Cameron 288A User manual

BARTON NUCLEAR MODEL 288A
DIFFERENTIAL PRESSURE
INDICATING SWITCH
User Manual
Part No. 9A-C10301, Rev. 08
AUGUST 2021
Contents
Safety ............................................................................................................ 2
Section 1—Introduction ................................................................................. 3
General ......................................................................................................... 3
Main Components ......................................................................................... 3
Indicating Switch ...................................................................................... 4
Relays ....................................................................................................... 5
Wiring ........................................................................................................ 5
Diff erential Pressure Unit (DPU) ............................................................... 5
Specifi cations ............................................................................................... 5
Nuclear Qualifi cations ............................................................................... 6
Section 2—Installation ................................................................................... 7
General ......................................................................................................... 7
Mounting/Piping/DPU Installation ................................................................. 7
Electrical Connection (Switches/Relays) ...................................................... 7
Switch Use .................................................................................................... 7
Startup .......................................................................................................... 8
Switch and Relay Wiring Diagrams............................................................... 9
Section 3—Maintenance and Calibration ................................................... 14
Tools............................................................................................................ 14
Bezel/Lens (or Cover) Installation and Removal......................................... 14
Calibration Check........................................................................................ 15
Pointer Installation and Removal ................................................................ 16
Pointer Installation .................................................................................. 16
Pointer Removal ...................................................................................... 16
Indicator Calibration .................................................................................... 17
Drive Arm Tightness Test ......................................................................... 19
Drive Arm Stop Adjustment .................................................................... 20
Switch Calibration ..................................................................................... 20
Calibration Setup ..................................................................................... 20
Calibration Procedure ............................................................................. 21
Changing Switch Set Point ........................................................................ 22
Defi nitions of Terms ................................................................................. 22

2
Safety
WARNING: This symbol identifi es information about practices or circum-
stances that can lead to personal injury or death, property damage, or
economic loss.
CAUTION: Indicates actions or procedures which if not performed correctly
may lead to personal injury or incorrect function of the instrument
or connected equipment.
IMPORTANT: Indicates actions or procedures which may aff ect instrument operation or
may lead to an instrument response that is not planned.
Product Brand
* Mark of Schlumberger.
Other company, product, and service names are the properties of their respective owners.
Copyright © 2017 Schlumberger. All rights reserved.
Best Practices for Set Points ................................................................... 22
Changing Set Point of an In-Service Instrument ..................................... 23
Changing Set Point of an Out-of-Service Instrument .............................. 24
Range Changes ...................................................................................... 24
Parts Replacement...................................................................................25
Troubleshooting ......................................................................................... 26
Section 4—Assembly Drawing and Parts Lists ..................................... 28
Section 5—Dimensional Drawings .......................................................... 34
Appendix A—Model 224 DPU ................................................................A-1
DPU Description ........................................................................................A-1
Specifi cations .........................................................................................A-1
Theory of Operation ...............................................................................A-3
DPU Installation .........................................................................................A-4
General...................................................................................................A-4
Mounting.................................................................................................A-5
Piping .....................................................................................................A-5
Piping Diagrams .....................................................................................A-6
Startup .....................................................................................................A-12
DPU Maintenance ....................................................................................A-12
Required Tools .....................................................................................A-12
DPU Cleaning/Inspection Procedure....................................................A-13
Changing the DPU Range ....................................................................A-14
Replacing the Bellows Unit Assembly (BUA) .......................................A-14
DPU Troubleshooting ...............................................................................A-15
DPU Assembly Drawing and Parts List ....................................................A-17
DPU Dimensional Drawings.....................................................................A-19

3
Model 288A Differential Pressure Indicating Switch Section 1
Section 1—Introduction
General
The Barton* weatherproof Model 288A is a diff erential pressure indicating
switch. The Model 288A has a NEMA-4 watertight die-cast aluminum case
(fi nished with a weather-resistant black epoxy resin paint). The cover lens is
secured in the bezel with an elastomer ring to reduce the possibility of acci-
dental breakage. This ring also acts as a seal between the bezel and the case to
ensure a moisture, fume and dust-free atmosphere for the indicator and switch
mechanism. The large cover lens allows maximum readability of the indicat-
ing pointer.
Switches and all adjustments are readily accessible when the cover is re-
moved.
The built-in switches energize either single or dual alarm circuits when the
measured diff erential pressures exceed predetermined limits. These limits
may be either maximum, minimum, or both.
Main Components
Switch
Arm
Adjust
Switch
Adjust
Adjust
Figure 1.1—Switch components

