The 220-HMK15 Humidity Calibrator makes calibration and spot checking of humidity probes and transmitters easy and reliable. The operating principle is based on the fact that a saturated salt solution generates a certain relative humidity in the air above it. The reading of the humidity probe can then be adjusted accordingly. This is a generally accepted and reliable method for calibrating humidity instruments. The structure of the HMK15 is designed to ensure fast and stable temperature equilibration. No external power is required. In addition to laboratory use, it is also suitable for on-site checks. Special transit covers make the HMK15 simple to transport. The HMK15 includes a thermometer for measuring the temperature during calibration. It can also be used for checking the temperature measurement accuracy of the transmitter. The accuracy of the thermometer is ± 0.54°F (± 0.3°C).