Campbell Scientific HMP155A Temperature and Relative Humidity Probe - Manual (Page 25)

HMP155A Temperature and Relative Humidity Probe
saturated NaCl solution is 75%. A buildup of salt on the filter or chip will
delay or destroy the response to atmospheric humidity.
The filter can be rinsed gently in distilled water. If necessary, the chip can be
removed and rinsed as well. Do not scratch the chip while cleaning.
Long term exposure of the HUMICAP  relative humidity sensor to certain
chemicals and gases may affect the characteristics of the sensor and shorten its
life. TABLE 8-1 lists the maximum ambient concentrations, of some
chemicals, that the HUMICAP  can be exposed to.
TABLE 8-1. Chemical Tolerances of HMP155A
Chemical Concentration (PPM)
Organic solvents 1000 to 10,000
Aggressive chemicals
(e.g., SO
2
, H
2
SO
4
, H
2
S,
HCl, Cl
2
, etc.)
1 to 10
Weak Acids 100 to 1000
Bases 10,000 to 100,000
Recalibrate the HMP155A annually. Refer to the Assistance page at the
beginning of this document for the procedure for returning the HMP155A to
the factory to get recalibrated.
9. Troubleshooting
Symptom: –9999, NAN, –80°C, or 0 % relative humidity
1. Check that the sensor is wired to the correct input channels as specified by
the measurement instructions.
2. Verify the range code is correct for the datalogger type.
3. Verify the red power wire is correctly wired to the 12V, switched 12V, or
SW12V power switch. The terminal the wire is connected to will depend
on the datalogger program.
Connect the red wire to a 12V terminal to constantly power the sensor for
troubleshooting purposes. With the red wire connected to12V, a
voltmeter can be used to check the output voltage for temperature and
relative humidity on the yellow and blue wires respectively (temperature
°C = mV * 0.14 – 80.0; relative humidity % = mV * 0.1).
Symptom: Incorrect temperature or relative humidity
1. Verify the multiplier and offset parameters are correct for the desired units
(TABLE 7-4 and TABLE 7-5).
17