L91A,B,D Proportioning
®
Pressuretrol Controllers
PRODUCT DATA
FEATURES
•
Models available for pressure systems up to 300 psi
(2068 kPa).
•
May be used with steam, air, noncombustible gases, or
other fluids noncorrosive to brass or phos-bronze (300
psi model) bellows.
•
•
•
•
When used with steam boilers, a steam trap (siphon
loop) is recommended.
Wiper on controller potentiometer moves in response
to pressure changes.
L91D has two potentiometers for unison control of two
motors.
L91B,D models have adjustable proportioning
(throttling) range to allow selection of desired
pressure control range.
•
•
Adjustments made with screws on case top.
Large, easily-read scaleplates in both U.S. customary
(oz/sq. in., psi, or in. Hg) and metric (kPa, MPa, or mm
Hg) units.
•
•
•
Steel case with clear plastic cover to observe pressure
settings and potentiometer action.
APPLICATION
Fitting with 1/4 -18 NPT threads allows rapid
installation.
®
L91 Proportioning Pressuretrol Controllers are Series 90
Modulating Pressure Controllers that provide direct control of
modulating motors or valves used on automatic burners or
steam heating systems.
Surface mount with screws through knockout holes in
case back.
Contents
Application
Features
Specifications
Installation
Wiring
Checkout
Service Information
1
1
2
5
6
8
9
60-2152—08
®
L91A,B,D PROPORTIONING PRESSURETROL CONTROLLERS
Electrical Connections: Internal screw terminals. Hole inside
23176CF Potentiometer: For all L91D models and most L91B
models (see Table 1); 140 ohms (nominal); length of active
winding is 1/4 in. (6.4 mm).
of case for 1/2 in. conduit.
Dimensions: See Fig. 1; see Fig. 2 for mounting steam trap
(siphon loop).
Accessories:
50024585-001 Steam Trap (siphon loop): 1/4 in. brass pipe
with 1/4 -18 NPT external threads on both ends.
14026 Steam Trap (siphon loop): 1/4 in. steel pipe with 1/4 -18
NPT external threads on both ends.
Weight: 1 lb, 15 oz (0.88 kg).
Finish: Gray.
33312B Knurled Adjustment Knob: With setscrew; fits on main
scale pressure adjusting screw.
4074BWJ Limit Stop Assembly: To limit setpoint ranges;
includes 129564 Range Stop 107194 Range Stop Screw,
and 23466 Wrench.
Replacement Parts:
129178 Thermoplastic Cover.
23176CB Potentiometer: For all L91A models and a few L91B
models (see Table 1); 140 ohms (nominal); length of active
winding is 7/64 in. (2.8 mm).
Table 2. Approximate value of each division (A to B, B to C, etc.) on proportioning
(throttling) range scaleplate (L91B,D,F only)
Operating Range
Value of Each Division
U.S. Customary
U.S. Customary Units
0 to 10 oz/sq in.
Metric Units
0 to 7 kPa
0 to 103 kPa
Units
6.2 oz/ sq in.
1.8 psi
Metric Units
2.7 kPa
0 to 15 psi
12.4 kPa
5 to 150 psi (L91B)
5 to 150 psi (L91D)
0.03 to 1.03 MPa 7.8 psi
0.03 to 1.03 MPa 6.7 psi
0.054 MPa
0.046 MPa
0.113 MPa
0.095 MPa
10 to 300 psi (L91B with 7/64 in. potentiometer) 0.07 to 2.07 MPa 16.4 psi
10 to 300 psi (L91B,D with 1/4 in. potentiometer) 0.07 to 2.07 MPa 13.8 psi
3
60-2152—08
®
L91A,B,D PROPORTIONING PRESSURETROL CONTROLLERS
(114.3) (COVER)
(110.3) (CASE)
4-1/2
L91A,B,D
4-11/32
2-3/4 (69.9)
3-57/64 (98.8)
3-13/32 (86.5)
1-3/16 (30.2)
1-1/16 (27.0)
1-5/32 (29.4)
3
4
2
2
3-23/32
(94.5)
1-3/32 (27.8)
3-7/8
2-5/64
(52.8)
(98.4)
ALL OTHER
MODELS
DIM C (SEE
TABULATION
TABLE)
7/8
1-13/16
(46.0)
(22.2)(2)
13/16
(20.1)
10 TO 300 PSI
0 TO 15 PSI
0 TO 16 OZ/IN 2
1/4-18 NPT
1
1-1/16
(27.0)
2-1/8 (53.5)
DIM A (SEE TABULATION TABLE)
DIM B (SEE
TABULATION
TABLE)
1
EXTERNAL THREADS ON 0 TO 15 PSI MODELS; INTERNAL THREADS ON ALL OTHER MODELS.
