If you’ve ever left your phone or laptop in your car on a hot day, you may have seen a warning that your device is likely to overheat. These electronics have an embedded temperature sensor that records the interior temperature of the device.
If it reaches a specific temperature, the sensor sends a signal to the device’s computer to restrict its use until it cools to a safe temperature.
This works similarly in other devices and lab equipment, measuring the temperature of the environment and converting it into electronic data to record, monitor, or warn of temperature fluctuations.
Temperature sensor calibration is necessary for the accuracy and performance of these devices.
An instrument for measuring temperature is known as a temperature sensor.
There are numerous types of temperature sensors – some require contact with the object being monitored, such as contact temperature sensors, and others can indirectly measure the temperature with accuracy, such as non-contact sensors.
In addition to thermocouples, thermistors are also examples of contact temperature sensors. An electrical thermocouple is composed of two conductors, each with a metal core, which are connected by a junction. When this junction is exposed to heat, the voltage generated corresponds to the temperature.
A thermistor functions differently – as the temperature increases, the resistance decreases. A thermometer with a positive temperature coefficient and a thermometer with a negative temperature coefficient are the two most common types. These are more precise than thermocouples, typically within 0.05 and 1.5 degrees Celsius,
Non-contact temperature sensors are typically infrared sensors that remotely detect IR energy coming from an object and send that information to an electronic circuit that calculates temperature.
When comparing the results of a calibration to those of a test device, a reference device is used. Calibration is used to verify the accuracy of the device under test multiple times in accordance with a predetermined tolerance.
If the device is within the reference tolerance range, it passes calibration. With these, calibration may be conducted with multiple temperature points for linearity.
Temperature calibration requires a reliable, repeatable, and documented comparison of a temperature sensor being tested against reference equipment. The device used as a reference must be exact and undergoes regular testing at an accredited laboratory.
Here’s the process for temperature sensor calibration of lab equipment:
Before calibrating, conduct a visual inspection of the sensor to ensure it’s in working order and hasn’t been damaged in any way. Be mindful of external contamination, as a result, the sensor may need to be cleaned before it can be calibrated.
In order to calibrate a temperature sensor, a temperature source must be available. For industrial sensors, a temperature dry block may be used for its portability and accuracy.
If you need more accuracy, a liquid bath is a preferred method. It’s not portable, but it’s ideal for laboratory conditions.
It is ideal to use a stirred ice bath for reaching zero degrees Celsius. This is an affordable, simple, and accurate method of calibration.
Of all the methods, however, the most accuracy comes from fixed-point cells. This is a more expensive calibration method, but it’s used for accurate and accredited temperature calibration laboratories.
The reference temperature for calibration is generated with a heat source. The temperature is an extremely crucial heat source factor with a high degree of accuracy.
Both dry blocks and liquid baths have an internal reference sensor that records the temperature, but it’s less accurate than using a separate reference temperature sensor. This provides a more direct comparison between the temperature reference and the sensor being tested.
A traceable calibration should also be provided for the reference sensor. It’s also important that the reference sensor is as similar as possible to the sensor that’s being tested. This ensures that these sensors will behave the same way when the temperatures change, providing a more accurate calibration.
With fixed-point cells, there’s no need for a reference sensor. Physical phenomena are used to determine temperature, which makes it easier to measure with greater accuracy.
These usually have an electrical output, whether in resistance or voltage, that must be measured and converted to a temperature.
If you choose to measure the electrical output, you need to convert that to a temperature using recognized standards. In industrial settings, there will typically be a measurement device that can handle the conversion. It does not matter which method you choose, make sure that it has a valid traceable calibration.
It takes time for temperatures to change. Once the device has reached the target temperature, wait until it has stabilized. In addition, your sensor under test and your reference sensor may have different characteristics and may take different times to reach stabilization.
When calibrating an industrial sensor, you must select points of calibration that are linear in order to ensure accurate measurement. Focus on three to five points through the range. If sensors are calibrated in a laboratory, the calibration points may be chosen according to the lab’s smallest amount of uncertainty.
Temp. sensors are often used in lab equipment that measures heat and ensures that a process is staying in a predetermined range, supporting safe use, or meeting a mandatory condition when dealing with extreme heat or hazardous substances. Temperature sensors calibration is essential to ensuring accuracy and proper function.