Lake Shore Model 331 Temperature Controller User’s Manual
4.4.4.2
Room-Temperature Calibration Procedure
Room-temperature calibration is used to calibrate the built-in compensation and is recommended
when a thermocouple is first installed or any time a thermocouple is changed.
Factory calibration of the instrument is accurate to within approximately ±1 K. Differences in
thermocouple wire and installation technique create errors greater than the instrument errors.
Therefore, the best accuracy is achieved by calibrating with the thermocouple actually being used
because it eliminates all sources of error. If that is not possible, use a thermocouple made from the
same wire. For less demanding applications, a short across the input terminals will suffice. If the
Model 331 is configured as dual thermocouple unit, calibrate both inputs even if they use the same
type of thermocouple. An appropriate curve must be selected and room temperature compensation
must be turned on before calibration can be started.
There are three options for room temperature calibration:
Cleared
. The previous room-temperature calibration value is cleared and no adjustment will be
made to the temperature value provided by the internal temperature sensor when
compensation is on.
No
. Use the room-temperature calibration value determined the last time the room-temperature
calibration procedure was performed.
Yes
. Perform the room-temperature calibration procedure that follows.
Calibration Procedure
1. Attach a thermocouple sensor or direct short across the input terminals of the thermocouple
input. See Figure 3-4 for polarity.
2. Place the instrument away from drafts. If calibrating using a short, place an accurate room-
temperature thermometer near the terminal block.
3. Allow the instrument to warm up for at least ½ hour without moving or handling the sensor.
4. If calibrating with a short skip to step 6, otherwise insert the thermocouple into the ice-bath,
liquid nitrogen, helium dewar, or other know fixed temperature. The temperature should be
close to the measurement temperature that requires best accuracy.
5. Read the displayed temperature. If the temperature display is not as expected, check to be
sure that the thermocouple is making good thermal contact. If possible, add a thermal mass to
the end of the thermocouple.
6. Press
the
Input Setup
key and press the Enter key until the “Room Cal” screen appears. Press
the
s
or
t
key until the “Yes” selection appears then press the
Enter
key.
Select for InputA °®
Room Cal Yes
7. The current temperature reading is displayed in Kelvin.
Select for InputA
Temp 294.15½
Enter the true temperature that the thermocouple should read. If input is shorted, then enter the
actual room temperature measured by the thermometer. Press the
Enter
key to save the value.
8. To verify calibration, check that the temperature reading for the calibrated input matches the
room-temperature calibration setting value.
Operation
4-11
