Troubleshooting humidity sensors – American Standard UV05 User Manual
Page 45
McQuay OM 751
45
Diagnostics and Service
3
Use the temperature reading from Step 2 to determine the expected sensor resistance from
Table 23.
4
Using a calibrated ohmmeter, measure the actual resistance across the two sensor leads.
5
Compare the expected resistance to the actual resistance.
6
If the actual resistance value deviates substantially (more than 10%) from the expected
resistance, replace the sensor.
Table 23: Temperature versus resistance
Troubleshooting Humidity Sensors
The UVC is configured to use a 0–100% RH, 0–5 VDC, capacitive humidity sensor. Each
sensor is calibrated according to the table shown.
Use the following procedure to troubleshoot a suspect sensor:
1
Disconnect the sensors output voltage lead from the UVC analog input.
2
Using some other calibrated humidity sensing device, take a humidity reading at the sensor
location.
3
Use the humidity reading from Step 2 determine the expected sensor voltage from
Table 24.
4
Using a calibrated multi-meter, measure the actual voltage across the yellow and white
sensor leads.
Wire color definitions:
White = ground
Yellow = output VDC
Blue = supply VDC
5
Compare the expected voltage to the actual voltage.
6
If the actual voltage value deviates substantially (more than 10%) from the expected
voltage, replace the sensor.
°F (°C)
Resistance in ohms
°F (°C)
Resistance in ohms
–40 (–40)
613
113 (45)
1195
–31 (–35)
640
122 (50)
1237
–22 (–30)
668
131 (55)
1279
–13 (–25)
697
140 (60)
1323
–4 (–20)
727
149 (65)
1368
5 (–15)
758
158 (70)
1413
14 (–10)
789
167 (75)
1459
23 (–5)
822
176 (80)
1506
32 (0)
855
185 (85)
1554
41 (5)
889
194 (90)
1602
50 (10)
924
203 (95)
1652
59 (15)
960
212 (100)
1702
68 (20)
997
221 (105)
1753
77 (25)
1035
230 (110)
1804
86 (30)
1074
239 (115)
1856
95 (35)
1113
248 (120)
1908
104 (40)
1153
CAUTION
The humidity sensor is not protected against reversed polarity.
Check carefully when connecting the device or damage can
result.