SOME MODELS ARE ALSO AVAILABLE WITH 1/4-19 BSP-TR INTERNAL THREADS; SEE TABLE 1.
2
3
PROPORTIONING RANGE ADJUSTING SCREW ON L91B,D MODELS ONLY.
33312B KNURLED ADJUSTMENT SCREW KNOB, 7/8 IN. [22.2 MM] DIAMETER,. KNOB IS INCLUDED WITH 10 TO 300 PSI [0.07 TO .07 MPa] MODELS;
OPTIONAL ACCESSORY FOR OTHER MODELS.
4
FOR 10 TO 300 PSI [0.07 TO 2.07 MPa] MODELS. DIM C INCLUDES THE KNURLED ADJUSTMENT KNOB.
TABULATION OF DIMENSIONS A, B, AND C
OPERATING RANGE
DIM A
DIM B
DIM C
CUSTOMARY UNITS
METRIC UNITS
0 TO 103 kPa
IN.
MM
61.9
41.3
31.8
IN.
1-7/32
13/16
5/8
MM
31.0
20.6
15.9
IN.
MM
2-7/16
1-5/8
1-1/4
6-7/8
5-3/4
6-1/16
174.6
146.1
154.0
0 TO 15 PSI
5 TO 150 PSI
10 TO 300 PSI
0.03 TO 1.03 MPa
0.07 to 2.07 MPa
4
4
M29781
®
Fig. 1. Mounting dimensions of the L91 Proportional Pressuretrol Controllers, in in. (mm).
60-2152—08
4
®
L91A,B,D PROPORTIONING PRESSURETROL CONTROLLERS
INSTALLATION
When Installing This Product...
L91
1. Read these instructions carefully. Failure to follow them
could damage the product or cause a hazardous
condition.
PRESSURETROL
CONTROLLER
2. Check the ratings given in the instructions and on the
product to make sure the product is suitable for your
application.
PRESSURE
GAUGE
3. Installer must be a trained, experienced service
technician.
PRESSURETOL
4. After installation is complete, check out product opera-
tion as provided in these instructions.
TEE
2
WARNING
Electrical Shock Hazard.
Can cause severe injury, death or property damage.
1. Disconnect power supply before beginning
installation to prevent electrical shock and
equipment damage.
1
STEAM TRAP
(SIPHON LOOP)
4-1/2 (114) TO
5-1/2 (140)
2. When using the controller with a compressor, install
a dampening device (such as a needle valve,
header, or surge tank) to dampen pulsations that can
damage the controller or reduce its life.
BOILER
IMPORTANT
1. Locate the controller where the ambient temperature
will not exceed 150° F (66° C).
2. When the controller is used on a boiler, be sure to
connect a steam trap (siphon loop) between the
controller and the boiler.
3. Before installing controller, be sure the siphon loop
has enough water in it to fill lower trap.
4. Use pipe compound sparingly to avoid clogging the
hole in the pipe or bellows fitting.
1
2
50024585-001 STEAM TRAP IS A 1/4 IN. BRASS PIPE WITH
1/4 - 18 NPT EXTERNAL TRHEADS ON BOTH ENDS.
FITTING ON BELLOWS HAS 1/4-18 NPT EXTERNAL THREADS
ON 0 TO 16 OZ/SQ. IN. AND 0 TO 15 PSI MODELS; INTERNAL
THREADS ON ALL OTHER MODELS. SOME MODELS ARE
ALSO AVAILABLE WITH 1/4-19 BSP-TR INTERNAL THREADS;
SEE TABLE 1.
