Non-contact (IR) temperature thermometers are gaining favor in the paint industry due to the ease of use, the rapid response time (less than 1 second), and the range they work over. At higher temperatures, temperatres over 200F, if accuracy is required, it is important to calibrate the emmisivity of the temperature gun. The best way to do this is using a thermocouple theromometer. The most common thermocouple in our industry is a Type K thermocouple. When accuracy is important, verify temperature taken with an IR gun with a thermocouple type thermometer. There are some combination meters such as the Extech 42515 that have both in one unit. Will my IR meter measure accurately 10 feet from the target?
Answer: Measurements should normally be made as close as possible to the device under test. The meter can measure from moderate distances but the measurement may be affected by external sources of light. Steam, dust, smoke, etc. can also obscure measurements. In addition, the spot size may be so large that it encompasses surface areas not intended to be measured.
My meter seems to provide readings that are too high or to low when measuring metal surfaces. Why?
Answer: IR Thermometers measure the surface temperature of an object. The thermometer’s optics sense emitted, reflected, and transmitted energy. The thermometer’s electronics translate the information into a temperature reading which is then displayed on the LCD. The amount of IR energy emitted by an object is proportional to an object's temperature and its ability to emit energy. This ability is known as emissivity and is based upon the material of the object and its surface finish. Emissivity values range from 0.1 for a very reflective object to 1.00 for a flat black finish. If an object's surface is highly reflective, apply masking tape or flat black paint to the surface before measuring. Allow time for the paint or tape to adjust to the temperature of the surface it is covering.
Why do I need a IR meter with adjustable emissivity?
Answer: An IR thermometer with adjustable emissivity can be used to compensate for the emissivity of different materials. Most organic materials and painted or oxidized surfaces have an emissivity factor of 0.95.
Emissivity Factors for Common Materials
| Material under test | Emissivity | Material under test | Emissivity | | Asphalt | 0.90 to 0.98 | Cloth (black) | 0.98 | | Concrete | 0.94 | Skin (human) | 0.98 | | Cement | 0.96 | Leather | 0.75 to 0.80 | | Sand | 0.90 | Charcoal (powder) | 0.96 | | Soil | 0.92 to 0.96 | Lacquer | 0.80 to 0.95 | | Water | 0.92 to 0.96 | Lacquer (matt) | 0.97 | | Ice | 0.96 to 0.98 | Rubber (black) | 0.94 | | Snow | 0.83 | Plastic | 0.85 to 0.95 | | Glass | 0.90 to 0.95 | Timber | 0.90 | | Ceramic | 0.90 to 0.94 | Paper | 0.70 to 0.94 | | Marble | 0.94 | Chromium Oxides | 0.81 | | Plaster | 0.80 to 0.90 | Copper Oxides | 0.78 | | Mortar | 0.89 to 0.91 | Iron Oxides | 0.78 to 0.82 | | Brick | 0.93 to 0.96 | Textiles | 0.90 | | A: In the U.S.A:
Type K = yellow-red
Type J = white-red
Type T = blue-red
Type E = purple-red
Red is always negative in thermocouples. There is a comprehensive emmisivity table on the Cole Palmer website: http://www.coleparmer.com/techinfo/techinfo.asp?htmlfile=Emissivity.htm&ID=254#anchor44
The table is repoduced below in a PDF formate.
EMMISIVITY TABLE - CLICK HERE |
