Cold Junction Measurement Errors

Modified on Wed, 3 Mar, 2021 at 8:32 AM

The EA001A offers measurement of Cold Junction for compensation of thermocouple inputs and outputs.

A large error can be caused by not allowing the cold junction sensor to stabilise to the ambient temperature, or differences between a UUT or Measurement Standards cold junction sensor and that of the EA001A.

The EA001A sensor is contained within the thermocouple plug for SOURCE/OUTPUT modes, and within the input connector for MEASUREMENT/INPUT modes.

It is critical that the source connector is as close to the UUT/Measuring devices cold junction sensor as possible, otherwise there will be a large error between these two measurements.

It is quite normal for a lot of measuring devices to have their cold junction sensor mounted internally within the unit, and not near to the connection with the Thermocouple. This can cause a large difference in temperature between the temperature measured by the EA001A and the reference temperature indicated by the measurement device.

To help compensate for this, we highly advise the following method is used when sourcing/measuring temperature with the EA001A.

  • Ensure that the socket the OUTPUT/SOURCE connector is plugged into is Copper-Copper i.e. Neutral, and clean from any contaminants (grease, dirt etc). The OUTPUT/SOURCE connector can be cleaned with an alcohol based cleaner and cotton swabs if it gets dirty over normal use, as long as no residue is left on the connector.
  • Allow ALL connections to stabilise for at least 20 minutes after handling for the most accurate measurements. Most indicators have limited accuracy and can be tested much faster but more accurate indicators require a longer settling time to match their accuracy specifications.
  • Cover the point of connection with the UUT from any drafts that may cause temperature differences.
  • If at all possible, cover both the UUT and EA001 with a clear box to allow the temperature inside the box to stabilise. This may assist with indicators that have internal power supplies that are generating heat to reach thermal equilibrium between the cold junction sensor and the input connector.
  • Do NOT use any extension cables between the OUTPUT/SOURCE connector, if extensions are needed wire a low thermal Mini TC connector to low thermal banana plugs using high quality wire, making sure interconnections such as crocodile clips are not used.

If after these steps are followed and errors are still found, compare the cold junction temperature reading indicated by the 1000/3000A/4000/9000A Series calibrator against your laboratory environmental conditions. If a large error is found then the EA001A may require re-calibration and adjustment.

Please note that this advise applies to all generations of Transmille's Thermocouple adapters, including those supplied with 2000 Series Calibrators.

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