Lake Shore Model 331 Temperature Controller User’s Manual
5.3.3
SoftCal With Platinum Sensors
The platinum sensor is a well-accepted temperature standard because of its consistent and
repeatable temperature response above 30 K. SoftCal gives platinum sensors better accuracy than
their nominal matching to the DIN 43760 curve.
SoftCal Point 3
High Temperature
Point
480 K
SoftCal Point 1
SoftCal Point 1
Liquid Nitrogen
Boiling Point
77.35 K
SoftCal Point 2
Room Temperature
Point
305 K
0
50
100
150
200
250
300
350
400
600 K
50
100 K
200
325 K
400
450
500
550
600
650
Acceptable Temperature Range for Platinum SoftCal Inputs
C-331-5-2.eps
Figure 5-2. SoftCal Temperature Ranges for Platinum Sensors
One, two, or three calibration data points can be used. If using one point, the algorithm shifts the
entire curve up or down to meet the single point. If using two points, the algorithm has enough
information to tilt the curve, achieving good accuracy between the data points. The third point extends
the improved accuracy to span all three points.
Point 1:
Calibration data point at or near the boiling point of nitrogen (77.35 K). Temperatures
outside 50 K to 100 K are not allowed.
Point 2:
Calibration data point near room temperature (305 K). Temperatures outside 200 K to
350 K are not allowed.
Point 3:
Calibration data point at a higher temperature (480 K). Temperatures outside 400 K to
600 K are not allowed.
5.3.4
SoftCal Accuracy With Platinum Sensors
A SoftCal calibration is only as good as the accuracy of the calibration points. The accuracies listed
for SoftCal assume ±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 with platinum sensors have no specified accuracy.
Two-point SoftCal calibrations for applications above 70 K are performed at liquid nitrogen (77.35 K)
and room temperature (305 K). Accuracy for the PT-102, PT-103, or PT-111 platinum sensor is as
follows:
±250 mK from 70 K to 325 K
≈
±500 mK from 325 K to
≈
±1400 mK at 480 K
(DIN Class A or Class B tolerance)
Three-point SoftCal calibrations are performed at liquid nitrogen (77.35 K), room temperature (305 K),
and high temperature (480 K). Accuracy for the PT-102, PT-103, or PT-111 platinum sensor is
±250
mK from 70 K to 325 K, and ±250 mK from 325 K to 480 K.
Advanced Operation
5-9