4
Section 1 Model 288A Differential Pressure Indicating Switch
Indicating Switch
(refer to Figure 1.2, Figures 2.1 to 2.6, and Table 2.1)
Rotation of the DPU torque tube shaft is coupled through connecting linkage
within the switch case to move the pointer across the scale plate. An actuat-
ing cam, directly connected to the torque tube shaft, rotates with the motion
of the shaft. Two cam follower roller/actuator arm assemblies, one for each
switch, respond to torque tube rotation by opening and closing the switches as
they ride on and off the cam. The levels of diff erential pressure at which the
switches actuate are adjustable with high and low alarm switch adjustments
on the scale plate.
F igure 1.2—Switch actuation example

5
Model 288A Differential Pressure Indicating Switch Section 1
Standard models can have one or two alarm switches. Each switch can be
connected to operate normally-opened or normally-closed. The direct-set
switch contacts are adjustable over a scale range of 5-95% nominal.
The cam rotates counterclockwise with increased pressure. In Figure 1.2,
page 4, the low switch is set at 25% diff erential pressure, and the high switch
is set at 75% diff erential pressure.
Switches are available in several variations.
• SPDT: This is the standard model (low, high, or both)
• DPDT: Two switches are stacked and actuated by a single lever (low,
high, or both)
• Three or four SPDT: Switches have independent switch points.
Switches 1 and 3 are usually low switches set for decreasing pressures;
switches 2 and 4 are usually high switches set for increasing pressures.
Relays
Relays are actuated by internal switches and are available in several varia-
tions:
• SPDT
• DPDT
• Two SPDT
• Two DPDT
Wiring
No. 22 AWG is used for internal wiring and No. 18 AWG is used for external
wiring.
Diff erential Pressure Unit (DPU)
For detailed information on the Model 224 DPU, see Appendix A.
Specifi cations
General:
Actuating Unit (DPU) ...................... Model 224 DPU
Dial Size ......................................... 6 inches (150 mm)
Temperature Limits (Ambient) ........ -40°F (-40°C) to +180°F (+82°C)
Switch Repeatability ....................... ±0.25% of full scale
Switch Deadband ........................... ±5% (SPDT); ±6% (DPDT)
Switch Type .................................... Mechanical, Snap-Acting; all switches are SPDT
(DPDT switches are stacked SPDT switches with a
common actuator)
Relay Contact Type ........................ Single Pole, Double Throw (SPDT)
Double Pole, Double Throw (DPDT)
Adjustability .................................... 5% to 95% of factory calibrated scale
Activation ........................................ Increasing or decreasing scale

6
Section 1 Model 288A Differential Pressure Indicating Switch
Switch Contact Rating:
5.0 Amps @ 250 VAC, 50/60 Hz1
3.0 Amps @ 30 VDC (Resistive)1,2
1.0 Amp @ 30 VDC (Inductive)1,2,3
1. CSA Approved
2. CE Approved (Voltage limited to less than 50 VDC or 35 VAC for CE applications)
3. Arc suppression recommended for inductive loadings.
Relay Contact Ratings:
10 Amps @ 150/250 VAC
10 Amps @ 14/28 VDC
1.0 HP @ 208/240 VAC
Relay Coil Voltages:
120 VAC @ 5VA Max.
110 VDC @ 2W Max.
Coil Power Requirement:
DC Relay ........................................ 1.5 Watts
AC Relay ........................................ 2.75 Volt Amps
Accuracy of Indications (1 or 2 SPDT Switches):
0 to 30" WC to 0 to 50" WC...............................±1-1/4% of full scale DP
0 to 51" WC to 0 to 60 PSI ................................±1% of full scale DP
0 to 61 PSI to 0 to 150 PSI ...............................±1-1/4% of full scale DP
0 to 151 PSI to 0 to 400 PSI .............................±1-1/2% of full scale DP
0 to 401 PSI to 0 to 600 PSI .............................±2% of full scale DP
0 to 601 PSI to 0 to 1000 PSI ...........................±4-1/2% of full scale DP
1 or 2 DPDT Switches (S401) .......................... Add ±1/2% to above values
Near switch setpoint (±10% full scale) ............. Add ±1/2% to above values
For suppressed ranges .................................... Add ±1/4% to above values
Switch Deadband:
SPDT .............................................. ±5% of full scale DP (max)
DPDT .............................................. ±6% of full scale DP (max)
Accuracy of Repeatability ............... ±0.25% of full scale DP
Nuclear Qualifi cations
The following nuclear qualifi cation applications are based on Cameron Engineering
Report 9A-CR3-288A-13 and 50277306-C-0000193 with switch chatter sensitivity ad-
dressed in Cameron Engineering Report 9A-CR3-288A-19:
• One or two SPDT switches: Radiation Augmented (3 MRads), Full Functional, 12G,
Mild Environment Applications
• One or two DPDT switches: Structural and Pressure Boundary Integrity Applica-
tions
• One or two relays: Structural and Pressure Boundary Integrity Applications
• Three or four independently adjustable SPDT switches: Structural and Pressure
Boundary Integrity Applications

