Vaisala HMP230 - Manual (Page 18)

HMP230 SERIES
User's Guide
M210225en-B
12
Figure 10. HMP237 cable installation.
3.2.7. HMP238 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).
It is recommended that the sensor head is installed directly in the process
through the ball valve assembly. When the ball valve set is used, the chamber
or the duct does not have to be emptied or shut down for installation or
removal of the probe. Install the sensor head transversely against the direction
of the process flow.
However, if direct installation is not possible for some reason, the probe can
be installed in a "leak-through" position provided that there is a slight
overpressure in the process. In this installation, the probe is mounted behind
the ball valve assembly. The flow passes through the sensor head and leaks
out through a vent hole in the fitting body. However, make sure that the
temperature at the measurement point is equal to that of the process.
Temperature < 180ºC
Pressure < 10 bar
1. Make a hole as described in duct installation,
Figure 9.
2. Take out the rubber sealing from the AGRO
Nr 1013.30.91. Drill a 6 mm hole in the middle
of the rubber sealing. Cut the jacket of the
sealing.
3. Thread the probe through the AGRO-fitting
body and nut (without the cut rubber).
4. Set the cut rubber sealing through the cable
between the fitting body and the nut.
5. Turn the fitting body to the hole, push the
rubber sealing into the fitting body and tighten
the nut.