Seven-state resistance sensing supervisory system utilizing single pole-double throw switches

Claim 2

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 having a common terminal and first and second switching terminals, and each operable between a first position in which the common terminal is connected to the first switching terminal and a second position in which the common terminal is connected to the second switching terminal, a first resistance device connected between the first switching terminal of the first switching device and the first switching terminal of the second switching device, a second resistance device connected between the first switching terminal of the second switching device and the second switching terminal of the first switching device, and a third resistance device connected between the second switching terminal of the first switching device and the second switching terminal of the second switching device; a pair of conductors each connected to a different one of the common terminals of the first and second switching devices 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 defined when both the first and second switching devices are in the first position, when both the first and second switching devices are in the second position, when the first switching device is in the first position and the second switching device is in the second position, when the first switching device is in the second position and the second switching device is in the first 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.

Claim 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 having a common terminal and first and second switching terminals and each operable between a first position in which the common terminal is connected to the first switching terminal and a second position in which the common terminal is connected to the second switching terminal, a first sensing resistor connected between the first switching terminal of the first sensing switch and the first switching terminal of the second sensing switch, a second sensing resistor connected between the first switching terminal of the second sensing switch and the second switching terminal of the first sensing switch, and a third sensing resistor connected between the second switching terminal of the first sensing switch and the second switching terminal of the second sensing switch; 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 common terminals of the first and second sensing switches in a different 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 first position, when both the first and second sensing switches are in the second position, when the first sensing switch is in the first position and the second sensing switch is in the second position, when the first sensing switch is in the second position and the second sensing switch is in the first 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.

Claim 4

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 having a common terminal and first and second switching terminals and each operable between a first position in which the common terminal is connected to the first switching terminal and a second position in which the common terminal is connected to the second switching terminal, a first sensing resistor connected between the first switching terminal of the first sensing switch and the first switching terminal of the second sensing switch, a second sensing resistor connected between the first switching terminal of the second sensing switch and the second switching terminal of the first sensing switch, and a third sensing resistor connected between the second switching terminal of the first sensing switch and the second switching terminal of the second sensing switch; 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 common terminals of the first and second sensing switches in a different 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 first position, when both the first and second sensing switches are in the second position, when the first sensing switch is in the first position and the second sensing switch is in the second position, when the first sensing switch is in the second position and the second sensing switch is in the first 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.

Claim 5

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 one of the remote stations, the supervisory circuits each including first and second sensing switches each having a common terminal and first and second switching terminals and each operable between a first position in which the common terminal is connected to the first switching terminal and a second position in which the common terminal is connected to the second switching terminal, a first sensing resistor connected between the first switching terminal of the first sensing switch and the first switching terminal of the second sensing switch, a second sensing resistor connected between the first switching terminal of the second sensing switch and the second switching terminal of the first sensing switch, and a third sensing resistor connected between the second switching terminal of the first sensing switch and the second switching terminal of the second sensing switch; 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 common terminals of the first and second sensing switches in 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 first position, a fourth greater level when the first sensing switch is in the second position and the second sensing switch is in the first position, a fifth greater level when both the first and second sensing switches are in the second position, a sixth greater level when the first sensing switch is in the first position and the second sensing switch is in the second position, and a seventh greater level when the sensing conductors are short circuited together, 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 input 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.

Claim 6

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 one of the remote stations, the supervisory circuits each including first and second sensing switches each having a common terminal and first and second switching terminals and each operable between a first position in which the common terminal is connected to the first switching terminal and a second position in which the common terminal is connected to the second switching terminal, a first sensing resistor connected between the first switching terminal of the first sensing switch and the first switching terminal of the second sensing switch, a second sensing resistor connected between the first switching terminal of the second sensing switch and the second switching terminal of the first sensing switch, and a third sensing resistor connected between the second switching terminal of the first sensing switch and the second switching terminal of the second sensing switch; 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 common terminals of the first and second sensing switches in 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 first position, a fourth greater level when the first sensing switch is in the second position and the second sensing switch is in the first position, a fifth greater level when both the first and second sensing switches are in the second position, a sixth greater level when the first sensing switch is in the first position and the second sensing switch is in the second position, and a seventh greater level when the sensing conductors are short circuited together, 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 input 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.