7
Model 288A Differential Pressure Indicating Switch Section 2
Section 2—Installation
General
The instrument should be inspected at time of unpacking to detect any dam-
age that may have occurred during shipment.
IMPORTANT: The DPU was checked for accuracy at the factory. Do not change any of
the settings during examination or accuracy could be aff ected.
For applications requiring special cleaning/precautions, a polyethylene bag
is used to protect the instrument from contamination. This bag should be
removed only under conditions of extreme cleanliness.
Mounting/Piping/DPU Installation
Dimensional drawings are provided in Section 5, page 34. See Appendix A for
Model 224 DPU installation and maintenance information.
Electrical Connection (Switches/Relays)
Units are supplied with either single or dual alarm switches and/or relays
(depending on customer order). The direct-set switch contacts are adjustable
over 5% to 95% of the scale range.
Table 2.1, page 8, shows switch and relay wiring color coding for legacy and
current confi gurations. Figures 2.1 through 2.6 show switch and relay wiring.
The high switch and low switch set point adjustment procedures are covered
in Changing Switch Set Point, page 22.
For physical location of switches, see Figure 1.1, page 3.
Switch Use
Switch contact life and setpoint repeatability are infl uenced by various ap-
plication conditions such as temperature, humidity, airborne contamination,
vibration, amount of plunger travel, cycling rate, and rate of plunger travel
(and others), as well as by the electrical (circuit) characteristics.
IMPORTANT: Field calibrations and switch setpoint testing should be performed at
the same application conditions as expected when the instruments are
required to perform their safety functions. Performance testing at one ap-
plication condition may not necessarily ensure appropriate performance
at another condition.

8
Section 2 Model 288A Differential Pressure Indicating Switch
IMPORTANT: Arc suppression for inductive loads will prolong the life of the switch
contacts.
IMPORTANT: Due to their size, subminiature switches have small mechanical clear-
ances; therefore, no rating above 250 VAC has been established.
Table 2.1—Switch/Relay Wire Color Coding (4/06c)
288A LEGACY CONFIGURATIONS
(prior to Apr. 2006) 288A CURRENT CONFIGURATIONS
NO C NC NO C NC
SPDT SWITCHES
Low Red Yellow Blue Red Yellow Blue
High Black Green White Black Violet Orange
DPDT SWITCHES
Low #1 Red Yellow Blue Red Yellow Blue
Low #2 White/Red White/Yellow White/Blue White/Red White/Yellow White/Blue
High #1 Black Green White Black Violet Orange
High #2 White/Black White/Green White/Violet White/Black White/Violet White/Orange
4-INDEPENDENTLY ADJUSTABLE SWITCHES
Low #1 Red Yellow Blue Red Yellow Blue
Low #2 White/Red White/Yellow White/Blue White/Red White/Yellow White/Blue
High #1 Black Green White Black Violet Orange
High #2 White/Black White/Green White/Violet White/Black White/Violet White/Orange
SWITCHES FOR RELAYS
Low Red Yellow Blue (Note 1) White/Brown Brown White (Note 1)
High Black Green White (Note 1) White/Gray Gray White (Note 1)
RELAYS
Low #1 Gray Blue Brown Red Yellow Blue
Low #2 White/Gray White/Blue White/Brown White/Red White/Yellow White/Blue
High #1 Violet White Orange Black Violet Orange
High #2 White/Violet White/Black White/Orange White/Black White/Violet White/Orange
Coil
Wiring:
Legacy Ver.: Low = Red and High = Black Current Ver.: Low = White/Brown and High = White/
Gray
Note 1: Wire is NOT connected.
Startup
For startup procedures, warnings, and other information, refer to Appendix A .
IMPORTANT: To ensure the unit calibration is within factory-set calibration tolerances,
perform the Calibration Check procedure on page 15.

