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HMP230 SERIES

M210225en-B User's Guide

1. PRODUCT DESCRIPTION

The HMP230 series transmitters are microprocessor based instruments for the

measurement of relative humidity and temperature; from these variables they

can calculate dewpoint temperature, absolute humidity, mixing ratio, wet bulb

temperature and enthalpy. The transmitters have two analogue outputs and

they can be connected to a serial bus via the RS 232C interface or through an

RS 485/422 serial module or a current loop module. At dewpoint temperatures

below 0 °C, the user can select whether the transmitter calculates dewpoint or

frostpoint reading; as default, the transmitter calculates dewpoint.

The series consists of four types of transmitters:

• HMP231, wall installation

• HMP233, ifor tight places; temperatures up to +80 or +120 °C

• HMP234, forpressure or vacuum chambers

• HMP235, for high temperatures of +180 °C

• HMP237, leak proof small size probe for pressures up to 10 bar

• HMP238, for pressurized processes

The transmitters can be configured in many ways. They can have either a

blank cover or a cover with a local display and keypad with which the user can

operate the transmitter. The power supply voltage can be selected from three

alternatives. Two analogue output signals are selected from the measured and

calculated quantities; the signals can be scaled and the measurement ranges

changed within certain limits. The HMP233, HMP234, HMP235, HMP237

and HMP238 probes can be supplied with two, five or ten metre sensor head

cable.

The humidity measuring range is 0...100 %RH. The temperature is measured

with a Pt 100 sensor. Temperature measurement range depends on the model;

the HMP234, HMP235, HMP237 and HMP238 have the widest range, -

40...+180 °C. The analogue temperature output can be scaled quite freely, for

example-20...+60 °C can be set to correspond to 0...10 V. The dewpoint

temperature, absolute humidity, mixing ratio, wet bulb temperature and

enthalpy ranges are also scalable.

In some applications the sensor gain may gradually decrease because of an

interference caused by some chemical present in the ambient. These changes

can be recovered with an optional re-gaining function. Transmitters including

this function are equipped with a composite humidity and temperature sensor.

The HMP230 series units incorporate the HUMICAP

sensor, which uses an

operating principle based on changes in the capacitance of the sensor as its

thin polymer film absorbs water molecules.

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Vaisala HMP230 Manuel d'utilisateur Page 7