nexus

Display

Modem/Ethernet

Option

RJ-11 or RJ-45

Connection

Nexus Meter

Figure 2.1: The Nexus 1250/1252 System

e Electro Industries/GaugeTech Doc # E107706 V1.25

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Nexus 1250/1252 Revenue Metering:

•

Delivers laboratory-grade 0.04% Watt-hour accuracy in a field-mounted device.

Autocalibrates when there is a temperature change of more than 10 degrees centigrade.

Exceeds all ANSI C-12 and IEC 687 specifications.

Adjusts for transformer and line losses, using user-defined compensation factors.

Automatically logs time-of-use for up to eight programmable tariff registers.

Counts pulses and aggregates different loads.

Nexus 1250/1252 Power Quality Monitoring:

•

Records up to 512 samples per cycle on an event.

Records sub-cycle transients on voltage or current readings.

Measures and records Harmonics to the 83rd order.

Offers inputs for neutral-to-ground voltage measurements.

Synchronizes with IRIG-B clock signal.

Nexus 1250/1252 Memory, Communication and Control:

•

Up to 4 Meg NVRAM.

4 High Speed Communication Ports.

Multiple Protocols (see section below on DNP V3.00).

Built-in RTU functionality.

Built-in PLC functionality.

90msec High Speed Updates for Control.

2.2: DNP V3.00 Level 1 and Level 2

Nexus 1250 supports DNP V3.00 Level 1.

Nexus 1252 supports DNP V3.00 Level 2.

DNP Level 2 Features:

•

Up to 136 measurement (64 Binary Inputs, 8 Binary Counters, 64 Analog Inputs) can be mapped

to DNP Static Points (over 3000) in the customizable DNP Point Map.

Up to 16 Relays and 8 Resets can be controlled through DNP Level 2.

Report-by-Exception Processing (DNP Events) Deadbands can be set on a per-point basis.

Freeze Commands: Freeze, Freeze/No-Ack, Freeze with Time, Freeze with Time/No-Ack.

Freeze with Time Commands enable the Nexus meter to have internal time-driven Frozen and

Frozen Event data. When the Nexus meter receives the Time and Interval, the data will be

created.

•

For complete details, download the appropriate DNP User Manual from our website

www.electroind.com.

2.3: Flicker

Nexus 1252 provides Flicker Evaluation in Instantaneous, Short Term and Long Term Forms.

For a detailed explanation of Flicker, see Chapter 12 of this manual.

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2.4: INP2 Internal Modem with Dial-In/Dial-Out Option

2.4.1: Hardware Overview

The INP2 Option for the Nexus 1250/1252 meter provides a direct connection to a standard tele-

phone line. No additional hardware is required to establish a communication connection between the

meter and a remote computer. The RJ-11 Jack is on the face of the meter. A standard telephone RJ-

11 plug can connect the meter to a standard PSTN (Public Switched Telephone Network).

The modem operates at up to 56k baud. The modem supports both incoming calls (from a remote

computer) and automatic dial-out calls when a defined event must be automatically reported.

With the device configured with the INP2 Option, the meter has dial-in capability and provides

remote access to other Modbus-based serial devices via the meter’s RS-485 Gateway over your

phone line. The meter will recognize and respond to a Modbus Address of 1. With any other

address, the command will pass through the gateway and become a virtual connection between the

Remote Modbus Master and any Modbus Slave connected to the RS-485 Gateway.

2.4.2: Dial-In Function

The modem continuously monitors the telephone line to detect an incoming call. When an incoming

call is detected, the modem will wait a user-set number of rings and answer the call.

The modem can be programmed to check for a password on an incoming call. If the correct

password is not provided the modem will hang up on the incoming call. If several unsuccessful

incoming call attempts are received in a set time period, the modem will lock out future incoming

calls for a user-set number of hours.

When an incoming call is successfully connected, the control of communications is passed to the

calling software program. The modem will respond to computer commands to download data or

other actions authorized by the meter passwords.

Refer to the Communicator EXT Software Manual for instructions on programming the modem.

2.4.3: Dial-Out Function

The Dial-Out Function (INP2) is intended to allow the meter to automatically report certain

conditions without user intervention. The modem is normally polling the meter to determine if any

abnormal or reportable conditions exist. The modem checks programmed meter conditions and

programmed events (set in Nexus Communicator) to determine if a call should be placed.

If any of the monitored events exist, the modem will automatically initiate a call to a specified

location to make a report or perform some other function. For log full conditions, the meter will

automatically download the log(s) that are nearing the full state.

