Instruction Manual

HMP230 SERIES
M210225en-B User's Guide
7
The sensor head can also be installed vertically.
Figure 4 Vertical installation of the HMP233 sensor head
3.2.4. HMP234 transmitter
The atmospheric pressure has an effect on mixing ratio, wet bulb temperature
and enthalpy. Therefore, accurate calculations can be achieved only when the
ambient pressure is taken into consideration. The pressure is used for pressure
compensation of the HUMICAP

sensor in order to ensure the best possible
measurement accuracy. If the process pressure differs from normal
ambient pressure, the value has to be entered in the transmitter memory
when using the transmitters HMP234 or HMP238. The pressure to be
entered is the absolute pressure in hPa or mbar (for pressure unit conversion,
see Appendix 10).
The HMP234 is supplied with a nut, a fitting body and a sealing washer. Dur-
ing handling the fitting body and the nut should remain in place on the body of
the sensor head to prevent damage to the highly polished surface.
To achieve a leak-tight assembly:
1. Remove the fitting body from the nut and the sensor head.
2. Fasten the fitting body to the chamber wall. Tighten the fitting body
into the threaded sleeve with a torque spanner. The tightening torque
is 150 ±10 Nm.
3. Insert the body of the sensor head into the fitting body and screw the
nut manually to the fitting body until the connection feels tight.
When a bushing is used, its
size is selected according to
the diameter of the sensor
head; the diameter of the
cable is increased by using
e.g. tape at the bushing