Lake Shore Model 218 Temperature Monitor User’s Manual
Special Features
5-7
5.2.2 SoftCal™ Accuracy with Silicon Diode Sensors
NOTE:
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 a calibrated standard sensor if possible.
The boiling point of liquid helium, though quite accurate, is affected by atmospheric pressure.
One-point SoftCal™ calibrations for applications under 30 K are performed at liquid helium (4.2 K).
Resultant accuracy for the DT-470-SD-13 diode is:
±0.5 K from 2 K to <30 K (no 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). Resultant accuracy for the DT-470-SD-13 diode sensor is:
±1.0 K from 2 K to <30 K (no change below 30 K)
±0.25 K from 30 K to <60 K
±0.15 K from 60 K to <345 K
±0.25 K from 345 K to <375 K
±1.0 K from 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). Resultant accuracy for the DT-470-SD-13 diode sensor is:
±0.5 K from 2 K to <30
±0.25 K from 30 K to <60 K
±0.15 K from 60 K to <345 K
±0.25 K from 345 K to <375 K
±1.0 K from 375 to 475 K
5.2.3 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.
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 across 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.
C-218-5-2.bmp
Figure 5-2. SoftCal™ Temperature Ranges for Platinum Sensors
