Lakeshore Learning Materials 622 - Manual (Page 63)

Lake Shore Model 620/622/623/647 Magnet Power Supply User’s Manual
Error Messages & Troubleshooting 5-5
5.3 CALIBRATION
NOTE: Calibration is only as accurate as the current monitor shunt. The factory uses a current monitor shunt
rated at 0.02% accuracy. Shunt manufacturers typically stock accuracy values of 0.25% or better. To use a
different value, adjust readings given in the procedure.
1. Equipment requirements for MPS calibration:
a. Current monitor shunt, 100 mV output at 100A (1 milliohm), 0.02% accurate.
b. Load resistor, 10V at 100A (0.1 ohm), 1 kW.
c. Digital Volt Meter (DVM) with a resolution of 100 nV, 6½ digits, 0.0035% accurate (HP 3457A or
equivalent).
d. A computer with a RS-232C serial interface.
e. LSCI Model 2002 RJ-11 to DB-25 adapter or Model 2003 RJ-11 to DE-9 adapter, depending on the
computer serial output connector.
2. Turn OFF and unplug the MPS before configuring it for calibration.
3. Configure the Control Bus Serial Interface for RS-232C Operation. See Paragraph C4.0. Connect output
to a computer using a modular cable, or if equipped, use the IEEE 6224 card.
4. Connect current monitoring shunt and load resistor in series to +OUT and –OUT terminals.
5. Enable MPS calibration. Locate rear panel CAL AND ID switches and turn ON (up) switch 8. Verify that
both MODE switches in the INTernal (up) position.
6. Plug the MPS in, turn it ON, and allow it to warm up for one hour.
NOTE: To terminate calibration at any time, send CALDN. Cycle MPS power to recover calibration
constants present prior to calibration initiation.
Calibration determines a zero, positive span, and negative span digital calibration constant for both current
and voltage. Enter calibration constants with extreme caution. If a constant is entered incorrectly,
terminate calibration with CALDN and re-start the sequence.
7. When calibrating current, the MPS forces ISET to calibration current. When calibrating voltage, the MPS
forces VSET to calibration voltage and ISET to IMAX. Set IMAX to equal or greater than calibration
current. Input and note the IMAX value using IMAX?. For this calibration, send IMAX+50 to set IMAX to
50. Turn OFF the output current step feature during calibration. Input and note the output current step
status using ISTPS?. Send ISTPS0 to turn OFF output current step limiting.
8. Connect the DVM reading voltage across the +OUT and –OUT terminals.
9. Send VZER to inform the MPS of output voltage calibration and force output voltage to 0V. Verify a DVM
reading of 0V ±0.1V. Allow MPS output to settle for 2 minutes.
10. Read actual output voltage from DVM. Send the MPS the actual voltage using CALZ+xxx.xxxx. If actual
voltage is +0.0123V, send CALZ+0.0123. The MPS determines the zero voltage calibration constant.
11. Send VCAL5 to force output voltage to +5 volts. Verify that the DVM reads +5V ±10%. Allow MPS output
to settle for 2 minutes.
12. Read actual output voltage from the DVM. Send the actual voltage using CALPL+xxx.xxxx. If actual voltage
is +5.1234V, send CALPL+5.1234. The MPS determines the positive voltage calibration constant.
13. After the MPS determines the positive voltage calibration constant, it automatically sets output voltage to
the same value with the opposite sign. Verify a DVM reading of -5V ±10%. Allow MPS output to settle for 2
minutes.
14. Read actual output voltage from the DVM. Send the actual voltage using CALMN-xxx.xxxx. If actual
voltage is -4.8766V, send CALMN-4.8766. The MPS determines the negative voltage calibration constant.
15. The MPS stores the zero, positive, and negative voltage calibration constants, then sets the output voltage
to 0. Verify a DVM reading of 0V ±0.1V before continuing the calibration.
16. Connect DVM across current monitoring resistor.