Vaisala MMT330 Moisture & Temperature in Oil Transmitter Series


  • Analog outputs, RS-232/485, LAN
  • Modbus protocol support (RTU/ TCP)
  • Continuous online measurement of moisture in oil
  • Ball-valve installation – no need to shut down the process or drain the oil
  • Proven Vaisala HUMICAP sensor, used for over 15 years in oil applications

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 MMT330 series features the latest Vaisala HUMICAP sensor, developed over 15 years of field experience, for precise moisture measurement in liquid hydrocarbons. Its strong chemical tolerance ensures accurate readings across a wide range. Vaisala MMT330 series enables quick and dependable detection of moisture in oil, making it suitable for online monitoring and control applications. It helps optimize operations by starting separators and oil driers only when necessary.

Vaisala MMT330 measures moisture in oil using water activity (aw), relative saturation (%RS), and temperature (T). These readings directly indicate if there’s a risk of free-water formation, regardless of oil type or age. It can also provide ppm, the average mass concentration of water in oil, with preset conversions for mineral transformer oil. For other oils, specific conversion coefficients can be programmed if the water solubility is known.

Key Benefits

Easy To Install & Operate
No need to shut down the process. Installation through ball valve.

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.


Measurement Performance
Water Activity
Measurement range aw 0 … 1
Response time (90 %) at +20 °C in still oil (with stainless steel filter) 10 min
Sensor HUMICAP 180L2
Accuracy (Including Non-linearity, Hysteresis, and Repeatability):
0 … 0.9 ±0.02
0.9 … 1.0 ±0.03
Measurement range (-40 … +180 °C) (-40 … +356 °F)
Accuracy at +20 °C (+68 °F) ±0.2 °C (0.36 °F)
Operating Environment
EMC compliance EN61326-1, Industrial environment1
Pressure range for probes See probe specifications
Operating Temperature
For probes Same as measurement ranges
For transmitter body (-40 … +60 °C) (-40 … +140 °F)
With display (0 … +60 °C) (+32 … +140 °F)
1) Note: Transmitter with display test impedance of 40 Ω is used in IEC61000-4-5 (Surge immunity)
Inputs and Outputs
Operating voltage 10 … 35 VDC, 24 VAC ±20 %
Operating voltage with optional power supply module 100 … 240 VAC 50/60 Hz
Power Consumption at 20 °C (Uin 24 VDC)
RS-232 Max. 25 mA
Uout 2 x 0 … 1 V / 0 … 5 V / 0 … 10 V Max. 25 mA
Iout 2 x 0 … 20 mA Max. 60 mA
Display and backlight (+20 mA)
Analog Outputs (2 Standard, 3rd Optional)
Current output 0 … 20 mA, 4 … 20 mA
Voltage output 0 … 1 V, 0 … 5 V, 0 … 10 V
Accuracy of analog outputs at 20 °C ±0.05 % full scale
Temperature dependence of the analog outputs ±0.005 %/°C full scale
External Loads
Current outputs RL < 500 Ω
0 … 1 V output RL > 2 kΩ
0 … 5 V and 0 … 10 V outputs RL > 10 kΩ
Max. wire size 0.5 mm2 (AWG 20) stranded wires
Digital outputs RS-232, RS-485 (optional)
Protocols ASCII commands, Modbus RTU
Service connection RS-232, USB
Relay outputs 0.5 A, 250 VAC, SPDT, potential-free
Ethernet Interface (Optional)
Supported standards 10BASE-T, 100BASE-TX
Connector 8P8C (RJ45)
IPv4 address assignment DHCP (automatic), static
Protocols Telnet, Modbus TCP/IP
Display LCD with backlight, graphical trend
display of any parameter
Menu languages English, Chinese, Finnish, French,
German, Japanese, Russian, Spanish,
Optional Data Logger with Real-time Clock
Logged parameters Max. four with trend/min./max. values
Logging interval 10 sec (fixed)
Max. logging period 4 years, 5 months
Logged points 13.7 million points per parameter
Battery lifetime Min. 5 years
Mechanical Specifications
Weight 1.0 – 3.0 kg (depends on selected
probe, cable, and modules)
Sensor protection Stainless steel grid standard filter/
Stainless steel grid filter for high flow
rates (> 1 m/s)
Cable bushing M20x1.5 for cable diameter 8 … 11 mm
(0.31 … 0.43 in)
Conduit fitting 1/2″ NPT
USB-RJ45 Serial Connection Cable
(incl. MI70 Link software)
Probe cable diameter 5.5 mm (0.2 in)
Standard probe cable lengths 2 m, 5 m or 10 m (6.6 ft, 16.4 ft,
32.8 ft)
(Additional cable lengths available,
please see order forms for details)
Housing material G-AlSi 10 Mg (DIN 1725)
Interface cable connector (optional) M12 series 8-pin (male)
Option 1 Female plug with 5 m (16.4 ft) black
Option 2 Female plug with screw terminals
IP rating IP66
IP rating with local display IP65
NEMA rating with local display 4X


Vaisala-MMT330-Moisture and Temperature in Oil Transmitter Series_DpstarGroup