M23884
5. Do not tighten the controller by hand by holding onto
the case and turning it.
Fig. 2. Approximate dimensions in in. (mm) for mounting
L91 Pressuretrol Controller beside Pressure Gauge on
®
Steam Trap (Siphon Loop).
Location and Mounting
Mounting Beside a Pressure Gauge
When used with steam boilers, always mount the controller
above the water line in the boiler. A steam trap (siphon loop)
must always be connected between the controller and the
boiler (Fig. 2) to prevent boiler scale and corrosive vapors from
attacking the bellows. Before installing controller, be sure the
siphon loop has enough water in it to fill lower trap.
To mount the controller beside a pressure gauge (Fig. 2),
remove the gauge. In its place, install a steam trap (siphon
loop) with a tee on top. Using elbows and pipe nipples, mount
the controller and pressure gauge on the ends of the tee.
Mounting on a Boiler
The controller can be mounted (1) beside the pressure gauge,
(2) in a fitting on the boiler provided by the manufacturer, or (3)
at a remote location in case of excessive vibration.
If it is not convenient to mount the controller beside the
pressure gauge, install a steam trap (siphon loop) in the fitting
provided by the boiler manufacturer. If there is no fitting, mount
the steam trap at a location recommended by the boiler
manufacturer. Screw the controller directly to the steam trap, if
possible.
Make all pipe connections in accordance with approved
standards. Use only a small amount of pipe compound to seal
the connection joints. Excess pipe compound may clog the
small hole in the fitting and prevent the controller from
operating properly.
Mounting at a Remote Location
If there is excessive vibration at the boiler that may adversely
affect the operation of the controller, mount the controller at a
remote location. All piping from the boiler must be suitable and
solidly mounted. The piping must be properly pitched to drain
all condensation back to the boiler. If this causes the controller
to be located at an inconvenient height (on large boilers), it
may be mounted at a lower level if the connecting piping is
filled with clean water. A steam trap (siphon loop) must be
mounted between the remote piping and the controller.
To avoid leaks and damage to the case, use a parallel jaw
wrench on the controller fitting. Do not tighten the controller by
hand by holding onto the case and turning it.
5
60-2152—08
®
L91A,B,D PROPORTIONING PRESSURETROL CONTROLLERS
6. Refer to Fig. 4 for typical hookup. W and B connections
may be interchanged at the motor for reverse action
(cooling). Follow the burner or boiler manufacturer’s
wiring diagram if provided. Also refer to the wiring
diagrams in the motor instructions.
ACTION ON
PRESSURE FALL
W
B
7. Replace the front cover when wiring is completed.
R
W
B
1
SERIES 90
MODULATING MOTOR
L91 PROPORTIONING
CONTROLLER
M9484
M9494
CLOSED
R
W1
R1
B1
(LOW FIRE)
1
W
OPEN
(HIGH FIRE)
B
2
L91A,B
T2
T1
ACTION ON
PRESSURE FALL
TRANSFORMER
W
B
1
WIPER MOVES TOWARD W END OF
POTENTIOMETER ON PRESSURE RISE,
AND TOWARD B END ON
3
R
W
B
PRESSURE FALL.
(HOT) L1 L2
2
3
TERMINALS ARE LABELED.
REAR POTENTIOMETER
POWER SUPPLY. PROVIDE DISCONNECT MEANS AND
OVERLOAD PROTECTION AS REQUIRED.
M8520A
R
W
B
1
®
ACTION ON
PRESSURE FALL
Fig. 4. Hookup of L91 Proportioning Pressuretrol
Controller to Series 90 Modulating Motor.
B
W
Setting
In all models, the proportioning range (also called throttling
range) extends above the main scale setpoint (Fig. 5). The
proportioning range is fixed on L91A models, but is adjustable
on L91B,D models. (For values, refer to Table 1 in the
Specifications section.)
FRONT POTENTIOMETER
TERMINALS ARE LABELED.
L91D
1
M8522A
Main Scale Set Point (All models)
Fig. 3. L91 terminal blocks and internal schematics.
