Thermistors and Calibration

Temperature monitoring hasn’t changed much in the last decades in terms of temperature sensors, a thermal sensoring device is used to evaluate and display the current thermal conditions of an item, room, or sample. However, there are two major choices for type of sensors: thermocouples and thermistors; the latter being the most recent player joining the ranks and the more controversial when it comes to calibration.

Product Description

Thermocouples had been the gold standard in temperature measuring equipment for hundreds of years, and what the majority of the people involved in the industry are familiar with. In the last decades, the thermistor technology has gained a large presence in the industry to the extent of being the dominating technology currently used. However, the basic concepts of thermistor operations and functionality have not spread as fast as the product itself, and are constantly confused with those of the thermocouple.

Understanding the principles of resistance thermometry as they apply to thermistors will help you understand the reliability and accuracy of this type of temperature sensors and why the industry has completely shifted in this direction.

A thermistor consists of a semiconductor material whose resistance decreases as temperature increases. Key benefits of the thermistor are their small size, high accuracy and precision, and most importantly the stability of retaining its measuring characteristics for years with minimal degrading effects. Thermistors, with all these benefits, are used inside many other devices as temperature sensing and correction devices as well as in specialty temperature sensing probes for commerce, science and industry.

Thermistors are calibrated by the manufacturer by performing calculations regarding resistance/temperature characteristics and the temperature coefficient of resistance, and these conditions should not change for the life of the thermistor when used under the manufacturer’s normal operating conditions, and not damaged through physical or electrical abuse.

Calibration

There is a common misconception about the meaning of certain terminology used in connection with calibration. Calibration is the process of checking a given instrument against a reference with a calibration table of values and errors being generated. Any instrument can be calibrated. What consumers usually refer to is the ability to “adjust” a thermistor. Adjustment (or recalibration as it is sometimes called) is when an instrument is adjusted to read in accordance with a reference instrument. The readout of the instrument after the adjustment is then the same as the reference instrument.

All temperature measuring devices used by Procuro, Inc. use thermistors, which have been adjusted by the manufacturer according to the set of standards or stated references of the National Institute of Standards and Technology (NIST) and other recognized international standards laboratories such as the National Physics Laboratory. Temperature calibration therefore is not required, unless it is a third party requirement to modify the adjustment for the application in which they are to be used.

Manufacture’s information regarding the specifications and performance data for the specific component used in all different temperature sensing modules used by Procuro, Inc. is available upon request.

Calibration Checks

Food safety and food quality assurance programs have long standing policies and practices for calibration. In general terms, calibration measurements should be taken at least once per year to validate the accuracy of the temperature collecting devices.

Since the temperature measuring devices used by Procuro, Inc. use thermistor technology, the accuracy of the readings should remain constant unless there is physical damage to sensors and/or the monitor. Damage to the sensor and/or monitor could cause the temperature readings to be significantly inaccurate, therefore calibration verification and/or certification would be unnecessary as the unit would have to be returned to the factory for repair or replacement.

It is also important to remember that the process of verifying calibration is dependent upon the accuracy of the verifying device and the similarities in specifications with the verified device. The NIST has strict standards for calibration services to ensure accuracy. The devices used for calibration verification have to be properly calibrated before any verification test can be performed. Procuro, Inc. follows these procedures to test devices whose accuracy is believed to be compromised.

For more information about calibration policies and practices you can visit the National Institute of Standards and Technology (NIST) website.