Temperature Calibration

November 3, 2021

What is temperature calibration?

Temperature calibration refers to the calibration of any device that is used in a system that measures temperature. Mainly, it means the temperature sensor, which is typically a platinum resistance thermometer (PRT or PT-100), thermistor, or thermocouple. The readings of these thermometers are made using «temperature reading» devices that measure electrical power and convert it into temperature according to the

Calibration of thermometers is typically done by placing them in a stable temperature environment (heat source) and comparing their output to that of a calibrated “standard thermometer” or “reference thermometer”.

Field temperature calibration  (or “industrial” or “portable” temperature calibration) applies to thermometers that are tested outside of a laboratory environment, typically with accuracies ranging from 5 to 0.5 ° C.

Dry wells, metrology wells, micro baths, infrared targets, and other portable heat sources provide stable temperatures, while portable temperature gauges and temperature standards can provide reference temperatures that go beyond that available directly from the heat source.

Secondary or field temperature calibration  is related to the calibration of reference quality PT-100 or platinum resistance thermometers, precision thermistors and noble metal thermocouples. Ultra stable, uniform temperature baths and horizontal furnaces (for the high temperatures required by thermocouples) are used in conjunction with standard platinum resistance thermometer reference thermometers and highly accurate temperature gauges. Such systems can offer calibration accuracies of 0.5 to 0.02 ° C.

Fixed-point or primary temperature calibration  uses fixed-point cells, such as triple point water, which provide extremely accurate and repeatable temperature when properly achieved, typically in a laboratory setting. These systems are used for the calibration of SPRTs and noble metal thermocouples, whose precision can reach 0.001 ° C.

Types of temperature sensors

There are five common devices in manufacturing processes:

  1. Bimetallic or spring thermometers. Despite the slow response and lack of accuracy, they are widely used because they are cheap and easy to adjust.
  2. Thermocouples. The most widely used industrial sensor, consisting of two different metal cables joined at one of the ends, producing a voltage proportional to the temperature.
  3. Resistance temperature detectors (RTD). In general, they have platinum wound wire and are expensive, but give a fast response and good measurement accuracy.
  4. Thermistors These semiconductor-based devices measure temperature in a limited range and are often used in medical applications.
  5. Infrared radiation detectors. These non-contact sensors measure surface temperature and can be of two types: infrared pyrometers and thermal imaging cameras. The use of both is growing rapidly as many other products hit the market.

Temperature detection and documentation

In many industries, a control alone is not enough: it is important to document the temperature or thermal cycle to which the product was subjected. These records are required in food processing and production and storage in the pharmaceutical industry. For that, temperature controllers with recording capabilities can be used.

In the case of critical safety items, such as wheel hubs, suspension links or brake components, the documentation helps the manufacturer to verify that a certain part was heat treated in the correct way and that it was neither too brittle nor too malleable.

Quality management systems require, without exception, the calibration of all measuring equipment that can affect the quality of the final product. While the importance of calibrating verification equipment is generally understood, this issue is sometimes neglected in the case of temperature sensors.

What should I consider before doing my calibration?

Calibrating a temperature sensor can be challenging, but it is perfectly possible if you know the right products. The first step is to know the thermometer that is being calibrated, for which we suggest you ask yourself the following questions:

  • What type of electrical signal does it produce or is it completely mechanical?
  • What are its physical characteristics (size and shape of the sensor hidden inside the probe cover, etc.)?
  • In what temperature range is it used?
  • How accurately are you counted on these temperatures?
  • Can it be calibrated in a lab or should it be calibrated in the field?

Why the devices have to be calibrated

All devices used for critical process measurements should be periodically checked to see if they continue to show the necessary accuracy. When adjustments are possible, a device that makes measurements outside the expected limits should be readjusted to an acceptable level of performance, but in the case of non-adjustable equipment, the deviation or performance of the measurement should be recorded and decided. whether the equipment remains fit for purpose.}

Quality standards in general leave it up to the user to decide the frequency of calibration of a certain device. However, an auditor expects a good justification for the chosen frequency, whatever it may be. In defining it, the intended use of the device, the risk of damage and the rate of drift (which can be determined based on the history of calibration records) must be considered .

Essential for product quality

Many manufacturing processes use heat to modify the characteristics of the product. In some cases, accurate temperature control is essential to ensure suitability for its intended use and a written check (temperature records plus calibration evidence) confirms that the manufacturer followed the correct procedures to maintain the quality of the products. items produced. The calibration of temperature sensors, whether done in-house or in a specialized laboratory hired, is a fundamental part of this activity.

Dr. Loony Davis5
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Born and raised in Brussels in an English family, I have always lived in a multicultural environment. After several work experiences in marketing and communication, I came to Smart Water Magazine, which I describe as the most exciting challenge of my career.
I am a person with great restlessness and curiosity to learn, discover what I do not know, as well as reinvent myself daily, someone who is curious about life and wants to know. I enjoy sharing knowledge.
This is my personal project but I also collaborate in other blogs, it is the case, the most important web on water currently exists in the US, if you are interested you can read my articles here.

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