ITT BARTON 581A User manual

BARTON®NUCLEAR MODEL 581A
DIFFERENTIAL PRESSURE
SWITCH
User Manual
Part No. 9A-C10766, Rev. 01
October 2011
Model 581A-0
Contents
Safety............................................................................................................ 2
Section 1—Introduction................................................................................. 3
General ......................................................................................................... 3
Wiring ........................................................................................................ 5
Differential Pressure Unit .......................................................................... 5
............................................................................................... 6
General:..................................................................................................... 6
............................................................................... 6
......................................................................... 7
.............................................................................. 7
Section 2—Installation................................................................................... 9
Mounting/Piping/DPU Installation ................................................................. 9
Electrical Connection .................................................................................... 9
Switch Use.................................................................................................... 9
Startup ........................................................................................................ 10
Switch Wiring .............................................................................................. 10
Section 3—Maintenance and Calibration....................................................11
Tools.............................................................................................................11
Bezel/Lens Assembly or Cover Installation and Removal........................... 12
Pointer Installation and Removal ................................................................ 13
Pointer Installation .................................................................................. 13
Pointer Removal...................................................................................... 14
Scale Plate Installation and Removal ......................................................... 14
Indicator Calibration.................................................................................... 15
Drive Arm Tightness Test......................................................................... 17
Drive Arm Stop Adjustment ..................................................................... 17
Switch Calibration ..................................................................................... 17
Calibration Setup..................................................................................... 18
Linkage Calibration Procedure ............................................................... 18
Changing Switch Set Point ........................................................................ 20
................................................................................. 20
Best Practices for Set Points................................................................... 20
Changing Set Point of an In-Service Instrument ..................................... 20
Changing Set Point of an Out-of-Service Instrument .............................. 21
Range Changes ...................................................................................... 22
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Model 581A Dierential Pressure Switch Section 1
Section 1—Introduction
General
The 581A Differential Pressure Switch actuates single or dual signal circuits
-
nected to the process or vessel by tubing or piping. Changes in differential
pressure (DP) at the DPU produce a mechanical output which moves a pointer
and switch actuation controls.
and low-pressure sides of a primary device in the process run. Normally the
For liquid level measurement applications, the instrument is connected to
measure changes in differential pressure caused by variations in hydrostatic
pressures of the liquid in a tank.
The 581A switch is available in three model variations:
• Indicating Switch (Model 581A-0). This model, shown on the manual
cover, has a thick tempered plate glass lens and provides a visual indica-
tion of the difference in the two monitored pressures.
• Blind Switch (Model 581A-2).This model has a solid metal cover and
provides no visual indication of differential pressure.
• Blind Switch with Internal Indicator. Unlike the indicating model with
the glass lens, there is no externally visible indicator. However, internally,
components are the same as in Model 581A-0. With the cover removed, a
user can use the internal indicator to determine DPU input pressure when
making adjustments to the switch setpoints.
The Model 581A uses two independently adjustable single-pole double-throw
(SPDT) snap-acting switches that are rated for high temperatures. Both sides
of the switchesare wired, enabling the switchesto serve both normally-open
and normally-closed applications. The direct-set switch contactsare adjustable
overa scale range of10-90%nominal. Switchesand all adjustmentsare read-
ily accessible when the coveris removed (see Figures 1.1and 1.2,page 4).
IEEE 344-1975, IEEE 381-1977and NUREG 0588, Rev. 1 for either Func-
tional and/or Pressure Boundary Integrity service in limited harsh environ-
ment applications.
The switch case is drawn stainless steel with a sealed glass header for the
electrical interface with the switches. No additional conduit seals are required
to ensure the integrity of the instrument.

