• Professional users
  • Performs complicated measurements
  • Basic parameters for humidity, temperature and pressure
  • Optional CO2, rpm, current and voltage
  • AW Value (Water Activity)
  • Indicates Moisture Equilbrium
  • Clear graphics display
  • 3 User defined function buttons
  • 45000 LCD, 4 lines memory


The Testo 650 precision humidity measuring instrument is a reference class meter that has everything the professional user needs to complete complicated measurement tasks efficiently, accurately and conveniently. While the Testo 650 is primarily a humidity meter, it also includes the basic parameters temperature and pressure measurments. The meter also has the option of measuring CO2, rpm, current and voltage.

Water activity is one of the most important parameters in respect of product quality in the food production sector. The aw value provides information on chemically non-bonded water. For this reason, it is an important parameter when determining the product quality in many foodstuffs. The water activity in food determines color, stability, taste and shelf life. Potential risks exist if the food has very high water activity and is not adequately refrigerated.

The Testo 650 reference measurement system sets standards in aw value measurement. The 650 has an accuracy ±0.01 aw and reproducibility of ±0.003 aw. The accuracy of the precision sensor has been proven in international inter-laboratory tests.

The trend display in the Testo 650 automatically indicates when the equilibrium moisture has been reached and the measurement is complete. Constant monitoring is therefore not required. The Testo 650 ensures the long-term stability of the measurement for years, i.e. frequent, time-consuming readjustments are no longer necessary.

The Testo 650 measuring system is traceable to national standards. Its supplied with a DKD calibration certificate if required. This also gives assurance in legal questions. Uncomplicated and reliable documentation of the measured results are available via an attachable printer or on a PC.

The Testo 650 meter is available as a meter only or in one of two kit options:

650 Ref. Class 1% RH Accuracy Kit:

  • 650 Reference Meter / Logger
  • 1% RH probe
  • Probe connection cable
  • Service case
  • Comsoft 3 Software
  • RS232 cable

650 Transmitter Field Calibration Kit:

  • 650 Reference Meter / Logger
  • 1% RH probe
  • Probe connection cable
  • Service case
  • 400/650 to Xmitter interface cable