ABB PFCL 201CE User Manual

ABB ME ASUREMENT & ANALY TICS  
Pressductor Pillowblock Load Cells  
Vertical Measuring PFCL 201  
User manual  
3BSE023881R0101 en Rev I  
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NOTICE  
The information in this document is subject to change without notice and should not be construed as a commitment by ABB  
AB. ABB AB assumes no responsibility for any errors that may appear in this document.  
In no event shall ABB AB be liable for direct, indirect, special, incidental or consequential damages of any nature or kind arising  
from the use of this document, nor shall ABB AB be liable for incidental or consequential damages arising from use of any  
software or hardware described in this document.  
This document and parts thereof must not be reproduced or copied without ABB ABs written permission, and the contents  
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ance with the terms of such license.  
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© Copyright 2004- 2020 ABB. All rights reserved.  
Table of Contents  
2
Pressductor PillowBlock Load Cells, Vertical Measuring PFCL 201, User Manual  
1 Introduction  
Introduction  
1
1.1  
About this Manual  
This manual describes the load cells PFCL 201C/201CE/201CD in a Pressductor® Strip Tension  
Measuring System.  
The purpose of this manual is to describe the general function and design of the load cells and also  
to be a guidance at installation, commissioning, preventive maintenance and fault tracing.  
1.2  
Disposal and Recycling  
1.2.1  
Environmental Policy  
ABB is committed to its environmental policy. We strive continuously to make our products envi-  
ronmentally more sound by applying results obtained in recyclability and life cycle analyses. Prod-  
ucts, manufacturing process as well as logistics have been designed taking into account the envi-  
ronmental aspects.  
Our environmental management system, certified to ISO 14001, is the tool for carrying out our  
environmental policy. However it is on the customers responsibility to ensure that local legislation is  
followed.  
1.2.2  
Recycling Electrical and Electronic Equipment, WEEE  
The crossed – out wheeled bin symbol on the product(s) and / or accompanying documents  
means that used electrical and electronic equipment (WEEE) should not be mixed with general  
household waste.  
If you wish to discard electrical and electronic equipment (EEE), in the European Union, please  
contact your dealer or supplier for further information.  
Outside of the European Union, contact your local authorities or dealer and ask for the correct  
method of disposal.  
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1 Introduction  
Disposing of this product correctly will help save valuable resources and prevent any potential neg-  
ative effects on human health and the environment, which could otherwise arise from inappropriate  
waste handling.  
1.2.3  
Recycling the Transport Material  
ABB designs all transport material to be recyclable where practical. The recycling of the transport  
material depends on the material type and availability of local recycling programs.  
After receiving the system into the site, the package and the transportation locking have to be  
removed. Recycle the transport material according to local regulations.  
1.2.4  
Disposal of the Product  
When the product is to be disposed, it should be dismantled and the components recycled  
according to local regulations.  
1.2.4.1  
Dismantling and Recycling of the Product  
Dismantle and recycle the components of the product according to local regulations.  
CAUTION  
Some of the components are heavy! The person who performs the dismantling of  
the system must have the necessary knowledge and skills to handle heavy  
components to avoid the risk of accidents and injury from occurring.  
Load cell: These parts are made of structural steel, which can be recycled according to  
local instructions. All the auxiliary equipment, such as cabling or hoses must be removed  
before recycling the material.  
1.3  
Function and Design  
1.3.1  
General  
A complete measuring system normally consists of two load cells, a junction box, one control unit  
with two measurement channels and cabling.  
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1 Introduction  
Load cells  
Load cell cabling  
Adapter plates  
Output signals  
Control unit  
Junction box  
A
Sum A+B  
Differential A-B  
B
Figure 1. Complete Measuring System  
1.3.2  
Load Cells PFCL 201  
The load cells are installed under the roll bearings, where they measure forces at right angles to the  
mounting surface.  