9
Model 288A Differential Pressure Indicating Switch Section 2
Switch and Relay Wiring Diagrams
IMPORTANT: Figures 2.1 through 2.6 show: switch & relay contacts in the relaxed
(shelf) condition, the low switch set to trip at a position below the pointer
scale position, and the high switch set to trip at a position above the
pointer scale position. NO = Normally Open in (shelf) condition. NC =
Normally Closed in (shelf) condition. C= Common.
Figure 2.1—Low/high SPDT switch diagrams
(current confi guration color codes - see Table 2.1, page 8)

10
Section 2 Model 288A Differential Pressure Indicating Switch
Figure 2.2—Low/high DPDT switch diagrams
(current confi guration color codes - see Table 2.1, page 8)

11
Model 288A Differential Pressure Indicating Switch Section 2
Figure 2.3—3-switch diagram
(current confi guration color codes - see Table 2.1, page 8)
Figure 2.4—4-switch diagram (3 or 4 independently adjustable switches)
(current confi guration color codes - see Table 2.1, page 8)

12
Section 2 Model 288A Differential Pressure Indicating Switch
Figure 2.5—Low/high switch(es) w/SPDT relay(s) diagrams
(current confi guration color codes - see Table 2.1, page 8)

13
Model 288A Differential Pressure Indicating Switch Section 2
Figure 2.6—Low/high switch(es) w/DPDT relay(s) diagrams
(current confi guration color codes - see Table 2.1, page 8)

14
Section 3 Model 288A Differential Pressure Indicating Switch
Section 3—Maintenance and Calibration
The following checks are recommended for preventive maintenance:
• Periodically inspect alarm switch mechanism to verify that all mounting
screws are seated properly.
• Inspect linkage for wear.
• Inspect integrity of electrical circuits. Tighten as necessary.
When repairs are necesssary, review this section for maintenance procedures
such as bezel/lens installation and removal, pointer installation and removal,
indicator calibration, switch calibration, and switch set point changes.
IMPORTANT See Appendix A for related warning/caution notices and instructions
on DPU inspection, cleaning, service, repair, range change, and BUA
replacement. Never perform maintenance/repair on the instrument
or DPU without fi rst reviewing all procedures and warning/caution
notices in Appendix A.
Tools
The following tools are recommended for general maintenance of the Model
288A DP indicating switch.
Table 3.1—Tools
Equipment Purpose
Pointer Puller Pointer removal
Small Screwdriver Calibration adjustment
Medium Screwdriver Bezel removal and replacement
1/4" and 1/8" Open-end Wrenches Zero (1/4") and Range (1/8") adjustments
1/8 Hex Allen Wrench Switch set point adjustment
3/32" Hex Allen Wrench Drive Arm Tightness Test
B ezel/Lens (or Cover) Installation and Removal
To remove the bezel and lens (or cover), perform the following steps, using
Figure 3.1 for reference.
1. Loosen the three screws on the front of bezel.
2. Tilt the bottom of the bezel and slide the bezel upward.
To reinstall the bezel and lens, assemble the components per Figure 3.1, page
15. The two snubbers (Part No. 9A-C0266-0028C) on the scale plate should
not be compressed against the lens cover and the pointer should not touch the
lens.

15
Model 288A Differential Pressure Indicating Switch Section 3
Figure 3.1—Bezel and lens cover
IMPORTANT: Ensure the bezel gasket is properly oriented before placing the instru-
ment back in service. Incorrect gasket orientation will cause the instru-
ment indicator to jam, resulting in inaccurate readings.
Calibration Check
To ensure the unit calibration is within factory-set calibration tolerances,
perform the following procedure.
IMPORTANT: Review all procedures, WARNINGS/NOTICES in Appendix A BEFORE
performing this procedure.
Figure 3.2—"Slipping" pointer
1. Mount the instrument in an approximately level position and connect to a
standard pressure source (see Mounting, page A-5).
2. If the zero indication is incorrect, adjust it as follows:
a. Remove the bezel/lens assembly.
b. Using a 1/4" open-end wrench (included in calibration toolkit, Part
No. 9A-0288-1032B), hold the hexagon pointer hub fi xed and rotate
the pointer with fi ngers until the pointer indicates zero on the scale.
See Figure 3.2.
c. Replace the bezel/lens assembly.

