Lake Shore Model 331 Temperature Controller User’s Manual
SoftCal Point 1
SoftCal Point 1
Liquid Helium
Boiling Point
4.2 K
SoftCal Point 2
Liquid Nitrogen
Boiling Point
77.35 K
SoftCal Point 1
Room Temperature
Point
305 K
0
25
50
75
100
125
150
175
200
225
250
275
300
325
350
2
10 K
50
100 K
200
325 K
Acceptable Temperature Range for Silicon Diode SoftCal Inputs
C-331-5-1.eps
Figure 5-1. SoftCal Temperature Ranges for Silicon Diode Sensors
Point 1:
Calibration data point at or near the boiling point of helium, 4.2 K. Temperatures
outside 2 K to 10 K are not allowed. This data point improves between the calibration
data point and 28K. Points 2 and 3 improve temperatures above 28 K.
Point 2:
Calibration data point at or near the boiling point of nitrogen (77.35 K). Temperatures
outside 50 K to 100 K are not allowed. This data point improves accuracy between 28
K and 100 K. Points 2 and 3, together, improve accuracy to room temperature and
above.
Point 3:
Calibration data point near room temperature (305 K). Temperatures outside the range
of 200 K to 350 K are not allowed.
5.3.2
SoftCal Accuracy With Silicon Diode Sensors
A SoftCal calibration is only as good as the accuracy of the calibration points. The accuracies listed
for SoftCal assume ±0.01 K for 4.2 K (liquid helium), ±0.05 K for 77.35 K (liquid nitrogen), and 305 K
(room temperature) points. Users performing the SoftCal with Lake Shore instruments should note
that the boiling point of liquid cryogen, though accurate, is affected by atmospheric pressure.
Use calibrated standard sensors if possible.
One-point SoftCal calibrations for applications under 30 K are performed at liquid helium (4.2 K)
temperature. Accuracy for the DT-470-SD-13 diode is ±0.5 K from 2 K to <30 K with no accuracy
change above 30 K.
Two-point SoftCal calibrations for applications above 30 K are performed at liquid nitrogen (77.35 K)
and room temperature (305 K). Accuracy for the DT-470-SD-13 diode sensor is as follows:
±1.0 K
2 K to <30 K (no change below 30 K)
±0.25 K 30 K to <60 K
±0.15 K 60 K to <345 K
±0.25 K 345 K to <375 K
±1.0 K
375 to 475 K
Three-point SoftCal calibrations are performed at liquid helium (4.2 K), liquid nitrogen (77.35 K), and
room temperature (305 K). Accuracy for the DT-470-SD-13 diode sensor is as follows:
±0.5 K
2 K to <30
±0.25 K 30 K to <60 K
±0.15 K 60 K to <345 K
±0.25 K 345 K to <375 K
±1.0 K
375 to 475 K
5-8
Advanced Operation
