AN INEXPENSIVE THERMOCOUPLE MULTIPLEXING DEVICE

The expense of monitoring large numbers of thermocouples has constrain ed many research and development projects. We developed an inexpensive multiplexing device which allows 640 or more thermocouples to be acce ssed from a microcomputer. The multiplexing unit is connected to a mic rocomputer expansion box equipped with a 16-channel digital input/outp ut (1/0) board and a preamp connected to an analog-to-digital (A/D) co nverter with cold junction compensation. A BASIC program controls the sequencing of each of the 640 channels and storage of information on t he microcomputer's disk system. Temperatures measured through the syst em were accurate to +/- 1-degrees-C when channel switching intervals o f 1 s or more were used. Temperature at the thermocouple junctions wit hin the multiplexing unit does not significantly affect the observatio ns. We found the device suitable for monitoring temperatures by thermo couples, and the programming gave us complete flexibility over timing and selection of thermocouples read. The multiplexing capability reduc ed the amount of expensive thermocouple wire needed for sensing at rem ote sites.