Browse Prior Art Database

Protection Against Electrostatic Noise

IP.com Disclosure Number: IPCOM000078304D
Original Publication Date: 1972-Dec-01
Included in the Prior Art Database: 2005-Feb-25
Document File: 2 page(s) / 30K

Publishing Venue

IBM

Related People

Breton, LA: AUTHOR [+2]

Abstract

Electrostatic and other extraneous signals of a high-frequency nature can result in erroneous inputs in data handling apparatus. Unwanted signals of this kind can be shunted to ground, if an adequate low-impedance path to machine ground is provided.

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Protection Against Electrostatic Noise

Electrostatic and other extraneous signals of a high-frequency nature can result in erroneous inputs in data handling apparatus. Unwanted signals of this kind can be shunted to ground, if an adequate low-impedance path to machine ground is provided.

In the exploded view, a card punch has a reading board 10 of plastic coated wood, having an aperture 12 in which a keyboard 14 is mounted rotatably. Keyboard 14 has a logic cable 16 connecting to the card punch apparatus of the unit, not shown. Cable 16 has a logic ground conductor, but this does not provide a sufficiently low-impedance path to divert steep wave fronts such as is found in the discharge of an electrostatic spark, for example. Accordingly, if the operator acquires an electrostatic charge and then touches the keyboard unit, it is possible that an erroneous input will be transmitted from the keyboard unit via the logic cable 16 to the card punch.

To prevent this, a low-impedance shunt to ground can be provided by a wide foil band 18 attached to the underside of reading board 10 and extending from the metal legs or other massive portion of the unit, not shown, to the edge of 12, and up through 12, ending in a return portion 20 on the upper surface of 10 at the periphery of 12. Spring electrical brushes 22 make contact from 20 to an electrical ring contact 20, not shown, on the undersurface of keyboard unit. The shunt ground provided by 18, 20, 22, 24 is dimensionally...