Lake Shore Model 330 Autotuning Temperature Controller User’s Manual
3-6
Operation
3.2.7.2
Customer Performed SoftCal
Depending on the desired temperature range, the Customer may perform a 2-point or 3-point SoftCal. This
example assumes a 3-point SoftCal. For 2-point, omit the steps associated with reading the voltage at 4.2 K.
Requirements are a stable temperature source at three temperatures: 4.2 K (Liquid Helium), 77.35 K (Liquid
Nitrogen), and <300 K (room temperature). It does not matter in which order SoftCal data is taken.
NOTE:
Allow the instrument to warm up for an hour before beginning the SoftCal procedure.
In this example, we will take our first SoftCal measurement around 4.2 K.
1.
Select the input channel that needs calibration as the Sample sensor.
2.
Immerse the temperature sensor in Liquid Helium and allow the controller temperature reading to
stabilize. The temperature controller knows which point is being entered by the temperature range.
3.
Select K units for low temperatures and C units for higher temperatures. This takes advantage of display
resolution.
4.
Press
the
SoftCal
key to display the “CUR” indicator. Enter a curve number from 11 to 31. Be sure to
select a number not currently holding another curve; this procedure overwrites any data in that location.
5.
Push
the
Enter
key.
6.
The Sample window shows the current sensor reading. In the Control window, enter the exact
temperature of the sensor (versus the displayed value).
7.
Push
the
Enter
key. The “CAL” indicator turns off and normal operation resumes.
8.
When the “CAL” indicator turns off, the instrument accepts the new point and generates a new curve from
it. To verify the new point, push the
Curve
key and use the
s
or
t
key to increment the display to the
Curve number of the SoftCal curve. Verify the Sample display reads the same as the value just entered. If
the curve number changes back to the default value for that type sensor, then no calibration occurred and
no new curve was generated.
SoftCal automatically logs points based on the temperature range of the sensor. The low temperature point is
taken in the range of 0 to 10 K. The medium temperature point is taken in the range of 50 to 100 K. The high
temperature point is taken in the range of 200 to 300 K. If the actual reading is somewhere between these
ranges, no data point will be taken and no curve generated.
To take a second SoftCal measurement near 77.35 K, immerse the sensor in liquid nitrogen and allow the
reading to stabilize. Repeat Steps 3 thru 8. To take the third SoftCal measurement, allow the temperature
sensor to stabilize at ambient temperature. Take an independent temperature measurement of the air at the
location of the temperature sensor. Repeat Steps 3 thru 8.
Erase old calibration points if calibrating a new sensor. To erase old calibration points, enter zero as a
calibration point. This will not erase any curves. To turn off SoftCal without the loss of the calibration, select
another Curve number.
3.2.7.3
Entering Voltage Values from a Lake Shore SoftCal Report
If a Lake Shore SoftCal Report was purchased, the voltage values for the 2 or 3 point calibration can be
entered and the resulting modified Lake Shore Curve 10 stored as Curve number 11 to 31 in the controller
memory. The voltages can only be entered using an IEEE-488 or Serial Interface. See the SCAL Command in
Chapter 4 for how to enter SoftCal voltages.