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Letter - S
Sample hold

A temperature taken from a target and displayed or held for a set period of time or until the next external reset occurs.


Radiant energy reaching the detector of an instrument from the background other than that which is reflected from the target.

Set point

Process or measurement variable setting which when crossed by the measured value will trigger an event and/or cause a relay to change state.

Shock test

An impact test where an object or test unit is subjected to an impulsive force which is capable of exciting mechanical resonances of vibration.

Signal processing

Manipulation of temperature data for purposes of enhancing the data. Examples of signal processing functions include Peak Hold, Valley Hold, and Averaging.

Silicon (Si) detector

A photon detector used in measurement of high temperatures.

Size-of-source effect

The effect by which the energy collected by, and temperature reading of, an instrument continues to increase as the size of a target increases beyond the field-of-view of the
instrument. It is caused by two occurrences: the remaining energy above the percentage used to define location and scattering of radiation as it enters the instrument such that energy from outside the FOV of the instrument enters it. The existence of this effect means that the accuracy of the instrument may be affected by targets that are too large as well as two small. This effect is also called Target Size Effect. [ASTM STP 895]


The ratio of the emissivities for the two spectral bands of a 2-color radiometer. The emissivity of the shorter wavelength band is divided by the emissivity of the longer wavelength band. Slope can be greater than, equal to, or less than unity. Slope accounts for materials where emissivity varies with wavelength.

Specific humidity

The specific humidity is the ratio of the mass of water vapour to the total
mass of the humid gas.

Spectral filter

An optical or infrared element used to spectrally limit the transmission of radiant energy reaching an instruments detector.

Spectral range

The wavelength region in which the IR Thermometer is sensitive.


The diameter of the area on the target where the temperature determination is made. The spot is defined by the circular aperture at the target which allows typically 90 % of the IR energy from the target to be collected by the instrument. See also Size-of-Source Effect.

Stare or lag

A saturation effect whereby the signal from an instrument endures beyond the response
time after the target has been removed from the field of view. Can be caused by exposing the sensor to a target of high temperature for an extended period. The effect is expressed as the increase in response time required for the sensor to return to within 5 % of the correct reading.

Storage temperature

The ambient temperature range an instrument can survive in a non-operating Range mode and perform within specifications when operated.

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