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Dual Push-Button Safety Start Circuit

IP.com Disclosure Number: IPCOM000037426D
Original Publication Date: 1989-Jan-01
Included in the Prior Art Database: 2005-Jan-29
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Barnhart, SR: AUTHOR [+2]

Abstract

This arrangement provides an improved cycle start circuit of the type using dual push buttons.

This text was extracted from a PDF file.
This is the abbreviated version, containing approximately 64% of the total text.

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Dual Push-Button Safety Start Circuit

This arrangement provides an improved cycle start circuit of the type using dual push buttons.

It is well known to provide safety operating controls for machinery using dual push buttons which must be operated simultaneously to initiate the operating cycle of the machine and thus ensure that the operators' both hands will be clear of the machine before it can operate. Such a safety provision is sometimes negated by the operator by taping or otherwise holding one of the push buttons in its operated state.

The circuit arrangement shown in the figure uses a retriggerable monostable multivibrator 4 basically controlled by two push buttons S1 and S2 to provide the desired results.

The two manually operated push buttons S1 and S2 are connected to the positive source of energy through respective pull up resistors 2. The push buttons S1 and S2 will ground these connections when operated. Thus, the inputs to the nand circuit 7, are normally at the positive voltage level as well as the inputs to the OR circuit 9. The output of NAND circuit 7 is supplied to the one input of the retriggerable monostable multivibrator 4. The timing of this multivibrator is set by the combination of the resistor RE and capacitor CE. A resetting circuit for the retriggerable multivibrator 4 is provided over the line RD, which extends from a junction of a pull up resistor 2' to a capacitor CP, and a switch SW. Normally the line RD is at the positive level bu...