Campbell Scientific HMP50 Temperature and Relative Humidity Sensor - Manual (Page 16)

HMP50 Temperature and Relative Humidity Probe
;Limit the maximum value of relative humidity
;to 1 (expressed as a fraction).
;
03: If (X<=>F) (P89)
1: 2
X Loc [ RH_frac ]
2: 3 >=
3: 1 F
4: 30 Then Do
04: Z=F (P30)
1: 1
F
2: 0 Exponent of 10
3: 2 Z Loc [ RH_frac ]
05: End (P95)
;Compute the saturation vapor pressure in kPa.
;The temperature must be in degrees Celsius.
;
06: Saturation Vapor Pressure (P56)
1: 1
Temperature Loc [ T_C ]
2: 3 Loc [ e_sat ]
;Compute the vapor pressure in kPa.
;Relative humidity must be a fraction.
;
07: Z=X*Y (P36)
1: 3
X Loc [ e_sat ]
2: 2 Y Loc [ RH_frac ]
3: 4 Z Loc [ e ]
8. Maintenance
The HMP50 Probe requires minimal maintenance. Check monthly to make
sure the radiation shield is free from debris. The white screen at the tip of the
probe should also be checked for contaminants.
When installed in close proximity to the ocean or other bodies of salt water
(e.g., Great Salt Lake), a coating of salt (mostly NaCl) may build up on the
radiation shield, sensor, filter and even the chip. NaCl has an affinity for
water. The humidity over a 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 (see Figure 6 and Section 8.1). Do not scratch the
silver chip while cleaning. It might be necessary to repeat rinsing.
12