Adjust the main scale setpoint for the desired operating
pressure by turning the main scale adjusting screw (Fig. 7) or
knurled adjustment knob on 10 to 300 psi (0.07 to 2.07 MPa)
models, on the top of the case, until the main scale setting
indicator is at the minimum pressure desired. The
proportioning range extends above this value. The scaleplate
is marked in both customary (oz/sq in., psi, or in. Hg) and
metric (kPa, MPa, or mm Hg) units.
WIRING
1. Disconnect power supply before beginning installation to
prevent electric shock and equipment damage. All wiring
must comply with applicable electrical codes,
ordinances, and regulations. Use NEC Class 1 (line
voltage) wiring.
Use of L91 Proportioning Controller with
Limit Controllers
The L91 main scale setpoint plus the value of the differential
(proportioning range) must be less than or equal to the limit
controller’s (L404) main scale setpoint.
2. For normal installation, use moisture-resistant No. 14
wire suitable for at least 167°F (75°C) if you are using
the controller with a flame safeguard primary control, or
at least 194°F (90°C) if you are using it with a program-
ming control.
3. For high temperature installations, use moisture-
resistant No. 14 wire, selected for a temperature rating
above the maximum operating temperature.
4. Disconnect the power supply before beginning wiring to
prevent electrical shock and equipment damage.
5. All models have a terminal block inside the cover (Fig. 3)
and two 7/8 in. (22.2 mm) holes in one side for 1/2 in.
conduit, cable, or wires. Remove the front cover by loos-
ening the screw at the bottom of the scaleplate.
For example, to control system pressure between 70 and 80
psi: select an L91B, 5-150 psi operating range, adjustable
differential (proportioning, throttling range) of 5 to 23 psi and an
L404A, 10-150 psi, adjustable differential of 8 to 16 psi. Set the
L404A main scale setpoint at 80 psi and its adjustable
differential at 10 psi. The L404A settings will then provide boiler
pressure limit control between 70 and 80 psi. An L91B
differential (proportioning range) pressure of 5 psi is desired.
Therefore, an L91B main scale setpoint of between 70 and 75
psi is required (L91 main scale setpoint plus its differential
must be less than or equal to the limit controller main scale set
60-2152—08
6
®
L91A,B,D PROPORTIONING PRESSURETROL CONTROLLERS
point). The L91B settings provide system modulation between
70 and 75 psi or between 75 and 80 psi, depending on the
exact setting of the L91B main scale setpoint.
MAIN SCALE
ADJUSTING
SCREW
PROPORTIONING RANGE
ADJUSTING SCREW (L91B,D ONLY)
CONTROLLER
POTENTIOMETER
Due to device tolerances, the scaleplate settings are
approximate and, therefore, the settings should be fine-tuned
with the system operating.
1
WIPER ARM(S)
Proportioning Range (L91B,D Only)
PROPORTIONING
RANGE
Adjust the proportioning range (throttling range) by turning the
proportioning range adjusting screw (Fig. 6) on the top of the
case until the proportioning range setting indicator is at the
desired value. The proportioning range scale is graduated from
A to F with a MIN (minimum) value below A. The value of each
division depends on the operating range of the controller. Refer
to Table 2 in the Specifications section.
SCALEPLATE
(L19B,D ONLY)
PROPORTIONING
RANGE SETTING
INDICATOR
(L91B,D ONLY)
TERMINAL BLOCK
MAIN SCALE
SETTING
Typical Operation
INDICATOR
BELLOWS
HOUSING
Pressure variations cause the bellows to expand or contract.
Linkage between the bellows and the potentiometer wiper
causes the wiper to move across the potentiometer windings.
This varies the resistance between R and B, and between R
and W, causing an unbalance in the circuit connected to the
controller. See Fig 7.
MAIN
SCALEPLATE
1
KNURLED ADJUSTMENT KNOB ON 10 TO 300 PSI
[0.07 TO 2.07 MPa] MODELS.
M8525
®
Fig. 6. Setting L91 Proportioning Pressuretrol Controller.
