Introduction to HMT120 series - HMT120

HMT120 User Guide

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User guide

Vaisala HMT120 series transmitters measure relative humidity and temperature and convert the measurements to analog current loop outputs. Other measurement parameters, such as dew point (Td), can be calculated from the basic relative humidity and temperature values according to the device configuration. HMT120 is powered with 10 ... 30 V DC external loop voltage (20 ... 30 V DC when RL <500 ohms) and it outputs two analog current signals with nominal 4 ... 20 mA range. The HMP110 series measurement probes used with HMT120 incorporate the reliable Vaisala HUMICAP® humidity sensor technology.

The HMT120 transmitter's output parameters are configurable. The available parameters for outputs are limited to two at a time. These two parameters can be used freely at any outputs (display, service port, and analog current loop outputs).

Available parameters are RH, T, Td, Td/f, a, x, h, Tw, pws, and pw.

The default output parameters are set at the factory during order time. These factory preset parameter selections can be changed afterwards via the service port if necessary.

The TMT120 transmitter is a single-parameter model, with temperature as the only output parameter.

Vaisala relative humidity measurement instruments

The Vaisala range of relative humidity measurement instruments covers all the applications from ventilation to process control in demanding conditions. For more information about other Vaisala relative humidity instruments, please contact your Vaisala representative or visit