Lakeshore Learning Materials 642 - Manual (Page 112)

Lake Shore Model 642 Electromagnet Power Supply User’s Manual
7-20 Service
7.13.3.6 Calibrate Current Reading Gain
1. Send “CALG 0, 1”. To set the output current reading gain constant to 1.
2. Set the Model 642 output current to –70 A. (Ramp rate 30 A/s nominal).
3. Wait 30 seconds.
4. Measure the actual voltage across the shunt and record (V
shunt
).
5. Calculate and record (I
measuredneg
): V
shunt
/R
shunt
.
6. Get the Model 642 output current reading (by front panel or interface) and record (I
readingneg
).
7. Set the Model 642 output current to +70 A (Ramp rate 30 A/s nominal).
8. Wait 30 seconds.
9. Measure the actual voltage across the shunt and record (V
shunt
).
10. Calculate and record (I
measuredpos
): V
shunt
/R
shunt
.
11. Get the Model 642 output current reading (by front panel or interface) and record (I
readingpos
).
12. Calculate gain constant per the following equation:
Current Reading Gain Constant = (I
measuredpos
– I
measuredneg
)/(I
readingpos
– I
readingneg
)
13. Verify gain factor to be 1, ±0.02.
14. Send “CALG 0, gain constant”.
15. Verify the Model 642 output current reading to equal I
measuredpos
, ±0.010 A.
16. Set the Model 642 output current to 0 A.
17. Send “CALSAVE” to write this calibration to non-volatile memory.
This method is somewhat lengthy, but averages the differences between positive (+) and negative (–) excursions.
7.11.3.7 Calibrate Voltage Reading Gain
1. Send “CALG 5, 1”. To set the output voltage reading gain constant to 1.
2. Set the Model 642 output current to 65 A.
3. Wait 30 seconds.
4. Measure the Model 642 actual output voltage at the output terminals and record (V
measuredpos
).
5. Get the Model 642 output voltage reading (by front panel or interface) and record (V
readingpos
).
6. Set the Model 642 output current to –65 A.
7. Wait 30 seconds.
8. Measure the Model 642 actual output voltage at the output terminals and record (V
measuredneg
).
9. Get the Model 642 output voltage reading (by front panel or interface) and record (V
readingneg
).
10. Calculate gain constant per the following equation:
Voltage Reading Gain Constant = (V
measuredpos
-V
measuredneg
)/(V
readingpos
-V
readingneg
)
11. Verify the gain factor to be 1, ±0.02.
12. Send “CALG 5, gain constant”.
13. Verify the Model 642 output voltage reading to match the actual output voltage within, ±0.001 V.
14. Set the Model 642 output current to 0 A.
15. Send “CALSAVE” to write this calibration to non-volatile memory.