Digital thermometer

Description

A digital thermometer reads water temperature from a sensor rather than a column of liquid. What separates a usable instrument from a decorative one is traceability, and the US Geological Survey's National Field Manual writes the requirement down. Its procedures, the chapter says, aim to bring traceability standards of the National Institute of Standards and Technology to all USGS measurements of temperature, and a temperature sensor is defined there as any device that contains a detector creating a signal used to infer temperature according to a calibration. The numbers USGS attaches to field work are specific. A field sensor is required to have a temperature range of at least minus 5 to 45 degrees C and an accuracy of less than or equal to plus or minus 0.2 degrees C, and it is required to be compared directly to a certified sensor having a valid certificate, using a refrigerated water bath, at no less than five points between 0 and 40 degrees C, annually. Each point in that comparison is required to agree with the certified sensor by less than or equal to 0.2 degrees C. The certified thermometer used as the reference is held to a tighter bar: accuracy of less than or equal to plus or minus 0.05 degrees C and a readout resolution of at least 0.001 degrees C, with a current certificate of calibration. For a tank, EPA's Volunteer Stream Monitoring manual is the gentler guide. It tells volunteers that supply houses sell armored thermometers best suited for stream work, although you can obtain a good thermometer from an aquarium store, and that some thermometers need to be calibrated before use.

Sources

• pubs.usgs.gov — https://pubs.usgs.gov/tm/09/a6.1/tm9a6.1.pdf
• epa.gov — https://www.epa.gov/sites/default/files/2015-04/documents/volunteer_stream_monitoring_a_methods_manual.pdf

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