Cryo-con Model 24C
Basic Setup and Operation
Device Calibration Errors
Variation in the manufacture of thermocouple wire and it’s annealing over time can
cause errors in temperature measurement.
Instruments that measure temperatures above about 0
o
C will usually allow the user to
correct calibration errors by adjusting an offset in order to zero the error at room
temperature. Unfortunately, in cryogenic applications, thermocouples lose sensitivity
at low temperatures so a single offset voltage correction is insufficient.
Thermocouples used over a wide temperature range may need to be calibrated at two
temperature extremes.
AC Power Line Noise Pickup
AC power noise pickup is indicated by temperature measurements that are
significantly in error. In extreme cases, there may be no valid measurements at all.
When a grounded sensor is used, a poor quality ground may have sufficient AC
voltage to exceed the input range of the module. This can often be corrected by
running a copper connection from a point near the sensor ground and the chassis
ground of the controller. Defective building wiring or insufficient grounding is usually
the root cause.
General recommendations to minimize AC pickup include:
1. Minimize the length of the thermocouple wires. Connect the module as near
as possible to the sensor so that thermocouple wires are converted to
copper as soon as possible.
2. Twist the wires.
3. Avoid running sensor wires near, or parallel to AC power lines.
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