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1098 . CHAPTER 50 1954 Guide 1 Room Air Distribution Research for.Year 'Round. Air Conditioning, Part II-- Supply Outlets at Three Locations, by H. E. Straub, and S. F. Gilman. (A.S.H.V.E' Jouhnai. Section of Heating, Piping, and Air Conditioning, November 1953, p. 145) 8 Investigation of Summer Cooling in the Warm Air Heating Research Residence, by A. P. Kratz, M. K. Fahnestock and S. Konzo, (University of Illinois, Engineering Experiment Station Bulletin 290j 1930)1 CHAPTER 51 INSTRUMENTS AND MEASUREMENTS Temperature Measurement, Pressure Measurement,, Air Flow Measurement,. Air Change Measurement, Humidity Measurement, Heat Transfer Through Building Materials, Evaluation of Thermal Environment. Combustion Analysis, Smoke Density Measurements, Determination of Air Contaminants, Sound and Vibration Measurements HEATING and air conditioning engineers and technicians require instruments for both laboratory and field use and somewhat more pre cision is attainable and essential in the laboratory, where research and de velopment are undertaken, than in the field, where acceptance and adjust ment tests are conducted. Some instruments have attained an adequate state of development, while others fall far short of the desirable. For in stance, temperatures can now be measured readily with ample accuracy for most purposes, while a convenient and precise method for determining or comparing the dustiness of atmospheres is lacking, and improvement in existing hygrometers and humidity controllers is essential.- Codes and standards covering different types of heating and air condi tioning devices and apparatus have been promulgated by various authori tative organizations, and instruments essential for performance or com pliance testing are enumerated in the relevant publications.1,2,i3, * The present purpose is to discuss the use and characteristics of the more im portant instruments. TEMPERATURE MEASUREMENT5,6 Thermometers Any device capable of indicating temperature is a thermometer, but in common usage the term thermometer without qualification has come to signify the ordinary mercury-in-glass temperature indicating device. This type has a useful range from -- 40 F, the freezing point of mercury, to about 1000 F, at or near which the glass usually softens. Lower temperatures can be measured with alcohol-filled thermometers for which the range is ^. +248 F. The better thermometers have their scales, either Fahrenheit or Centigrade, etched with acid into the glass which forms their stems. The probable error for etched stem thermometers'is plus or Jjnnus one scale division, and calibration is desirable for much test work, thermometers are calibrated during manufacture at not less than two temperatures--the freezing and boiling points of water--and calibration ls ,"n accomplished with the instrument completely immersed in. a bath known temperature. The intervening scale divisions are then apP led to the stem. When such a thermometer is used with the stem in- mpletely immersed, a correction known as the stem correction is necesry for accurate measurements, and its magnitude is usually computed, y means of the following formula: where K = 0.00009 D (t, - t,) K = correction to be added, Fahrenheit degrees. (1) 1099