# US 4,399,537 A · Control circuit and fuel burner incorporating a control circuit

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- Number: US 4,399,537 A
- Document ID: US4399537A
- Status: Granted
- Kind: A
- Application number: 06/237,765
- Filed: 1981-02-24
- Granted: 1983-08-16
- Earliest claimed: 1980-11-06
- Assignees: British Gas Corporation
- Inventors: Gregory E. Jones
- Web page: https://patentgrep.com/patent/US4399537A

## CPC

- G06F 11/0757: {by exceeding a time limit, i.e. time-out, e.g. watchdogs}
- G06F: ELECTRIC DIGITAL DATA PROCESSING (computer systems based on specific computational models G06N)

## Abstract

A fail-safe supervisory circuit for a microprocessor-controlled fuel burner has a diode pump circuit (C4, C5, D7, D8) triggered by a resettable monostable (R7, T2, R8, C3) responsive to an encoded signal from the microprocessor, to act as a watch-dog timer. A triggered bistable (D1, T1, R2, IC8) provides a RESET signal on power-on or manually. A direct connection from this bistable to the monostable enables the timer circuit until the microprocessor program commences.

## Claims

### Claim 1

A fail-safe supervisory system for a control computer which generates repetitively a set of predetermined signals indicative of computer operation, comprising:
first input means responsive to the set of signals repetitively generated by said computer to produce trigger pulses based thereon;
resettable monostable circuit means responsive to said trigger pulses for producing an alternating signal when the frequency of said trigger pulses is below a first predetermined level; and
diode pump circuit means responsive to said alternating signal for producing an output signal coupled to said computer and allowing the computer to operate when the frequency of the alternating signal is above a second predetermined level lower than said first predetermined level.

### Claim 2

A fail-safe supervisory system for a control computer which generates repetitively a set of predetermined signals indicative of computer operation, comprising:
first input means responsive to the set of signals repetitively generated by the computer to produce trigger pulses based thereon;
resettable monostable circuit means responsive to said trigger pulses for producing an alternating signal when the frequency of the trigger pulses is below a first predetermined level;
diode pump circuit means responsive to said alternating signal for producing an output signal coupled to said computer and allowing the computer to operate when the frequency of the alternating signal is above a second predetermined level which is lower than said first predetermined level; and
bistable circuit means connected to a power supply for said computer to produce an output signal in response to a drop in power supply voltage, said output signal of said bistable circuit means activating a reset of the computer.

### Claim 3 (depends on 2)

A supervisory system as claimed in claim 2, wherein said bistable circuit means has a predetermined input trigger level that produces said output signal when the output signal of the power supply voltage drops below said predetermined input trigger level of said bistable circuit.

### Claim 4 (depends on 3)

A supervisory system as claimed in claim 3, wherein said bistable circuit means comprises:
means for producing an additional input signal equivalent to the output signal of the power supply falling to a predetermined level in order to test the operability of the bistable circuit means, said additional input signal coupled to said resettable monostable circuit means and being factored into the production of said alternating signal.

### Claim 5 (depends on 2)

A supervisory system as claimed in claim 2, wherein said bistable circuit means is connected to said resettable monostable circuit means to reactivate said monostable circuit means when the power supply voltage returns to a predetermined operational level.