SEVEN STATE RESISTANCE SENSING SUPERVISORY SYSTEM

• US 3,702,474 A
• Filed: 08/27/1971
• Issued: 11/07/1972
• Est. Priority Date: 08/27/1971
• Status: Expired due to Term

• Current Assignee: Systems Research Laboratories Incorporated
• Original Assignee: William C. Fink, William R. Stewart
• Inventors: Fink, William C., Stewart, William R.
• Primary Examiner(s): Trafton, David L.
• Application Number:
  US05/175,572
• Time in Patent Office: 438 Days
• Field of Search: 340/409,412,177R,177VA,182,188R,188CH,161,172
• US Class Current: 340/510
• CPC Class Codes: G08C 19/025 using fixed values of magnitude of current or voltage
• CPC Class Codes: H03M 11/24 using analogue means , e.g. by coding the states of multiple switches into a single multi-level analogue signal or by indicating the type of a device using the voltage level at a specific tap of a resistive divider

Abstract

A supervisory circuit is located at a remote station which is to be monitored from a central station. The supervisory circuit includes first and second sensing switches each operable between an opened position and a closed position. In addition, the supervisory circuit includes first, second and third sensing resistors interconnected with the first and second sensing switches. A pair of sensing conductors connects the supervisory circuit from the remote station to the central station where a signal resistance is presented between the sensing conductors. The signal resistance indicates the state of the supervisory circuit by assuming one of seven different values each corresponding to a different one of seven possible states of the supervisory circuit.

Claims

1. A supervisory system for monitoring a remote station from a central station located away from the remote station, comprising:

a supervisory circuit located at the remote station, the supervisory circuit including first and second switching devices each operable between an opened position and a closed position, the first switching device connected between a first output terminal and a first internal terminal, the second switching device connected between a second output terminal and a second internal terminal, a first resistance device connected between the first output terminal and the second internal terminal, a second resistance device connected between the second output terminal and the first internal terminal, and a third resistance device connected between the first and second internal terminals;

a pair of conductors each connected to a different one of the first and second output terminals and each extending to the central station for providing a signal resistance between the conductors at the central station, the signal resistance assuming one of seven different resistance values each corresponding to a different one of seven possible states which may exist in each of the supervisory circuits as defined when both the first and second switching devices are in the opened position, when both the first and second switching devices are in the closed position, when the first switching device is in the opened position and the second switching device is in the closed position, when the first switching device is in the closed position and the second switching device is in the opened position, when one of the conductors is grounded, when one of the conductors is open circuited, and when the conductors are short circuited together; and

means located at the central station and connected to the pair of conductors for indicating the state of the supervisory circuit in response to the value of the signal resistance.

2. A supervisory system for monitoring a plurality of remote stations from a central station located away from the remote stations, comprising:

a plurality of supervisory circuits each located at a different associated one of the remote stations, the supervisory circuits each including first and second sensing switches each operable between an opened position and a closed position, the first sensing switch connected between a first output terminal and a first internal terminal, the second sensing switch connected between a second output terminal and a second internal terminal, a first sensing resistor connected between the first output terminal and the second internal terminal, a second sensing resistor connected between the second output terminal and the first internal terminal, and a third sensing resistor connected between the first and second internal terminals;

a plurality of monitoring circuits each located at the central station, the monitoring circuits each including a voltage divider network having at least first and second detecting resistors;

a plurality of different pairs of sensing conductors each connecting the first and second output terminals of a different associated one of the supervisory circuits across the first detecting resistor of a different associated one of the monitoring circuits thereby to establish a signal voltage across the second detecting resistor, the signal voltage assuming one of seven different voltage levels each corresponding to a different one of seven possible states which may exist in each of the supervisory circuits as defined when both the first and second sensing switches are in the closed position, when both the first and second sensing switches are in the opened position, when the first sensing switch is in the closed position and the second sensing switch is in the opened position, when the first sensing switch is in the opened position and the second sensing switch is in the closed position, when one of the sensing conductors is grounded, when one of the sensing conductors is open circuited, and when the sensing conductors are short circuited together; and

a control circuit located at the central station and connected to each of the monitoring circuits for indicating the state of each of the supervisory circuits located at the remote stations in response to the level of the signal voltage provided by each of the monitoring circuits. 3. A supervisory system for monitoring a plurality of remote stations from a central station located away from the remote stations, comprising;

a plurality of supervisory circuits each located at a different associated one of the remote stations, the supervisory circuits each including first and second sensing switches each operable between an opened position and a closed position, the first sensing switch connected between a first output terminal and a first internal terminal, the second sensing switch connected between a second output terminal and a second internal terminal, a first sensing resistor connected between the first output terminal and the second internal terminal, a second sensing resistor connected between the second output terminal and the first internal terminal, and a third sensing resistor connected between the first and second internal terminals;

a plurality of monitoring circuits each located at the central station, the monitoring circuits each including a voltage divider network having at least first and second detecting resistors;

a plurality of different pairs of sensing conductors each connecting the first and second output terminals of a different associated one of the supervisory circuits across the first detecting resistor of a different associated one of the monitoring circuits thereby to establish a signal voltage across the second detecting resistor, the signal voltage having a first level when one of the sensing conductors is grounded, a second greater level when one of the sensing conductors is open circuited, a third greater level when both the first and second sensing switches are in the closed position, a fourth greater level when one of the first and second sensing switches is in the closed position and the other of the first and second sensing switches is in the opened position, a fifth greater level when the other of the first and second sensing switches is in the closed position and the one of the first and second sensing switches is in the opened position, a sixth greater level when both the first and second sensing switches are in the closed position, and a seventh greater level when the sensing conductors are short circuited together, and a plurality of gates each connected with the first detecting resistor in a different associated one of the monitoring circuits for passing the signal voltage when activated; and

a control circuit located at the central station, the control circuit including generator means for producing a reference voltage having a unidirectionally varying level when energized, address means connected to each of the gates in the monitoring circuits and to the generator means for successively activating each of the gates and simultaneously energizing the generator means, comparator means connected to each of the gates in the monitoring circuits and connected to the generator means for producing an output signal when the level of the reference voltage exceeds the level of the signal voltage, and indicator means connected to the comparator means and to the generator means for sensing and recording the level of the reference voltage in response to the occurrence of an output signal thereby to successively indicate the state of each of the supervisory circuits located at the remote stations.