INSTRUCTION MANUAL S3497X Psychrometer Software and A3497 TC Psychrometer Cooling Current Interface Revision: 1/92 C o p y r i g h t ( c ) 1 9 8 4 - 1 9 9 2 C a m p b e l l S c i e n t i f i c , I n c .
Model S3497X Psychrometer Software and Model A3497 Interface Table of Contents PDF viewers note: These page numbers refer to the printed version of this document. Use the Adobe Acrobat® bookmarks tab for links to specific sections. 1. Function.......................................................................1 2. TCP Measurement Sequence.....................................1 3. TCP Base Temperature Measurement.......................2 4. Input and A3497 Interface Connections ....................2 5.
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25 PELTIER THERMOCOUPLE PSYCHROMETER 15: 1. FUNCTION Instruction 25 measures up to five thermocouple psychrometers (TCP) excited through Campbell Scientific's Model A3497 Psychrometer Cooling Current Interface. Groups of TCPs may be read by using an A3497 for each group of five TCPs and programming Instruction 25 within a Loop. An option is provided for drying the TCP junction by heating before the cooling current is applied.
25 PELTIER THERMOCOUPLE PSYCHROMETER If zero delay between wet-bulb readings is specified in Parameter 14, the time between recorded readings for a given TCP is equal to tr. The time interval between initiating the first measurement and completing the fifth measurement for a given TCP is approximated by ti = (4) (60) +45(4Np+1) = 285+180Np where ti is in milliseconds. 3. TCP BASE TEMPERATURE MEASUREMENT Three wire psychrometers such as those manufactured by J.R.D.
25 PELTIER THERMOCOUPLE PSYCHROMETER Figure 1. Connection to CR7 using the A3497 Psychrometer Cooling Current Interface 5. THE A3497 INTERFACE AND CURRENT CALCULATION Figure 2 is a schematic of the A3497 Interface. The A3497 performs several functions. The switched analog output is held at ground through a 10K resistor preventing leakage of current through the TCP junction when the analog output is disabled. The leakage current is typically a negligible 2nA but can be as high as 30nA.
25 PELTIER THERMOCOUPLE PSYCHROMETER 6. OUTPUT FORMAT Instruction 25 stores all readings from a given TCP sequentially in Input Storage. The base temperature is first, followed by the zero reading, and then the sequence of wet-bulb readings with the zero reading subtracted. The series of readings from the next TCP then follows, etc. The number of Input Storage locations allocated must be based upon the number of TCPs excited by one A3497 Interface and the number of wet-bulb readings per TCP.
25 PELTIER THERMOCOUPLE PSYCHROMETER 11: 01: 02: P 31 95 12: P 13: P 70 Sample Reps Loc TCP 4 #1 95 End End Table 1 5
25 PELTIER THERMOCOUPLE PSYCHROMETER Table 2. Example Output Wescor .1 molal NaCl (4.62 Bars) 01+0107. 02+24.90 09+2.916 10+2.936 17+2.753 18+2.753 25+2.669 26+2.664 03-0.310 11+2.891 19+2.709 27+2.674 04+3.370 12+2.842 20+2.713 28+2.620 05+3.064 13+2.837 21+2.679 29+2.664 06+2.985 14+2.792 22+2.684 30+2.644 07+2.980 15+2.773 23+2.694 31+2.674 08+2.945 16+2.812 24+2.674 32+2.679 .5 molal NaCl (22.81 Bars) 01+0109. 02+24.90 09+10.02 10+09.94 17+09.50 18+09.42 25+08.61 26+08.34 03-0.039 11+09.
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