Vaisala HMT310 - Manual (Page 57)

Chapter 4 _________________________________________________________________ Operation
VAISALA ________________________________________________________________________ 57
Set Error Outputs
Syntax: AERR
The factory default state for analog outputs during error condition is
0 mA. Be careful when selecting the new error value, the error state of
the transmitter should not cause problems in process monitoring.
Example:
>aerr
Ch1 error out : 0.000mA ?
Ch2 error out : 0.000mA ?
NOTE Error output value needs to be within the valid range of the output type.
NOTE The error output value is shown only when there are minor electrical
faults such as a humidity sensor open circuit. When there is a severe
device malfunction, such as an analog output electronics failure or a
microprocessor ROM/RAM failure, the error output value is not
necessarily shown.
Chemical Purge (Optional)
General
In some specific applications the sensor gain may decrease gradually due
to an interference caused by some particular chemical present in the
ambient (see Figure 16 on page 58). The sensor polymer absorbs the
interfering chemical; this reduces the ability of the polymer to absorb
water molecules and so decreases the sensor gain. In chemical purge, the
humidity sensor is heated to a temperature level of approximately
+180 °C for several minutes, which evaporates the interfering chemical.
The purge function starts with a heating stage, continues with a settling
stage, and when the temperature of the sensor is decreased, the
transmitter returns to normal mode. The whole cycle takes about 8
minutes.
NOTE The chemical purge function locks the output values for about 8 minutes.