Vaisala MMT162 Moisture & Temperature Transmitter for Oil


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

Dpstar is a leading supplier of environmental measurement sensors for temperature, relative humidity, pressure, dew point, CO2, and other environmental condition monitoring for industrial process application and research. Since the ’90s, we earned a reputation as a trusted partner to our clients through our commitment and dedication. We are an authorized distributor and supplier of measuring sensors solutions from renowned manufacturers Vaisala. Vaisala is a global leader in environmental and industrial measurement. Building on 80 years of experience, Vaisala provides observations for a better world. Vaisala is a reliable partner for customers around the world, offering a comprehensive range of innovative observation and measurement products and services.

Vaisala MMT162 features the latest Vaisala HUMICAP sensor, designed for precise moisture measurement in liquid hydrocarbons. It’s been successfully used in oil applications for over 20 years. This transmitter offers a cost-effective solution for detecting moisture in oil reliably. MMT162 measures moisture in oil using water activity (aw) and temperature (T), directly indicating the risk of free water formation. Its measurement is unaffected by oil type, age, or temperature.


Key Benefits

Small size
Easy to integrate.

Excellent chemical tolerance
Accurate and reliable measurement over the measurement range.

The Vaisala HUMICAP Sensor has been successfully used in applications for over 40 years.


Measurement Performance
Water activity
Measurement range 0 … 1 aw
Accuracy (including non-linearity, hysteresis, and repeatability):
0 … 0.9 aw
0.9 … 1.0 aw
± 0.02 aw
± 0.03 aw
Response time in oil flow (typical) < 1 min (dry-wet)
Accuracy at +20 °C (+68 °F) ± 0.2 °C (0.36 °F)
Calculated moisture content in ppm for mineral transformer oil
Operating environment
EMC compliance EN61326-1, Industrial environment
Operating temperature (−40 … +60 °C) (−40 … +140 °F)
Storage temperature (−40 … +80 °C) (−40 … +176 °F)
Oil temperature (−40 … +80 °C) (−40 … +176 °F)
Oil flow Some flow recommended
Pressure range Up to 200 bar
Inputs and Outputs
Alarm level indication by analog signal User selectable
Digital outputs RS-485, non-isolated, Vaisala
protocol, Modbus RTU protocol
Analog current output 0 … 20 mA, 4 … 20 mA
Analog voltage output 0 … 5 V, 0 … 10 V
Spare Parts and Accessories
Stainless steel filter (standard) 225356SP
Stainless steel filter for high flow
(> 1 m/s)
Connection cable for MM70 handheld meter 219980
USB serial interface cable 219690
Sealing ring set (U-seal) ISO G1/2, 3 pcs 221525SP
Sealing ring set (copper) ISO G1/2, 3 pcs 221524SP
ISO 1/2″ plug 218773
NPT 1/2″ plug 222507
Sampling cell DMT242SC
Sampling cell with Swagelok connectors DMT242SC2
Connection cables
0.32 m (1 ft) shielded, M8 threaded HMP50Z032
3.0 m (9.8 ft), shielded, M8 threaded HMP50Z300SP
5.0 m (16.4 ft), shielded, M8 threaded HMP50Z500SP
10 m (32.8 ft), shielded, M8 threaded HMP50Z1000SP
3 m, shielded, connector 90° angle 231520SP
5 m, shielded, connector 90° angle 231521SP
M8 threaded, Ch1 signal + Ch2 LED MP300LEDCBL
Mechanical Specifications
Cable connections (2 ports) M8 4-pin male
Mechanical connections with bonded seal ring (washer) G 1/2″ ISO or NPT 1/2’’
Weight 200 g (7 oz)
Minimum operating voltage with
RS-485 output 14 … 28 VDC
Voltage output 16 … 28 VDC
Current output 22 … 28 VDC
Supply current
Normal measurement 20 mA + load current
External load for
Voltage output Min. 10 kΩ
Current output Max. 500 Ω
Probe body material Stainless steel (AISI 316L)
IP rating IP66