The HVACR tester was developed and constructed for the permanent monitoring of temperature or humidity. The compact dimensions of the HVACR tester are the characteristics of this instrument. The measurement of the temperature and humidity is via a semiconductor component. Internally, the physical quantities to be measured are converted toa 4 ... 20 mA standard signal. The power of this measuring instrument is connected to a DC voltage into a current loop and is thus ideally suited for displays with transmitter power supply. But it can also be connected to the paperless recorder for long-term monitoring of environmental conditions.