Vaisala HMP240 - Manual (Page 123)

HMP243
M210300en Appendix 7: Re-gaining
121
2. TO BE NOTED IN RE-GAINING
Re-gaining cannot be started automatically or manually unless the
security lock jumper is on. This prevents automatic re-gaining during a
sensor calibration (when the security lock jumper must be removed).
Furthermore, re-gaining can be started only if the sensor temperature is below
100 °C. At higher temperatures the chemicals evaporate spontaneously from
the sensor, and the re-gaining is not necessary. The power consumption during
re-gaining is 270 mA maximum (24 VDC).
NOTE
The possible re-gaining must always take place before a
humidity calibration of the transmitter and not after.
Make sure that the temperature of the composite sensor
has come down to normal temperature before starting a
calibration.
Re-gaining can be automatic or it can be started manually. For automatic re-
gaining, five parameters are stored in the transmitter memory: the re-gaining
interval, the duration of the sensor heating, the settling - cooling - time, the
difference between the current sensor temperature and the ambient
temperature measured before re-gaining and the k parameter (the power level
the sensor is heated at). The parameter values can be changed by the user;
however, please note that it is necessary to remove the security lock jumper
first. The factory settings are:
Interval min : 720
Duration s : 120
Temp diff : 0.50
Settl time s : 240
k % : 95.00
The time interval between subsequent re-gainings starts at the end of the
settling time.
During heating and settling periods both the analogue and serial outputs as
well as the local display are locked to the values measured before re-gaining
started. The outputs are released again when the sensor has cooled within the
temperature difference setting or when the settling period is completed
irrespectively of whether the sensor has cooled within the temperature
difference or not.
The k parameter should not be changed from 95%. The recommended duration
of heating is 120 s and it should not be altered. The cooling time needed for
the sensor to stabilize to the ambient temperature is strongly dependent on
process conditions, especially on the speed of the air flow around the sensor
head. After the re-gaining has been completed, wait for a few seconds before
you start the measurement.