Infrared Thermometers

Mike does a great job summing up a wide variety of temperature sensors.  Back in high school I learned that the bimetallic strip was used to control thermostats.  The expansion of the metal at a specific temperature would close a circuit, thus turning on/off the HVAC system.  Now we have NEST, which is more accurate and efficient. 

I would like to expand on Infrared (IR) Thermometers.  These thermometers are essentially a laser gun that can read the temperature of an object without any contact.  This type of thermometer is has an increasing popularity in the food industry.  Chefs are using them to read the temperature of food so that they don’t have to puncture the food and because it gives a fast and accurate reading. 

Every object emits an invisible infrared energy.  IR is located on the electromagnetic spectrum between visible light and microwaves.  There are three ways to transfer this invisible heat: reflected, transmitted, and emitted.  The emitted energy is the only type of energy that can be used to get the actual surface temperature.  This is a disadvantage to this type of thermometer.  As I mentioned before this thermometer is becoming popular in the food industry.  If the food is under a heating lamp the temperature measured will also include that of the lamp.  Therefore, when taking the temperature of the food it should be in low light, or the light should be covered with a cloth.

 

Depending on how advanced the IR thermometer the emissivity value can be altered based on the material.  These values can be looked up in charts.  As a comparison, emissivity of aluminum and water are 0.77 and 0.95, respectively. 

Again these thermometers are growing in the food service industry. They are also great for monitoring equipment.  For example, they can be used to find hot or cold spots detecting leaks in HVAC equipment. 

Sources:

http://www.allqa.com/IR.htm

http://www.thermoworks.com/emissivity_table.html

http://www.buzzle.com/articles/laser-thermometer-how-does-it-work.html