Vaisala HMP260 - Manual (Page 56)

HMP260 SERIES
Operating Manual
HMP260-U017en-1.5
50 1997-11-25
7. MAINTENANCE
7.1 Reference measurements
Reference measurements are necessary for the verification of whether the
transmitter readings are within specifications. This way the user can check if
the transmitter needs calibration or service.
The reference meter should preferably use the same technology as the instru-
ment checked, i.e. transmitters with capacitive sensors should be checked with
instruments using capacitive sensors. This minimizes the risk of errors caused
by different measurement techniques.
Whatever technique is used, make sure the reference instrument is at the same
temperature as the checked instrument in order to avoid errors caused by tem-
perature differences. If the sensor head is installed in a potentially explosive
area, the reference instrument must have the same Exi-classification. The
reference measurement should be done as close to the checked sensor as
possible and the readings should be read at the same time, when possible.
The best reference measurements are done in laboratories. If it is possible to
take the transmitter out of process or control system, perform the reference
measurement in a laboratory where the conditions are stable.
7.2 Self-diagnostics
The HMP260 transmitters go through a self-diagnostics procedure when the
power is switched on. If the procedure does not reveal any errors or faults, the
transmitter starts operating normally. If errors or faults are found, first check
whether the humidity and temperature sensors are damaged. If they are intact,
send the transmitter to Vaisala or a Vaisala representative for repairs. The
error messages the transmitter outputs are listed in Appendix 3.
If any errors occur during operation, the error messages are output on the local
display if the transmitter displays measurements; if the menus are used, error
messages are not output. The LEDs indicate errors at all times. During opera-
tion, however, the error messages are not output automatically through the se-
rial interface. If there is any reason to doubt that there is something wrong
with the transmitter, use command ERRS:
ERRS <cr>
If there are no error messages, only a prompt is displayed:
>ERRS <cr>
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