In order to maintain
consistent quality of manufactured
products, it is necessary to perform
periodic calibrations on process sensors
and instruments. There are several
philosophies for calibration of
measurement and control circuits. The
basis of the chosen method should always
be to include the temperature sensor.
It does not make any sense only to
calibrate and adjust the electronic part
of the loop. A rule of thumb says that
only 10% of the total error is in the
electronics, the other 90% is due to the
sensing element. So it is essential that
the temperature sensor is tested,
meaning physically exposed to the
desired temperature. A dry-block
calibrator is an easy method to create
the 'process' temperature.
The output from the sensor can be taken
from anywhere in the loop. And the rest
of the loop may be tested
electronically. |
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1. The raw sensor output
2. After a transmitter (4-20 mA)
3. Manual reading on an indicator
4. The control data in the control room
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