—
ABB ME ASUREMENT & ANALY TICS
Pressductor Pillowblock Load Cells
Vertical Measuring PFCL 201
User manual
3BSE023881R0101 en Rev I
USE OF SYMBOLS
This publication includes the following symbols with information regarding safety or other important information:
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Information icon alerts the reader to relevant facts and conditions.
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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 AB’s written permission, and the contents
thereof must not be imparted to a third party nor be used for any unauthorized purpose.
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ance with the terms of such license.
CE-marking
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that the installation is carried out in accordance with the instructions given in this manual.
© Copyright 2004- 2020 ABB. All rights reserved.
Table of Contents
2
Recycling the Transport Material................................................................... 6
Technical Data............................................................................................ 10
Definitions................................................................................................... 11
Measuring principle of the sensor................................................................ 14
Mounting Arrangement............................................................................... 14
Coordinate System..................................................................................... 14
The Electrical Circuit................................................................................... 17
Fault Tracing Procedure.............................................................................. 25
Force Shunting........................................................................................... 26
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 customer’s 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
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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
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
•
•
•
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.
18
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3 Installation
•
•
Locking fluid (medium strength) to lock mounting screws.
other screws for bearing housings etc.
3.4
Mounting
The instructions below apply to a typical mounting arrangement. Variations may be allowed, provi-
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
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).
For achievable cable directions, see Figure 17. Possible directions of cable for PFCL 201CE page
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
20
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3 Installation
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
3BSE023881R0101 en Rev I
27
Pressductor PillowBlock Load Cells, Vertical Measuring PFCL 201, User Manual
Alphabetical index
Alphabetical index
accuracy and accuracy class ........................................... 12
hysteresis ........................................................................ 12
linearity deviation ............................................................. 12
nominal load .................................................................... 11
repeatability error ............................................................. 13
sensitivity ......................................................................... 11
sensitivity drift .................................................................. 13
working temperature range .............................................. 13
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3BSE023881R0101 en Rev I
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Industrial Automation
Measurement & Analytics
Force Measurement
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