MMT310 Series Moisture and Temperature
Transmitter for Oil
Water content as
ppm calculation for
transformer oils
PPM units are traditionally used
in transformer applications.
They indicate the average mass
concentration of water in oil. The
ppm calculation for mineral oil based
transformer oil is optional in the
MMT310 series.
Diverse applications and
demanding conditions
The MMT310 series can be used in
lubrication and hydraulic systems
as well as in transformers. It can be
used for on-line moisture monitoring
and as a control function, allowing
separators and oil purifiers to be
started only when necessary.
Two probe options: MMT317 and MMT318
Continuous measurement of
moisture in oil
Proven Vaisala HUMICAP®
sensor, 10 years in oil
Measurements in lubrication,
hydraulic and transformer oils
Excellent pressure and
temperature tolerance
Measuring water activity - ppm
calculation for transformer oil
Small size, easy to integrate
NIST traceable calibration
Applications: e.g. monitoring
of transformer oil and of
lubrication systems in marine
and paper industry
The Vaisala HUMICAP® Moisture and
Temperature Transmitter Series for
Oil MMT310 is a fast and reliable online detector for moisture in oil.
Reliable Vaisala
HUMICAP® technology
The MMT310 series incorporates
the latest generation of the Vaisala
HUMICAP® Sensor, developed for
demanding moisture measurement
in liquid hydrocarbons. The sensor’s
excellent chemical tolerance provides
accurate and reliable measurement
over the wide measurement range.
Measuring water activity
The MMT310 series measures
moisture in oil in terms of the water
activity (aw) and temperature (T).
Water activity directly indicates if
there is a risk of free water formation.
The measurement is independent of
oil type, age, and temperature.
Installation options
The MMT318 has two adjustable
probe lengths. The transmitter can
be ordered with a ball valve set that
enables the insertion and removal of
the moisture probe for calibration,
without the need to empty the oil
The MMT317 has a small pressuretight probe with optional Swagelok
Several outputs, one
The MMT310 series has two analog
outputs and an RS-232 serial output.
The output signals and the supply
power travel in the same cable, the
only cable connected to the unit.
Technical data
Measured values
Water activity
Measurement range aw
Accuracy (including non-linearity,
hysteresis and repeatability)
0 ... 0.9
0.9 ... 1.0
Response time (90 %) at +20 ˚C in still oil
(with stainless steel filter)
0 ... 1
10 min
Vaisala HUMICAP®
Measurement range
Typical accuracy at +20 ˚C
Typical temperature dependence
of electronics
-40 ... +180 ˚C (-40 ... +356 ˚F)
±0.1 ˚C (±0.18 ˚F)
±0.05˚C/ ˚C (±0.005 ˚F/˚F)
Pt100 IEC751/3 class B
Electrical connections
Two analog outputs, selectable and
0 ... 20 mA or 4 ... 20 mA
Typical accuracy of analog output at +20 ˚C
±0.05 % full scale
Typical temperature dependence
0.005 %/˚C (0.003 %/˚F)
of analog output
full scale
Serial output
8-pole connector with RS-232C, current
outputs (two channels) and Uin
Operating voltage Uin
24 VDC (10 ... 35 VDC)
Minimum operating voltage Uin
with RS-232C
10 VDC
11 VDC + (Rload/60) VDC
Iout 0 ... 20 mA, 4 ... 20 mA
Power consumption at +20 ˚C, Uin = 24 VDC
with RS-232C
20 mA
60 mA
Iout 2 x 0 ... 20 mA
For more information, visit or contact
us at [email protected]
Operating temperature range for
-40 ... +60 ˚C (-40 ... +140 ˚F)
Storage temperature
-55 ... +80 ˚C (-67 ... +176 ˚F)
Pressure range for MMT318 with ball
valve up to 120 ˚C
0 ... 40 bar
Pressure range for MMT317
0 ... 10 bar
External load
R1<500 Ohm
transmitter housing
G-AlSi 10 Mg
transmitter base
Housing classification
to be protected from direct rain
Cable feed through alternatives 8-pole connector with 5 m cable,
female 8-pin connector screw
joint for cable diameter 4 ... 8 mm
Sensor protection
stainless steel grid
Probe cable length
0.5, 2, 5 or 10 meters
2, 5 or 10 meters
Probe installation MMT317
NPT 1/2”, ISO 3/8” or ISO 1/2”
Probe installation MMT318
Fitting bodies
ISO 1/2”, NPT 1/2”
Ball Valve Set
Complies with EMC standard EN61326-1, Industrial environment
Note: When using the current output, the RF field susceptibility
level according to standard EN61000-4-3 with a frequency band
of 110 ... 165 MHz, is only 3 V/m (generic environment) with the
specified accuracy.
HUMICAP® is a registered trademark of Vaisala.
Ref. B210831EN-A ©Vaisala 2009
This material is subject to copyright protection, with all
copyrights retained by Vaisala and its individual partners. All
rights reserved. Any logos and/or product names are trademarks
of Vaisala or its individual partners. The reproduction, transfer,
distribution or storage of information contained in this brochure
in any form without the prior written consent of Vaisala is strictly
prohibited. All specifications — technical included — are subject
to change without notice.
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