Lake Shore Model 218 Temperature Monitor User’s Manual
5-6
Special Features
5.2.1 SoftCal™ and Silicon Diode Sensors
Lake Shore Silicon Diode Sensors incorporate remarkably uniform sensing elements that exhibit
precise, monotonic, and repeatable temperature response. For example, the Lake Shore DT-470
Series of silicon diode sensors has a repeatable temperature response from 2 K to 475 K. These
sensors closely follow a standard curve response and are interchangeable. SoftCal™ is an
inexpensive way to improve the accuracy of an already predictable sensor.
NOTE:
Standard Curve 10 is the name of the temperature response curve, not its location inside
the Model 218. Standard Curve 10 stores in Curve Location #1 in the Model 218 under
the name “DT-470”.
C-218-5-1.bmp
Figure 5-1. SoftCal™ Temperature Ranges for Silicon Diode Sensors
A unique characteristic of DT-400 Series diodes is that their temperature responses pass through
28 K at almost exactly the same voltage. This knowledge improves SoftCal™ operation by providing
an extra calibration data point. It also explains why SoftCal™ calibration specifications are divided
into two temperature ranges, above and below 28 K. See Figure 5-1.
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 accuracy 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.