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2.5: Total Web Solutions

The 10/100BaseT Ethernet Option (INP 100) is a fully customizable web server that uses XML to

provide access to real time data via Internet Explorer. EIG’s name for this dynamic system is Total

Web Solutions. The system incorporates a highly programmable network card with built-in memory

that is installed in the 100BaseT Option meters. Each card can be programmed to perform an

extensive array of monitoring functions and the system is much faster than the 10BaseT Ethernet

Option.

NOTE: Nexus meters with the INP10 Option do not support Total Web Solutions.

2.5.1: Hardware Overview

The Nexus 1250/1252 with the 10/100BaseT Ethernet Option (INP 100) has all the components of

the standard Nexus 1250/1252 PLUS the capability of connection to a network through an Ethernet

LAN or through the Internet via Modbus TCP, HTTP, SMTP, FTP and/or DHCP.

The Internal Network Option of the Nexus Meter is an extremely versatile communication tool.

•

Adheres to IEEE 802.3 Ethernet standard using TCP/IP.

Utilizes simple and inexpensive 100BaseT wiring and connections.

Plugs right into your network using built-in RJ-45 jack.

Programmable to any IP address, subnet mask and gateway requirements.

Communicates using the industry standard Modbus/TCP protocol.

2.5.2: Hardware Connection

Use Standard RJ-45 10/100BaseT cable to connect with the Nexus. The RJ-45 line is inserted into

the RJ-45 Port on the face of the Nexus with IMP100 Ethernet Option.

To make the software connection, use the following steps.

1. Using Port 1 or Port 4 (RS-485 connection), connect a PC to the meter. An RS-232/RS-485

Converter may be required (Example: Electro Industries Unicom 2500).

2. Double click on Communicator EXT Software to open.

3. Click the Quick Connect or the Connection Manager icon in the icon tool bar. Click the

Serial Port button. Make sure data matches the meter then click Connect.

Set the Network Settings using the following steps:

(Refer to Section 3.6 of the Communicator EXT User Manual for more details).

1. From the Device Profile screen, double-click on the Communications Ports line, then

double-click on any of the ports. The Device Profile Communications Settings screen appears.

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2. If you are going to use DHCP, click the Advanced Settings Button:

Click the tab at the top of the DHCP screen. Click Enable.

DHCP will automatically enter the IP Address and some or all of the Interface Settings.

Click OK at the bottom of the screen to return to the Device Profile: Communication Ports

screen. You may have to manually enter DNS, Email, Gateway Setting and/or a Unique

Computer Name. Click OK.

3. If you are NOT using DHCP, in the Network Settings section, enter data provided by your

systems manager:

IP Address:

10.0.0.1

255.255.255.0 (Example)

0.0.0.0 (Example)

NETWORK (Example)

(Example)

Subnet Mask:

Default Gateway:

Computer Name:

Enter the Domain Name Server and Computer Name.

Customize Web Content, if desired. Default Pages with an extensive array of readings comes with

the meter. The content of the pages can be customized using FTP Client.

From the Device Profile: Communications Ports screen, click Advanced Settings. Click the FTP

Client tab on the top of the folder. Using FTP, you can easily replace any file by using the

SAME FILE NAME as the one you want to replace.

Enter the Email Server IP Address. The Default Settings store ONE Email Server IP Address for

administrative purposes or to send an alarm, if there is a problem. An ADDITIONAL 8 can be con-

figured with FTP Client.

Update FIRMWARE, if needed, with TFTP protocol (see Appendix C).

After the above parameters are set, Communicator EXT will connect via the network using a Device

Address of “1” and the assigned IP Address using the following steps:

1. Double click on Communicator EXT icon to open.

2. Click the Connect icon in the icon tool bar. The Connect screen will appear.

3. Click the Network button at the top of the screen. The screen will change to one requesting the

following information:

Device Address:

Host:

IP Address (per your network administrator).

Example: 10.0.0.1

502

Modbus TCP

Network Port:

Protocol:

4. Click the Connect button at the bottom of the screen. Communicator EXT connects to the

Nexus with the Host IP Address via the Network.

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2.6: Measurements and Calculations

The Nexus 1250/1252 Meter measures many different power parameters. The following is a list of the

formulas used to conduct calculations with samples for Wye and Delta services.