The reactive force from the strip, which is proportional to the strip tension, is transferred to the load  
cells via the roll and the bearings.  
The load cells are connected to the control unit via a junction box. The control unit converts the  
load cell signals to DC voltages that are proportional to the reaction force. Depending on which  
control unit is chosen, it is possible to have the analog signals for the two individual load cells (A  
and B), the sum of the load cell signals (A+B), and/or the difference between the load cell signals  
(A-B).  
1.3.3  
Principle of Measurement  
The load cell only measures force in the direction FR. The measurement force may be positive or  
negative. The load cell is normally installed under the roll bearings. When there is a strip in tension  
over the roll, the tension (T) gives rise to two force components, one in the direction of measure-  
ment of the load cell (FR) and one at right angles (FV).  
The measuring force depends on the relationship between the tension (T) and the wrap angle  
formed by the strip around the measuring roll.  
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1 Introduction  
Wrap  
angle  
T
FV  
T
FR  
Figure 2. Measuring Roll with Force Vectors  
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2 Description  
Description  
2
2.1  
General  
The load cell is machined from a single piece of stainless steel. The sensors are machined directly  
in the piece of steel and are positioned so that they are sensitive to force in the direction of meas-  
urement and insensitive in other directions.  
The load cell is mounted on a base with four screws, and the bearing housing is mounted on top  
of the load cell with four screws.  
Every load cell comes calibrated and temperature compensated.  
The load cells PFCL 201C/201CE/201CD are available in four measurement ranges, all variants  
have the same external dimensions.  
The load cell PFCL 201C is equipped with a connector for the pluggable connection cable.  
The load cell PFCL 201CE has a fixed connection cable with protective hose.  
The load cell PFCL 201CD is provided with an acid-proof cable gland with a fixed PTFE- insulated  
connection cable.  
Connector  
Sensor  
Mounting screw hole  
Measurement  
direction  
Mounting screw hole  
Figure 3. Load Cell PFCL 201C  
Fixed cable connector  
Pressductor R  
Technology  
Figure 4. Load Cell PFCL 201CE with protective hose for cable  
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2 Description  
Figure 5. Load Cell PFCL 201CD with insulated cable connection  
2.2  
Technical Data  
Table 1 Technical Data Load Cell PFCL 201  
PFCL 201  
Type  
Data  
Unit  
kN  
Nominal Loads 1)  
Nominal load in measuring direc-  
tion, Fnom  
C/CD/CE  
5
10  
5
20  
10  
50  
25  
Permitted transverse force within  
the accuracy, FVnom (for h = 300  
mm)  
2,5  
Permitted axial load within the  
accuracy, FAnom (for h = 300 mm)  
1,25  
7,5  
2,5  
15  
5
12.5  
75  
Extended load in measuring direc-  
tion with accuracy class ±1%, Fext  
30  
Max permitted load  
5003)  
125  
In the direction of measurement  
C/CD/CE  
C/CD/CE  
50  
100  
25  
200  
50  
kN  
without permanent change of data,  
2)  
Fmax  
In the transverse direction without  
permanent change of data, FVmax  
(for h = 300 mm)  
12,5  
250  
2
)
Spring constant  
Mechanical data  
Length  
500  
1000  
2500  
kN/mm  
mm  
C/CD/CE  
C
450  
110  
138  
156  
124,6  
37  
Width  
CD  
CE  
Height  
Weight  
C/CD/CE  
kg  
10  
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2 Description  
Material  
C/CD/CE  
C/CD/CE  
Stainless steel SIS 2387 DIN X4CrNiMo 165  
Accuracy  
Accuracy class  
± 0,5  
%
Linearity deviation  
Repeatability error  
Hysteresis  
< ± 0,3  
< ± 0,05  
<0,2  
Compensated temperature range  
Zero point drift  
+20 - +80  
50  
°C  
ppm/K  
Sensitivity drift  
100  
Working temperature range  
Zero point drift  
-10 - +90  
100  
°C  
ppm/K  
Sensitivity drift  
200  
Storage temperature range  
-40 - +90  
°C  
1) Definitions of directions designations “V”and “A” in FV and  
FA are given in Section 2.5.1 Coordinate System.  
