SOLENOID PROTECTION CIRCUIT

• US 20120106019A1
• Filed: 12/02/2010
• Published: 05/03/2012
• Est. Priority Date: 11/01/2010
• Status: Active Grant

• Current Assignee: Zipher Limited
• Original Assignee: Zipher Limited
• Inventors: Buxton, Keith
• Granted Patent: US 8,649,150 B2
• Time in Patent Office: Days
• US Class Current: 361/152
• CPC Class Codes: H01F 7/1877 controlling a plurality of loads

Abstract

A system prevents solenoids from overheating. The solenoid circuit has solenoids connected across a power supply. Control switches energize the solenoids by controllably connecting the solenoids to and from the power source. The protection system includes a master switch connected between the power source and the solenoids for simultaneously connecting and disconnecting all of the solenoids with the power source. A current sensor is positioned between the supply terminal of the power supply and the solenoids for detecting a current flowing between the supply and any of the solenoids and for producing a current-sensed signal. A controller detects abnormalities based on the current-sensed signal and responsively opens the master switch to disconnect all of the solenoids from the power source.

Claims

1. A protection system for a solenoid circuit of the type having a plurality of solenoids connected across a power supply and a plurality of switches for controllably connecting and disconnecting the solenoids to and from the power source, the apparatus comprising;

a master switch connected between the power source and the solenoids for simultaneously connecting and disconnecting all of the solenoids with the power source;

a current sensor positioned between the power source and the solenoids for detecting a current flowing between the power source and any of the solenoids and for producing a current-sensed signal;

a controller configured to detect an abnormality based current-sensed signal and to responsively open the master switch, thereby disconnecting all of the solenoids from the power source.

2. The apparatus of claim 1, wherein the current sensor produces the current-sensed signal in response to the current-sensed exceeding a predetermined threshold.

3. The apparatus of claim 2, wherein the controller detects an abnormality in response to the presence of the current-sensed signal when none of the solenoids are supposed to be active.

4. The apparatus of claim 2, wherein the current sensor comprises:

a resistor connected between the master switch and the solenoids; and

a differential amplifier having its inputs connected across the resistor and an output that produces a signal indicative of the level of current flowing through the resistor.

5. The apparatus of claim 4, further comprising a comparator having a first input connected to the output of the differential amplifier, a second input connected to receive a voltage indicative of the predetermined current threshold, and an output that indicates if the first input signal exceeds this predetermined current threshold.

6. The apparatus of claim 5, further comprising signal conditioning and an amplifier connected between the output of the differential amplifier and the first input of the second comparator.

7. The apparatus of claim 1, further comprising a voltage sensor for detecting a voltage at a location between the master switch and solenoids and producing a voltage-sensed signal in response thereto;

and

wherein the controller is further configured to detect an abnormality based voltage-sensed signal.

8. The apparatus of claim 7, wherein the controller is further configured to open the master switch in response to detecting an abnormality based on the voltage-sensed signal.

9. The apparatus of claim 7, wherein the controller is configured to detect an abnormality in response to the presence of the voltage-sensed signal at a time when the master switch is supposed to be open.

10. The apparatus of claim 7, wherein the controller is configured to detect an abnormality in response to the absence of the voltage-sensed signal at a time when the master switch is supposed to be closed.

11. An apparatus comprising:

a power supply having a supply terminal and a return terminal;

a plurality of solenoids, each solenoid having a coil with respective first and second terminals;

a master switch connected between the supply terminal of power source and the first terminals of the solenoid coil for simultaneously connecting and disconnecting all of the solenoids with the power source supply terminal;

a plurality of solenoid control switches, each switch being connected between the second terminal of a respective one of the solenoid coils and the power source return terminal for controllably connecting and disconnecting a respective solenoid coil with the power source return terminal;

a current sensor that senses current anywhere between the supply terminal of the power supply and the first terminals of the solenoids for detecting a current flowing between the supply terminal of the power source and any of the solenoids and for producing a current-sensed signal;

a controller configured to detect an abnormality based on the current-sensed signal, and to open the master switch in response to the detected abnormality, thereby disconnecting all of the solenoids from the power source.

12. The apparatus of claim 11, wherein the current sensor produces the current-sensed signal in response to the sensed current exceeding a predetermined threshold.

13. The apparatus of claim 12, wherein the controller detects an abnormality in response to the presence of the current-sensed signal when none of the solenoids are supposed to be active.

14. The apparatus of claim 12, wherein the current sensor comprises:

a resistor connected in the circuit anywhere between the supply terminal of the power supply and the first terminals of the solenoid coils; and

a differential amplifier having its inputs connected across the resistor and an output that produces a signal indicative of the level of current flowing through the resistor.

15. The apparatus of claim 14, further comprising a comparator having a first input connected to the output of the differential amplifier, a second input connected to receive a voltage indicative of the predetermined current threshold, and an output that produces a signal indicative of the voltage difference between the first and second inputs.

16. The apparatus of claim 15, further comprising an amplifier connected between the output of the differential amplifier and the first input of the comparator.

17. The apparatus of claim 15, further comprising a voltage sensor for detecting a voltage at any location between the master switch and first terminals of the solenoid coils and producing a voltage-sensed signal in response thereto;

and

wherein the controller is further configured to detect an abnormality based voltage-sensed signal.

18. The apparatus of claim 17, wherein the controller is further configured to open the master switch in response to detecting an abnormality based on the voltage-sensed signal.

19. The apparatus of claim 17, wherein the controller is configured to detect an abnormality in response to the presence of the voltage-sensed signal at a time when the master switch is supposed to be open.

20. The apparatus of claim 17, wherein the controller is configured to detect an abnormality in response to the absence of the voltage-sensed signal at a time when the master switch is supposed to be closed.

21. A method of detecting an abnormality in a circuit of the type comprising a power supply having a supply terminal and a return terminal;

a plurality of solenoids, each solenoid having a first terminal connected to the power source supply terminal and second terminal connected to the power source return terminal through a respective control switch, the method comprising;

detecting an abnormality by sensing for current flowing between the power source and the solenoids at a time when the solenoids are not supposed to be energized; and

disconnecting all of the solenoids from the power source supply terminal when an abnormality is detected.

22. The method of claim 21, further comprising positioning a switch between the power supply source terminal and the first terminals of the solenoids and opening the switch when an abnormality is detected.