HR-33T Dew Point Microvoltmeter Instruction/Service Manual ...

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4.5 – Effect of Ambient TemperatureThermocouple output as a function of water potential and ambient temperature is easily obtained for the <strong>HR</strong>-<strong>33T</strong>.Thermocouple output is simply the thermocouple sensitivity, P ab multiplied by the dew point depression, )T.When the dew point depression is small (as is the case for water potential measurement), )T = )e/S, where )eis the difference between saturation and chamber vapor pressure, and S is the slope of the vapor pressuretemperaturefunction at ambient temperature. The Clausius-Clapeyron equation gives S as a function oftemperature, saturation vapor pressure, (e 0 ), and latent heat of vaporization (8):S =e 0 8RT 2(11)where R is the universal gas constant. A relationship between )e and water potential (8) is obtained using theexpression,e = e 0 expRRT(12)Thus,)e = e 0 – e = e 0 (1 – expRRT) (13)and )E = P ab )T = P ab )e/S =P ab RT 2 (1 – exp R/RT) (14)8Equation (14) is the desired relationship between thermocouple output and water potential. At high waterpotentials where the exponential can be approximated by the first two terms of a series, equation (14) becomesE =-P ab TR8(15)indicating a linear relationship between E and 8 with a sensitivity of about &0.75 µvolts bar -1 . Figure 4 showsthe agreement between theoretical and actual calibration curves. Values of constants used were T = 298°K, R =4.60 bars °K -1 , 8 = 24330 bars and P ab = 63 µvolts °K -1 .22
23Theoretical vs. Actual Instrument OutputFigure 4
Page 1 and 2: HR-33T Dew Point MicrovoltmeterInst
Page 3: CONTENTSSECTION 1 - INSTRUMENT SPEC
Page 7: SECTION 1 - INSTRUMENT SPECIFICATIO
Page 11 and 12: A v SET control. The numerical valu
Page 13 and 14: Output For Dew Point, Psychrometric
Page 15 and 16: 11Temperature Correction CurveFigur
Page 17 and 18: SECTION 3 - ADDITIONAL OPERATING IN
Page 19 and 20: 3.3 - Effect of Zero Drift on Readi
Page 21 and 22: SECTION 4 - THEORY OF OPERATION4.1
Page 23 and 24: 4.2 - Psychrometric MethodThermocou
Page 25: Heat transfer due to Peltier coolin
Page 29 and 30: SECTION 5 - ELECTRONICSThe electron
Page 31 and 32: 27Typical Control and Signal Wavefo
Page 33 and 34: SECTION 6 - MAINTENANCE6.1 - Genera
Page 35 and 36: SECTION 7 - TROUBLESHOOTINGIf the i
Page 37 and 38: Output Characteristics for Contamin
Page 39 and 40: HR-33T Schematic DiagramFigure 835
Page 41 and 42: Test Point LocationsFigure 1037
Page 43 and 44: Front Panel AssemblyFigure 1239
Page 45 and 46: SECTION 8 - PARTS LIST5106 - 110 Vo
Page 47 and 48: Front PanelRef. No. Part No. Qty. U
Page 49: 5112 Battery PackRef. No. Part No.

HR-33T Dew Point Microvoltmeter Instruction/Service Manual ...

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