How to place infrared temperature devices?

Is there a way of estimating the magnetic field range? to be able to determine at what distance to place the infrared temperature measurement devices.

General rule of thumb for induction is that metallic objects should be placed 2-2.5 times the internal opening of the induction coil. This opening is the internal diameter for round coils. There are some instances where the intensity of the magnetic field is strong enough that larger separation is required. If this is not practical then a Faraday cage or shield may be used to block the magnetic field from reaching the temperature measuring device.