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A Diagnostic to Validate Wetting Current and Measure Switch Contact Resistance Degradation

IP.com Disclosure Number: IPCOM000236442D
Publication Date: 2014-Apr-25
Document File: 4 page(s) / 89K

Publishing Venue

The IP.com Prior Art Database

Abstract

Automotive vehicles and industrial applications employ numerous switches of various types. Even though today’s switch detection systems apply a wetting current to burn off contact oxide, excessive contact resistance can still produce false detections. A methodology, using the existing features in a switch detection system, to validate the wetting current actually flows and to measure changes in contact resistance thereby providing the ability to monitor system health and develop a preventative maintenance schedule is presented.

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Title: A Diagnostic to Validate Wetting Current and Measure Switch Contact Resistance Degradation

Abstract: Automotive vehicles and industrial applications employ numerous switches of various types.  Even though today’s switch detection systems apply a wetting current to burn off contact oxide, excessive contact resistance can still produce false detections.   A methodology, using the existing features in a switch detection system, to validate the wetting current actually flows and to measure changes in contact resistance thereby providing the ability to monitor system health and develop a preventative maintenance schedule is presented.

A Diagnostic to Validate Wetting Current and Measure Switch Contact Resistance Degradation

Unlike the simple powered switches and relays (figure 1) used in cars 30 years ago, today’s systems of automotive vehicles, industrial and automated applications, employ unpowered switches whose state must be detected. 

             

          Figure 1 Powered switch                                    Figure 2 System for operating windows

The switch is part of a control loop (figure 2) consisting of an unpowered switch, a switch detection circuit, a master controller and an output device.  Switch detection is comprised of two (2) separate elements, an applied current and a voltage measurement, performing three (3) operations: a forcing function to establish the voltage to be measured, a wetting current to burn off oxidation on the switch contacts and the detection of the switch state.  Integrated circuit (IC) implementations of switch detection may also require an external ESD capacitor and a series...