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Section 1 Model 581A Dierential Pressure Switch
Left Switch Right Switch
Pointer
Left Switch
Lock Screw
Plunger Screw
Actuating Cam
Left Switch
Adjustment
Assembly*
Switch Adjust Linkage
Plunger Screw
Right Switch
Lock Screw
Drive Arm
Stop Bracket
Movement Assembly
Terminal Strip
Switch Adjust Linkage
Right Switch
Adjustment
Assembly*
Range Adjust
* Switch Adjustment Assembly includes crank, index shaft, and index pointer.
Figure 1.1—581A (with indicator), internal components
Left Switch Right Switch
Left Switch
Lock Screw
Plunger Screw
Actuating Cam
Left Switch
Adjustment
Assembly*
Switch Adjust Linkage
Plunger Screw
Right Switch
Lock Screw
Terminal Strip
Switch Adjust Linkage
Right Switch
Adjustment
Assembly*
Cam Actuator
* Switch Adjustment Assembly includes crank, index shaft, and index pointer.
Figure 1.2—581A (without indicator), internal components
The cam rotates counterclockwise with increased pressure. In Figure 1.3, page
5, the LOW switch (typically set to alarm at decreasing pressure) is set at 25%
differential pressure while the HIGH switch (typically set to alarm at increas-
ing pressure) is set at 75% differential pressure.

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Model 581A Dierential Pressure Switch Section 1
1000
50
Zero DP
1000
50
Maximum DP
DER
Y OLLE W
B UL E
B CAL K
NEERG
WHITE
1000
50
SW I T C H "A"
(LEFT)
SW I T C H "B"
(RIGHT)
CAM
TERM I NAL
BLO C K I N
CAS E
BO T H S W I TCHES RELAX ED
SWITCH
PLUNGER
SC REW
Mid-point DP
HIGHLOW
SW I T C H "A" AC T UAT ED/S WITCH "B" RELAX ED
SW I T C H "A" RELAX ED/SW I T CH "B" AC TUAT ED
SWITCH CLOSED
CONTACTS
OPEN
CONTACTS
GREEN/WHITE GREEN/BLACK
A (LEFT)
B (RIGHT)
YELLOW/BLUE YELLOW/RED
SWITCH CLOSED
CONTACTS
OPEN
CONTACTS
GREEN/WHITE GREEN/BLACK
A (LEFT)
B (RIGHT)
YELLOW/RED YELLOW/BLUE
SWITCH CLOSED
CONTACTS
OPEN
CONTACTS
GREEN/WHITEGREEN/BLACK
A (LEFT)
B (RIGHT)
YELLOW/BLUE YELLOW/RED
SW I T C H "A"
(LEFT)
SW I T C H "B"
(RIGHT)
SW I T C H "A"
(LEFT)
SW I T C H "B"
(RIGHT)
Notes:
1. CAM ROTATES COUNTER-CLOCKWISE WITH INCREASED DIFFERENTIAL PRESSURE
2. EACH SWITCH MAY BE SET AT ANY POINT FROM 10% TO 90% OF DP RANGE
3. WIRES: No. 22 AWG (Internal) and No. 18 AWG (External)
Figure 1.3—Switch wiring connections and actuation example
Wiring
Each switch is wired internally to a glass-sealed header using No. 22 AWG
®) insulated wire for radiation service per
IEEE Standard 393-1974. Externally, from the header, permanently color
coded No. 18 AWG Tefzel®wires exit through a female conduit connection.
Differential Pressure Unit
For detailed information on the Model 199 DPU, see Appendix A.