2) Fmax and FVmax are allowed at the same time.  
h
3) Max. permitted load for the load cell is 10 × Fnom. The  
overload capacity for the total installation may be limited by  
the screws.  
Pressductor  
System  
h= Building Height  
2.3  
Definitions  
Nominal load  
Nominal load, Fnom, is the maximum load in the measurement direction for which the load cell is  
dimensioned to measure within the specified accuracy class. The load cell is calibrated up to Fnom  
.
Sensitivity  
Sensitivity is defined as the difference in output values between nominal load and zero load.  
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2 Description  
Signal  
Rated output value  
at nominal load  
Sensitivity  
Fnom  
Force  
Figure 6. Sensitivity  
Accuracy and Accuracy Class  
Accuracy class is defined as the maximum deviation, and is expressed as a percentage of the sen-  
sitivity at nominal load. This includes linearity deviation, hysteresis and repeatability error.  
Linearity Deviation  
Linearity deviation is the maximum deviation from a straight line drawn between the output values  
at zero load and nominal load. Linearity deviation is related to the sensitivity.  
Signal  
Fnom  
Figure 7. Linearity Deviation  
Force  
Hysteresis  
Hysteresis is the maximum difference in the output signal at the same load during a cycle from zero  
load to nominal load and back to zero load, related to the sensitivity at nominal load. The hysteresis  
of a Pressductor transducer is proportional to the load cycle.  
Signal  
Fnom  
Force  
Figure 8. Hysteresis  
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2 Description  
Repeatability error  
Repeatability error is defined as the maximum deviation between repeated readings under identical  
conditions. It is expressed as a percentage of the sensitivity at nominal load.  
Compensated temperature range  
The temperature drifts of the load cell have been compensated for in certain temperature  
ranges. That is the temperature range within which the specified permitted temperature drifts (i.e.  
zero point and sensitivity drifts) of the load cell are maintained.  
Working temperature range  
Working temperature range is the temperature range within which the load cell can operate within  
a specified accuracy. The maximum permitted temperature drifts (i.e. zero point and sensitivity  
drifts) of the load cell are not necessarily maintained in the whole working temperature range.  
Storage temperature range  
Storage temperature range is the temperature range within which the load cell can be stored.  
Zero point drift with temperature  
Zero point drift is defined as the signal change with temperature, related to the sensitivity, when  
there is zero load on the load cell.  
Sensitivity drift with temperature  
Sensitivity drift is defined as the signal change with temperature at nominal load, related to the sen-  
sitivity, excluding the zero point drift.  
Signal  
Sensitivity  
drift  
Zero  
point  
drift  
Fnom  
Force  
Figure 9. Sensitivity drift with temperature  
Compression  
Compression is the total reduction in the height of the load cell when the load is increased from  
zero to the nominal value.  
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2 Description  
2.4  
Measuring principle of the sensor  
The measuring principle of the sensor is based on the Pressductor® technology and the fact that  
the permeability of a magnetic material changes under mechanical stress.  
The sensor is a membrane machined in the load cell. Primary and secondary windings are wound  
through four holes in the load cell so that they cross at right angles.  
The primary winding is supplied with an alternating current which creates a magnetic field around  
the primary winding. Since the two windings are at right angles to each other, there will be no mag-  
netic field around the secondary winding, as long as there is no load on the sensor.  
When the sensor is subjected to a mechanical force in the direction of measurement, the propaga-  
tion of the magnetic field changes so that it surrounds the secondary winding, inducing an alternat-  
ing voltage in that winding.  
The control unit converts this alternating voltage into a DC voltage proportional to the applied  
force. If the measurement force changes direction, the sensor signal changes also polarity.  