16
Section 3 Model 288A Differential Pressure Indicating Switch
3. To test for reverse travel, connect the pressure source to the LP housing
and vent the HP housing. Apply pressures approximately 150% of the DP
range. The pointer should move approximately 5% to 10% below zero.
4. To test for overtravel, connect the pressure source to the HP housing and
vent the LP housing. Apply pressures approximately 150% of DP range.
The pointer should move approximately 5% to 10% above full scale.
5. Apply 0, 50, and 100% of full scale pressure. If indication is within
specifi ed limits, no adjustments are necessary. If indication is not within
specifi ed limits, perform a complete calibration (see Indicator Calibra-
tion, page 17).
6. Make sure the instrument zero indication is correct; otherwise, repeat
step 2.
7. Verify the switch set points (refer to Changing Switch Set Point, page 22).
Pointer Installation and Removal
During adjustment and calibration of the unit, it may be necessary to remove
and reinstall the pointer according to the following procedures.
Pointer Installation
1. Position the pointer on the movement shaft with the pointer set at zero
scale. Obtain 75% to 90% pointer hub engagement on the movement
pinion shaft. The pinion shaft must not extend through the pointer hub.
It may be necessary to enlarge the hub hole, using a tapered broach (in-
cluded in the calibration toolkit, Part No. 9A-0288-1032B).
2. Lightly tap the pointer hub with a hand-set or other fl at-end tool. Use
perpendicular blows to avoid bending the shaft.
3. Check the calibration of the indicating switch over its entire range (refer
to Indicator Calibration, page 17). If the indicating switch is correctly cali-
brated, secure the pointer to the movement shaft by tapping the hub with
a hand-set or other fl at-end tool.
4. Test the pointer for tightness by moving the pointer from the zero to the
50% position manually, and then letting the pointer return freely to zero.
If the pointer indicates a shift, tap the pointer hub to tighten it to the
shaft.
Pointer Removal
The pointer is removed with a pointer puller shown in Figure 3.3, page 17. This
tool is included in the calibration toolkit, Part No. 9A-0288-1032B.
To remove the pointer, perform the following steps:
1. Slide the pointer puller along the pointer until the pin protruding from the
tip of the screw in the pointer puller is directly over the movement shaft
and the arms of the pointer puller are directly under the pointer.

17
Model 288A Differential Pressure Indicating Switch Section 3
2. Gently turn the knurled head of the screw clockwise, pushing the pin
against the movement shaft and lifting the pointer with the arms. Finger
pressure should be suffi cient to pull the pointer free. If more pressure is
required, an Allen wrench (inserted into head of the screw) can be used.
However, care should be exercised to avoid breaking the pin.
Figure 3.3—Pointer puller (Part No. 9A-0163-0005B)
Indicator Calibration
A complete calibration of the instrument is required whenever the DPU as-
sembly is replaced.
IMPORTANT: Review all procedures, WARNINGS/NOTICES in Appendix A BEFORE
performing this procedure.
1. Securely mount the instrument in an approximately level position and
connect the DPU, as described in Mounting, page A-5.
2. Remove the bezel/lens assembly.
3. Align the linkage between the drive arm and the movement at 50% diff er-
ential pressure (DP) as shown in Figure 3.4. Inspect parts for straightness
and pivot-fi t without binding.
Figure 3.4—Range/linearity adjustment (50% DP)

18
Section 3 Model 288A Differential Pressure Indicating Switch
4. Check the pointer for zero indication. If necessary, set the pointer to zero
by slipping the pointer on the hub, per Calibration Check, step 2, page
15.
5. Apply 100% pressure. If the pointer exceeds full-scale, lengthen the
movement range arm by adjusting the range adjust screw with a 1/8-in.
open-end wrench.
6. Release pressure. Set the pointer to zero, by slipping the pointer on the
hub, per Calibration Check, step 2, page 15.
7. Repeat steps 4 and 5, as necessary, to obtain the correct zero/full-scale.
8. Apply 50% DP. If the pointer indicates 50%, proceed to step 9. If the
pointer does not indicate 50% scale, adjust linearity as follows.
a. Loosen the drive arm screw (Figure 3.5) and move the arm to shift
the pointer in the direction of the error a distance of about 10 times
the linearity error.
b. Check to see that the drive arm clears the end of torque-tube housing
by approximately 0.030 in. before retightening the drive arm screw
to prevent interference.
c. While supporting the block/shaft, tighten clamp screw until snug to
shaft.
d. Still supporting block/shaft, tighten clamp screw an additional 1/3
to 1/2 turn. (This screw can normally turn one full revolution before
breaking.)
e. Perform the Drive Arm Tightness Test described on page 19.
Figure 3.5—Drive arm to torque tube connection
9. Release pressure and reset the pointer at zero. Check the span. If the gear
in the movement reaches a limit of travel as a result of linearity adjust-
ment (step 7), slip the range arm along the gear approximately 5 degrees
from the normal 37.5 degree angle to approximately 43 degrees (see step