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Section 1 Model 581A Dierential Pressure Switch
General:
Actuating Unit (DPU) ...................... Model 199 DPU
Dial Size ......................................... 6 inches (150 mm)
Service Conditions (Normal)........... 40°F (4.4°C) to +180°F (+57.2°C) @ <90% R.H.
Switch Repeatability ....................... ±1% of calibrated span
Switch Set-point Range.................. 10 to 90% of calibrated span
Switch Deadband ........................... ±10% of calibrated span (maximum)
Switch Type .................................... Mechanical, Snap-Acting; both switches are SPDT
Activation........................................ Increasing or decreasing scale
Switch Contact Rating:
5.0 Amps @ 125 VAC
5.0 Amps @ 250 VAC
3.0 Amps @ 30 VDC (resistive)
1.0 Amp @ 30 VDC (inductive w/arc suppression)
0.4 Amp @ 125 VDC (resistive)
0.2 Amp @ 125 VDC (inductive w/arc suppression)
Input Range.................................... 0-10" WC to 0-115 psid
Indicator Accuracy .......................... ±2.0% of calibrated span (for ranges to 400 psid)1
Indicator Repeatability.................... ±0.5% of calibrated span
Safe Working Pressure................... 3000 psig
Maximum Overrange...................... To safe working pressure
Process Connections...................... 1/4" NPT top and bottom
1/2" NPT top and 1/4" NPT bottom
Electrical Connections.................... Female, 3/4" NPT, 20 ft., color-coded Tefzel®
insulated 18 AWG wire (40 ft. leads available by
special order)
Torque Tube Rotation ..................... 8° (nominal)
Accuracy of Repeatability............... ±0.5% of calibrated span
1Additional 2% is applicable near the switch setpoints (±10% span).
-
neering Report 9A-CR3-580A-29.
Design Basis Event (DBE) Performance Error1(% of calibrated span):
Radiation (1 x 107Rads) ................ ±10%
Seismic (12.5 Gs):
During Event................................... ±10%
Following Event .............................. ±5%
Harsh Environment (≤ 200°F):
During Event................................... ±10%
Following Event .............................. ±10%
1Includes the cumulative effect of accelerated aging.

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Model 581A Dierential Pressure Switch Section 1
-
cation testing, which found the devices suitable for functional service in a
limited harsh environment. The service conditions associated with the limited
• 1normal conditions of 104°F and 0 psig
• Radiation exposure to 1 x 107Rads (TID)
• 85 days @maximum DBE conditions of 200°F, 10 psig ambient pressure
and ≥ 95% R.H.
•
– OBE @ 6.25 Gs (series of 5)
– SSE @ 12.5 Gs
– 5% critical damping
– No resonance in frequencies below 33 Hz
• Mechanical aging included:
– 25,000 pressure cycles during accelerated aging
– 12,500 electrical cycles during accelerated aging
– Vibration cycling using 0.2 G sinusoidal sweeps over the 1 to 200
Hz range at 1.0 octave/min.
1
governed by factors such as environmental temperature, radiation exposure, and activa-
tion energy.
Storage per ANSI N45.2.2-1978 Level B at 70°F (21°C) ±20°F (±11°C) in
factory sealed package for 2.5 years maximum will not affect installed service
life.

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Section 1 Model 581A Dierential Pressure Switch

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Model 581A Dierential Pressure Switch Section 2
Section 2—Installation
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 affected.
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
Mount the instrument with four 5/16" (8mm) bolts, Grade 5 or greater,
torqued to 17 ft/lbs (see Figure 7.1). Mounting structures should be designed
Response spectra at mounting surface of the instrument shall not exceed those
conduit shall be supported by the same mounting as the DP instrument base
in order to minimize relative motion of the DP instrument and connections.
Dimensional drawings are provided in Section 5, page 32.
See Appendix A for Model 199 DPU installation and maintenance informa-
tion.
Electrical Connection
Units are supplied with dual alarm switches. The direct-set switch contacts
are adjustable over 10% to 90% of the scale range.
The high switch and low switch set point adjustment procedures are covered
in Changing Switch Set Point, page 20.
For physical location of switches, see Figures 1.1 and 1.2, page 4.
Switch Use
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: Arc suppression for inductive loads will prolong the life of the switch
contacts.

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Section 2 Model 581A Dierential Pressure Switch
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 12.
Switch Wiring
IMPORTANT: Figure 2.1 shows switch 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.
LOW & HIGH SPDT SWITCHES
NO NOC CNC NC
RED YELLOW BLUE
RED YELLOW BLUE
WHITE GREEN BLACK
WHITE GREEN BLACK
1 2 3 4 5 6 7 8 9 10
Figure 2.1—Low/high SPDT switch diagrams
Table 2.1—Switch Wire Color Coding
581A Current
NO C NC
Low Red Yellow Blue
High Black Green White

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Model 581A Dierential Pressure Switch Section 3
Section 3—Maintenance and Calibration
The following checks are recommended for preventive maintenance:
• Periodically inspect the alarm switch mechanism to verify that all mount-
ing 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. Refer
Figure 3.1—Model 581A adjustment controls
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 Model 581A
differential pressure switch or DPU without reviewing all proce-
dures and warning/caution notices in Appendix A.

