Starting at $1,349.00

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  • RH measurement range: 0 to 100%
  • Temperature range: 0 to 180°C (356°F)(Model specific)
  • Pressure tolerance: up to 100 bar (Model specific)
  • Next generation Vaisala HUMICAP Sensor
  • Models:
    • HMT331: Demanding Wall-mount Applications
    • HMT333: Ducts and Tight Spaces
    • HMT334: High Pressure and Vacuum Applications
    • HMT335: High Temperature Applications
    • HMT337: High Humidity Applications
    • HMT338: Pressurized Pipelines
  • IP65 housing
  • NIST certificate (included)
  • Analog outputs, WLAN/LAN
  • Six point factory calibration

The Vaisala HUMICAP® Humidity and Temperature Transmitter Series HMT330 is designed for demanding industrial applications where stable measurement and wide customization is important. The HMT330 series incorporates an updated, stable and chemical resistant HUMICAP® sensor.

In environments with high concentrations of chemicals and cleaning agents, chemical purge helps to maintain measurement accuracy between calibration intervals. Chemical purge involves heating the sensor to remove harmful chemicals. The function can be initiated manually or programmed to occur at set intervals.

The HMT330 can be ordered with a large numerical and graphical display, which allows the user to clearly monitor operational data, measurement trends and 1-year measurement history. The display alarm allows tracking of any measured parameter, with a freely configurable low and high limit.

The optional data logger with real-time clock makes it possible to generate over four years of measured history. The recorded measurement data can be viewed on the display or transferred to a PC with Microsoft Windows® software. The transmitter can also be connected to a network with an optional (W)LAN interface, which enables a (wireless) Ethernet connection. A USB-RJ45 cable makes it easy to connect the service port of the HMT330 to a PC.

Vaisala HMT331 for Wall-Mounted Applications

The HMT331 offers higher measurement performance, better chemical tolerance, advanced graphical display features, more powering options, more output options and a wider variety of output humidity parameters compared to regular wall-mounted transmitters. Applications include: cleanrooms, pharmaceutical processes, greenhouses, swimming halls, museums and archives.

Vaisala HMT333 for Ducts and Tight Spaces

Vaisala HMT333 Transmitters are a versatile instrument for applications where a small remote probe is needed. An installation kit is available with an aluminum flange, lead-through piece, and steel support bar to install the probe in ducts, channels and through walls.

Vaisala HMT334 for High Pressure and Vacuum Applications

The Vaisala HMT334 Transmitter is designed to measure humidity in pressurized spaces or vacuum chambers. Each probe is tested to ensure a gas and vacuum tight installation. The sensor is immune to particulate contamination and most chemicals.

Vaisala HMT335 for High Temperatures

Vaisala HMT335 Transmitters have a long stainless steel probe designed for high temperatures. It is ideal for duct measurements. The probe tolerates mechanical stress and withstands high flow rates. The HMT335 can be used, for example, in a hot drying process.

Vaisala HMT337 for High Humidity Applications

The HMT337 is delivered in one of three configurations:

  • Basic: Non-warmed probe for moderate humidity
  • Warmed Probe: For near-condensing conditions and dew point measurement
  • Warmed Probe and additional temperature sensor: For near-condensing conditions and relative humidity measurement

The warmed probe provides fast and reliable measurement in environments where humidity is near saturation. The warming prevents condensation from forming on the sensor.

Vaisala HMT338 for Pressurized Pipelines

The Vaisala HMT338 Transmitter is ideal for installations in pressurized processes where the probe needs to be removed while the process is running ("hot tapping") without the need for venting of lowering the process pressure.


Vaisala Standard Humidity Re-Calibration
Re-calibration with traceable certificate for 5 points (15, 33, 54, 75 & 95% RH) and temperature at ambient, meets ISO 9001 standards


Vaisala 219685 USB Cable
5ft (1.5m) USB-RJ45 serial connection cable with software driver CD
In Stock
Vaisala HMP247CG AGRO Cable Gland
M20 x 1.5 with split seal


Vaisala MI70LINK Software
Vaisala MI70LINK Software with USB or serial port cable
In Stock


Vaisala 214829 Wall Mount Plate
Plastic mounting plate with 4 screws for fixing to transmitter
Vaisala 210696 Mounting Flange
Duct installation flange designed for 13.5mm diameter probes, includes plastic sealing ring, screws, and washers


Please consider these optional accessories.

