Lake Shore Model 330 Autotuning Temperature Controller User’s Manual
Operation
3-5
3.2.7 SoftCal
SoftCal improves the accuracy of a DT-400 Series Silicon Diode Sensor. It enables the user to reduce the
error between a silicon diode and the Standard Curve 10 which the controller uses to convert diode input
voltage to a corresponding temperature. In short, SoftCal generates inexpensive calibrations for Model 330
DT-400 Series sensors.
The Lake Shore DT-400 Series Sensors incorporate remarkably uniform sensing elements that exhibit
precise, stable, and repeatable temperature response in the range from 2 K to 475 K. They exhibit excellent
uniformity from device to device and, as a result, are routinely interchanged with one another. This diode
feature makes SoftCal possible.
For the DT-400 Series diodes, five tolerance bands of tracking accuracy are available (see Figure 3-3). Band
11 sensors offer absolute accuracy to within ±0.25 K at low temperature, and to within ±0.5 K at room
temperature. Band 13 sensors are accurate to within ±1.0 K at low temperature, and to within ±1.0% of
temperature or better from 100 K to 475 K. For better accuracy, use SoftCal.
Implement SoftCal as a method or a service:
1.
The Customer may perform the SoftCal procedure. Use the Model 330 and the silicon diode sensor to
sense either two or three sources of a stable temperature. For a 3-point SoftCal, sense stable
temperatures of 4.2 K (Liquid Helium), 77.35 K (Liquid Nitrogen), and 295 K (Room Temperature). For a
2-point SoftCal, sense stable temperatures of 77.35 K and 295 K. See Paragraph 3.2.7.2. User performed
SoftCal has the advantage of nulling both sensor and controller inaccuracies.
2.
Lake Shore provides an inexpensive SoftCal Calibration Service that provides voltages corresponding to
the 2 or 3 point calibrations. The calibration consists of a modified (T vs. V) Curve 10 Table for a specific
DT-400 Series Sensor. A SoftCal Report is generated that includes the voltages for data points and a
unique sensor curve table interpolated from these 2 or 3 points. Enter the voltages over the remote
interface (see Paragraph 3.2.6.3).
With either method, the Model 330 creates a new curve for this specific diode and stores it as Curve 11 thru
31 in controller memory. This procedure can make an inexpensive Band 13 diode more accurate than our
tightest Band 11 diode. The calibration cannot transfer from one sensor to another.
3.2.7.1 SoftCal
Errors
The advantage of performing a SoftCal with the actual sensor and Model 330 that take measurements is that
it compensates for the combined temperature error of the sensor and controller. If the sensor is calibrated
separate from the Model 330, the specified accuracy of the Model 330 must be added to the sensor accuracy.
SoftCal accuracy also depends on the precision of the setting points. An error in the setting temperature can
actually degrade sensor performance beyond normal tolerance bands. For example, the boiling point of
nitrogen at standard pressure is near 77.4 K. During a storm, this can change as much as 0.2 K because of
the change in atmospheric pressure. These types of errors must be added to the sensor accuracy.