In-situ calibration-what is the best method for temperature sensor calibration?

In the sanitary process industry, the most commonly used standard calibration procedure for temperature sensors is two-point or three-point calibration. Calibration can be performed in the facility’s laboratory or near the access point. This reflects the most advanced method of obtaining the clearest temperature profile for the sensor and detecting deviations. This approach also meets the expectations of auditors and regulators.

In the sanitary industry, standard thermal resistance (RTD) measuring process temperature can last for several years. Even so, the biggest risk for temperature meters in sanitary systems is the calibration process. Opening the device, removing the plug-in, connecting and disconnecting the power cord, introducing the thermometer into an oil bath or blocking the calibrator, or transporting the thermometer to the laboratory increases the possibility of mechanical damage.

Removing the sensor from the process or thermowell is the biggest cause of thermal resistance failure. One of the most concerned questions for users is: "After removing the sensor for calibration, what is the best way to reinstall the sensor to the exact same measurement location in the process?" If the temperature sensor can be calibrated in-situ, the risk will be significant reduce.

Temperature calibration sequence

The main limitation of traditional three-point calibration is the calibration cycle time. What is the performance of the thermal resistance between calibration cycles? Most factories determine the cycle time based on risk management and cost analysis. More calibrations (shorter cycles) can reduce risk but increase costs.

Fewer calibrations (longer periods) are the opposite. Sensors with self-calibration or self-verification functions can continuously monitor the thermal resistance. The sensor will perform calibration every time it is disinfected, without the need to:

    1. Stop the production process;

    2. Remove the thermal resistance from the process;

    3. Any effort by maintenance or metering personnel.

At this time, the calibration will immediately identify or eliminate the risk of inconsistency with the thermal resistance before the start of the calibration week to ensure the highest product quality.

According to the design specification of the sensor, the minimum temperature threshold required to start the self-calibration is 118°C. This usually occurs during each cycle of disinfection.

However, since not all sanitary applications have a disinfection process, there are other ways to use self-calibration. One method is to remove the sensor from the process and place it in a ceramic dry block heat source to reach a temperature of 118°C.

Once this temperature is reached, the drying block can be turned off and allowed to cool down while leaving the sensor in the drying block heater. When the temperature is lower than 118°C, it will perform self-calibration and ensure that the thermal resistance is kept within tolerance, which will greatly reduce the process downtime.

This article is from Allicdata Electronics Limited which offer electronic components, semiconductors, antennas, capacitors, connectors, diodes, transistors, IC,resistors. For more product information, please go to the website to get it.