In using the radiation thermometers, the most significant element is an emissivity. Effective measurement is allowed by properly setting this, but mainly obstructed by the following two factors.
All the objects emit infrared rays, but at different emissivities.
At same 100°C, for example, brass with 0.1 emissivity emits only 10% worth of infrared rays of 100°C and rubber with 0.9 emissivity emits only 90% worth of infrared rays of 100°C.
If measurement is made in this state, 10°C is displayed for brass and 90°C for rubber despite the actual temperature being 100°C.
The radiation thermometers are usable only after setting this emissivity.
You may think, “Why don’t you examine the emissivity and adjust to an appropriate value?” However, the emissivity changes from one object to another. Even with the same kind of object, it changes depending on the surface condition (emissivity easily changes by 0.1 to 0.4), making it difficult to set the appropriate value.
Measure:
Our products are capable of measuring the actual temperature with a contact thermometer only at condition setting time and setting the emissivity to ensure the same temperature as the actual one, allowing easy emissivity adjustment.
When measuring an object with high reflectance or permeability, correct measurement may not be expected if there is a heat source nearby.
Reason:
The characteristics of the object against infrared rays consist of a combination of emission (absorption), reflection and permeation.
There ratios are emissivity + reflectance + permeability = 1.00.
In the cases of metals and resins, only emissivity and reflectance are generally taken into account because permeability is basically ignorable.
For brass, emissivity is 0.1 and reflectance is 0.9. For rubber, emissivity is 0.9 and reflectance is 0.1.
Now, what matters is brass with low emissivity.
When not affected by disturbance (impossible in the real world, though), any emissivity can be measured without problem by properly adjusting it.
When there is a heating element (200°C) near the measurement object, measurement can be made heedless of influence of the heating element if reflectance is 0 (emissivity = 1.0). With reflectance being 0.9 as in this case of brass, however, even if emissivity is properly set, 90% worth of infrared rays of the heating element are reflected and converted at emissivity = 0.1, displaying 1,900°C (actually a measurement error).
In short, if reflectance is high, disturbance is reflected and reflected infrared rays are displayed severalfold, resulting in a measurement error very frequently.
Measure:
A radical measure is difficult to take, but it is a possible to employ a control method such as determining in the same environment without fail because there is reproducibility. Anritsu Meter has paints and tapes increasing the emissivity of the work surface. It is effective to increase apparent emissivity with those materials to measure.