Samples for Wye: v , v , v , i , i , i , i

an bn cn a b c n

Samples for Delta: v , v , v , i , i , i

ab bc ca a b c

Root Mean Square (RMS) of Phase to Neutral Voltages: n = number of samples

For Wye: x = an, bn, cn

v²

∑

(

)

V_RMS

Root Mean Square (RMS) of Currents: n = number of samples

For Wye: x=a, b, c, n

For Delta: x = a, b, c

i²

∑

(

)

I_RMS

Root Mean Square (RMS) of Phase to Phase Voltages: n = number of samples

For Wye: x, y= an, bn or bn, cn or cn, an

−

v_y

)

∑

(

)

(

)

V_RMS

For Delta: xy = ab, bc, ca

v²

∑

(

)

V_RMS

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Power (Watts) per phase:

For Wye: x = a, b, c

_xn(t)•i_x(t)

∑

W_X=

Apparent Power (VA) per phase:

For Wye: x = a, b, c

VA_x

•

RMS_XN

RMS_X

Reactive Power (VAR) per phase:

For Wye: x = a, b, c

VAR_x

VA_x²

−

Watt_x²

Power (Watts) Total:

For Wye:

W_T

W_a

W_b

W_c

For Delta:

•i_A− v_BC•i_C)

∑

AB_{(t )}

(t )

W_T=

e Electro Industries/GaugeTech Doc # E107706 V1.25

2-7

Reactive Power (VAR) Total:

For Wye:

VAR_T=VAR_A+VAR_B+VAR_C

For Delta:

⎡

⎢

⎤

⎥

₎•i_A

∑

(

)

VAR_T(V_RMS• I_RMS) −

⎢

⎣

⎥

⎦

⎡

⎢

⎤

₎•i_C

∑

(

)

⎥

(V_RMS• I_RMS) −

⎢

⎣

⎥

⎦

Apparent Power (VA) Total:

For Wye:

VA_T=VA_A+VA_B+VA_C

For Delta:

VA_T

W_T²VAR_T²

Power Factor (PF):

For Wye: x = A, B, C, T

For Delta: x = T

Watt_x

PF_x

VA_x

e Electro Industries/GaugeTech Doc # E107706 V1.25

2-8

Phase Angles:

∠ = cos⁻(PF)

% Total Harmonic Distortion (%THD):

For Wye: x = V , V , V , I , I , I

AN BN CN A B C

For Delta: x = I , I , I , V , V , V

A B C AB BC CA

127

(RMS )²

∑

x_h

THD =

RMS_x

K Factor: x = I , I , I

A B C

127

(h• RMS )²

∑

x_h

KFactor =

127

(RMS )²

∑

x_h

h=1

Watt hour (Wh):

W_T

(

)

∑

3600

sec/hr

VAR hour (VARh):

VAR_T

(

)

VARh

∑

3600

sec/hr

e Electro Industries/GaugeTech Doc # E107706 V1.25

2-9

2.7: Demand Integrators

Power utilities take into account both energy consumption and peak demand when billing customers.

Peak demand, expressed in kilowatts (kW), is the highest level of demand recorded during a set period

of time, called the interval. The Nexus 1250/1252 supports the following most popular conventions for

averaging demand and peak demand: Thermal Demand, Block Window Demand, Rolling Window

Demand and Predictive Window Demand. You may program and access all conventions concurrently

with the Communicator EXT software (see the Communicator EXT User Manual).

Thermal Demand: Traditional analog watt-hour (Wh) meters use heat-sensitive elements to

measure temperature rises produced by an increase in current flowing through the meter. A pointer

moves in proportion to the temperature change, providing a record of demand. The pointer remains

at peak level until a subsequent increase in demand moves it again, or until it is manually reset. The

Nexus 1250/1252 mimics traditional meters to provide Thermal Demand readings.

Each second, as a new power level is computed, a recurrence relation formula is applied. This

formula recomputes the thermal demand by averaging a small portion of the new power value with a

large portion of the previous thermal demand value. The proportioning of new to previous is

programmable, set by an averaging interval. The averaging interval represents a 90% change in

thermal demand to a step change in power.

Block (Fixed) Window Demand: This convention records the average (arithmetic mean) demand

for consecutive time intervals (usually 15 minutes).

Example: A typical setting of 15 minutes produces an average value every 15 minutes (at 12:00,

12:15. 12:30. etc.) for power reading over the previous fifteen minute interval (11:45-12:00, 12:00-

12:15, 12:15-12:30, etc.).

Rolling (Sliding) Window Demand: Rolling Window Demand functions like multiple overlapping

Block Window Demands. The programmable settings provided are the number and length of

demand subintervals. At every subinterval, an average (arithmetic mean) of power readings over the

subinterval is internally calculated. This new subinterval average is then averaged (arithmetic

mean), with as many previous subinterval averages as programmed, to produce the Rolling Window

Demand.

