Title:
【発明の名称】ループ過電流回路付きプロセス制御機器
Document Type and Number:
Japanese Patent JP3222886
Kind Code:
B2
Abstract:
A process control instrument receives a DC current from a two wire loop and has overcurrent protection and reverse current protection circuits which pass a portion of the DC current as a device current to a process controlling device. The overcurrent protection circuit includes a current sensing circuit which conducts the device current and generates an output indicative of device current. The overcurrent protection circuit also includes a current diverting circuit coupled across the two wire loop and responsive to the sensor output for diverting loop current in excess of a predetermined upper limit of device current back to the loop when the sensor output indicates the upper limit is reached. The reverse current protection circuit is coupled across the loop and includes a variable impedance which conducts the device current. The variable impedance inhibits the device current from flowing through the device when a loop potential is reversed from a predetermined polarity. Thus, the device current is limited to a current range controlled by the variable impedance and the upper limit.
Inventors:
Robner, Bruce Dee.
Application Number:
JP51336191A
Publication Date:
October 29, 2001
Filing Date:
July 19, 1991
Export Citation:
Assignee:
Rosemount Incorporated
International Classes:
H02H3/08; H02H3/087; H02H9/02; H02H11/00; H02H9/00; (IPC1-7): H02H9/02; H02H3/08; H02H3/087; H02H11/00
Other References:
【文献】米国特許3582713(US,A)
【文献】米国特許4857985(US,A)
【文献】米国特許4481967(US,A)
【文献】西独国特許出願公開3313051(DE,A1)
【文献】米国特許4857985(US,A)
【文献】米国特許4481967(US,A)
【文献】西独国特許出願公開3313051(DE,A1)
Attorney, Agent or Firm:
Michito Hiraki (1 person outside)