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Indoor Aspirated Shield

Sometimes making temperature measurements can be a challenge. Thermocouple measurements can be biased due to undesired heat transfer effects (i.e. a nearby hot surface). Further, a thermocouple only measures at one point in space. To get around these limitations, you can use an aspirated shield. This assembly is useful for protecting sensors while measuring outdoor temperature or estimating a room’s average air temperature.

An aspirated shield is composed of several parts:

  • A thermocouple, to make the measurement
  • A radiant shield, to block radiant heat transfer from sunlight, or hot/cold objects in the vicinity
  • A fan, to convect air across the thermocouple and encourage some level of mixing, and
  • A stand, to suspend the assembly in the air being measured
Photo of an aspirated shield held in place by several strings and wire.

An aspirated shield in use

Indoor aspirated shields can be purchased, or fabricated inexpensively. Two pieces of thin polyvinyl chloride (PVC) pipe can be used, the smaller of which fits within the larger diameter pipe with an air gap. The cylindrical surfaces which face each other should be coated with a shiny material such as aluminum tape or aluminum foil. The pipes can be supported using bolts, screws, or metal or plastic rods. A thermocouple is located at the center of the inner pipe. The fan, such as a computer case fan, is located to blow outward at the exit of the tubes. In that way, the fan heat does not affect the measurement. This assembly can be screwed to a tripod or hung from the ceiling.

Outdoor aspirated shields can be purchased from many sources. For more information on usage of aspirated shields for outdoor measurement, see outdoor aspirated shield.