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Measurement errors due to distance on overhead lines

Supplier: Irtek
29 June, 2012

One would normally assume a thermal camera which has in-built cross hairs (+) that shows the size of the spot being measured is the correct temperature without taking into account the target distance and size.

This can lead to a significant error, especially when measuring the temperature of overhead line connections.

Frequently behind these targets is a clear, dry sky which can be quite cool in temperature.

The thermal camera averages area out of the spot size if the spatial resolution is poor and does not allow the camera to cover the small target at a given distance (say 15m/36ft). With the surrounding cooler air, the thermal camera will read a much lower temperature which lead to significant measurement errors.

In comparison, we measured the connection on a 23kV distribution system using three different IRtek thermal cameras of different pixels and resolution and a popular medium range IRtek IR thermometer LR300 with D/S ratio of 300:1.

The test results are show on the table below:

Ti50 camera

160x120 pixels





Ti500+ camera

320x420 pixels





Ti600 camera

384x288 pixels





LR300 IR Thermometer

D:S: 300:1

Measuring distance: 5-15m





The red highlight shows a significant measurement error and severe problem while amber highlight shows inconsistent result whilst the green colour shows correct measurement value.

It is obvious we can easily overlook a potential problem if we do not take camera resolution into consideration.

IRtek LR300 offers a more economical method of measurement, with the cost less than that of a low resolution camera and yet is on par with a high resolution thermal camera. In addition, the LR300 requires minimal maintenance and effortless usability.