pluggable input and output modules provide a low cost, versatile method for interconnecting real world analog and digital signals to data acquisition, monitoring, or control systems. All modules provide an optically isolated barrier between sensitive microprocessors or digital logic circuits and field power devices. Grayhill I/O modules are hard potted with thermally conductive epoxy to withstand harsh industrial environments. These input and output modules provide immunity to mechanical shock and vibration. Also, they operate over a wide range of temperatures.