Lakeshore 325, Руководство пользователя, Страница: 83 / 166

Lake Shore Model 325 Temperature Controller User’s Manual
Advanced Operation 5-7
5.3.1
SoftCal™ with 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 the Standard Curve 10 response and routinely
interchange with one another. 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 325. Standard Curve 10 is stored in curve location number 1 in the Model 325.
A unique characteristic of DT-400 Series diodes is that their temperature responses pass through 28 K at almost exactly
the same voltage. This improves SoftCal algorithm 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 between the calibration data point and 28 K. 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.
C-325-5-1.bmp
Figure 5-1. SoftCal Temperature Ranges for Silicon Diode Sensors
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 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