Non-contact infrared temperature measurements
The ideal distance in most applications for the non-contact digital infrared thermometers is from 2 to 4 inches (5 to 10 cm), measuring a 0.8-2.5 inch (2 to 6.3 cm) diameter circle. As the distance (D) from the object increases, the spot size (S) of the area measured by the handheld infrared thermometer becomes larger. You can observe this because the distance between the two red laser points projected on the measured object increases as the distance between the handheld infrared thermometer and the measured object increases. Make sure that the target is larger than the non-contact digital infrared thermometers spot size. The smaller the target, the closer you should hold the handheld infrared thermometer to it. When accuracy is critical, make sure the target is at least twice as large as the portable infrared thermometers spot size.
Infrared thermometer emissivity
Inaccurate readings will result from using the handheld digital infrared thermometers to measure shiny or polished metal surfaces like stainless steel or aluminum. To compensate, cover the surface to be measured with masking tape or flat black paint. Allow time for the tape to reach the same temperature as the material underneath it. Use the portable infrared thermometer to measure the temperature of the tape or painted surface. When measuring a grill, for example, aim the handheld infrared thermometer at a portion of the grill that has been blackened by the high temperatures. The portable infrared thermometers cannot measure through transparent surfaces such as glass or plastic. The handheld digital infrared thermometers will measure the surface temperature of the transparent surface instead. Steam, dust, smoke, etc., can prevent accurate measurement by obstructing the non-contact digital infrared thermometers optics. Hold the non-contact infrared thermometer back and at an angle to ensure the most accurate measurements. http://www.roktools.com/en/product/mati/
An infrared (IR) thermometer functions like a camera—if the lens is partially obstructed, the resulting image will be underexposed on the film. Similarly, partial obstructions in the Field-of-View (FOV) of an infrared thermometer will cause the thermometer to read incorrectly.
Incorrect temperature readings result when the measured object does not completely fill the FOV of the IR thermometer or when the IR energy emitted by the measured object is attenuated constantly or intermittently before it reaches the sensor. Examples include:
- Partial attenuation—a dirty lens or dirty IR window
- Intermittent attenuation—smoke, steam, or dust between the sensor and the measured object
- Partial obstruction—an induction heating coil partially blocking the view of the object
- Intermittent obstructions—clumps of material in a mixer or kiln falling through the FOV
- Low or changing emissivity of the measured object—changes in alloy or surface condition.
- Small objects (too small to fill the FOV of the IR thermometer) or moving objects (wire for example) that are difficult to keep in the FOV.
When an infrared thermometer "looks" at an object, it measures the it measures the intensity of the radiant energy from the object within its FOV. To obtain accurate readings from a "single-color*" IR thermometer, the following conditions must be met:
- the object must fill the FOV of the IR thermometer http://www.roktools.com/en/product/mati/infraredthermometers/
- IR energy emitted by the object can not be attenuated by something (e.g. smoke, moisture, dust) between the object and the IR thermometer
Sometimes this is not possible. The object does not fill the FOV, an obstruction cannot be moved or the smoke or dust will always be present in the process area. In these cases the energy from the measured object is attenuated or partially blocked and the resulting temperature reading is incorrect—with a single-color thermometer.
A two-color** or "ratio" thermometer can usually solve these problems. While a single-color thermometer needs a clear unobstructed view of a target, some partially obstructed targets can be accurately measured with a two-color thermometer.