Since months we have done a lot of tests with the following Fieldpoint modules
:
FP1000 (interface), RLY420 (relays), AI110 (16 bits analog intput), TC120
(thermocouple input), AO200 (current output).
We noticed that randomly an important shift appears on the measurement. This
can occurs after only a few hours or after several days of normal operation.
Thus we read on one input of the AI110, configured in 4-20 mA, without load,
4.08 mA on an input measured actually at 4.000 mA, which translates in load
by an error of 8 volts for an input measured at 230 V. The same applies for
the thermocouple inputs.
There are no electromagnetic disturbances near our different applications.
We even use different supplies circuit for the po
wer and Fieldpoint modules
(regulated).
When it arrives the only way to come back to normal is to power down a second
all the modules.
National is unable to provide a solution, although one of their engineer
acknowledged that he succeeded one time (only ?) to reproduce the defect.
Is it because of the continuous auto-calibration that is operated by the
FP1000 interface ?
Is it a bug in the firmware of this interface ?
Did you encounter the same problems ? Have you got any ideas about this problem
?
I precise that our lab is accredited for calibration. We use standard reference
instrument.
