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A non-contact thermometer pointed at bright bare steel pipework will read

  • A.correctly, provided the distance is under a metre
  • B.low, the emissivity of the polished surface being small
  • C.high, the surface reflecting the surroundings into the sensor
  • D.correctly, metal being a good radiator

Answer: B

Emissivity of the order of 0.1 means only a tenth of the expected radiation reaches the instrument, and the reading can be a hundred degrees low on a steam line. A matt sticker or a contact probe resolves it in seconds.

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