19
Model 288A Differential Pressure Indicating Switch Section 3
2). The range arm is slipped by applying pressure to the range arm with
thumb, while holding the gear fi rmly in place. Retest the pointer response
at 50%, 0%, and 100% of full-scale diff erential pressure, and adjust the
linkage until the readings are acceptable.
10. Apply 0%, 25%, 50%, 75%, 100%, 75%, 50%, 25%, and 0% of full-scale
diff erential pressure consecutively to the instrument without overshoot.
Lightly tap the indicator to overcome friction. The pointer should accu-
rately indicate each applied pressure.
11. Test the instrument repeatability by applying 0%, 50%, 0%, 50% of full-
scale diff erential pressure. The indicator should accurately indicate each
applied pressure.
12. Set the drive arm stop to prevent the pointer from striking the snubbers
on the scale. (See Drive Arm Stop Adjustment, page 20.)
13. Test the pointer for tightness per the pointer installation instructions on
page 16.
14. If the drive arm screw has been loosened, verify that it is adequately tight
by performing the Drive Arm Tightness Test described below.
15. Reassemble the unit per the cover installation instructions on page 14.
Drive Arm Tightness Test
This procedure tests the tightness of the drive arm's connection to the torque
tube by applying torque developed by the DPU onto a fi xed drive arm. Care
should be taken to apply pressure slowly, as torque is being applied to the
connection through the torque tube drive shaft.
1. With the pointer at normal 0% torque tube rotation position (0% on a
normal 0 to 100% scale unit), adjust the drive arm stop bracket (or use
alternate means) to prevent the pointer from moving (stop bracket inter-
feres with drive arm movement).
IMPORTANT: On reverse acting/split range units, it will be necessary to pressurize the
DPU to move the pointer to maximum minimum scale position, and on
suppressed units, it will be necessary to apply pressure to establish a
reference point to check for "zero" shift.
2. Pressurize the DPU to full calibrated scale DP (100% of full scale range)
to achieve 8 degrees of torque tube equivalent torque onto the connec-
tion.
3. Observe the shift in the unit "zero" following DPU depressurization (as
required) and drive arm stop bracket readjusting (to allow free move-
ment of drive arm and pointer). A downscale (counter-clockwise) shift in
"zero" of greater than 1/2% is indicative of drive arm slippage, necessi-
tating further clamp block tightening.

20
Section 3 Model 288A Differential Pressure Indicating Switch
Drive Arm Stop Adjustment
1. Apply suffi cient pressure to the high-pressure housing to defl ect the
pointer against the full range stop snubber on the scale plate.
2. Slide the upper drive arm stop bracket against the drive arm and tighten
the drive arm stop bracket screw.
3. Apply suffi cient pressure to the low pressure housing to defl ect the
pointer against the zero stop snubber on the scale plate.
4. Bend the zero drive arm stop against the drive arm.
5. Verify calibration as applicable.
Switch Calibration
Before performing a complete calibration procedure, verify that the instru-
ment is out of calibration, by performing a calibration check procedure (page
15). If the instrument is out of calibration, before performing a complete
calibration procedure, remove the bezel/lens and scale plate and inspect the
switch mechanism (Figure 3.6) to verify the following:
• The roller rotates without wobble or binding.
• The cam is relatively centered under the roller.
• The actuator arm moves freely on its pivot.
• All switch mounting screws are tight.
• Linkages are straight and do not bind at the pivots.
Correct any problems that are observed.
Figure 3.6—Switch mechanism
Calibration Setup
1. Connect the lamp or buzzer to the switch output leads.
2. Connect a test voltage to the switch input terminals on the terminal strip.
(A low voltage is recommended for safety.) If a relay is installed in the
instrument, coil voltage must be applied to the switch.