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Agronomy Journal Abstract -

An Inexpensive Thermocouple Multiplexing Device


This article in AJ

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

    * Corresponding author(s):
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  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



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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