Vaisala MMP8 Moisture In Oil Probe


  • Modbus RTU over RS-485
  • Compatible with Indigo series transmitters and Insight PC software
  • Continuous online measurement of moisture in oil and temperature
  • Temperature measurement range −40 … +180 °C (−40 … +356 °F)
  • Measurement accuracy up to ±0.01 aw (±1 %RS)
  • Incorporates the proven Vaisala HUMICAP sensor, used for over 20 years in oil applications
  • Traceable calibration certificate: 6 points for humidity, 1 point for temperature



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.

MMP8 incorporates the latest-generation Vaisala HUMICAP 180L2 sensor, which is the result of over 20 years of field experience. It was developed for demanding moisture measurement in transformer and lubrication oils and other liquids. The sensor’s excellent chemical tolerance provides accurate and reliable measurement over a wide measurement range. The HUMICAP 180L2 sensor has excellent sensitivity in the dry end of the range, which is typically needed in transformer applications. Vaisala HUMICAP Moisture in Oil Probe MMP8 enables fast and reliable measurement of moisture in oil. It uses the proven Vaisala HUMICAPâ sensor, which was developed for demanding dissolved moisture measurements in transformer and lubrication oils, hydraulic fluids, and other liquids.

MMP8 measures dissolved moisture in oil in terms of the water activity (aw), relative saturation (%RS), and temperature (T). Water activity or Easy installation relative saturation indicate directly whether there is a risk of free water formation. This data is relevant in lubrication oil applications where detecting water ingress and preventing free water formation is crucial. The measurement is independent of oil type and age.


Key Benefits

Robust & Reliable Out Of The Box
Its excellent chemical tolerance provides accurate and reliable measurement over a wide measurement range, with outstanding sensitivity in the dry end — making it ideal for transformer applications.

Easy Installation
The MMP8 can be installed (and removed) even while a process is running — thanks to its ball-valve installation kit. Its probe installation depth is adjustable and pressure fitting options are ISO 1/2″ and NPT 1/2″.

Measure The Margin To Water Saturation
Water activity or relative saturation directly indicate whether there is a risk of free-water formation.

Superb Connectivity
The MMP8’s smart measurement and digital Modbus RTU over RS-485 connection within the probe fully support standalone use. The MMP8 offers a robust display for data visualization, easy access to probe configuration, and more extensive options for connectivity, supply voltage and wiring. Whether using the MMP8 on its own or with an Indigo transmitter, the Vaisala Insight software offers easy field calibration, probe configuration, and device analytics.


Measurement Performance
Water Activity
Measurement range 0 … 1 aw
T90 response time 1) 10 min
Sensor HUMICAPâ 180L2
Accuracy 2) ±0.01 aw (±1 %RS)
Measurement range (−40 … +180 °C) (−40 … +356 °F)
Accuracy at +20 °C (+68 °F) ±0.2 °C (0.36 °F)
1) At +20 °C (+68 °F) in still oil.
2) In range 0 … 0.5 aw, including non-linearity, hysteresis, and repeatability. See accuracy graph below.
Operating Environment
Operating temperature of probe head (−40 … +180 °C) (−40 … +356 °F)
Operating temperature of probe body (−40 … +80 °C) (−40 … +176 °F)
Storage temperature range (−40 … +80 °C) (−40 … +176 °F)
Operating pressure range 0 … 40 bar (0 … 580 psia)
Installation pressure Up to 10 bar (145 psia)
IP rating of probe body IP66
Ball valve
Operating temperature Up to +120 °C (+248 °F)
Operating pressure Up to 40 bar (0 … 580 psia)
Inputs and Outputs
Operating voltage 15 … 30 V DC
Current consumption 10 mA typical
Digital output RS-485, non-isolated
Protocols Modbus RTU
Output parameters Relative saturation (%RS)
Temperature (°C)
Water activity
Water mass fraction (ppmw)
EU directives EMC Directive (2014/30/EU)
RoHS Directive (2011/65/EU)
EMC compatibility EN 61326‑1, industrial environment
Type approvals DNV GL certificate no. TAA00002YT
Compliance marks CE, China RoHS, RCM, WEEE
Mechanical Specifications
Connector M12 5-pin A-coded male
Weight 510 g (18.0 oz)
Filter options Stainless steel grid standard filter
Stainless steel grid filter for high flow
rates (> 1 m/s)
Probe cable length 2 m (6.56 ft)
Adjustable installation depth 35 … 179 mm (1.37 … 7.05 in)
Probe AISI 316L
Probe body AISI 316L
Cable jacket FEP
Ball valve ISO 1/2″ with welding joint BALLVALVE-1
Ball valve ISO 1/2″ – ISO 3/4″ with thread joint BALLVALVE-2
Indigo USB adapter 1) USB2


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