Vaisala HMP260 - Manual (Page 7)

HMP260 SERIES
HMP260-U017en-1.5 Operating Manual
1997-11-25 1
1. PRODUCT DESCRIPTION
NOTE
Before installing and using the HMP260 transmitter
study carefully Appendix 2: SAFETY SUMMARY.
The HMP260 series transmitters are associated electrical apparatuses. This
means that the housing of the transmitter is mounted into a safe area and the
sensor head and its cable can go to a potentially explosive environment
(hazardous area). The transmitters incorporate a protective unit which contains
the power limiting components. This unit prevents the entry of any hazardous
energies to the potentially explosive area.
The transmitters are microprocessor based instruments which measure relative
humidity and temperature; from these variables they can calculate dewpoint
temperature, absolute humidity, mixing ratio and wet bulb temperature. The
transmitters have two analogue outputs and can be connected to a serial bus
via the RS 232C interface or through an RS 485/422 serial module or a digital
current loop module.
The series consists of three types of transmitter:
• HMP263, installation in tight places; temperatures up to +120 °C
• HMP264, installation in pressure or vacuum chambers
• HMP265, installation in high temperatures up to +180 °C
There are various possibilities for the configuration of the transmitters. They
can have either a blank cover or a cover with a local display and keypad with
which to operate the transmitter. 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 HMP263, HMP264
and HMP265 can be supplied with two, five, ten or 15 metre probe 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 HMP264 and HMP265 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 and wet bulb temperature ranges are also scalable.
The HMP260 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.