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22. METER CALIBRATION
All analog input and analog output ranges
of the meter have been digitally calibrated at the
factory prior to shipment using calibration equipment certified to NIST standards. Calibration
constants are stored digitally in non-volatile memory in EEPROM on the signal conditioner board
and analog output board. This allows the boards to be changed without requiring meter
recalibration. Digital calibration also eliminates much of circuitry that would be associated with
analog calibration, providing superior long term accuracy and stability.
If periodic recalibration is required,
the meter may be returned to the factory or to any author-
ized distributor. A modest fee will apply, which also covers a Calibration Certificate.
DC, load cell, AC RMS, and thermocouple signal conditioner boards
can be calibrated using
Instrument Setup Software running on a host PC (Section 20). An RS232, RS485, USB or
Ethernet interface board must be installed in the meter for communication to the PC. This board
may be removed following calibration. A certified, calibrated signal source is also required. The
Calibration screen of Instrument Setup Software is accessed by clicking on Calibration at the top
of the DPM Main Menu screen. The PC first recognizes the type of board, then prompts you to
apply specific jumpers and specific known signals for each range. Press Repeat to take more
readings. When you have decided on which reading to accept, press on the number 1 through
10 of that reading.
The RTD/Ohms signal conditioner board
cannot be calibrated using the Calibration screen of
Instrument Setup Software. Instead, use the Scaling tab under Setup. Here you can enter values
for Scale and Offset for a specific range. These corrections apply to resistance, not to RTD
temperature. To calibrate RTD temperature, refer to the published resistance table for your RTD
type, and calibrate resistance. For example, if your measured resistances are 0.1% low, apply
a scale factor of 1.01.
