Instrumentation To record volume of reagent added as a function of time, an integrator can be used to sum a constant input each time the relay closes. The output con sists of a series of steps displayed by a strip-chart recorder. I t is better to integrate a signal from another source rather than use the output of amplifier 3. This is a rather messy signal and may not give constant steps. The figure shows a setup in which the im pulse buret is operated by a 20-V dc supply. This same supply provides the input for the integrator. Note the addition of a resistor and capacitor across the relay contacts to suppress arcing. The complete pION-stat is shown in Figure 8. The op-amp power supplies are omitted for clarity. As discussed above, they should be fairly well regu lated. Note that the relay and impulse buret are grounded to the instrument chassis rather than the high-quality signal ground. This is to keep these large currents from mixing with the low-level signal currents and causing ir drops along the signal ground buss. The digital pION-stat may seem like a fairly complex instrument. However, it was built up from only a few basic building blocks. By analyzing other instrument tasks the same way we ap proached this one, you, too, can make use of functional electronics to fill your instrumentation needs.
References (1) John Springer, ANAL. CHEM., 42, No.
8, 22A (1970). (2) L. P. Morgenthaler, "Basic Opera tional Amplifier Circuits for Analytical Chemical Instrumentation," 2nd Ed., McKee-Pedersen Instruments, Dan ville, Calif., 1968. (3) "Applications Manual for Computing Amplifiers," Philbrick Researches, Inc., Dedham, Mass., 1966. (4) "MP-System 1000, Operation and Applications," 3rd Ed., McKee-Pedersen Instruments, Danville, Calif., 1968. (5) "Handbook of Operational Amplifier Applications," Burr-Brown Research Corp., Tucson, Ariz., 1963. (6) MPI Applications Notes, 4, 17-20 (1969). (7) Ibid., 1,5-8 (1966). (8) Ibid.,*, 1-4 (1969). (9) Ibid., McKee-Pedersen Instruments, Danville, Calif., Bi-monthly publica tion, illustrating the use of operational amplifiers in chemical instrumentation. (10) H. V. Malmstadt, "Digital Elec tronics for Scientists," Benjamin, New York, Ν. Υ., 1969. (11) P. M. Kintner, "Electronic Digital Techniques," McGraw-Hill, New York, Ν. Υ., 1968. (12) H. N. Bode, "Network Analysis and Feedback Amplifier Design," D. Van Nostrand, Princeton, N. J., 1951.
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