Example: With settings of 3 five-minute subintervals, subinterval averages are computed every 5

minutes (12:00, 12:05, 12:15, etc.) for power readings over the previous five-minute interval (11:55-

12:00, 12:00-12:05, 12:05-12:10, 12:10-12:15, etc.). Further, every 5 minutes, the subinterval aver-

ages are averaged in groups of 3 (12:00. 12:05, 12:10, 12:15. etc.) to produce a fifteen (5x3) minute

average every 5 minutes (rolling (sliding) every 5 minutes) (11:55-12:10, 12:00-12:15, etc.).

Predictive Window Demand: Predictive Window Demand enables the user to forecast average

demand for future time intervals. The Nexus uses the delta rate of change of a Rolling Window

Demand interval to predict average demand for an approaching time period. The user can set a relay

or alarm to signal when the Predictive Window reaches a specific level, thereby avoiding

unacceptable demand levels. The Nexus 1250/1252 calculates Predictive Window Demand using the

following formula:

e Electro Industries/GaugeTech Doc # E107706 V1.25

2-10

Example: Using the previous settings of 3 five-minute intervals and a new setting of 120%

prediction factor, the working of the Predictive Window Demand could be described as follows:

At 12:10, we have the average of the subintervals from 11:55-12:00, 12:00-12:05 and 12:05-12:10.

In five minutes (12:15), we will have an average of the subintervals 12:00-12:05 and 12:05-12:10

(which we know) and 12:10-12:15 (which we do not yet know). As a guess , we will use the last

subinterval (12:05-12:10) as an approximation for the next subinterval (12:10-12:15). As a further

refinement, we will assume that the next subinterval might have a higher average (120%) than the

last subinterval. As we progress into the subinterval, (for example, up to 12:11), the Predictive

Window Demand will be the average of the first two subintervals (12:00-12:05, 12:05-12:10), the

actual values of the current subinterval (12:10-12:11) and the predistion for the remainder of the

subinterval, 4/5 of the 120% of the 12:05-12:10 subinterval.

# of Subintervals = n

Subinterval Length = Len

Partial Subinterval Length = Cnt

Prediction Factor = Pct

Sub

...

Partial

Cnt

Predict

Len

−1

Value

∑

Sub =

Len

Cnt−

Value

∑

Partial

Cnt

n−

⎡

⎢

⎤

⎥

Value

∑

⎡

⎤

⎥

⎦

⎡

Len

−

Cnt

⎤

⎡

⎤

⎢

Partial

−

Pct

⎢

⎣

⎢

⎣

⎥

⎦

⎢

⎣

⎥

⎦

Len

⎢

⎣

⎥

⎦

n−

⎡

⎢

⎤

⎥

Sub

∑

Sub₀

−

Sub_n−

⎡

Len

−

Cnt

⎤

⎡

⎤

⎢

⎣

⎥

⎦

⎢

⎣

⎥

⎦

−

2x(n

−

Len

⎢

⎣

⎥

⎦

e Electro Industries/GaugeTech Doc # E107706 V1.25

2-11

2.8: Nexus External I/O Modules (Optional)

The following multiple analog or digital I/O modules mount externally to the Nexus 1250/1252 Monitor.

The Nexus 1250/1252 Monitor supports up to four I/O modules using internal power. Use the additional

power supply, EIG PSIO, to extend I/O capability. See section 3.4 for mounting diagrams. See Chapter

9 for details on installation and usage of the Nexus External I/O Modules.

Analog Transducer Signal Outputs (Up to two modules can be used with the Nexus 1250/1252.)

•

1mAON4: 4 Analog Outputs, self powered, scalable, bidirectional.

1mAON8: 8 Analog Outputs, self powered, scalable, bidirectional.

20mAON4: 4 Analog Outputs, self powered, scalable.

20mAON8: 8 Analog Outputs, self powered, scalable.

Analog Transducer Inputs (Multiple modules can be used.)

•

8AI1: 8 Analog Inputs 0–1mA, scalable and bidirectional.

8AI2: 8 Analog Inputs 0–20mA, scalable.

8AI3: 8 Analog Inputs 0–5V DC.

8AI4: 8 Analog Inputs 0–10V DC.

Digital Dry Contact Relay Outputs (Multiple modules can be used.)

4RO1: 4 Relay Outputs 10 Amps, 125V AC, 30V DC, Form C.

