MM70 Hand-Held Moisture and Temperature Meter for Spot-Checking in Oil

The Vaisala HUMICAP® Hand-held Moisture Meter for Oil MM70 is an ideal tool for the preventive maintenance of oil-filled systems.

The water activity measurement indicates the margin to free water formation, which causes severe problems in lubrication systems.

  • Measurement independent of oil type, age and temperature - indicates margin to oil saturation
  • In-line process checking through ball valve, no need to drain the oil
  • Rugged and reliable construction
  • Multiprobeoperation; dewpoint and CO2 probes can also be connected
  • Vaisala HUMICAP® Sensor - proven field performance since 1973

MM70 Hand-Held Moisture and Temperature Meter for Spot-Checking in Oil

Operating Principle

The Vaisala transmitters used for measuring moisture in oil feature the HUMICAP® sensor, a capacitive thin-film polymer sensor especially developed for demanding moisture measurements in liquid hydrocarbons. The HUMICAP sensor consists of four functional layers: glass substrate, lower electrode, water-active polymer layer, and porous upper electrode.

The thin-film polymer either absorbs or releases water as the surrounding moisture level changes. Water molecules move to/from the polymer layer until there is moisture equilibrium between the polymer and the oil. 

The dielectric properties of the polymer depend on the moisture level. As the moisture level changes, the dielectric properties of the polymer film change, and so does the capacitance of the sensor. 

The instrument’s electronics measure the capacitance of the sensor and convert it into water activity. Oil molecules or additives do not penetrate the electrode. Thus the sensor output is independent of the oil type.