What is Temperature Calibration?
Temperature calibration is a way of checking and, in most cases, modifying the accuracy of a temperature measuring device. You calibrate a temperature measuring device, usually a thermometer of some sort, by checking its reading against a very accurate device that is known to be correct. Any difference in the reading indicates that your device needs to be calibrated to read the same as the standard device. Sometimes the thermometer is one that is entirely mechanical and depends on the expansion or contraction of a liquid. At other times, it is a digital device.
“Calibration services are available for fixed point cells, resistance thermometers, thermocouples, radiation thermometers, liquid-in-glass thermometers, AC resistance bridges, and calibrators,” according to the Australian government.
Types of Temperature Measuring Devices
- Spring Type Thermometers: These are very common due to their low cost and ease of adjustment, but they are slow to respond and lack accuracy.
- Thermocouples: This is by far the most used temperature device. It consists of two different metals that produce a voltage that reflects the temperature.
- Resistance Temperature Detectors (RTD): These are often made from platinum wound wire. Although they are expensive, they are accurate and have a rapid response.
- Thermistors: They consist of a semiconductor base and measure temperature over a limited range. They are often used in medical situations.
- Infrared Radiation Detectors (IR): These are unique in that they are non-contact sensors. They use one of 2 types of technology – thermal imaging camera or IR pyrometers.
- Liquid in Glass Thermometers: These are very inexpensive but fragile. Due to their mechanical nature, they cannot be calibrated, but the error difference can be noted as above or below the standard reading.
Why Do Devices Change in their Accuracy?
For gauges that consist of bimetals or a thermocouple, note that wire can change with use and over time especially if high temperatures are involved. Thermocouples can suffer damage due to corrosion, being dropped or hit. RTDs, thermistors, IR thermometers, and thermal imaging cameras are very fragile and therefore are susceptible to mechanical damage.
Possible Dangers Due to Temperature Reading Fluctuations
For any product that is consumed by humans or animals, temperature fluctuations can result in spoilage as in the food processing and pharmaceutical production industries. In manufacturing, certain procedures depend on the precise application of temperature. For example, wheel hubs, suspension links, and brake components all depend on being heated to a certain temperature. Deviance can lead to failure in the part, resulting in considerable damage if not a danger to life. Carbon fibre is becoming a popular material for parts. Its integrity depends on strict temperature control.
Often the temperature control device is also linked to a recording component so that there is an accurate record of the manufacturing condition, should a problem develop. Records can be used to explain failures or to confirm the integrity of the materials.
Complications of the Testing Procedure
Calibrating a device that measures the temperature can be very simple or quite complex. One of the deciding factors is the physical characteristics of your measuring device. Can the device be transported to a testing facility or does the calibration need to take place onsite?
At A Professional Laboratory
If you send your temperature sensors to a lab, they will be tested using a specific calibration bath, and then the reading will be compared to a device that is regulated by national or international standards. The calibration bath is an excellent medium to provide accurate readings for several reasons. The uniformity of temperature throughout the liquid is the same. This uniformity reduces uncertainties in the measurements. The size of the baths accommodates different size and shape measuring devices. Many different devices can be tested at once due to the substantial nature of the bath container.
The professional lab has a number of baths so that each measuring device can be tested at different temperature levels, for example, above and below specific standard temperatures you require.
Onsite Calibration of Temperature Devices
Moveable temperature calibrators are often dry-well calibrators. These are electronic controllers that automatically supply a temperature. They are highly reliable, accurate, and simple to operate. Their large openings make them highly adaptable to various types of temperature measuring instruments.
Frequency of Calibration
Standards may not describe an exact frequency, but the calibration of devices depends on the situation and the type of equipment used. An auditor will demand a rationale for the rate of calibration used in a commercial location.
An Accredited Lab vs. Non-Accredited Lab
Labs that are not accredited by the governing body are able to perform the routine work of temperature calibration. Formal accreditation provides an extra layer of confidence and protection to the customer without having to go to the expense of verifying that the work completed is up to standard.
How Do I Know that the Lab is Accredited?
Every professional lab will have several means of informing the clients of its standing. At the very least, the appropriate stamp of approval will be located in the advertising material and on the website. Inquiries made to staff members should result in written documentation of the status.