Let's see the accuracy of the infrared thermometer. The accuracy can vary depending on
different types. Also, as they don’t touch the surfaceof the object, to get precise accuracy is
very difficult. The accuracy of the pyrometer is measuredin terms of D:S (Ratio of distance from
the object to the spot). The spot here means the diameterof the measuring area. Thus it's the
ratio between the distance of the pyrometer from theobject and the diameter of the area of the
object.
Let’s take an example of the D:S ratio of 10:1. Thismeans that the distance is 1/10 of the area
that can be measured accurately. So if the distancebetween the surface and the pyrometer is
50cm, then it can accurately measure an area of diameter5cm. It's just like a cone from the tip
of the gun. So can you guess which pyrometer is moreuseful, one with high D:S or low D:S?
Yes, the one with a high D:S ratio. Because if ata large distance it can measure a large area
accurately, then it can measure temperature froma small distance very accurately, as
practically the distance is not very large. So higherD:S value the better thermometer.
So now we know that the infrared thermometer is anexcellent device to measure the
temperature of the object without touching it accurately.But its accuracy can suffer because of
some factors. Let’s see what can affect the accuracyof the pyrometer.
1. DUST
The dusty environment can affect the accuracy ofthe thermometer, as the infrared
radiations that are small then the size of the dustparticles get scattered and don't reach the
detector.
2. DISTANCE
As we already know about the D:S ratio. Distanceis inversely proportional to the
accuracy, i.e. more the distance between the thermometerand the surface of the object, less is
the accuracy. This is because if the distance is large,infrared rays have to travel more distance,
and there are high chances that they get scattered.Also, infrared rays from the surrounding get
detected hence affecting the measurement.
3. EMISSIVITY
It's not always the external factors and the equipment.Sometimes accuracy can be
affected by the object material. Different materialsemit infrared rays in different intensities. The
measure of this intensity of emitted infrared raysis known as Emissivity. It is measured on the
scale of 0 and 1. When emissivity is 1 it means thatthe object first absorbs all the infrared rays
in the surrounding and then transmits its own raysand not ones in the surrounding. When the
object has 0 emissivity, it reflects all the raysin the surrounding plus emits its own. So it gets
difficult to measure the temperature of the item withless emissivity accurately.