Lakeshore Learning Materials 642 - Manual (Page 111)

Lake Shore Model 642 Electromagnet Power Supply User’s Manual
Service 7-19
Calibrate Output Current Gain (Continued)
12. Measure the actual voltage across the shunt and record (V
shunt
).
13. Calculate and record (I
minpostrim
): V
shunt
/R
shunt
.
14. Send “CALG 10, 0”. To set the output current gain trim constant to 0.
15. Set the Model 642 to –65A V (ramp rate 30 A/s nominal).
16. Wait 30 seconds for settling.
17. Measure the actual voltage across the shunt and record (V
shunt
).
18. Calculate and record (I
min
): V
shunt
/R
shunt
.
19. Send “CALG 10, –100”. To set the output current gain trim constant to maximum.
20. Wait 10 Seconds.
21. Measure the actual voltage across the shunt and record (V
shunt
).
22. Calculate and record (I
maxnegtrim
): V
shunt
/R
shunt
.
23. Send “CALG 10, +100”. To set the output current gain trim constant to minimum.
24. Wait 10 seconds.
25. Measure the actual voltage across the shunt and record (V
shunt
).
26. Calculate and record (I
minnegtrim
): V
shunt
/R
shunt
.
27. Send “CALG 10, 0”. To return the output current gain trim constant to 0.
28. Set the Model 642 output current to 0 A.
29. Calculate the gain constant per the following equation:
Current Output Gain Constant = 200((I
max
-I
min
) – 130)/((I
maxpostrim
-I
minpostrim
) – (I
maxnegtrim
-I
minnegtrim
))
30. Send “CALG 10, gain constant”.
This method, while somewhat lengthy, averages the trim spans between negative and positive settings to split the error
between positive and negative operation.
This gain calibration may shift the initial zero calibration for the Current Output DAC slightly. It is best to repeat the
current zero calibrations at this point.
31. Recalibrate Current Output Zero (refer to Section 7.13.3.1).
32. Recalibrate Current Reading Zero (refer to Section 7.13.3.2).
33. Set the Model 642 output current to 65 A (ramp rate 30 A/s nominal).
34. Wait 30 seconds.
35. Measure the actual voltage across the shunt and record (V
shunt
).
36. Calculate and record (I
out
+): V
shunt
/R
shunt
.
37. Verify I
out
= 65 A ±0.010 A (0.015%).
39. Set the Model 642 output current to –65 A (ramp rate 30 A/s nominal).
40. Wait 30 seconds.
41. Calculate and record (I
out
–): V
shunt
/R
shunt
.
42. Verify I
out
= –65 A ±0.010 A (0.015%).
43. Set the Model 642 output current to 0 A.
44. Send “CALSAVE” to write this calibration to non-volatile memory.