Figure 10. Propagation of magnetic field around secondary winding due to mechanical force on sensor  
2.5  
Mounting Arrangement  
When choosing a mounting arrangement it is important to remember to position the load cell in a  
direction that gives sufficient measuring force (FR) to achieve the highest possible accuracy.  
The load cell has no particular correct orientation; it is positioned in the orientation best suited for  
the application, bearing in mind the positions of the screw holes. The load cell can also be installed  
with the roll suspended under the load cell.  
The load cell has the same sensitivity in both tension and compression, so the load cell can be  
installed in the easiest manner.  
Typical mounting arrangements are horizontal and inclined mounting.  
2.5.1  
Coordinate System  
A coordinate system is defined for the load cell. This is used in force calculations to derive force  
components in the load cell principal directions.  
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2 Description  
Where direction designations R, V and A are recognized as suffixes for force components, F, this  
represents the force component in the respective direction. The suffix R may be omitted, when  
measuring direction is implied by the context.  
R
V
A
V
A
R= Measuring direction  
V= Transverse direction  
A= Axial direction  
R
Figure 11. Coordinate system defining directions used in force calculations  
2.5.2  
Horizontal Mounting  
In the majority of cases horizontal mounting is the most obvious and simplest solution. Stand,  
mounting surface and shims (if required) are simple and cheap to make.  
When calculating the force, the equations below must be used:  
FR = T × (sin α + sin β)  
FRT = Tare  
FRtot = FR + FRT = T × (sin α + sin β) + Tare  
FV = T × (cos β - cos α)  
FVT = 0  
FVtot = FV + FVT = T × (cos β - cos α) + 0 = T × (cos β - cos α)  
where:  
T = Strip tension  
FR = Force component from strip tension in measurement direction, R  
FRT = Force component from Tare in measurement direction, R  
FRtot = Total force in measurement direction, R  
FV = Force component from strip tension in transverse direction, V  
FVT = Force component from Tare in transverse direction, V  
FVtot = Total force in transverse direction, V  
Tare = Force due to tare weight  
α = Deflection angle on one side of the roll relative the horizontal plane  
β = Deflection angle on the other side of the roll relative the horizontal plane  
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2 Description  
Figure 12. Horizontal mounting  
2.5.3  
Inclined Mounting  
Inclined mounting means arrangements in which the load cell is inclined relative to the horizontal  
plane. In some cases this is the only option.  
When calculating the force, the equations below must be used:  
FR = T × [sin (α - γ) + sin (β + γ)]  
FRT = Tare × cos γ  
FRtot = FR + FRT = T × [sin (α - γ) + sin (β + γ)] + Tare × cos γ  
FV = T × [cos (β + γ) - cos (α - γ)]  
FVT = - Tare × sin γ  
FVtot = FV + FVT = T × [cos (β + γ) - cos (α - γ)] - Tare × sin γ  
γ = 90° - φ  
where:  
T = Strip tension  
FR = Force component from strip tension in measurement direction, R  
FRT = Force component from Tare in measurement direction, R  
FRtot = Total force in measurement direction, R  
FV = Force component from strip tension in transverse direction, V  
FVT = Force component from Tare in transverse direction, V  
FVtot = Total force in transverse direction, V  
Tare = Force due to tare weight  
α = Deflection angle on one side of the roll relative the horizontal plane  
β = Deflection angle on the other side of the roll relative the horizontal plane  
φ= Angle for measurement direction relative the horizontal plane  
γ = Angle for load cell mounting surface relative the horizontal plane  
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2 Description  
β
α
F
V
T
φ
F
R
Tare  
T
γ
Figure 13. Inclined mounting  
2.6  
The Electrical Circuit  
The electrical circuit of the load cell is shown in the diagram below.  
