Gating circuit

Details Gating circuit Gating circuit

1975-09-12

1977-05-10

Moose, Harry

Electricity: electrical systems and devices

Control circuits for electromagnetic devices

For relays or solenoids

361170, H01H 4732

Patent

active

040230775

ABSTRACT:
A current sensor provides a positive voltage when a non-desired condition is present, such as rotation of machinery above a predetermined speed, and a gating circuit causes contacts of a relay to close whenever the rotational speed drops below such predetermined speed, that is when the desired condition is achieved. The gating circuit also closes these relay contacts in response to failure of the electrical power to such gating circuit. The circuit includes a P-N-P transistor in series with the relay coil, which transistor is switched on or off by a NAND gate. A low level signal to the base of the P-N-P transistor is provided through the NAND gate when the inputs to the gate are high, thereby providing a fail-safe feature for the relay because one of the NAND gate inputs is provided from the sensor's reference voltage through a Schmitt-trigger circuit. Another NAND gate input is provided in pulse form through an amplification stage, and through another Schmitt-trigger circuit, to a retriggerable monostable integrated circuit chip. This input is also fail-safe in that any electrical interference on the input side of the MOS chip and Schmitt-trigger circuits will cause a low level output from the NAND gate, switching the relay contacts open, or off.

REFERENCES:
patent: 3564366 (1971-02-01), Worrell
patent: 3800139 (1974-03-01), Clark
patent: 3899716 (1975-08-01), Kaminski

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