Campbell Scientific HMP45C Temperature and RH Probe - Manual (Page 20)

Model HMP45C Temperature and Relative Humidity Probe
16
TABLE 8-1. Chemical Tolerances of HMP45C
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 HMP45C annually. Obtain an RMA number before returning
the HMP45C to Campbell Scientific for recalibration.
9. Troubleshooting
Symptom: -9999, NAN, -40 deg C, or 0 % relative humidity
1. Check that the sensor is wired to the correct excitation and analog 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 module. 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 * 0.1 – 40.0; 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 5-1).
10. References
Goff, J. A. and S. Gratch, 1946: Low-pressure properties of water from -160°
to 212°F, Trans. Amer. Soc. Heat. Vent. Eng., 51, 125-164.
Lowe, P. R., 1977: An approximating polynomial for the computation of
saturation vapor pressure, J. Appl. Meteor., 16, 100-103.
Weiss, A., 1977: Algorithms for the calculation of moist air properties on a
hand calculator, Amer. Soc. Ag. Eng., 20, 1133-1136.