W
LOW-FIRE
(CLOSED)
A proportioning controller is used most often to regulate the
firing rate of a burner by controlling a modulating motor (Fig. 4)
or a modulating valve. The controller potentiometer, the
feedback potentiometer in the motor (or in the valve actuator),
and a balancing relay in the motor (or actuator) form an electric
bridge circuit. As long as the pressure of the controlled medium
remains at the setpoint of the controller, the circuit is balanced;
that is, equal the relay contacts are open. When the circuit is
balanced, the motor (or actuator) does not run.
PRESSURE
RISE
PROPORTIONING
RANGE
POTENTIOMTER
2
R
1
(WIPER)
MAIN SCALE
SETPOINT
HIGH-FIRE
(OPEN)
If the pressure of the medium rises, the wiper in the controller
moves toward W. This unbalances the circuit, so a larger
current flows through one side of the balancing relay. The
close contacts in the relay make, causing the motor (or valve
actuator) to drive toward its closed position. As the motor (or
actuator) runs, the wiper on the feedback potentiometer moves
in a direction to balance the circuit. When the circuit is again in
balance, the balancing relay contacts open and the motor (or
actuator) stops. The valves and dampers connected to the
motor or actuator will be partially closed, decreasing the firing
rate and reducing the pressure.
B
1
2
FIXED ON L91A; ADJUSTABLE ON L91B,D.
L91D HAS TWO POTENTIOMETERS OPERATING IN UNISION.
M8519A
Fig. 5. L91A,B,D operating points.
Similarly, if the pressure of the controlled medium falls, the
wiper on the controller potentiometer moves toward B, and the
open contacts in the balancing relay make. The motor (or
actuator) drives toward its open position until circuit balance is
achieved. The valves and dampers will be opened wider and
the firing rate will increase, thus increasing the pressure.
A small change in the pressure of the controlled medium will
cause a change in the firing rate to compensate for it, thus
keeping the pressure constant. This process is called
modulation.
7
60-2152—08
®
L91A,B,D PROPORTIONING PRESSURETROL CONTROLLERS
CHECKOUT
MAIN SCALE
PROPOTIONING
RANGE ADJUSTING
SCREW
ADJUSTING SCREW
After the controller is installed, wired, and set, it should be
tested with the system in operation. First, allow the system to
stabilize. Then, observe the operation of the controller while
raising and lowering its setpoint. Pressure should increase
when the setpoint is raised and decrease when the setpoint is
lowered. Use accurate pressure testing equipment when
checking out the controller. Do not rely on inexpensive gauges.
The controllers are carefully calibrated at the factory.
1
(L91B,D ONLY)
MAIN SCALE
SETTING
INDICATOR
MAIN
7
DIFF.
16
14
12
10
8
6
4
2
0
F
E
6
5
4
3
2
1
0
D
2
Make sure the modulating motor or modulating valve actuator
reaches the low- and high-fire positions at the proper points. If
the motor or actuator runs in the proper direction when the
setpoint is adjusted, assume that the controller is operating
properly. If it runs in the wrong direction, reverse the B and W
wires. Observe the action of the motor or actuator until it
stabilizes. If the motor or valve is moving constantly, widen the
proportioning range (not adjustable on an L91A) incrementally
until the system is stable.
C
B
R
A
MIN
W
kPa
OZS
DIFF. IS
ADDITIVE
2
IN
B
If a Controller Seems to Operate
Improperly
OHMMETER
If the controller is suspected of operating improperly, it may be
further checked by:
OUTPUT
0
INPUT
1. Leaving the controller installed where it is, but discon-
necting all power to the controller motor or valve.
2. Loosening the cover screw below the main scaleplate
and removing the cover.
SETPOINT
INCREASE
135
3. Disconnecting the wires from the controller.
4. Connecting an ohmmeter between controller terminals B
and W to measure the resistance for the potentiometer in
the controller. The ohmmeter should read about 135
ohms for an L91A,B, or D.
R
B
W
ZERO
ADJ
5. Connecting the ohmmeter between controller terminals
W and R (Fig. 8) and raising the setpoint of the controller
above the actual pressure being measured. The ohmme-
ter should read the full value of the potentiometer mea-
sured in step 4 (135 ohms for an L91A,B, or D).
6. Slowly lowering the setpoint of the controller while
observing the ohmmeter reading. The resistance should
drop to zero at some setpoint below the actual pressure.