•

Digital Solid State Pulse Outputs (Multiple modules can be used.)

4PO1: 4 Solid State Pulse Outputs, Form A KYZ pulses.

•

Digital Inputs (Multiple modules can be used.)

8DI1: 8 Digital status inputs Wet/Dry Auto Detect, up to 300V AC/DC.

•

Other I/O Accessories

•

PSIO: Additional power supply for up to six I/O modules. This unit is necessary if you are

connecting more than four I/O modules to a Nexus 1250/1252 Monitor.

MBIO: Bracket for surface-mounting I/O modules to any enclosure.

•

e Electro Industries/GaugeTech Doc # E107706 V1.25

2-12

2.9: Nexus 1250/1252 Meter Specifications

Specification

Nexus Meter

Option D: 24V DC (-20%) – 48V DC (+20%)

Option D2: 120V AC/DC (-20%) – 230V AC (+20%)

150 Volts Phase to Neutral (Standard; for use with PTs)

300 Volts Phase to Neutral (Option -G)

10A Maximum (Programmable to any CT Ratio)

Current: Continuous 200% Rated

Control Power Requirements

Input Voltage Range

Input Current Range

Input Withstanding Capabilities

Current: Surge 10x maximum input for 3 seconds

Surge Withstanding Per IEEE C37.90.1

Voltage: 0.05VA @ 120V rms

Burden

Current: 0.002VA @ 5A rms

I/O Isolation

Sensing Method

Update Time

2500V DC, 60 Hz

RMS

90 msec

Fundamental 20–65 Hz

Frequency Range

Up to 83rd Harmonic Measuring Capability

3.4 x 7.3 x 10.5 inches / 8.6 x 18.5 x 26.6 centimeters

40 watts (with optional modules and display)

Approximately 12 watts (without optional modules and display)

-40°C to +80°C / -40°F to +176°F

15–20 V DC at 50–200mA

Dimensions (HxWxL)

Maximum Power Consumption

Nominal Power Consumption

Operating Temperature

Auxiliary Output Power Voltage

Maximum Auxiliary Power Current 1.6A (short protected)

1244*

UL Listing

*Not evaluated for accuracy, reliability or capability to perform intended function.

Flicker (1252)

Evaluation per IEC 61000-4-15

e Electro Industries/GaugeTech Doc # E107706 V1.25

2-13

2.10: Nexus P40N, P41N, P43N LED External Display Specifications

Specification

Nexus P40N, P41N, P43N LED External Display

Maximum Input Voltage

30V DC

7V DC

Minimum Input Voltage

Maximum Power Consumption

Nominal Power Consumption

Operating Temperature Range

Overall Dimensions (HxWxL)

8 Watts

Approximately 6 Watts

-40°C to + 80°C / -40°F to +176°F

2.2 x 4.4 x 4.4 in / 5.9 x 11.1 x 11.1 cm

2.11: Nexus P60N Touch Screen Display Specifications

Specification

Nexus P60N Touch Screen Display

Maximum Input Voltage

30V DC

10V DC

Minimum Input Voltage

Maximum Power Consumption

Nominal Power Consumption

Operating Temperature Range

Overall Dimensions (HxWxL)

5 Watts

Approximately 4.5 Watts

0°C to + 50°C / +32°F to +122°F

1.6 x 5.4 x 8.0 in / 4.0 x 13.7 x 20.3 cm

e Electro Industries/GaugeTech Doc # E107706 V1.25

2-14

Chapter 3

Hardware Installation

3.1: Mounting the Nexus 1250/1252 Meter

The Nexus 1250/1252 Meter is designed to mount against any firm, flat surface. Use a #10 screw in

each of the four slots on the flange to ensure that the unit is installed securely. For safety reasons,

mount the Meter in an enclosed and protected environment, such as in a switchgear cabinet. Install

a switch or circuit breaker nearby; label it clearly as the meter’s disconnecting mechanism.

NOTE: The Nexus Meter with Internal Modem Option mounts the same way.

