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Tag Archives: Errors

Conduction Error in Temperature Sensors

Conduction error is a common problem for small application contact temperature sensors.

Temperature sensors can be very accurate devices, however poor probe design or bad installation can easily give a system significant temperature reading errors. Conduction error is primarily caused by inadequate immersion. Heavy Industrial applications usually have good immersions, but designers of small pieces of equipment must address the problem.

Sensors usually need protection sheaths and always use signal cables. Both items will conduct heat away from a system. Probe leads and sheath will pass through a thermal gradient at some point. If the thermal gradient is close to the measuring point, then the sensor will be influenced to some degree by ambient conditions.… Read more

My Sensor Assembly is not as accurate as I was expecting. Why is that?

Temperature sensors have defined accuracy. Thermocouples according to BS EN 60584.2:1993 and Resistance Thermometers to BS EN 60751:1996. Parties involved in accuracy include Calibration Laboratories, Element manufacturers making high volumes of standard sensing elements and Sensor makers who take the primary elements and fabricate a sensor assembly according to user design requirements. In use a sensor can then be in a poor location, or simply be an inadequate design.

Calibration labs

All calibrations have uncertainty ranges. Individual calibrations at laboratories can cost £ 200 or more each. With that a high quality lab does multiple readings in highly controlled conditions.… Read more

Temperature Sensor Radiation Error in an Aerospace Furnace

Measurement errors can be undetected and highly significant. I had a great example of sensor radiation error recently.

I took a telephone call from a customer telling me my temperature sensors were inaccurate. He was building an AMS 2750D compliant Aerospace Furnace. He bought a number of thermocouples from Peak Sensors which were all UKAS calibrated.

System Design

There was a combination of Mineral Insulated Type N and Ceramic Insulated Type R (wire Ø 0.25mm) sensors. In four locations, a type N and a type R were installed adjacent to each other. One would expect them to read very similar temperatures. During pre commissioning trials it was noticed that at times there was up to 50°C difference between the pair.… Read more