Externally Referenced Calibration - Pacific UPC-32 Operation Manual

8.3

EXTERNALLY REFERENCED CALIBRATION

The UPC metering is designed to be easily calibrated in the field. Calibration may be required in order to ensure
that the CSC function is able to precisely match the output voltage of the power source to the programmed
command voltage. Potential sources of error which may cause difference between these two voltages are:
a) Drift in oscillator signal level.
b) Power Amplifier gain drift.
c) Output transformer turns ratio error. i.e. Actual turns ratio different from encoded turns ratio.
d) Difference between INT SENSE metering circuit and EXT SENSE metering circuit.
e) Internal metering inaccuracy.
Since the UPC display can show both PROGRAM (Command) and METERED voltages, these errors will be
apparent - if they occur - as a slight difference between the two voltages. Only basic metering inaccuracy will not
reveal itself on the display.
To calibrate the metering functions of the UPC, it will be necessary to:
1. Set up the UPC to generate output voltage and current.
2. Measure the voltages and currents on all phases using an external Voltmeter and Current Meter
that have been calibrated to a traceable standard (i.e., NBS, NIST), and are at least 2x as
accurate as the UPC metering (see Section 2, SPECIFICATIONS)
3. Enter the measured values into the UPC via the keyboard or Remote Interface.
The UPC then creates calibration factors (kFactors,) for the metering functions and stores them in RAM. The
kFactors can be viewed on the display by pressing fn, 4, 3, (see para. 8.3.1), or through the control bus (see
para. 5.6, :CALibrate:KFACTORS).
Typically, calibration is performed with output settings of 60 Hz and 120 volts. Because of the precision and
stability of the system, the calibration factors are the same for all other values of volts and frequency. For
convenience, or if precision at a particular setting is needed, the system may be calibrated at any frequency,
voltage and current desired. Calibration of current metering is based on the Load Current set by the user.
Therefore a nominal Load Current should be chosen for this calibration process.
NOTE: Only RMS voltages and currents are corrected.
NOTE: If the Programmable Impedance Option is installed, it must also be calibrated, see para. 4.6.3.1.1
or 5.4.1, :[SOURce]:IMPEDance:CAL.
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SECTION 8 CALIBRATION