Install Instructions

TP970-72, TP970-74, TP9600, AND PNEUMATIC SENSORS, HUMIDISTATS, AND THERMOSTATS
Figure 49 shows humidistat components.
GAGE TAP
BIAS SPRING
757065 80 85 90 95
SETPOINT
SETPOINT
ADJUSTMENT
ELEMENT
THROTTLING
SPRING
RANGE
ADJUSTMENT
THROTTLING
RANGE SCALE
SETPOINT
SCALE PLATE
INDICATOR
CALIBRATION
SCREW
NYLON
ELEMENT
SETPOINT
LOCK SCREW
C3945
LOCKING STOPS
Fig. 49. Humidistat Front View, Cover Off.
Setpoint Lock
To set the minimum and maximum setpoint, refer to Figure 49
and use the following procedure:
1. Loosen setpoint lock screw.
2. Move locking stop to desired position.
3. Tighten setpoint lock screw.
4. Move setpoint adjustment to check stop positioning.
Throttling Range Adjustment (HP970 and HP972)
Use the following procedure if a change in the throttling range
(TR) is required:
1. Slide TR indicator to desired setting on TR scale (see
table).
2. Recalibrate humidistat (see RECALIBRATION).
Throttling Range Adjustment.
Humidistat
Setpoint
Range
Throttling Range
Indication Lines (% RH)
Model (% RH)
Minimum Maximum
HP970 12-75 3 5 10 15
HP970 65-95 3 5 10 15
HP972 15-75 8 12 20 35
Calibration Check
Direct-Acting Humidistat (HP970A)
1. Use Thermostat Tool to remove humidistat cover.
2. Use Digital Relative Humidity Indicator Pen to measure
actual relative humidity (rh) of space.
3. Turn setpoint indicator down 10 percent below
measured rh.
4. Allow humidistat to build up branchline pressure.
5. Turn setpoint indicator up slowly.
6. If humidistat bleeds off at ±3 percent rh of measured
humidity, no further calibration is necessary. Remove
Gage and replace humidistat cover.
7. If humidistat does not operate as described in Step 6,
recalibrate humidistat (see RECALIBRATION).
Reverse-Acting Humidistats (HP970B and HP972)
1. Use Thermostat Tool to remove humidistat cover.
2. Use Digital Relative Humidity Indicator Pen to measure
actual relative humidity (rh) of space.
3. Turn setpoint indicator up 10 percent above measured rh.
4. Allow humidistat to build up branchline pressure.
5. Turn setpoint indicator down slowly.
6. If humidistat bleeds off at ±3 percent rh of measured
humidity, no further calibration is necessary. Remove
Gage and replace humidistat cover.
7. If humidistat does not operate as described in Step 6,
recalibrate humidistat (see RECALIBRATION).
Recalibration
CAUTION
Humidistats are extremely sensitive. Handle
humidistats carefully during recalibration.
HP970 and HP972
The procedure in this section assumes that a calibration
check has been performed (see CALIBRATION CHECK) and
that the humidistat has not operated correctly.
1. Start with main air pressure at 18 psi (124 kPa)
nominal or system pressure between 13 and 18 psi
(91 and 124 kPa).
2. Assemble Gage and Gage Port Needle.
3. Insert Gage Port Needle in humidistat gage tap.
4. Set humidity setpoint indicator at humidity measured
during CALIBRATION CHECK procedure.
5. Turn calibration screw until Gage reads 0 psi.
6. Turn calibration screw in opposite direction until Gage
reads 8 psi (55 kPa) ±1 psi (±7 kPa).
7. Allow 5 to 10 seconds for HP970, 30 to 60 seconds for
HP972, for complete response. Setpoint and actual rh
should be within acceptable limits.
8. Repeat appropriate procedure under CALIBRATION
CHECK to verify calibration.
9. Remove Gage and replace cover.
10. Adjust humidistat setpoint indicator to desired setpoint.
HP971 Humidity Sensor
1. Supply sensor with 18 psi (124 kPa) air through 0.007-in.
internal or external restriction. The HP971A1024 (15 to
85% range) also has a 0.005-in. bleed restriction in the
output line.
2. Assemble Gage and Gage Port Needle.
3. Insert Gage Port Needle in sensor gage tap (same
location as humidistat gage tap shown in Fig. 49).
4. Allow sensor to acclimate to ambient conditions at least
20 minutes.
5. Use Digital Relative Humidity Indicator Pen to measure
actual relative humidity (rh) of space.
6. Adjust calibration screw (same location as humidistat
calibration screw shown in Fig. 49) until branchline
pressure is below that specified in the following table:
95-5597—1
46