Communications: electrical – Condition responsive indicating system – Specific condition
Patent
1993-04-14
1994-12-27
Hofsass, Jeffery A.
Communications: electrical
Condition responsive indicating system
Specific condition
340635, 324133, G08B 2100
Patent
active
053769201
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to power fail detection circuits for use with electrically powered apparatus of a kind which have a local switch, which ON/OFF controls the power supplied to the apparatus.
BACKGROUND OF THE INVENTION
In many situations electrically powered apparatus fulfill important and vital functions and that they operate continuously over predefined time periods is crucial. The time period which the apparatus is required to operate is generally controlled manually by an ON/OFF switch situated on or near the apparatus. However, on occasions, premature interruptions to the power supply may occur for many and various reasons including, for example, a disconnection in the power supply leads from the power source to the apparatus. Such interruptions may be extremely serious, particularly if a person's life depends on the continuous operation of the apparatus.
Accordingly, prior art systems provide a power fail detection circuit which enables an alarm each time a power fail is detected. The power fail is enabled each time the apparatus is switched off and so must be switched off at the same time.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an improved power fail detection system which is small, simple and cheap to make, and easy to install.
The invention provides a power fail detection circuit in electrically powered apparatus, comprising a power switch for the apparatus and power detection means responsive to the absence of electrical power from the power switch to provide a power fail indication, wherein the power switch has at least one double throw pole, switchable between power-ON and power-OFF terminals, and the circuit includes switch position detection means connected to the power-OFF terminal and responsive to the power switch being in the power-OFF position to disable the power fail indication.
Accordingly, the invention provides a means of detecting a power failure at the apparatus so that a signal is only produced in response to an event whereby the apparatus ceases to operate other than by way of ON/OFF controlling the switch.
In a preferred embodiment, the switch has two double throw poles switchable between power-ON and power-OFF terminals, and the switch position detection means is connected to both the power-OFF terminals, so that the detection circuit is dissociated from the power supply when the switch is on. Thus, when power is supplied the detection circuit is advantageously isolated from the power supply by the switch, enabling the power supply to operate as normal. The detection circuit then detects an open circuit at the switch. When the power supply is a mains power supply, this embodiment advantageously allows switching of both live and neutral power lanes, which is required by certain regulatory bodies in some cases of mains powered medical equipment.
In a preferred embodiment, the or each pole is connected directly to the apparatus and the or each power-ON terminal is arranged for connection to the power supply. Advantageously the switch position detection means is isolated from the power supply when the switch is in the power-OFF position.
Preferably, the detection circuit is responsive to a current path connected between the power-OFF terminals when the switch is in the power-OFF position. This current path may be provided, for example, by the primary winding of a transformer at the power input side of the apparatus. In one embodiment of the present invention the switch detection means includes a source of direct current for detecting a resistive path connected between the power-OFF terminals when the switch is in the power-OFF position. Alternatively, the switch position detection means includes a source of alternating current for detecting a resistive or reactive path connected between the power-OFF terminals when the switch is in the power-OFF position.
Also according to the present invention, there is provided a power switch in electrically powered apparatus comprising at least one double throw pole switch
REFERENCES:
patent: 3201650 (1965-08-01), Schultz
patent: 4530027 (1985-07-01), Berger
patent: 4575718 (1986-03-01), Ludowyk
patent: 4777479 (1988-10-01), Hinckley
patent: 4823021 (1989-04-01), Shimada et al.
Hofsass Jeffery A.
Huntleigh Technology PLC
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