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Section 3 Model 581A Dierential Pressure Switch
Tools
The following tools are recommended for general maintenance of the Model
581A differential pressure 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
Bezel/Lens Assembly or Cover Installation and Removal
To remove the bezel/lens assembly or cover, loosen the screws on the front
and lift the assembly or cover from the enclosure.
To reinstall the bezel/lens assembly (581A-0 only), install the O-ring in the
groove of the case, assemble the bezel, lens, and lens gasket, and realign the
screw holes with the holes in the case. Then, reinstall the screws in the bezel
to secure all components to the case. Torque the screws per Table 4.3, page 30.
To reinstall the cover (581A-2), install the O-ring in the groove of the case
and realign the screw holes in the cover with the holes in the case. Reinstall
the screws in the cover to secure it to the case. Torque the screws per Table
4.3, page 30.
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 and WARNINGS/NOTICES in Appendix A
BEFORE performing this procedure.
1. Mount the instrument in an approximately level position and connect to a
standard pressure source.
2. If the zero indication is incorrect, adjust it as follows:
a. Remove the bezel/lens assembly or cover.
b. Using a 1/4" open-end wrench (included in calibration toolkit, Part

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Model 581A Dierential Pressure Switch Section 3
See Figure 3.2, page 13.
c. Replace the bezel/lens assembly.
HUB
Pointer "slipped"
rotated on hub
Hub held in place
with 1/4" wrench
Figure 3.2—"Slipping" pointer
3. To test for reverse travel, connect the pressure source to the low-pressure
(LP) housing and vent the HP housing. Apply pressure to 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 pressure to approximately 150% of DP range.
The pointer should move approximately 5% to 10% above the full scale
mark.
5. Apply 0, 50, and 100% of full scale pressure. If the indication is within
Scale Plate
Installation and Removal, page 14).
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 20).
Pointer Installation and Removal
During adjustment and calibration of the unit, it may be necessary to remove
and reinstall the pointer. See the following procedures for instructions.
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 (includ-
ed in the calibration toolkit, Part No. 9A-0288-1032B).

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Section 3 Model 581A Dierential Pressure Switch
2.
perpendicular blows to avoid bending the shaft.
3. Check the calibration of the indicating switch over its entire range (refer
to Scale Plate Installation and Removal, page 14). If the indicating switch
is correctly calibrated, secure the pointer to the movement shaft by tap-
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. 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.
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
required, an Allen wrench (inserted into head of the screw) can be used.
However, care should be exercised to avoid breaking the pin.
HUB
MOVEMENT SHAFT
POINTER
HUB
POINTER PULLER
Figure 3.3—Pointer puller (Part No. 9A-0163-0005B)
Scale Plate Installation and Removal
During adjustments and calibration of the unit, it may be necessary to remove
and reinstall the scale plate. The scale plate is split to allow removal without
Figure 4.1,
page 25) and two mounting tabs at 12 o'clock and 6 o'clock positions. The scale
plate halves rest against the top tab (12 o'clock), and slide beneath the bottom
tab (6 o'clock).

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Model 581A Dierential Pressure Switch Section 3
To remove the scale plate, move the pointer to the 12 o'clock position, remove
the screws from the scale plate, and gently guide the scale plate halves from
beneath the bottom mounting tab. Screws are located at 12, 3 and 9 o'clock
positions and near the center of the plate which overlays a narrow bracket.
To reinstall the scale plate, repeat the installation steps in reverse order, as
follows. Holding the pointer in the 12 o'clock position, place the scale plate
halves against the top mounting tab and guide the bottom edges behind the
bottom tab. Replace the screws in the top tab and in the center of the scale
plate. No screw is used with the bottom tab.
Indicator Calibration
If the DPU assembly is replaced on a Model 581A differential pressure switch
with indicator, the indicator must be recalibrated. This procedure does not ap-
ply to the 581A-2 blind switch without indicator.
IMPORTANT: Review all procedures and 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 the Model 199 DPU user manual.
2. Remove the bezel/lens assembly or cover.
3. Align the linkage between the drive arm and the movement at 50% differ-
ential pressure (DP) as shown in Figure3.4. Inspect parts for straightness
Figure 3.4—Range/linearity adjustment (50% DP)
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 12.
5. Apply 100% pressure. If the pointer exceeds full-scale, adjust the range
adjust screw with a 1/8-in. open-end wrench to lengthen the movement
range arm.