R
1
C
Secondary circuit  
(signal)  
R
T
2
D
A
B
0.5 A/330 Hz  
Primary  
circuit  
(supply current)  
Figure 14. Load cell circuit diagram  
The load cell is supplied with a 0.5 A, 330 Hz alternating current. The secondary signal is calibrated  
for the correct sensitivity with a voltage divider R1 - R2, and temperature compensation is provided  
by thermistors T.  
All impedances on the secondary side are relatively low. The output impedance is typically 9-12 Ω ,  
which helps to suppress interference.  
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3 Installation  
Installation  
3
3.1  
General  
The equipment is a precision instrument which, although intended for severe operating conditions,  
must be handled with care. The load cells should not be unpacked until it is time for installation.  
To achieve the specified accuracy, the best possible reliability and long-term stability, the load cells  
must be installed in accordance with the instructions below. See also 6.4 Fault Tracing in the  
The foundation for the load cell must be made as stable as possible. A resilient stand lowers  
the critical frequency of the measuring roll and bearing arrangement.  
The surfaces closest to the load cell, and other surfaces that affect the fit, must be machined  
flat to within 0.05 mm.  
There must not be any shims immediately above or below the load cell, as this may  
adversely affect the flatness. Instead, shims may be placed between the adapter plate and  
the foundation or between the adapter plate and the bearing housing.  
The screws that secure the load cell must be tightened with a torque wrench.  
The bearing arrangement for the measuring roll must be designed to allow axial expansion of  
the roll with changes in temperature.  
Any drive to the roll must be applied in such a way that interfering forces from the drive are  
kept to a minimum.  
The measuring roll must be dynamically balanced.  
The mounting surfaces of the load cells must be on the same height and parallel with the  
measuring roll.  
In a corrosive environment, galvanic corrosion may occur between the load cell,  
galvanized screws and adapter plates. This makes it necessary to use stainless steel screws  
and adapter plates of stainless steel or equivalent. See adapter plates in  
3.2  
3.3  
Unpacking  
When the equipment arrives, check against the delivery document. Inform ABB of any complaint,  
so that errors can be corrected immediately and delays avoided.  
Preparations  
Prepare the installation in good time by checking that the necessary documents and material are  
available, as follows:  
Installation drawings and this manual.  
Standard tools, torque wrench and instruments.  
Rust protection, if additional protection is to be given to machined surfaces. Choose TEC-  
TYL 511 (Valvoline) or FERRYL (104), for example.  
Load cells, adapter plates, bearing housings, etc.  
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3 Installation  
Locking fluid (medium strength) to lock mounting screws.  
Screws as listed in Table 2. page 19 and Table 3. page 19 to secure the load cell, and  
other screws for bearing housings etc.  
3.4  
Mounting  
The instructions below apply to a typical mounting arrangement. Variations may be allowed, provi-  
ded that the requirements of 3.1 General are complied with.  
1. Clean the foundation and other mounting surfaces.  
2. Fit the lower adapter plate to the load cell. Tighten the screws to the torque stated in Table 2.  
3. Fit the load cell and the lower adapter plate to the foundation, but do not fully tighten the  
screws.  
4. Fit the upper adapter plate to the load cell, tighten to the torque stated in Table 2. page 19 or  
5. Fit the bearing housing and the roll to the upper adapter plate, but do not fully tighten the  
screws.  
6. Adjust the load cells so that they are in parallel with each other and in line with the axial direction  
of the roll. Torque tighten the foundation screws.  
7. Adjust the roll so that it is at right angles to the longitudinal direction of the load cells.Torque  
tighten the screws in the upper adapter plate.  
8. Apply rust protection to any machined surfaces that are not rust proof.  
Table 2 Galvanized MoS2 lubricated Screws according to ISO 898/1  
Strength class  
8.8 (1) (12.9)  
Dimension  
M16  
Tightening torque  
170 (286) Nm  
Table 3 Waxed Screws of Stainless Steel According to ISO 3506  
Strength class  
A2-80 (1)  
Dimension  
M16  
Tightening torque  
187 Nm  
(1) Strength class 12.9 is recommended for 50 kN load cells, when large overloads are expected, especially  
if the mounting screws are subjected to tension.  