Maintain the following conditions:

•

Operating Temperature: -40°C to +70°C / -40°F to +158°F

Storage Temperature: -45°C to +85°C / -49°F to +185°F

Relative Humidity: 5 to 95% non-condensing

10.5” (26.67cm)

2 x 3.25” (8.25cm)

2x4.0” (10.16cm)

7.25”

(18.41cm)

6.74”

(17.11cm)

4 x 0.221” (5.61mm) Thru Slot

(For #10 Screw)

Figure 3.1: Nexus Meter Mounting Diagram, Top View

Electro Industries/GaugeTech Doc # E107706 V1.25

3-1

Nexus Meter Mounting Diagram, Side View

2.35” (5.96cm)

3.40” (8.63cm) (MAX)

Figure 3.2

Electro Industries/GaugeTech Doc # E107706 V1.25

3-2

3.2: Mounting the Nexus LED External Displays

The Nexus 1250/1252 LED Displays, Model # P40N, P41N and P43N, mount using a standard

ANSI C39.1 drill plan.

Secure the four mounting studs to the back of the panel with the supplied nuts.

Six feet of RS-485 communication/power cable harness is supplied. Allow for at least a 1.25-inch

(3.17cm) diameter hole in the back for the cable harness. See Chapter 5 for communication and

power supply details.

The cable harness brings power to the display from the Nexus 1250/1252 Meter, which supplies

15–20V DC. The P40N (or P41N or P43N) can draw up to 500 mA in display test mode.

4.38”Sq.

(11.12cm)

.75” (19.05mm)

1.438”

(3.65cm)

Nexus P40N Display, Side View

Nexus P40N Display, Front View

3.38” (8.58cm) Sq.

4 X 0.198” (5.02mm)

4.00” (10.16cm)

ANSI C39.1 Drill Plan

1.687” (14.28cm)

Figure 3.3: Nexus P40N LED External Display Mounting Diagrams

Electro Industries/GaugeTech Doc # E107706 V1.25

3-3

3.3: Mounting the Nexus P60N Touch Screen External Display

Figure 3.4: Nexus P60N Touch Screen Display Mounting Diagram

The Nexus 1250/1252 P60N Touch Screen Display mounts easily, using the diagrams above and on

the next page. A bezel and a gasket are included with the P60N. Since the P60N employs an LCD

display, the viewing angle must be considered when mounting. Install the P60N at a height and

angle that make it easy for the operator to see and access the screen.

For optimum performance, maintain

the following conditions where the

Touch Screen Display is mounted:

•

Operating Temperature: 0°C to

+50°C / +32°F to +122°F

Factory

Test

Connector

Storage Temperature: -20°C to

+70°C / -36°F to +158°F

Relative Humidity: 25 to 65%

non-condensing

Connect

to NEXUS

Figure 3.5: Nexus P60N Back Detail

Electro Industries/GaugeTech Doc # E107706 V1.25

3-4

Figure 3.6: Cutout for Nexus P60N Touch Screen Display

To bezel mount the P60N, cut an opening in the mounting panel. Follow above cutout dimensions.

Carefully “drop in” the P60N with bezel and gasket attached.

Fasten the unit securely with the four 6-32 hex nuts supplied.

Electro Industries/GaugeTech Doc # E107706 V1.25

3-5

3.4: Mounting the Nexus External I/O Modules

Secure the mounting brackets to the I/O using the screws supplied (#440 pan-head screws). Next,

secure the brackets to a flat surface using a #8 screw with a lock washer.

If multiple I/O modules are connected together, as shown in Figure 3.4, secure a mounting bracket to

both ends of the group. One Nexus will supply power for up to four I/O modules. To connect more

than four I/O modules, use an additional power supply, such as the EIG PSIO. Connect multiple I/O

modules using the RS-485 side ports.

Six feet of RS-485 cable harness is supplied. The cable harness brings power to the display from the

Nexus Meter, which supplies 15–20V DC at 50–200mA. See Chapter 5 for power supply and com-

munication details.

Mounting Bracket

1.125” (2.85cm)

2 x .625” (1.58cm)

0.015” (.38mm)

4.215” (10.70cm)

Mounting Bracket

Figure 3.7: Nexus I/O Modules Mounting Diagram, Overhead View

Mounting Brackets (MBIO)

Female RS-485 Side Port

I/O Port

Male RS-485 Side Port

Figure 3.8: Nexus I/O Module Communication Ports

Electro Industries/GaugeTech Doc # E107706 V1.25

3-6

Nexus I/O Modules Mounting Diagram, Front View

Mounting Bracket (MBIO)

1.25” (3.17cm)+Y

Per Module

2.20” (5.58cm)

3.41” (8.66cm)

2x1.10” (2.79cm)

0.605” (1.53cm)

1.235” (3.13cm)

Figure 3.9

Electro Industries/GaugeTech Doc # E107706 V1.25

3-7

Electro Industries/GaugeTech Doc # E107706 V1.25

3-8

Chapter 4

Electrical Installation

4.1: Wiring the Monitored Inputs and Voltages

Select a wiring diagram from Section 4.8 that best suits your application. Wire the Nexus 1250/1252

exactly as shown. For proper operation, the voltage connection must be maintained and must

correspond to the correct terminal. Program the CT and PT Ratios in the Device Profile section of

the Communicator EXT software; see the Communicator EXT User Manual for details.