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Section 3 Model 581A Dierential Pressure Switch
6. Release pressure. Set the pointer to zero, by slipping the pointer on the
hub, per Calibration Check, step 2, page 12.
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. To prevent interference, check to see that the drive arm clears the
end of torque-tube housing by approximately 0.030 in. before re-
tightening the drive arm screw.
c. While supporting the block/shaft, tighten the clamp screw until it is
snug to the shaft.
d. Still supporting the block/shaft, tighten the clamp screw an addition-
al 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 17.
1/8” WRENCH
(PN 9A-0163-0044C)
CLAMP SCREW
DRIVE ARM
LINK SINTERED
CLAMP BLOCK
TO TIGHTEN
.03 (approx)
M199
SHAFT
Figure 3.5—Drive arm to torque tube connection
9. Release pressure and reset the pointer to zero. Check the span. If the gear
in the movement reaches a limit of travel as a result of linearity adjust-
ment (step 8), slip the range arm along the gear approximately 5 degrees
from the normal 37.5 degree angle to approximately 43 degrees (see
step 3). To slip the range arm, apply pressure to the range arm with the
at 50%, 0%, and 100% of full-scale differential 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
differential pressure consecutively to the instrument without overshoot.

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Model 581A Dierential Pressure Switch Section 3
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 differential pressure. The indicator should accurately indicate each
applied pressure.
12. Set the drive arm stop to prevent the pointer from striking the post lock
on the scale.
13. Test the pointer for tightness per the pointer installation instructions on
page 13.
14. If the drive arm screw has been loosened, check for tightness by perform-
ing the Drive Arm Tightness Test described below.
15. Reassemble the unit per the cover installation instructions on page 12.
Drive Arm Tightness Test
This procedure tests the tightness of the drive arm's connection to the torque
Ap-
ply 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 (the stop bracket
interferes with drive arm movement).
IMPORTANT: On reverse acting/split range units, it will be necessary to pressurize the
DPU to move the pointer to the minimum scale position. 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 scale DP (100% of full scale range) to apply 8
degrees of equivalent torque to the connection.
3. Observe the shift in the "zero" indication following DPU depressuriza-
tion (as required) and drive arm stop bracket readjusting (to allow free
movement of drive arm and pointer). A downscale (counter-clockwise)
shift in "zero" of greater than 1/2% indicates drive arm slippage, neces-
sitating further clamp block tightening.
Drive Arm Stop Adjustment
1.
pointer against the full range post lock 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.
pointer against the zero stop post lock on the scale plate.

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Section 3 Model 581A Dierential Pressure Switch
4. Bend the zero drive arm stop against the drive arm.
5. Verify calibration as applicable.
Switch Calibration
Before performing a complete calibration of the switch, perform a calibration
check (See Calibration Check, page 12). If the instrument is out of calibration,
remove the bezel/lens and scale plate and inspect the switch mechanism (Fig-
ure 3.6) to verify the following:
• The roller rotates without wobble or binding.
• The cam does not touch the roller side shields.
• 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. If no problems are observed, proceed
with a complete calibration.
SWITCH
ACTUATOR ARM
STOP
SCREW
PLUNGER
SCREW
CAM ROLLER
CAM
Figure 3.6—Switch mechanism
Calibration Setup
1. Connect an output device (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.)
3. Unlock the switch plate and move the plate until the roller is positioned
at the top of the cam.
4. Advance the plunger screw until the switch actuates, then advance the
5. Exercise the switch roller across the top of the cam to verify steady
operation. Advance the stop screw to touch the switch, then back out the