7. Making an approximation of the proportioning range by
observing the change in setpoint required for a resis-
tance change from zero to full value.
INCREASES TO
3
135 OHMS
1
KNURLED ADJUSTMENT KNOB ON 10 TO 300 PSI [0.07 TO 2.07 MPA]
MODELS.
2
3
TERMINALS ARE LABELED
135 OHMS ON L91A,B OR D.
M8546A
®
Fig. 7. Checking L91 Proportioning Pressuretrol
Controller.
8. When the controller is operating properly, reconnecting
the wires, replacing the cover, tightening the cover
screw, and resetting the controller to the desired value.
9. Reconnecting power to the controlled motor or valve.
CAUTION
Equipment Damage Hazard.
Failure to follow checkout instructions can damage
components or systems.
Do not put the system into service until you have
satisfactorily completed all applicable tests described in
this Checkout section, all tests in the Checkout section
of the applicable instructions, all tests for the flame
safeguard control, and any tests required by the burner
and boiler manufacturers.
60-2152—08
8
®
L91A,B,D PROPORTIONING PRESSURETROL CONTROLLERS
Replacing the Controller
Potentiometer (Fig. 8–10)
SERVICE INFORMATION
IMPORTANT:
CAUTION
1. Only qualified service technicians should attempt to
service or repair flame safeguard controls and
burner systems.
2. Disconnect power supply before cleaning the
potentiometer windings or wiper, or before replacing
the controller potentiometer.
1. Replace the controller potentiometer only when nec-
essary to obtain proper operation.
2. When replacing the potentiometer, be very careful not
to bend or damage the wiper arm, and not to change
the wiper tension. Any damage or change in tension
will decrease the life of the new potentiometer.
Electrical Shock Hazard
1. Disconnect all power to the controller.
2. Loosen the cover screw below the main scaleplate and
remove the cover.
3. Mark the wires to the external device (motor or valve
actuator) and disconnect them from the terminal block.
4. Remove the screw holding the terminal block bracket to
the top of the case (Fig. 8). Put this screw in a safe place
because it will be needed later.
Calibration
All controllers are carefully tested and calibrated at the factory
under controlled conditions. If the actual operating pressure
does not match the setpoint, move the main scaleplate slightly
up or down until the setpoint agrees with the actual pressure.
5. While careful not to damage the potentiometer wiper or
any of the internal wiring, lift out the terminal block and
bracket.
6. Before removing any potentiometer wires, carefully note
and record (sketch) the position (off-center) of the active
winding on the potentiometer and the location and con-
nections of all wiring terminals. The new potentiometer
must be inserted and connected the same.
Maintenance
Keep the cover of the controller in place at all times to protect
the internal components from dirt, dust, and physical damage.
Perform routine maintenance occasionally by inspecting and
blowing or brushing away any accumulated dirt and dust. To
assure proper functioning of the controller at all times, perform
an operational check of the entire system during routine
maintenance checks. Be sure to handle controllers carefully at
the time of installation, during actual use, and during
maintenance.
Example: In Fig. 9, the active winding is on the left half of
the potentiometer; the wire from the left end of the wind-
ing is connected to the (W) terminal on the terminal
block, and the wire from the right end of the winding is
connected to the (B) terminal on the terminal block.
Cleaning the Potentiometer Windings
or Wiper
7. Loosen the (W) and (B) screws on the terminal block,
and remove the two wires to the active winding of the
potentiometer. Leave the wire to the wiper arm intact.
8. Carefully unscrew the bolt that holds the potentiometer
to the bracket. Make sure the potentiometer wires do not
entangle with the wiper and bend it.
9. Carefully slide the old potentiometer off the bolt.
10. Carefully slide the bolt through the new potentiometer.
Make sure that:
Occasionally, the windings or wiper on the potentiometer (two
on the L91D) may need cleaning. Disconnect the power supply
before removing the cover from the controller and before
cleaning the potentiometer.
IMPORTANT
1. Use an electrical contact cleaner that does not con-
tain solvents.
2. Use extreme care to avoid bending the wiper arm,
changing the wiper tension and damaging the potenti-
ometer windings.
a. The off-center position of the winding on the new
potentiometer is the same as the old potentiometer.
