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This article in AJ

  1. Vol. 85 No. 3, p. 773-776
     
    Received: Aug 6, 1990
    Published: May, 1993


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doi:10.2134/agronj1993.00021962008500030045x

An Inexpensive Thermocouple Multiplexing Device

  1. C. K. Kvien ,
  2. J. E. Hook,
  3. S. J. Thomson and
  4. M. C. Smith
  1. D ep. of Agricultural Engineering, Virginia Polytechnic Inst., Blacksburg, VA 24061
    D ep. of Agricultural Engineering, Georgia Coastal Plain Exp. Stn., P.O. Box 748, Tifton, GA 31793

Abstract

Abstract

The expense of monitoring large numbers of thermocouples has constrained many research and development projects. We developed an inexpensive multiplexing device which allows 640 or more thermocouples to be accessed from a microcomputer. The multiplexing unit is connected to a microcomputer expansion box equipped with a 16-channel digital input/output (I/O) board and a preamp connected to an analog-to-digital (A/D) converter with cold junction compensation. A BASIC program controls the sequencing of each of the 640 channels and storage of information on the microcomputer's disk system. Temperatures measured through the system were accurate to ± 1 °C when channel switching intervals of 1 s or more were used. Temperature at the thermocouple junctions within the multiplexing unit does not significantly affect the observations. We found the device suitable for monitoring temperatures by thermocouples, and the programming gave us complete flexibility over timing and selection of thermocouples read. The multiplexing capability reduced the amount of expensive thermocouple wire needed for sensing at remote sites.

Contribution of the Univ. of Georgia Coastal Plain Exp. Stn.

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