Vaisala 215108 Pole Installation Kit
Metal mounting plate, fixing brakets, and mounting nuts for 30 to 102mm pole or pipeline
In Stock
Vaisala 215094 DIN Rail Kit
Transmitter installation plate with DIN rail clips
Vaisala 210697 Duct Installation Kit
0 to 10in (0 to 25cm) adjustable depth, includes flange, supporting bar, plastic sealing ring, screws, and washers
Vaisala DTR502B Radiation Shield
9-plate shield to protect humidity and temperature sensors from solar radiation and precipitation
Vaisala 19446ZZ Serial Interface Cable
RJ45 to DE9M connector, 6.2ft (1.9m) length
Vaisala HM47280SP Sintered Filter
12mm diameter, female thread, stainless steel with 38µm pore size
Vaisala SWG12NPT12 Swagelok
Fitting for 12mm diameter probe with 1/2in NPT male thread, rated for up to 145 psi (10 bar)

Application Notes

Here's how some of our customers used this product.

Humidity Control in Malting

The Background: Our customer is a brewer who needs a system to control the moisture during malting, the process by which the grain used for brewing is made to germinate by soaking in water then halted from further germination by drying with hot air.

The Problem: It is not possible to measure relative humidity accurately at high humidities with standard humidity meters because of the possibility of condensation and saturation of the probe.

The Solution: We turned to the Vaisala HMT337 humidity transmitter with warmed probe to monitor the humidity accurately with a Watlow DC21 power controller and PM6 temperature controller used to control the heaters and, thus, the temperature. The temperature probe and the humidity probe were placed in the exhaust duct with the displays mounted remotely for the operator to view from the floor. The temperature probe and the controller were calibrated as a system in our lab to meet their ISO requirements.

Monitoring Humidity and Temperature Inside Hay Bales

The Background: Our customer is a farm that needs to monitor the temperature and humidity inside bales of hay to protect against the possibility of barn fires caused by spontaneous combustion.

The Problem: If they hay is baled when moisture is above 22% there is an increased risk that microbiological activity can lead to self-heating, thermal runaway and finally autoignition. The customer wants a solutions that monitors both moisture inside the bales, a primary factor in microbiological activity, and temperature, an effect of that activity.

The Solution: The Vaisala HMT330 is ideal for the continuous monitoring of temperature and humidity and includes alarm output to notify personnel if conditions could lead to a fire.

Monitoring Moisture in a Dough Rising Machine

The Background: A commercial bakery needs to monitor the moisture content of their dough rising machines in order to optimize conditions.

The Problem: The dough rising machines get so wet inside that moisture readings are erratic.

The Solution: The Vaisala HMT337 with a heated probe controls the problem of wetness inside the machines and allows the customer to get accurate readings and control their process more accurately.

Monitoring Temperature and Humidity in a Server Room

The Background: Our customer is a large business that maintains their own computer servers in a dedicated room within their office building. They seek a means of monitoring humidity and temperature inside the server room.

The Problem: The server room has a raised floor upon which the servers are racked. The customer is concerned about humidity and high temperatures in the space under the raised floor. The company’s servers are both high dollar assets and critical to keeping the company running. They want a means to trigger ventilation if the humidity or temperature rises to levels which can damage the servers.

The Solution: We recommended the Vaisala HUMICAP humidity and temperature transmitter which provide rugged and reliable monitoring of the space under the raised floor.

Testing Dryer Prototypes

The Background: Our customer manufactures washers and dryers. They are seeking a reliable humidity and temperature transmitter for laboratory testing of their dryer prototypes. They also need to measure the mixing ratio to check the humidity level at air inlet and outlet - a better option for certain heat and mass balance calculations.

The Problem: Because the humidity level in dryers can be quite high before the clothes begin to dry, general-purpose RH transmitters are not the best choice due to possible condensation on the sensing element which can cause problems with measurement accuracy.

The Solution: We recommended the Vaisala HMT337 Humidity and Temperature Transmitter which is designed for demanding industrial applications where stable measurement and wide customization is important. The HMT337 can be fitted with a warmed humidity probe and an additional temperature probe and has three outputs, one each for RH, Temp, and mixing ratio.