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Capacitance Sensor Arc and Contamination Shield

IP.com Disclosure Number: IPCOM000083215D
Original Publication Date: 1975-Apr-01
Included in the Prior Art Database: 2005-Mar-01
Document File: 2 page(s) / 52K

Publishing Venue

IBM

Related People

Carmichael, JM: AUTHOR [+2]

Abstract

This structure protect a sensor from ink contamination and the preamplifier from electrical arcing. Charges on drops in an ink stream are sensed and the height of the deflected ink stream is controlled, using a capacitive-coupled sensor.

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Capacitance Sensor Arc and Contamination Shield

This structure protect a sensor from ink contamination and the preamplifier from electrical arcing. Charges on drops in an ink stream are sensed and the height of the deflected ink stream is controlled, using a capacitive-coupled sensor.

Sensor performance is degraded by the presence of ink. The sensor face (either passivated of unpassivated) when covered with ink which contacts electrical ground. cannot sense the charges on passing ink drops. The ground shield (ink) masks the charged drops from the sensor. The sensor passivation is penetrated and the ink attacks the sensor lands. (corrosion, resistance, leakage, dielectric is changed, etc.)

The sensor field-effect transistor (FET) preamplifier is subjected to electrical discharges (arcs), as a result of the ink stream or other objects contacting the deflection plate or the fog collector, not shown, due to voltage differentials between those components and the charge sensor. The electrical discharge (arc) will damage the preamplifier, necessitating its replacement.

To resolve the enumerated difficulties, an absorbent, conductive windshield is positioned in front of the sensor which is connected to circuit ground, as in Figs. 1 and 2. The stray ink is intercepted prior to impacting the sensor by the porous windshield. The windshield absorbs the stray ink such that it prevents any ink accumulation which could bridge to the sensor. The windshield is constructed of a ma...