Your business and the quality of your product depend on making precise temperature measurements, which means that accurate and reliable measurement tools are essential. Steel manufacturing requires careful attention to temperature throughout each step of the annealing process, and failing to keep the steel strip at the right temperature can result in unacceptable inconsistencies in the product.
There are two vital pieces that go into correctly measuring the temperature of the steel strip: selecting the right steel infrared temperature sensor and ensuring it is correctly calibrated. If you’ve already gone through the process of selecting the right pyrometer for your application, congratulations! You’re halfway there. The next step is to test the accuracy of your infrared thermometer to ensure you are getting the best possible measurements. So how can you test it? Try these three ways to calibrate your pyrometer.
1. Confirm Accuracy Using Another Trusted Pyrometer
For many applications, more than one pyrometer is used to ensure accurate measurement. In this case, calibrating your pyrometer is simple. By using both pyrometers to measure the same area of thermal energy, you can adjust the calibration of your new pyrometer to match the existing one.
It’s important to note that if you choose this method, you must compare measurements with a trusted pyrometer. If you are unsure whether your existing pyrometer is producing accurate measurements, adjusting your new infrared thermometer to match will only result in two pyrometers that are repeatable and can’t necessarily be trusted for accuracy. You should also keep in mind that it is important to measure the same area with each pyrometer; different areas can and often will have different temperature measurements, so measuring the same area is the only way to ensure accuracy.
2. Confirm Accuracy Using a Blackbody
Blackbody calibrators are very useful for calibration of infrared thermometers. A blackbody is a theoretical “perfect emitter,” meaning it emits the maximum amount of infrared energy for any given temperature. It is also a diffuse emitter, radiating the same intensity of radiation in all directions. While no perfect blackbody actually exists, the principle provides a strong basis for calibration.
A blackbody calibrator typically consists of an empty cavity with a small target opening. Inside, a conical or tube-shaped radiation source is embedded in a bath, furnace, or heat pipe. This radiation source is not a true blackbody, but it is close: typical laboratory sources emit radiation with 98% efficiency or higher. Using the pyrometer, the temperature of the laboratory blackbody is measured. Because the emissivity of the blackbody is a known value, it is possible to accurately calibrate the pyrometer.
This is a common method for infrared thermometer calibration; in fact, most manufacturers calibrate their pyrometers with multiple blackbody calibrators before selling them. However, it is not always the simplest method. Blackbody calibrators can be expensive and difficult to operate, which makes them less than ideal to be kept in a steel mill. It is more common to remove the pyrometer from the mill and send it to a qualified shop that already has a blackbody calibrator.
3. Confirm Accuracy with a Thermocouple
A thermocouple is another type of instrument used to measure temperature. This instrument is made up of two wires of different metals which are welded together at a junction. This junction creates a voltage when there is a change in temperature, and thermocouple reference tables are then used to interpret the voltage and calculate the temperature.
A somewhat accurate method of calibration with a thermocouple involves simply measuring the temperature of an object with a trusted thermocouple, then measuring it with the pyrometer. The tool can then be adjusted to reflect the accurate measurement provided by the thermocouple. Again, it is important to measure the same area with both tools to ensure accurate calibration.
When using this method, it’s important to keep in mind that thermocouples, when used alone, are not as accurate as pyrometers. Thermocouples get far more wear and tear while they are being used and often measure lower temperatures than infrared pyrometers. Thermocouples come in all different varieties and you often pay for what you get—cheaper thermocouples often will not read accurately right out of the box! So, if you are looking to confirm a pyrometer’s accuracy with a thermocouple, you also need to verify the accuracy of your thermocouple.
The Right Pyrometer for Your Application
It’s important to use accurate, reliable pyrometers, but it’s even more important to select the right pyrometer for your specific applications. We understand that a steel mill is a demanding environment that can make accurate temperature measurements difficult, which is why we want to help you learn how thoughtful wavelength selection can improve your process. Learn more by downloading your free white paper on Understanding Infrared Pyrometers for Demanding Steel Mill Applications.