ANALOG INTERFACE CIRCUITS FOR PROCESS CONTROLLERS AND PROCESS MONITORS

摘要

An interface circuit (70) for use with process controllers permits analog signals to be input to a process controller through a binary interface (72) of the process controller and permits analog signals to be output from the process controller through the binary interface (72). The input analog signal is converted to a digital sample of N bits (84). A start pulse and the N bits of the digital sample are transmitted to the process controller at a rate selected for compatibility with the scan time of the process controller. The process controller includes a software routine for recognizing the start pulse and the N bits of the digital sample which are transmitted serially with different periods. An equivalent approach is used for outputting analog signals through a binary interface of a process controller. The interface can include multiple channels for inputting or outputting multiple analog signals.