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3 Installation  
Roll  
Bearing housing  
Upper adapter plate  
Lower adapter plate  
Load cell  
Pressductor  
System  
Foundation  
Figure 15. Typical installation  
3.5  
Cabling for Load Cell PFCL 201CE  
Cabling with protective hose shall be mounted so that the forces related to the weight of the cable/  
hose do not act in the measuring direction of the load cell. A cable clamp is therefore necessary. If  
the load cell is prevented from movement in the measuring direction- it will shunt force, and the  
measured force will differ from the actual.  
The favourable direction of the cable/hose is the horizontal direction to the left or right as indicated  
in Figure 16. Position of cable from factory page 20. This as possible forces in the longitudinal  
direction of the cable/hose due to temperature, will act perpendicular to the measuring direction of  
the load cell (the direction in which the load cell is insensitive to loads).  
21.  
The direction of the cable and protective hose can be changed by unscrewing the two screws in  
the connection box and turning the cable to a suitable direction. Make sure to re-install the screws  
in the connection box.  
Pressductor R  
Technology  
Figure 16. Position of cable from factory  
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Pressductor R  
Technology  
Figure 17. Possible directions of cable for PFCL 201CE  
CAUTION  
Cable bending is not allowed in the connection  
Pressductor R  
Technology  
Figure 18. Cable bending, wrong installation  
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4 Commissioning  
Commissioning  
4
4.1  
General  
The actual procedure for commissioning a load cell is simple, provided that the load cells and  
cables have been properly installed. Commissioning of the control unit is described in the relevant  
chapter of the control unit manual.  
Check the following:  
that the load cells have been correctly installed and aligned  
that all screws have been tightened to the correct torque  
that all cables are correctly installed and connected  
that all connectors are plugged in  
4.2  
Preparatory Calculations  
To be able to set the correct measuring range, the measurement force per load cell FR/2 at maxi-  
mum tension T must be calculated. Each load cell is subjected to half the total measurement force  
FR. This calculation must be done before commissioning can begin. Calculation of FR is described  
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5 Maintenance  
Maintenance  
5
5.1  
General  
Strip Tensiometer Systems with Pressductor® load cells are extremely reliable and do not require  
daily servicing. As a preventive measure, checks should be done periodically on all parts subject to  
mechanical wear.  
5.2  
Preventive Maintenance  
Check mounting screws and tighten if necessary.  
The gaps between load cell and plates should be checked to ensure that they do not get clogged  
with dirt, causing shunt force past the load cell. Clean the gaps with compressed air if necessary.  
The cable between the load cell and the junction box is subjected to possible damage and should  
be checked and replaced if necessary.  
5.3  
Spare Parts  
Users are recommended to keep the following spare parts in stock:  
One load cell of correct type and size.  
One connector complete with cable (for PFCL 201C)  
Table 4 Ordering numbers for Load Cell PFCL 201  
Description  
Type  
Nominal load  
(kN)  