(Consult sketch in step 6.)
b. The wiper will contact bare wires. (Rotate the potenti-
ometer on the bolts so the surface of the winding
where the brown enamel was removed is toward
you.)
3. Do not use an abrasion or burnishing tool to clean the
potentiometer windings or wiper.
4. Do not use hard paper, such as a business card, or
abrasive materials (sandpaper, emery boards, file,
etc.) to clean the windings or wiper.
11. Screw the bolt into the potentiometer bracket. Make sure
the wiper is contacting bare wires (step 10.b); then
tighten the bolt.
12. Connect the two potentiometer wires to the (W) and (B)
terminals on the terminal block and tighten the screws.
Make sure these wires are connected to the same termi-
nals as in the old potentiometer. (Consult sketch in step
6.)
13. Carefully fit the hole in the bottom of the terminal block
bracket over the screw protruding upward from the bot-
tom of the case (Fig. 10). Insert the screw (removed in
step 4) through the hole in the top of the case (Fig. 8)
and into the top of the bracket, and tighten it.
14. Reconnect the wires from the external device (motor or
actuator) to the terminal block.
Solvent-type electrical contact cleaners can deteriorate plastic
components and wire insulation and leave an oily residue that
accumulates particulate matter (dust, etc.). The residue can
break down to form various carbonaceous substances that
cause early potentiometer failure.
Use of abrasive materials results in wearing of the
potentiometer windings and accumulation of particulate matter
that changes the resistance between the windings and the
wiper.
15. Replace the cover and tighten the cover screw.
16. Reconnect power to the controller.
9
60-2152—08
®
L91A,B,D PROPORTIONING PRESSURETROL CONTROLLERS
REMOVE BRACKET SCREW
FROM TOP OF CASE
TERMINAL
BLOCK
DIFF.
MAIN
7
TERMINAL
BLOCK
16
14
12
10
8
6
4
2
0
F
E
6
5
4
3
2
1
0
BRACKET
BRACKET
D
MAIN
7
DIFF.
16
14
12
10
8
6
4
2
0
C
F
E
6
5
4
3
2
1
0
B
A
TERMINAL
BLOCK
D
MIN
R
W
B
C
B
kPa
OZS
DIFF. IS
ADDITIVE
2
TERMINAL
BLOCK
IN
A
MIN
kPa
OZS
DIFF. IS
ADDITIVE
2
IN
FIT HOLE IN BOTTOM
OF BRACKET OVER SCREW
PROTRUDING UPWARD
M8521A
FROM BOTTOM OF CASE
M8548A
Fig. 8. Removing terminal block bracket.
Fig. 10. Replacing terminal block bracket.
ACTIVE WINDING
BARE WIRES
POTENTIOMETER
BRACKET
(ENAMEL REMOVED)
1
POTENTIOMETER
BOLT
WIPER ARM
MAIN
7
DIFF.
16
14
12
10
8
6
4
2
0
F
E
6
5
4
3
2
1
0
D
C
B
A
TERMINAL
BLOCK
MIN
R
kPa
OZS
DIFF. IS
ADDITIVE
W
2
IN
2
B
POTENTIOMETER WIRES
THE POTENTIOMETER IN AN L91A IS MOUNTED AT A 45 DEGREE
ANGLE INSTEAD OF HORIZONTALLY. AN L91D HAS TWO
POTENTIOMETERS.
1
2
TERMINALS ARE LABELED.
M8547A
Fig. 9. Replacing potentiometer in L91.
60-2152—08
10
®
L91A,B,D PROPORTIONING PRESSURETROL CONTROLLERS
11
60-2152—08
®
L91A,B,D PROPORTIONING PRESSURETROL CONTROLLERS
Automation and Control Solutions
Honeywell International Inc.
1985 Douglas Drive North
Golden Valley, MN 55422
Honeywell Limited-Honeywell Limitée
35 Dynamic Drive
® U.S. Registered Trademark
Toronto, Ontario M1V 4Z9
customer.honeywell.com
© 2009 Honeywell International Inc.
60-2152-—08 K.K. Rev. 12-09
Printed in U.S.A.
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