Lake Shore 625, User Manual

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Lake Shore Model 625 Superconducting MPS User’s Manual
7-16 Service
Calibrate Output Current Gain (Continued)
1. Send “CALG 10, 0”. To set the output current gain trim constant to 0.
2. Set the Model 625 output current to +55 A (ramp rate 20 A/s nominal).
3. Wait 30 seconds for settling.
4. Measure the Model 625 actual output voltage at the output terminals and record (V
measured
).
5. Measure the actual voltage across the shunt and record (V
shunt
).
6. Calculate and record (I
max
): V
shunt
/R
shunt
.
7. Send “CALG 10, –100”. To set the output current gain trim constant to maximum.
8. Wait 10 seconds.
9. Measure the actual voltage across the shunt and record (V
shunt
).
10. Calculate and record (I
maxpostrim
): V
shunt
/R
shunt
.
11. Send “CALG 10, +100”. To set the output current gain trim constant to minimum.
12. Wait 10 seconds.
13. Measure the actual voltage across the shunt and record (V
shunt
).
14. Calculate and record (I
minpostrim
): V
shunt
/R
shunt
.
15. Set the Model 625 to –55A V (ramp rate 20 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 625 output current to 0 A.
29. Calculate the gain constant per Equation 2.
Equation 2
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. It also measures the output terminal voltage and subtracts the calculated current
through the internal 25

damping resistor from the total ideal span.
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).
 
   
measured
max min
maxpostrim minpostrim maxnegtrim minnegtrim
2 V
I I 110 200
25
Gain Constant
I I I I
 
  
 
   
 
 
 
 
 
 

  