Nakinos Temperatures are not measured directly with this instrument. Add to Alert PDF. Secondary standards may be of the following types. Under these conditions oxidation adtm the mercury will occur and will normally be evidenced by the production of crystals of red oxide of mercury after 10 to 12 h of exposure.
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Some that are considered essential to this standard are given below. United States 1 3. Apparatus 5. The thickness of such gages should approximate the diameters of the holes to minimize errors resulting from the axis of the thermometer stem being other than normal to the plane of the gage.
Suitable types are described in Appendix X1. Temperatures are not measured directly with this instrument. Its electrical resistance is determined by comparison with a standard resistor, using a potentiometer, a Kelvin-type double bridge, or a Wheatstone bridge, preferably of the Mueller type or an AC resistance bridge.
Temperatures may then be calculated using suitable resistance-temperature equations. In order that it shall be satisfactory for such use, the thermometer should meet the requirement that the ratio of resistances at the steam and ice points shall be greater than 1. More complete information on the construction and use of primary standard thermometers may be obtained from NIST SP They are simpler to use than a primary standard thermometer with its accessory equipment, the latter being capable of an order of precision and accuracy far in excess of that attainable with liquid-in-glass thermometers.
The choice of a secondary standard will be governed by various factors. Scale corrections should always be applied in the use of these standards. Secondary standards may be of the following types. They should be completely recalibrated every 6 to 12 months, depending upon the temperatures of usage. Ice points should be taken every 3 months. For fraction- ally graduated thermometers a calibrated set of the following thermometers is recommended.
E77-14 Standard Test Method for Inspection and Verification of Thermometers