Emissivity
Emissivity is the measure of an object's ability to emit infrared energy. Emitted infrared energy is exponentially proportional to the temperature of the object. Emissivity can have a value from 0 (shiny mirror, perfect reflector) to 1.0 (blackbody, perfect emitter). Most organic, painted, or oxidized surfaces have emissivity values close to 0.95. If you are performing qualitative inspections with your imager, leave the emissivity set at 1.0. If you need to measure actual temperature values, set the emissivity value according to the emissivity of the material the object you are measuring is made of. Again, if you need accuracy, you will need to find the emissivity value of the material before taking the measurement. See Table 1 on page 68 and Table 2 on page 69 for the emissivity values for the most common materials.
There are a couple of methods that help you to find the emissivity value of materials:
ξ Tape method: this method requires the usage of the Scotch® brand PVC tape (emissivity value 0.97) or equivalent. Cover the surface you want to measure with tape. Wait some seconds for the temperature to stabilize. Set the emissivity of the imager at
0.97and measure the temperature. Make a note of the temperature value. Then, remove the tape and measure the new temperature value. Adjust the emissivity accordingly until the temperature value found previously is displayed on the unit. This emissivity value is the one of the material being measured. This method is good for objects that are at low temperatures (under 100θC (212θF)), not electrically energized and not in motion.
ξ Contact thermometer method: this method will need a contact probe and good quality temperature meter. Initially, use the contact probe temperature meter to measure the temperature of the object you want to know the emissivity value, allowing time for the contact probe to stabilize (this may take up to a minute). Make a note of the temperature value. Adjust the emissivity on the imager accordingly until the temperature value found previously with contact probe temperature meter is displayed on the imager display. This emissivity value is the one of the material being measured. This method is good for
objects that are at moderately high temperatures (under 250θC (482θF)), not electrically energized and not in motion.
To set or change the Emissivity value, complete the following:
1.Put the ThermoView Ti30 imager in regular Measurement mode.
2.Press the MODE button once. At this point you will be able to adjust Emissivity.
3.Set the Emissivity value to the proper value, according to the target material, by pressing the Up and Down buttons.
Reflected Temperature Compensation
Targets that have low emissivities will reflect energy from nearby objects. This additional reflected energy is added to target’s own emitted energy and may result in inaccurate readings (see Figure 31 below). In some situations objects near the target (machines,
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