2.3.3 Automatic Calibration

When using the automatic calibration, the calculations are done by the Demo Meter application firmware, so the Excel sheet is not needed. The automatic calibration is done by means of the CNF and the CAL commands:
  • The CNF command is used to configure the metrology library according to the input network hardware as well as the programmable gain of the internal amplifiers. Refer to 2.5 Demo Meter Application Commands for additional information.
  • The CAL commands include parameters to send the input conditions (voltages, currents and angles being applied by the Meter Tester) to the application firmware. When received, the Demo Meter application firmware computes the calibration parameters. There are two variants of the CALcommand: the first one calibrates one phase individually; the second one is valid for a poly-phase system and calibrates all the phases at the same time. Refer to 2.5 Demo Meter Application Commands for additional information.

The following steps describe the calibration procedure:
  • Send a CNF command. If the programmable gain of the internal amplifiers changes, then:
    • Send an RST command to apply the new gain.
    • Send the CNF command again.
  • Apply the input conditions (voltages, current and angles), then wait until the input stabilizes.
  • Send a CAL command.

Warning: The CNF command affects all channels, so it is not valid for meters with different kinds of sensors, for example, a combination of Rogowski coils and CTs or CTs with different current transformer ratio or different burden resistors.