For WMO-standard accuracy and stability we use HMP155 probes to measure Relative Humidity and air temperature in our Electronic Weather Stations.
This sensor probe, which supersedes the HMP45, measures Relative Humidity (RH), from 1% to 100%, with an accuracy of +/-3% RH. In the field, the probe is housed in a naturally-ventilated radiation shield to protect the sensors from solar radiation and rain.
On a routine site visit we check the calibration, comparing the sensor readings against those of our reference instrument.
Periodically, when we lower the 10m mast to inspect the instruments, we swap the probe head containing the sensor and electronics and take the 'removed' one away for laboratory calibration.
At NIWA we routinely carry out four-point calibrations on HMP155 (and HMP45) sensor heads at our Christchurch climate laboratory to ensure that the instruments remain within their specified accuracy.
We can advise on, supply, service and calibrate HMP155 (and HMP45) RH/Temperature probes.