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Model 581A Dierential Pressure Switch Section 3
Linkage Calibration Procedure
The switch linkage should be calibrated whenever the Model 581A switch has
been rebuilt.
To calibrate the switch linkage, perform the following steps. Refer to Figure
3.7 as needed.
1. Loosen the three linkage screws and turn the crank to the 12 o’clock
position.
2. Use a 1/8-inch Allen wrench to hold the index shaft and slip the index
pointer to 0 on the switch index. Tighten the screw on the crank to the
mid-slot position to set the crank radius.
3. Turn the index pointer to index number "1" on the outer edge of the
switch index.
4. Apply 10% differential pressure and adjust the switch plate until the
switch actuates. Lock the two linkage screws.
5. Rotate the index pointer to index number “9.” Apply 90% differential
pressure and adjust the crank radius until the switch actuates.
6. Recheck 10% and 90% set points. Adjust the crank radius and the index
pointer until both set points are accurate within a 2% tolerance (nominal).
Figure 3.7—Linkage arrangement
7.
2% of pressure range), check the crank to prevent a 12 o'clock position.
Otherwise, the minimum set point position will be restricted and the set
point may become reversed.
8. Adjust the low switch to actuate at the desired pressure by applying test
pressures in a decreasing direction, in discrete steps. Allow the unit and

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20
Section 3 Model 581A Dierential Pressure Switch
the pressure system to stabilize. Then change the pressure by a small
amount. The magnitude of the pressure change is determined by the
desired accuracy of the test. Tighten the lock screw before testing the
switch performance.
IMPORTANT: The high switch is usually set to actuate at increasing pressure. When
calibrating the high switch, apply test pressure in an increasing direction.
This amount of loading will prevent cam-runout of a similar condition.
IMPORTANT:
drag on the cam. Cam friction will be apparent by excessive hysteresis,
erratic pointer readings, and inconsistent switch response.
9. Check the switch deadband, (actuate to reset) by applying differential
(opposite for high switch direction). Observe pressures. To reduce the
10. Adjust the high switch to actuate at the desired pressure. The procedure is
the same as for the low switch.
Changing Switch Set Point
(Tools: Screwdriver, 1/8-in. hex Allen wrench)
Set Point. The measured pressure at which the snap-switch actuates and
thereby changes the states of the N.O. and N.C. contacts. For example, the set
point of the low switch is 24 psid with decreasing pressure.
Deadband. The difference in measured pressures between switch-actuation
and switch-reset. Deadband is usually expressed as percentage of full scale
(% of F.S.). Deadband is not adjustable. For example, the switch in the
example above was found to reset at 26.4 psid with increasing pressure. The
deadband was 2.4 psi, or 4% of the full scale for a unit calibrated 0 to 60 psid.
Best Practices for Set Points
1. Always check the set point after tightening switch lock screws.
2. Switch setpoints may be set at any point of the scale range, except in a
location that will prevent the deadband from enabling the switch to reset
itself. For example, the high switch (right side of scale) may be set at
full scale, but should not be set near zero. The low switch may be set at
zero, but should not be set near full scale. (Observe deadband values for
3. If switch performance is unsatisfactory (set point does not repeat, dead-
band is excessive, pointer exhibits hysteresis, contacts are unstable, etc.),

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21
Model 581A Dierential Pressure Switch Section 3
remove the scale plate and inspect the switch and the switch mechanism.
The scale plate is split to allow for removal without pulling the pointer.
Changing Set Point of an In-Service Instrument (Not Recommended for
Use the following procedure to set a set point for an instrument that is in ser-
vice, when calibration pressures cannot be applied. See Figure 3.8
locations denoted by items A, B, C and D.
1. Remove the bezel/lens assembly or cover. Do not remove the pointer or
scale plate.
2. Insert hex wrench in the switch adjust post.
3. Loosen the switch lock-screw (item B) 1/2 to 1 turn.
4. With the hex wrench, move the index pointer (item C) to the new set
point as indicated on the switch index (item D).
5. If possible, check the set point by varying the process pressures and ob-
serving the pointer readings when the switch actuates. (Open the mani-
fold bypass valve slowly and watch for “pointer-jump” at the set point or
by electrical signal.) Adjust the setting, if necessary, and repeat the test
several times to verify stability.
Figure 3.8—Set point adjustment
IMPORTANT: The switch index has 10 divisions, marked 0, 5, and 10. These match the
markings on the outer edge of the scale.