Water is a common contaminant in industrial oils. Water contamination deteriorates the performance of the oil, be it used for lubrication, cooling, insulation or other purposes. High moisture content increases the risk of corrosion, overheating, machine malfunction and other problems and can ultimately lead to costly failure and unscheduled downtime. Monitoring the oil for moisture is a simple way of improving the reliability of industrial machinery and equipment. With time, substantial savings in maintenance costs can be achieved.

On-line water activity measurement ensures reliable performance of equipment at all times. Time consuming sampling and laboratory analysis are no longer needed. This not only reduces the risk of human induced error but also provides cost savings in equipment and chemicals.


  • Power transformers
  • Lubrication systems
  • Maritime industry
  • Paper industry


Benefits of Vaisala Instruments in Oil Moisture Measurements

  • Online, real-time detection of moisture in oil without sampling
  • Tells the true margin to water saturation point in all changing conditions, taking into account e.g. temperature changes and aging of oil
  • Highly stable. Excellent pressure and temperature tolerance
  • Easy to install through ball valve – no need to shut down the process
  • Enables predictive maintenance work. Trends can be quickly identified.


Moisture in Oil Probe MMP8

For: Continuous Online Measurement​

  • Continuous online measurement of moisture in oil and temperature
  • Measurement temperature range -70 … +180 °C (-94 … +356 °F)
  • Measurement accuracy up to ±0.02 aw / 2 %RS
  • Temperature measurement accuracy up to 0.1 °C (0.18 °F)
  • Proven Vaisala HUMICAP® sensor, used for over 15 years in oil applications
  • Modbus RTU over RS-485 for flexible connectivity
  • Includes traceable calibration certificate: five points for humidity, one point for temperature
  • Compatible with Indigo series transmitters
  • Sensor has excellent sensitivity in the dry end of the range



Moisture and Temperature in Oil Transmitter Series MMT330
For: Hydraulic and Lubrication Systems and Transformer Oil Monitoring
  • Continuous online measurement of moisture in oil
  • Installation through ball valve. No need to shut down the process.
  • Proven Vaisala HUMICAP® sensor, used for over 15 years in oil application
  • Easy field calibration and maintenance – compatible with Vaisala HUMICAP® Hand-Held Moisture Meter for Oil MM70
  • Online, real-time detection of moisture in oil without sampling.
  • Integrated data logging, with over four years of measurement history
  • Traceable calibration to national standards (certificate included)
  • Multi-year Calibration Care agreement option to ensure as-good-as new accuracy for years

Moisture and Temperature Transmitter Oil MMT162
For Transformer Applications and OEM Systems


  •  Continuous measurement of moisture in oil
  •  Measures in lubrication, hydraulic,and transformer oils
  •  Excellent pressure and temperature tolerance
  •  Proven Vaisala HUMICAP® sensor:over 20 years in oil applications
  •  Measures water activity – ppm calculation available for transformer oil
  •  Digital output RS-485 with Modbus
  •  Traceable calibration (certificate included)