Ordering numbers  
Load cell  
Load cell  
Load cell  
Load cell  
Load cell  
Load cell  
Load cell  
Load cell  
Load cell  
Load cell PFCL 201C  
Load cell PFCL 201C  
Load cell PFCL 201C  
Load cell PFCL 201C  
Load cell PFCL 201CE  
Load cell PFCL 201CE  
Load cell PFCL 201CE  
Load cell PFCL 201CE  
Load cell PFCL 201CD  
5,0  
3BSE027070R5  
3BSE027070R10  
3BSE027070R20  
3BSE027070R50  
3BSE027062R5  
3BSE027062R10  
3BSE027062R20  
3BSE027062R50  
3BSE029774R5  
10,0  
20,0  
50,0  
5,0  
10,0  
20,0  
50,0  
5,0  
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5 Maintenance  
Load cell  
Load cell  
Load cell  
Load cell PFCL 201CD  
Load cell PFCL 201CD  
Load cell PFCL 201CD  
10,0  
20,0  
50,0  
3BSE029774R10  
3BSE029774R20  
3BSE029774R50  
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6 Fault Tracing  
Fault Tracing  
6
6.1  
General  
It is important to be thoroughly familiar with the description of operation in  
2 Description before starting fault tracing.  
6.2  
Interchangeability  
The load cells are factory calibrated and can be replaced directly with another load cell of the same  
type. The only adjustment required after load cell replacement is zero adjustment in the control  
unit.  
6.3  
Fault Tracing Procedure  
The measuring equipment can be divided into four parts:  
The mechanical installation.  
The load cell.  
The junction boxes and the cabling.  
The control unit (see the control unit manual).  
The fault symptoms indicate in which part the fault lies.  
Faults in the mechanical installation often result in an unstable zero point or incorrect sensi-  
tivity.  
If a fault follows something else in the process, such as temperature, or can be linked  
to a particular operation, it probably originates from something in the mechanical installation.  
Load cells are extremely robust and can withstand ten times their nominal load in the meas-  
uring direction. If a load cell has nevertheless been so overloaded that its data have been  
altered, this is probably due to an event in the mill, such as strip breakage. On excessive  
overload the first thing that happens is that the zero point shifts.  
Problems such as interference or unstable zero point may be caused by wiring faults. Some  
malfunctions may be due to the proximity of cables that cause interference. Incorrect instal-  
lation, such as imbalance in a cable or screens earthed at more than one end may cause the  
zero point to become unstable. Cables are subject to mechanical wear, and should be  
checked regularly. The junction box should also be checked, especially if it is subject to  
vibration.  
A fault in the control unit usually causes intermittent loss of a function. It is unusual for the  
control unit to cause stability problems. Faults in connected units may affect the operation of  
the control unit. For further details see the control unit manual.  
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6 Fault Tracing  
6.4  
Fault Tracing in the Mechanical Installation  
There are a number of parts in the mechanical arrangement that can cause faults. The extent to  
which these faults are repeatable differs. Possible causes fall into the following groups.  
Defective mounting surface, stand or adapter plates.  
Force shunting.  
Insufficient mounting of load cell and adapter plates.  
Rolls and bearings.  
Driven roll.  
6.4.1  
6.4.2  
Defective Mounting Surface, Support or Adapter Plates  
An unmachined or poorly machined mounting surface, which is uneven, may cause bending or  
twisting of the load cell. This may result in instability of the zero point.  
Force Shunting  
Force shunting means that some of the force is diverted past the load cell. This may be caused by  
some kind of obstruction to the force through the load cell. The connecting cables, for example,  
have been incorrectly installed and are preventing movement. Another possible cause is that the  
roll is not free to move in the direction of measurement, possibly because something is mounted  
too close to a bearing housing, or because an object has worked loose and become trapped  
between the bearing housing and adjacent parts.  
Force shunting causes the strip tension indication to be lower than the actual strip tension.  
6.4.3  
6.4.4  
Fastening of Load cell and Adapter Plates  
Screw joints that have not been properly tightened or have lost their pre-tightening force, cause  
sliding at the mating surfaces. Fastening of the load cell is especially critical. If a load cell is not  
properly secured, the zero point will be unstable. Sliding between other surfaces may cause the  
same symptoms.  
Rolls and Bearings  
An incorrectly designed bearing arrangement may give rise to high axial forces. The roll should be  
fixed at one end and free at the other.  
If both ends are fixed, there will be a high axial (thrust) force due to expansion of the shaft with  
rising temperature.  
Even a correctly designed bearing arrangement may deteriorate with time; bearings become worn,  
and so on. This may give similar symptoms, such as slow zero point drift between cold and hot  
machine, or sudden jumps in the signal.  