The cable required to terminate the voltage sense circuit should have an insulation rating greater than

600V AC and a current rating greater than 0.1 Amp.

Use a minimum of 14 AWG wire for all phase voltage and current connections.

4.2: Fusing the Voltage Connections

For accuracy of the readings and for protection, EIG requires using 0.25-Amp rated fuses on all

voltage inputs as shown in the wiring diagrams (see section 4.8).

The Nexus Meter can handle a maximum voltage of 150V phase to neutral and 300V phase to phase.

Potential Transformers (PTs) are required for higher voltages with the standard rating. With Option -

G, the direct voltage input is extended to 300V phase to neutral and 600V phase to phase.

4.3: Wiring the Monitored Inputs - VRef

The Voltage Reference connection references the monitor to ground or neutral.

4.4: Wiring the Monitored Inputs - VAux

The Voltage Auxiliary connection is an auxiliary voltage input that can be used for any desired

purpose, such as monitoring neutral to ground voltage or monitoring two different lines on a switch.

4.5: Wiring the Monitored Inputs - Currents

Install the cables for the current at 600V AC minimum insulation. The cable connector should be

rated at 10 Amps or greater and have a cross-sectional area of 14 AWG.

Mount the current transformers (CTs) as close as possible to the meter. The following table

illustrates the maximum recommended distances for various CT sizes, assuming the connection is via

14 AWG cable.

Electro Industries/GaugeTech Doc # E107706 V1.25

4-1

EIG Recommendations

CT Size (VA)

Maximum Distance from CT to Nexus (Feet)

2.5

5.0

7.5

10.0

15.0

30.0

120

WARNING!!

DO NOT leave the secondary of the CT open when primary current is flowing. This may

cause high voltage, which will overheat the CT. If the CT is not connected, provide a

shorting block on the secondary of the CT.

It is important to maintain the polarity of the CT circuit when connecting to the Nexus. If the

polarity is reversed, the Nexus will not provide accurate readings. CT polarities are dependent upon

correct connection of CT leads and the direction CTs are facing when clamped around the

conductors. EIG recommends using shorting blocks to allow removal of the Nexus Meter from an

energized circuit, if necessary. Shorting blocks are not required for proper meter operation.

4.6: Isolating a CT Connection Reversal

For a WYE System, you may either:

1. Check the current phase angle reading on the Nexus External Display (see Chapter 6). If it is

negative, reverse the CTs.

2. Or, go to the Phasors screen of the Communicator EXT software (see Communicator EXT

User Manual). Note the Phase Relationship between the Current and Voltage; they should be in

phase.

For a DELTA System:

Go to the Phasors screen of the Communicator EXT software program. The current should be

30 degrees off the phase-to-phase voltage.

4.7: Instrument Power Connections

The Nexus requires a separate power source. To use AC power, connect the line supply wire to the

L+ terminal and the neutral supply wire to the N- terminal on the Nexus. To use DC power, connect

the positive supply wire to the L+ terminal and the negative (ground) supply wire to the N- terminal

on the Nexus. Power supply options and corresponding suffixes are listed in the following table:

Electro Industries/GaugeTech Doc # E107706 V1.25

4-2

Control Power

18-60 Volts DC

Option Suffix

90-276 Volts AC/DC

Do not ground the unit through the negative of the DC supply. Separate grounding is required.

Externally fuse the power supply with a 5 Amp fuse.

4.8: Wiring Diagrams

Choose the diagram that best suits your application. Diagrams appear on the following pages. If the

connection diagram you need is not shown, contact EIG for a custom Connection diagram.

NOTE: If you purchased a “G” Option Nexus for a 300 Volt secondary, be sure to enable the

option on the CT and PT screen of the Communicator EXT software’s Device Profile (see the

Communicator EXT User Manual for details).

