71M6513/71M6513H Demo Board User’s Manual
Page: 48 of 112
©
2005-2006 TERIDIAN Semiconductor Corporation
Revision 5.6
2.2.2 CALIBRATION PROCEDURE WITH FIVE MEASUREMENTS
The calibration procedure is as follows:
1) All calibration factors are reset to their default values, i.e. CAL_IA = CAL_VA = 16384, and PHADJ_A
= 0.
2) An RMS voltage V
ideal
consistent with the meter’s nominal voltage is applied, and the RMS reading
V
actual
of the meter is recorded. The voltage reading error Axv is determined as
Axv = (V
actual -
V
ideal
) / V
ideal
3) Apply the nominal load current at phase angles 0°, 60°, 180° and –60° (-300°). Measure the Wh
energy each time and record the errors E
0
, E
60
, E
180
, and E
300
.
4) Calculate the new calibration factors CAL_IA, CAL_VA, and PHADJ_A, using the formulae presented
in section 2.1.2 or using the spreadsheet presented in section 2.2.4.
5) Apply the new calibration factors CAL_IA, CAL_VA, and PHADJ_A to the meter. The memory locations
for these factors are given in section 1.9.1.
6) Test the meter at nominal current and, if desired, at lower and higher currents and various phase
angles to confirm the desired accuracy.
7) Store the new calibration factors CAL_IA, CAL_VA, and PHADJ_A in the flash memory of the meter. If
a Demo Board is calibrated, the methods shown in sections 1.9.3 and 1.9.4 can be used.
8) Repeat the steps 1 through 7 for each phase.
9) For added temperature compensation, read the value in CE RAM location 0x54 and write it to CE RAM
location 0x11. If Demo Code 3.05 or later is used, this will automatically calculate the correction
coefficients PPMC and PPMC2 from the nominal temperature entered in CE location 0x11 and from
the characterization data contained in the on-chip fuses.
Tip: Step 2 and the energy measurement at 0° of step 3 can be combined into one step.
2.2.3 CALIBRATION PROCEDURE FOR ROGOWSKI COIL SENSORS
Demo Code containing CE code that is compatible with Rogowski coils is available from TERIDIAN Semi-
conductor.
Rogowski coils generate a signal that is the derivative of the current. The CE code implemented in the
Rogowski CE image digitally compensates for this effect and has the usual gain and phase calibration
adjustments. Additionally, calibration adjustments are provided to eliminate voltage coupling from the sensor
input.
Current sensors built from Rogowski coils have a relatively high output impedance that is susceptible to
capacitive coupling from the large voltages present in the meter. The most dominant coupling is usually
capacitance between the primary of the coil and the coil’s output. This coupling adds a component proportional
to the derivative of voltage to the sensor output. This effect is compensated by the voltage coupling calibration
coefficients.
As with the CT procedure, the calibration procedure for Rogowski sensors uses the meter’s display to calibrate
the voltage path and the pulse outputs to perform the remaining energy calibrations. The calibration procedure
must be done to each phase separately, making sure that the pulse generator is driven by the accumulated real
energy for just that phase. In other words, the pulse generator input should be set to WhA, WhB, or WhC,
depending on the phase being calibrated.
In preparation of the calibration, all calibration parameters are set to their default values.
VMAX
and
IMAX
are
set to reflect the system design parameters.
WRATE
and
PUSE_SLOW
,
PULSE_FAST
are adjusted to obtain
the desired Kh.
http://www.datasheetcatalog.com/
