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Temperature Measurement

There are two distinct categories of practical methods for measuring temperature of a building component: contact, and non-contact.

A contact measurement is taken with a sensor from the following instrumentation list:

Contact temperature measurements allow the researcher to measure the temperature of the body (solid, liquid, or gas) immediately adjacent to the instrument. Care is needed in many cases to prevent heat transfer from other nearby bodies from affecting the measurement.

A non-contact measurement relies on remote means to determine temperature. The primary buildings tool is an infrared (IR) camera. Non-contact measurements rely on radiant emissions from a body to infer its temperature. Infrared thermography is the most common used in building applications.

The table below summarizes some basic characteristics of the temperature measurement devices most commonly used in buildings research. Pricing for temperature sensors depends strongly on sensor packaging and cabling terminations. Thermocouple sensors that do not require protection (e.g. when used for air temperature measurement) can be fabricated by soldering or brazing the two wires together to form a junction.
This table displays 6 sensor types and shows their sensitivity in typical application, typical usable temperature range, and typical price range

Thermocouples

A thermocouple is comprised of two dissimilar materials (usually metallic wires) bonded together. The junction between the wires forms a microscopic region where voltage is induced between the wires. As the temperature of the junction changes, the voltage will vary in a repeatable, controlled manner, and can be measured at the other end of those wires.

Resistance Temperature Detectors (RTD)

Resistance Temperature Detectors, or RTDs, are an alternative to a thermocouple where accuracy and repeatability are of highest importance.

Thermistors

A thermistor is a temperature measuring device, composed of a resistor whose resistance changes with temperature.

Infrared Thermography

Infrared (IR) imaging, or thermography, is a useful diagnostic tool. All materials emit infrared radiation at levels dependent on their temperature. An IR camera is able to capture this radiation in the same way a standard camera captures visible light.

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.

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