Cryo-con Model 24C
Basic Setup and Operation
Offset Calibration
Thermocouple devices can vary significantly from their standard curves, especially at
cryogenic temperatures where their sensitivity is reduced. To accommodate these
variations, the Model 24C allows an offset calibration for individual thermocouple
devices. Note that device calibration do not affect the instrument's basic calibration.
Device calibration is
performed by using the
instrument's Input
Configuration menu. An
example is shown here.
Alternatively, calibration
may be performed by
using remote commands.
This menu is selected by
pressing the ChA key and then setting the Sensor field to the desired thermocouple
type. Next, select the Input Config field.
For cryogenic applications, an offset calibration is usually done at a low temperature
reference point. Examples being liquid nitrogen or even liquid helium. The result of
the calibration is that the controller will read the correct temperature when the sensor
is held at that reference. Setting the Reading field to zero turns offset calibration
OFF. This is useful to start a new calibration.
Since thermocouples lose sensitivity at low temperature, an offset calibration in that
range will generally have little effect on the higher temperature accuracy.
An offset calibration is done as follows:
1. Connect the controller as usual for thermocouple measurements. For best
accuracy, be sure that ambient temperature doesn't vary.
2. Allow the instrument to warm up for at least ½ hour without moving or
handling the sensor.
3. From the instrument front panel, first set the thermocouple sensor and then
go to the input configuration menu.
4. Establish the thermocouple device at a precisely known temperature. When
stable, enter the desired reading in the Set Reading field and press
Enter
. For
example, if the sensor is immersed in liquid nitrogen, enter a value of 77.35K
5. The input temperature reading should now stabilize at the value entered.
Note that the Set Reading temperature is always in units of Kelvin.
96
ChA:Radiation Shield
Thermocouple Sensor Configuration
+ 78.12K FS Input: 70mV
Set Reading: 0.00K
Return to ChA cfg
