Thermal camera reading fet temperatures...how far away to hold it?

[treez]

For assessing the temperature of FETs on the PCB, how far away from the fet should this thermal camera (HT-04) be held?
The spec appears to suggest 32 inches away?

We do notice that the temperature reading varies as we move the camera nearer/further from the fet.

https://www.fasttech.com/product/9666105-hti-ht-04-handheld-infrared-thermal-imaging-camera

 

[FvM]

The reading should not vary over distance, but small objects may not correctly focussed. The manual says fixed focus and 0.15 m minimal focus length, not sure if it's correct.

I would check what the actual focus is and also check the reading with a large object at homogenous temperature.

 

[c_mitra]

The spec appears to suggest 32 inches away?

The specifications says:

"Field Angle / Shortest Focal Length: 27'×35'/0.5m
Thermal Sensitivity: 0.07'C
Measuring Mode: Thermopile
Temperature Range: -20'C to 300'C(-4'F to 572'F)
Measuring Accuracy: ±2.5'C or ±2.5%
Emissivity: Adjustable from 0.1 to 1.0
Image Frequency: 8Hz
Wavelength Range: 8-14μm
Focus Mode: Fixed"

You need to bring the camera close enough so that the object of interest has some significant size in the screen. I guess the temp is computed for every 4X4 pixel (not so sure).

The temp can be off by +/- 2.5C or +/-2.5% (this must be referring to absolute temp; that can mean different- again you should see the detailed manual).

Just test with a small piece of ice on a kitchen sink!