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Letter - D

Optical resolution expressed as a ratio of the distance to the resolution spot divided by the diameter of the spot.


Temperature band (±) about the set point, wherein an alarm output or relay can not change state, thus providing Hysteresis.


Transducer which produces a voltage or current proportional to the electromagnetic energy incident upon it. See also Thermopile, MCT, Thermoelectric Cooled, Pyroelectric, and Lead Selenide and Si detectors.

Dew point

The dew point is the temperature up to which the gas is to be cooled down so that straight water vapour condenses out as liquid. Normally dew point is valid only for temperatures above the freezing point. In certain cases, water can also condense below the freezing point of liquid. However, in such a case, the dew point temperature is not identical with the frost point temperature.

Dielectric Withstand (Breakdown Voltage)

The maximum voltage an insulator of electricity can endure without voltage electrical conduction through the material.

Digital Data Bus

Two or more electrical conductors connecting several transmitters and receivers of digital data.

Digital Image Processing

Converting an image to digital form and changing the image to enhance it or prepare it for analysis by computer or human vision. In the case of an infrared image or thermogram, this could include temperature scaling, spot temperature measurements, thermal profiles, image addition, subtraction, averaging, filtering, and storage.

Digital Output Interval

The time interval between transmission of packets of digital data (DOI) containing temperature and system status information.

DIN Deutsches Institut

The German standard for many instrumentation products.


The change in instrument indication over a period of time not caused by external influences on the device.

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