Lake Shore Model 340 Temperature Controller User’s Manual
Instrument Programming
8-5
8.2.2 SoftCal Accuracy with Silicon Diode Sensors
SoftCal allows an abbreviated calibration, based on 1, 2, or 3 points, to generate a voltage-versus-
temperature curve over the useful range of a Lake Shore DT-400 Series silicon diode sensor.
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, and ±0.01 K for
4.2 K (liquid helium). Users performing the SoftCal with silicon diodes and Lake Shore instruments should
note that liquefied nitrogen and ice point temperatures can vary as much as ±0.5 K. Use calibrated standard
sensors if possible. The boiling point of liquid helium, though accurate, is affected by atmospheric pressure.
Perform one-point SoftCal calibrations for applications under 30 K at liquid helium (4.2 K). 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.
Perform two-point SoftCal calibrations for applications above 30 K 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 from 2 K to <30 K (no change below 30 K)
±0.25 K from 30 K to <60 K
±0.25 K from 345 K to <375 K
±0.15 K from 60 K to <345 K
±1.0 K from 375 to 475 K
Perform three-point SoftCal calibrations 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
±0.25 K 345 K to <375 K
±0.15 K 60 K to <345 K
±1.0 K 375 to 475 K
8.2.3 SoftCal and 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.
Use one, two, or three calibration data
points. 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.
8.2.4 SoftCal Accuracy with Platinum Sensors
The SoftCal procedure makes small adjustments to the DIN curve so that the resulting curve matches the
resistance-versus-temperature characteristic of the individual sensor more closely.
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 (liquid nitrogen) K and 305 K (room temperature) points. If you are
performing the SoftCal yourself with Lake Shore instrumentation, be aware that liquefied nitrogen and ice
point temperatures can vary as much as ±0.5 K. Use a calibrated standard sensor if possible. One-point
SoftCal calibrations with platinum sensors have no specified accuracy.
Room
Temperature Point
305 K
High
Temperature Point
480 K
Liquid Nitrogen
Boiling Point
77.35 K
SoftCal Point 1
SoftCal Point 2
SoftCal Point 3
0
50
100
150
200
250
300
350
kelvin
Acceptable Temperature Range for Platinum SoftCal Inputs
50 - 100 K
200 - 325 K
400 - 600 K
400
450
500
550
600
650
Figure 8-2. SoftCal Temperature Ranges for Platinum Sensors