Controlled DC current supply device with open circuit detecting means
First Claim
1. In a control system of the type comprising controller means for providing a control signal on a signal line, and DC output means for converting the control signal on the signal line into a DC current output signal for supply to a current loop including one or more load devices, the improvement which comprises:
- open-circuit detecting means for detecting an open circuit condition in the load current loop;
shorting means in the DC output means for shorting the signal line in response to detection of an open-circuit by the open circuit detecting means; and
level detecting means for detecting the shorting of the signal line;
whereby an indication of an open-circuited load condition may be supplied back to the controller means without use of an added signal carrying line.
2 Assignments
0 Petitions
Accused Products
Abstract
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.
-
Citations
5 Claims
-
1. In a control system of the type comprising controller means for providing a control signal on a signal line, and DC output means for converting the control signal on the signal line into a DC current output signal for supply to a current loop including one or more load devices, the improvement which comprises:
-
open-circuit detecting means for detecting an open circuit condition in the load current loop; shorting means in the DC output means for shorting the signal line in response to detection of an open-circuit by the open circuit detecting means; and level detecting means for detecting the shorting of the signal line; whereby an indication of an open-circuited load condition may be supplied back to the controller means without use of an added signal carrying line. - View Dependent Claims (2, 3, 4, 5)
-
Specification