Infrared thermometers are highly effective when you want to take temperature readings without contacting the target surface. It measures the infrared radiation emitted by the surface to show you the surface temperature. The reading might not always be accurate for several reasons. So, you need to check the accuracy first.
But how to check accuracy of infrared thermometers? You can perform an ice bath test to measure the accuracy. A comparator cup with a known base temperature is also used to check the accuracy. If you want a more precise accuracy check, you can do a black body test in laboratories.
This guide will elaborate on how an infrared thermometer works and how to check its accuracy in various methods.
What Is an Infrared Thermometer?
To understand what an infrared thermometer is or how it works, you need to know about infrared first. All electromagnetic radiations have specific wavelengths. In the electromagnetic spectrum, infrared refers to wavelengths from 700 nm to 1 mm. The wavelength of infrared radiation is longer than visible light.
So, we can’t see infrared radiation. But it can be felt as heat. Any object around us emits this radiation, and the amount of emission varies depending on the emissivity of that object.
What Is Emissivity, Then?
In simple words, emissivity refers to the infrared energy an object can emit. The emissivity range is from 0 to 1. If the emissivity of an object or surface is close to 1, the object will absorb almost all the reflected infrared radiation. So, we will only get the emitted infrared radiation from the surface.
Back to Main Question, What Is an Infrared Thermometer?
When you point an infrared thermometer to an object, the emitted energy travels to the thermometer lens. The lens focuses the infrared light on top of a sensor.
It then processes the light to convert it into electronic signals. And these signals are shown as a temperature reading on display. Sometimes, the display can show thermal imagery depending on its type.
Why Should You Check the Accuracy of Infrared Thermometer?
In most cases, infrared thermometers are used to take human body temperature readings. According to ASTM E 1965-98, the accuracy of an infrared thermometer should be +/- 0.54 degrees Fahrenheit within the actual temperature.
This is applicable when you measure the skin temperature. But if you measure core temperatures, such as ear canals, the accuracy should be within +/- 0.36 degrees Fahrenheit. So, measuring the accuracy of the thermometer before taking the actual reading is crucial.
How to Check Accuracy of Infrared Thermometer?
You can use three methods to check the accuracy of an infrared thermometer. We will break these three methods down into simpler steps so that you can perform the tests easily. Keep reading.
Using an Ice Bath – The Most Affordable Method
It is an extremely easy and affordable method for checking the accuracy of an infrared thermometer. You will need the following things to perform the test.
- A glass
- Some ice cubes
- Some water
Here are the steps you need to follow.
- Step 1: Place the IR thermometer you are going to test in the room where you will conduct the test. Allow it to be stable at room temperature.
- Step 2: Take some ice cubes in a glass. Add some water to the glass so that the ice cubes are fully immersed.
- Step 3: Stir the ice cubes gently so that the temperature is uniform everywhere. The ice cubes will start melting soon. And the temperature will be constant at 32 degrees Fahrenheit until all the ice is melted.
- Step 4: Take the infrared thermometer you want to test and point it toward the ice water. Remember, the distance between the ice water and the thermometer lens should not be more than three inches. Otherwise, the thermometer can take readings from the glass or surroundings.
- Step 5: Also, the lens should be perpendicular to the water surface. When holding at an angle, the target area will be changed.
- Step 6: After a few seconds, the thermometer will show the temperature on display. It should be 32 degrees Fahrenheit if your thermometer is accurate. Check if the reading deviates from the accuracy range.
Using a Comparator Cup – An Accurate But Costly Method
A comparator cup or pot with a known base material is used in this method. You will need the following things to check the accuracy of an infrared thermometer.
- A comparator cup
- A probe thermometer
Follow these steps to check the accuracy.
- Step 1: Place both the comparator cup and the infrared thermometer you want to test at room temperature. Let them rest at that temperature for about 15 minutes.
- Step 2: There is a solid base with a matte black coating inside the comparator cup. The walls of the cup prevent airflow from changing the temperature of the base. And there are two holes on top of the base.
- Step 3: You need to insert the probe thermometer into one of these holes. Stabilizing the reference thermometer is important for accurate readings. So, let it sit for some time.
- Step 4: Take the infrared thermometer you want to test and point it to the bottom of the cup. Again, remember the correct distance and angle of holding the infrared thermometer for perfect readings.
- Step 5: The temperature reading should come up on display. Check if it matches the reading on the probe thermometer. If so, your infrared thermometer is accurate. If not, you can calculate the deviation.
Using a Blackbody In a Laboratory – Most Complex and Expensive Method
Everyone might not have access to a laboratory to test their infrared thermometers. Still, we have the process below. By the way, Blackbodies are considered perfect emitters. So, testing the accuracy with a blackbody might give you the best result.
- Step 1: A blackbody, according to certification standards, is placed inside a cone or tube. There is a cavity between the base and the opening of the tube.
- Step 2: The infrared thermometer is used to take the temperature reading of the blackbody.
- Step 3: As the emissivity of the blackbody is known, the accuracy of the thermometer can be calculated. You can learn more about how to determine emissivity accurately.
Factors Affecting the Accuracy Test of Infrared Thermometer
Before you test an infrared thermometer for accuracy, you must ensure the test environment is ideal. Besides knowing how to check accuracy of infrared thermometers, you should consider some factors. Below are the factors that affect the accuracy of an infrared thermometer.
Stabilizing at Room Temperature
If you bring the thermometer from outside, where the temperature is different, it might not give an accurate reading instantly. You must let it stabilize before doing the test.
Cleanliness of the Lens
If the lens isn’t clean, the IR sensor might not detect infrared radiation accurately. So it will give a faulty reading. You need to clean any dirt or debris from the lens before testing the thermometer.
Also, there shouldn’t be any condensation on the lens. To clean the lens, you can use cotton swabs or alcohol pads. Make sure there is no scratch on the lens.
Distance to Target Ratio
It indicates the distance from where you need to hold the thermometer for optimal results. If the ratio is 10:1, the target area will be 1 inch when you hold the thermometer 10 inches away from a target object or surface. The test area will be bigger if you increase the distance.
Field of View
Imagine it like a cone. When you point the thermometer perpendicular to the target subject, it clearly captures the target area. But if you hold it at an angle, the thermometer will take reading from the surroundings.
The setting can be adjusted on some thermometers. If you have such a thermometer, you should keep the value between 0.95 and 0.97.
Check answers to some frequently asked questions regarding teh accuracy testing of an infrared thermometer.
Q1 Can infrared thermometers give false readings?
Ans: If you hold the thermometer incorrectly, it can give false readings. Make sure the target area is small, and the thermometer is held at a 90-degree angle.
Q2: How do I understand that the comparator cup test is accurate?
Ans: You can do two tests at two different temperatures. This makes sure the thermometer is giving an accurate reading.
Q3: Which infrared thermometer is the most accurate?
Ans: Considering the temperature range and accuracy, Fluke 62 Max and ennoLogic eT650D are some of the best-infrared thermometers.
Infrared thermometers measure the infrared radiation emitted from various sources to show the surface temperature. Though the process is straightforward, the thermometer should be calibrated for accurate readings.
So, how to check accuracy of infrared thermometers? In the laboratory, you can check the accuracy of an infrared thermometer using an ice bath, a comparator cup, or a blackbody. Several factors, such as the stabilization, lens, D-T ratio, FoV, and emissivity, should be considered for an infrared thermometer’s accuracy.