| 摘要 |
A control system of the type used in process control and comprising a controller which provides a control signal on a signal line, and a DC output circuit for converting the control signal on the signal line into a DC current output signal varying in a range of, e.g., 4 to 20 milliamperes, which is supplied to a current loop including one or more load devices. The control system is characterized by open circuit detecting means for detecting an open circuit condition in the load current loop by detecting the fall of the DC current output signal below a predetermined minimum value, and shorting means in the DC output circuit for shorting the signal line in response to detection of an open circuit condition. Level detecting means are provided for detecting the shorting of the signal line, and thus an indication of an open-circuited load condition may be supplied back to the controller without requiring added signal carrying lines. |
