Why does my Infrared Camera read higher than my Infrared Temperature Gun?

  The answer is, in a word, resolution. Take a look at the image below.

The infrared camera is able to locate and measure much smaller objects than an IR temperature gun. Note the spot measurement on the infrared image; its reading is 250 F. Contrast that to the average area measurement typical of an infrared gun at a reading of 184 F. The gun is averaging all the hot areas along with the cold areas of the grating we see in the image.

Another common question is why the IR camera reads a higher temperature than a contact temperature probe? Contact temperature probes require an extremely good contact in order to read a decent temperature. In fact these probes measure their own temperature, so if the heat transfer is not good from the substrate, and the probe sensor is colder than the surface, the temperature will be lower. Also remember that contact thermometers act as heat sinks, sucking heat out of a surface.

IR Pictures Through a Grating or Mesh

Question from a customer: “Scanning through the steel grating I read a temperature 5 to 15 degrees Celsius lower than scanning without the grating. I know it is to do with the steel grating but I was wondering why.”

Great question. Let’s take a look at a typical situation with and without a grating, and then placing the grating at different distances to the camera.
The distance between the fuse and the camera remains constant, and the camera is always focused on the fuse. The only changes are the insertion of the grating, and the distance of the grating from the infrared camera.

Figure 1. Looking at a fuse directly with no grating. Max temperature is 51.4 C.

Figure 2. We have inserted the grating close to the fuse.
Max temperature dropped to 51 C, a small error.

What does Sensitivity (NETD) mean when applied to a Thermal Imager?

Sensitivity expresses the ability of an infrared camera to display a very good image even if the thermal contrast in a scene is low. Put another way, a camera with good sensitivity can distinguish objects in a scene that have very little temperature difference between them.
Sensitivity is most often measured by a parameter called Noise Equivalent Temperature Difference or NETD, for example, NETD @ 30 C : 80mK. A Kelvin degree is the SI base unit of thermodynamic temperature equal in magnitude to a degree Celsius, so mK means thousandths of a degree (80mK = 0.080 K).
What is NETD? NETD is defined as the amount of infrared radiation required to produce an output signal equal to the systems own noise. This is a noise rating of the system and should be as low as possible. We are not talking about how loud the system is here!!! We are talking about electronic noise that we translate into a temperature difference at an object temperature of 30 C (86 F).