Vaisala HMP240 - Manual (Page 10)

HMP240
User's Guide
M210300en
8
3. INSTALLATION
3.1 Selecting the place of installation
The transmitter should be installed in a place that gives a true picture of the
environment or process and is as clean as possible. Air should circulate freely
around the sensor. If necessary, the transmitter can be installed in a place
where a hot spot may develop. However, cold spots should be avoided.
When the sensor head is installed in a duct or a process channel where the
temperature is different from the ambient temperature, insulate the point of
entry; this is particularly important if the transmitter is installed with the
sensor head pointing downwards. Installing the sensor head of the HMP240
vertically is not recommended because in high humidities, the humidity may
condence on the sensor head cable and then flow on to the sensor head.
When there is no alternative but to install the sensor head in the process
vertically, the point of entry must be carefully insulated. The cable must also
be allowed to hang loosely in order to prevent any water that possibly
condenses on the cable from running onto the sensor head.
Install the humidity sensor head in the process wherever possible. Avoid
sample flows where the gas temperature can drop below dewpoint
temperature; this might result in erroneous measurement readings. Install the
sensor head transversely against the direction of the process flow. If the
process temperature is much higher than that of the environment, the whole
sensor head and preferably part of the cable must be inside the process.
In duct or channel installations drill a hole ready for a reference meter. Plug
the reference hole tightly (see Figure 3.2).
Install the electronics housing away from possible steams escaping from the
process.