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Checking thermocouple drift

15 November 2009

The accuracy of temperature sensors deteriorates at varying rates, depending on the process, so they must be calibrated regularly. A thermocouple always drifts downwards by several degrees a year.

To counteract this phenomenon, industrial companies set their processes to overheat with a sufficient margin to overcome this drift until the next calibration, which is usually done once a year. In this way, they define a setpoint which is higher than the optimum temperature for the heat treatment required.

This overheating obviously has consequences and may cause defects, premature refractory wear and excessive energy consumption. So it makes sense to control the drift of the sensors.

Pyro-Contrôle's temperature sensor assemblies with in-situ calibration can be used to monitor thermocouple drift over time with a simple method. Calibration is carried out with the equipment still operating, without having to dismantle the sensors, so there is less risk of breakage.

The method is called ‘verification by comparison.’ The connection head of the sensor to be checked is opened. a standard sensor is inserted into the guide tube and connected to the precision thermometer. After temperature stabilisation, the process sensor is calibrated by comparison with the temperature indicated by the standard sensor.

Thus, temperature drift can be detected at regular intervals, and recording the data.

Advantages

This technology offers three primary advantages in terms of energy saving, productivity, quality and traceability:

1. The reduced measurement uncertainty makes it possible to lower the heating setpoint, thus saving energy. By avoiding overheating, the life span of the equipment is also extended.

2. The process remains available so there is no longer any need to stop production. Intervention time is also reduced. This technology offers considerable flexibility for metrological test scheduling.

3,  Because the measurements are more accurate, the standard deviations can be reduced, the quality of the finished product is improved and quality can be monitored more simply. This all contributes to better traceability of the thermal process.


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