A-A-2579
Stain. Permanent stain imprinting on the glass stem is permissable. Imprinted data shall be sharp and clear.
Wick. The wick shall be chemically clean muslin or bleached cotton sewn or woven into a tubular shape. The lower end of the shall be appropriately secured immediately below the wet-bulb thermometer.
Pocket case. Each psychrometer shall be furnished with a pocket case, fitted with a protective metal insert, and designed to protect the complete instrument, including the handle and chain.
Calculator. Shall be provide with a plastic calculator for determining the relative humidity.
Instrument container. When specified, each psychrometer, including pocket case and a plastic calculator, shall be furnished in a wood or plastic case.
Workmanship. Each psychrometer shall be free from defects which impair their durability, appearance or serviceability.
Test procedures.
Thermometer accuracy. A standard test thermometer of which the calibration is known to be within 0.1 degree F. over the operating range of thermometers to be tested shall be used as references for the accuracy testing. The reference thermometer shall be placed centrally among the thermometers being tested and immersed to top of the liquid column in a liquid bath being constantly acitated. Both the reference and test thermometers shall have their bulbs placed in approximately the same level in the bath. The temperature of the liquid bath shall be held constant to + 0.1 degree F. of the test point selected. Data shall not be recorded until the temperature stabilizes.
The thermometers to be tested shall be compared with the reference thermometer in an ice bath and at a series of points taken over the entire range. Test points shall be selected such that the uppermost and lowermost points shall fall within 0.5 degree F. of the end points of the specified ranges and the interval between consecutive test points shall not be closer than 10 scale divisions and no further apart than 50 scale divisions. An ice points should always be included as one of the test points, where an ice point is covered by the range of the thermometer. The thermometer shall indicate true temperature within the tolerance of + 0.5 degree F. the change in error for an interval of 20 degree F. shall be no greater than 0.5 degree F. on any part of the scale. The change in the ice point during a 90 day period shall be not more than + 0.1 degree F. each pair of thermometers furnished with a psychrometer shall be in agreement within 0.5 degree F. throughout their range the maximum allowable error shall be + 1 degree F.
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