Lake Shore Model 647 Magnet Power Supply User’s Manual
Troubleshooting
5-4
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 manufactur-
ers typically stock accuracy values of 0.25% or
better. To use a different value, adjust the 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, 6 1/2 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, depend-
ing 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
the CALDN command. 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 the calibration procedure with the CALDN
command and re-start the sequence.
7.
When calibrating current, the MPS forces ISET
to the calibration current. When calibrating
voltage, the MPS forces VSET to the calibration
voltage and ISET to IMAX. Set IMAX to equal or
greater than the calibration current. Input and
note the IMAX value using the IMAX? command.
For this calibration procedure, 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 the ISTPS?
command. Send the ISTPS0 command to turn
OFF output current step limiting.
8.
Connect the DVM reading voltage across the
+OUT and –OUT terminals.
9.
Send the command ‘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 the DVM. Send
the MPS the actual voltage using the command
‘CALZ+xxx.xxxx’. If actual voltage is +0.0123
volts, send ‘CALZ+0.0123’. The MPS deter-
mines 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 with the command
‘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 with the command ‘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 the DVM across the current monitoring
resistor.
17.
Send ‘IZER’ to force output current to 0 amps for
output current calibration. Verify a DVM reading
of 0V ±0.01V. Allow MPS output to settle for 2
minutes.
18.
Convert the DVM voltage reading to current. A
reading of +0.000345V 0.345A. Send
the actual current with the command
‘CALZ+xxx.xxxx’. If the actual current is +0.345
amps, send ‘CALZ+0.3450’. The MPS deter-
mines the zero current calibration constant.
19.
Send ‘ICAL50’ to inform the MPS of output
current calibration and to force output current to
+50 amps. Verify a DVM reading of +0.05V
±10%. Allow MPS output to settle for 2 minutes.
