Instruction Manual

C7100A,B,C,D AVERAGING TEMPERATURE SENSORS
3 62-0214
OPERATION AND CHECKOUT
Operation
The C7100A,C,D Averaging Temperature Sensors
consist of a platinum alloy resistance element, mounted
in a tubular probe. The C7100B Averaging Temperature
Sensor consists of a thermistor sensing element
mounted in a tubular probe. They are applied at various
locations throughout the systems. The probe has five
shear-formed inlet openings that face into the air stream.
The air entering these inlet openings is directed by the
shear forms toward the sensor located within the probe.
The probe mixes the various air samples entering the
inlets to present an average temperature air sample to
the sensing element. The sensing element resistance is
therefore dependent on the average temperature of the
sampled air.
This method of temperature averaging provides more
accurate temperature control by reducing or eliminating
the effects of duct and/or plenum air stratification.
Fig. 6 shows how the sensor resistance varies with
temperature for a sensor having a positive temperature
coefficient (PTC) of 4.8 ohms per degree F (8.6 ohms per
degree C).
Fig. 7 shows how thermistor resistance varies with
temperature for a sensor having a negative temperature
coefficient (NTC).
Fig. 8 shows how sensor resistance varies with
temperature for a sensor having a positive temperature
coefficient (PTC) of 2.1 ohms per degree F (3.85 ohms
per degree C).
Fig. 6. C7100A,C Sensor resistance vs. temperature.
Fig. 7. C7100B Sensor resistance vs. temperature.
Fig. 8. C7100D Sensor resistance vs. temperature.
Checkout
Allow the C7100 Averaging Temperature Sensor to soak
in the air moving through the duct or plenum for a
minimum of ten minutes before taking a resistance
measurement.
1. Disconnect the sensor leadwires from the associ-
ated system components.
2. Connect an ohmmeter across the leadwires.
3. Assure nominal resistance measurements are in
accordance with the resistance/temperature curves
(see Fig. 6 through 8).
4. Reconnect sensor leadwires to associated system
components.
5. Check operation of the complete control system.
RESISTANCE
(OHMS)
4200
4000
3800
3600
3400
3200
20 40
60
80 100 120
140 160
180 200 220
-7
0
10
20 30
40 50
60
70 80 90
100
F
C
3484 ± 6.5 OHMS
AT 77¡F (25¡C)
M2829
TEMPERATURE (DEGREES)
120K
100K
80K
60K
40K
20K
20
40
60 80
100
120
140 160 180
200
RESISTANCE (OHMS)
TEMPERATURE (DEGREES)
M3398
0 10 20 30 40
F
220
C
-7 50 60 70 80 90 100
22,800 OHMS AT
77 F (25 C)
RESISTANCE
(OHMS)
1400
1317
1231
1145
1059
973
20 40
60
80 100 120
140 160
180 200 220
-7
0
10
20 30
40 50
60
70 80 90
100
F
C
1097 ± 0.08 OHMS
AT 77¡ F [25¡ C]
M2824
TEMPERATURE (DEGREES)