Figure #

Description

4.1

4-Wire Wye, 3-Element Direct Voltage with 4 CTs

4.2

4.3

4.4

4.5

4.6

4.7

4.8

4-Wire Wye, 3-Element with 3 PTs and 4 CTs

4-Wire Wye, 3-Element with 3 PTs and 3 CTs

3-Wire, 2-Element Open Delta with 2 PTs and 3 CTs

3-Wire, 2-Element Open Delta with 2 PTs and 2 CTs

3-Wire, 2-Element Delta Direct Voltage with 3 CTs

3-Phase, 4-Wire Wye, 2.5 Element with 2 PTs and 3 CTs

4-Wire, 3-Element Grounded Delta with 4 CTs - G Option

Electro Industries/GaugeTech Doc # E107706 V1.25

4-3

0.25 A

INPUT

Figure 4.1: 4-Wire Wye, 3-Element Direct Voltage with 4 CTs

Electro Industries/GaugeTech Doc # E107706 V1.25

4-4

0.25A

INPUT

Figure 4.2: 4-Wire Wye, 3-Element with 3 PTs and 4 CTs

Electro Industries/GaugeTech Doc # E107706 V1.25

4-5

0.25 A

INPUT

Figure 4.3: 4-Wire Wye, 3-Element with 3 PTs and 3 CTs

Electro Industries/GaugeTech Doc # E107706 V1.25

4-6

0.25 A

Figure 4.4: 3-Wire, 2-Element Open Delta with 2 PTs and 3 CTs.

Electro Industries/GaugeTech Doc # E107706 V1.25

4-7

0.25 A

Figure 4.5: 3-Wire, 2-Element Open Delta with 2 PTs, 2 CTs.

Electro Industries/GaugeTech Doc # E107706 V1.25

4-8

0.25 A

INPUT

Figure 4.6: 3-Wire, 2-Element Delta Direct Voltage with 3 CTs.

Electro Industries/GaugeTech Doc # E107706 V1.25

4-9

0.25 A

INPUT

Figure 4.7: 3-Phase, 4-Wire Wye, 2.5 Element with 2 PTs, 3 CTs.

Electro Industries/GaugeTech Doc # E107706 V1.25

4-10

0.25 A

INPUT

Figure 4.8: 4-Wire, 3-Element Grounded Delta with 4 CTs - G Option.

Electro Industries/GaugeTech Doc # E107706 V1.25

4-11

Electro Industries/GaugeTech Doc # E107706 V1.25

4-12

Chapter 5

Communication Wiring

5.1: Communication Overview

ꢀ

RS-232 communication is used to connect a single Nexus 1250/1252 Meter with another device,

such as a computer, RTU or PLC. The link is viable for a distance up to 50 feet (15.2 m) and is

available only through the Nexus 1250/1252 Meter’s Port 1. You must set the selector switch beneath

the port to RS-232 (see Figure 5.3).

ꢀ

RS-485 communication allows multiple Nexus Meters to communicate with another device at a local

or remote site. The I/O modules and the Nexus Display use RS-485 to communicate with the Nexus

Meter. All RS-485 links are viable for a distance up to 4000 feet (1220 m). Ports 1 through 4 on the

Nexus 1250/1252 Meter are two-wire, RS-485 connections operating up to 115,200 baud. To use

Port 1 for RS-485, set the selector switch to RS-485 (see Figure 5.3).

1 device, 50 feet maximum, Nexus Port 1

RS-232

RS-485

Nexus

RS-232/485

RS-232

Converter

Nexus

(Unicom 2500)

Up to 31 Devices, 4000 feet maximum (without a

repeater), connected in series via RS-485 (daisy chain)

MODEM

RS-232

Nexus

Null Modem

Telephone Line,

Fiber Optic Link or

Radio Link

MODEM

RS-485

RS-232/485 Converter

(Modem Manager)

RS-232

Nexus

Figure 5.1: Communication Overview

e Electro Industries/GaugeTech Doc # E107706 V1.25

5-1

ꢀ

RJ-11 Telephone Line allows a Nexus Meter with the Internal Modem Option to communicate with

a PC. No other hardware is necessary for this easy-to-use connection. The Nexus 1250/1252 Meter

with the Internal Modem Option can connect via RS-485 to other Nexus Meters in local or remote

sites in a daisy chain configuration, as depicted below.

The Nexus Meter with the Internal Modem Option has a unique label; Port 2 is labeled Modem

Gateway. If you are going to use RS-485 to connect multiple Nexus 1250/1252 meters, you MUST

use the Modem Gateway. For more details, see Chapter 10 of this manual.

RS-485

RJ-11

Daisy Chain

Originate Modem

(or Internal to PC)

Figure 5.2: RJ-11 Communication with Internal Modem Option

e Electro Industries/GaugeTech Doc # E107706 V1.25

5-2