Rh Sensor; Rh Sensor Stability - Decagon Devices VP-3 Operating Manual

Vapor pressure, temperature & relative humidity sensor

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VP-3 User's Manual

3. RH Sensor

Each VP-3 sensor is verified as accurate before leaving our

facility. However, all capacitance RH sensors will drift over long

periods of exposure to environmental conditions. The VP-3 RH

sensor typically drifts less than 0.5% RH per year.

recommend that VP-3 sensors be re-calibrated every 1 to 2 years

under normal use conditions to ensure best possible accuracy. To

have your VP-3 fully calibrated or re-calibrate contact

support@decagon.com and ask about our calibration service.

The polymer RH sensing element in the VP-3 can also be

"poisoned" by exposure to volatile organic compounds, solvents,

and other chemicals. The effects of exposure to these chemicals

can range from subtle loss of accuracy to catastrophic failure. If

you suspect that your VP-3 has suffered chemical exposure or

notice questionable RH measurements, you can check the sensor

accuracy using known RH conditions.

A convenient method for generating known RH conditions is

through the use of salt solutions.

For an initial check, we

recommend preparing a saturated NaCl solution, which has an

equilibrium RH of 0.75 (75%). To prepare the salt solution, start

with lab grade NaCl and mix in enough water that there is a thin

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