6.4.5  
Driven Roll  
A source of error that is seldom suspected is the roll itself. The effect is especially critical when  
measuring forces on the load cell are relatively low. Long drive shafts with their associated universal  
joints may cause unstable signals if they are not properly maintained. It is important to lubricate  
universal joints. Longitudinal expansion of the drive shaft should also be taken into account. Since  
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Pressductor PillowBlock Load Cells, Vertical Measuring PFCL 201, User Manual  
6 Fault Tracing  
such expansion is often taken up by splines, these must also be lubricated. The symptoms are  
instability of the signal, for instance jumps in the signal during slow running.  
6.5  
Fault Tracing of Load Cells, Junction Boxes and  
wiring  
The load cell is very robust and can withstand high overloads. The data of a Pressductor load cell  
does not change slowly, but in steps, usually in connection with an event in the mill. Excessive  
overloading usually results in permanent shifting of the zero point.  
Poor contact in the junction box causes intermittent faults. Both sensitivity and zero point may vary.  
Check all screw terminals. Do not use pins crimped to the connecting wires, as these often work  
loose after a time.  
The cabling, especially the cable to the load cell, is the part that is most exposed to damage.  
Since the resistance of the load cell windings is low, it is easy to check the load cells and cabling  
from the control unit.  
Typical readings are 2 Ω for the resistance of the primary winding and 9-12 Ω  
for the output impedance of the secondary winding.  
Insulation faults in the cabling or the load cell may cause incorrect sensitivity or unstable zero point.  
When the load cell circuits have been isolated from earth and from the control unit at the discon-  
nectable terminals, it is easy to measure the insulation from the control unit.  
If the cables are not routed correctly, they may pick up interference from other cables.  
Junction box  
Load cell A  
Control unit  
Blue  
B
C
3
2
Black  
White  
Red  
D
A
4
1
Load cell B  
B
C
D
3
2
4
Blue  
Black  
White  
A
Red  
1
Figure 19. Typical load cell cabling  
For circuit diagram applications, see the manual for the applicable control unit:  
Millmate Strip Tension Systems with Millmate Controller 400, 3BSE023139Rxxxx  
Web Tension Systems with Tension Electronics PFEA 111/112, 3BSE029380Rxxxx  
Web Tension Systems with Tension Electronics PFEA 113, 3BSE029382Rxxxx  
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Pressductor PillowBlock Load Cells, Vertical Measuring PFCL 201, User Manual  
Appendix A Drawings  
Drawings  
A
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Appendix A Drawings  
A.1  
Load Cell PFCL 201C, Dimension Drawing  
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Pressductor PillowBlock Load Cells, Vertical Measuring PFCL 201, User Manual  
Appendix A Drawings  
A.2  
Load Cell PFCL 201CE, Dimension Drawing  
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Appendix A Drawings  
A.3  
Load Cell PFCL 201CD, Dimension Drawing  
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Appendix A Drawings  
A.4  
Adapter Plate Upper PFCL 201, Dimension  
Drawing  
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Appendix A Drawings  
A.5  
Adapter Plate Lower PFCL 201, Dimension  
Drawing  
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Pressductor PillowBlock Load Cells, Vertical Measuring PFCL 201, User Manual  
Alphabetical index  
Alphabetical index  
accuracy and accuracy class ........................................... 12  
compensated temperature range .................................... 13  
hysteresis ........................................................................ 12  
linearity deviation ............................................................. 12  
nominal load .................................................................... 11  
repeatability error ............................................................. 13  
sensitivity ......................................................................... 11  
sensitivity drift .................................................................. 13  
with temperature ............................................................. 13  
working temperature range .............................................. 13  
zero point drift ................................................................. 13  
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ABB AB  
Industrial Automation  
Measurement & Analytics  
Force Measurement  
SE-721 59 Västerås Sweden  
Tel: +46 21 32 50 00  

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