Ametek California Instruments MX15 Series User Manual page 120

6.5.2 Output Impedance Calibration (MX15-1Pi only)
For the output impedance calibration, two HP 34401A DMM's or equivalent must be used. The
following modes must be programmed: 6 digits, AC Filter, slow: 3 Hz and 6 digits. One DMM is
used to measure the output voltage, one to measure the load current using a suitable CT. The
calibration should be done for each phase individually. Furthermore, an accurate phase meter
with at least 0.01° resolution is needed. (See equipment list section 6.1). The reference input of
the phase meter must be connected to the LOCK output of the controller at the rear panel. This
is a square wave TTL signal. The input of the phase meter must be connected at the output of
the phase being calibrated. The phase meter is used to determine the phase shift between no
load and full load conditions (∆Φ).
1. Program the power source to 230.0VAC and 50Hz. Turn off the ALC mode from the
CONTROL screen. The ALC must be off to use programmable impedance.
2. Program the output impedance resistance and inductance to the lowest values from the
CONTROL screen. This will be the IMP. REAL MIN and IMP. REACT MIN values that have
been set in the OUTPUT CAL screen.
3. Measure the output voltage of the power source with no load and record this value (V
4. Using a resistive load bank, load the output of the power source to about 48 ± 9 amps.
Measure the output voltage of the power source under load and record this value (V
measure the load current and record this value. (I).
5. Calculate the resistive and inductive component R and L using the formulas shown in Table
6-5.
6. Enter these values, in the OUTPUT CAL screen for the IMP. REAL MIN and IMP. REAC
MIN value respectively. Make sure the correct phase is selected or use the PHASE key if
not.
7. Remove or turn off the load.
8. From the CONTROL screen, select OUTPUT IMPEDANCE. Program the output inductance
to 200 uH and the resistance to 200 mOhms.
9. Select the Calibration, Output screen and move the cursor to the IMP REAL FS field.
Measure the R and L by removing and applying the load as described before and calculating
the R and L using the formulas in Table 6-5
Adjust the resistive output impedance using the shuttle until the measured output is as close
as possible to 200 mOhm. Do the same with the IMP REACT FS field. Note that the
adjustment range for R is 0 to 100, for L is 0 to 300.
10. Press SET to save the calibration coefficients.
11. If there is not enough range in the full-scale calibration coefficient for either resistive or
inductive portion, it may be necessary to tweak the adjustment pots on the MX controller.
These pots were originally adjusted at the factory and normally do not have to be adjusted
again. The Full Scale calibration coefficients should have enough adjustment range. Double
check the connections and phase measurements if this is not the case to make sure the
measurement readings you get are indeed correct.
If it is necessary to adjust the pots, see Table 6-4 for the corresponding pot designators. The
top cover must be removed to access these pots. They are located along the top edge of the
controller board.
).
NL
). Also
L
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