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Diagnostic Current Sourcing and Sinking Meter for Testing Digital Electronic Cards and Boards

IP.com Disclosure Number: IPCOM000043579D
Original Publication Date: 1984-Sep-01
Included in the Prior Art Database: 2005-Feb-05
Document File: 4 page(s) / 39K

Publishing Venue

IBM

Related People

Kranz, RH: AUTHOR

Abstract

This article describes a diagnostic current sourcing and sinking meter for testing digital electronic cards and boards. It allows easy diagnosing of errors on common bus structured networks and printed circuit lands (NET) which are often found in active digital electronic cards, boards and systems. It provides accurate determination of bus/NET problems, saves considerable time over other methods, and reduces the number of cards that have to be scrapped. Having a meter that tells a tester, engineer or technician which node or element on a bus/NET is sinking or sourcing the current is often necessary when trying to determine why that bus/NET is not functioning properly at a certain point in time.

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Diagnostic Current Sourcing and Sinking Meter for Testing Digital Electronic Cards and Boards

This article describes a diagnostic current sourcing and sinking meter for testing digital electronic cards and boards. It allows easy diagnosing of errors on common bus structured networks and printed circuit lands (NET) which are often found in active digital electronic cards, boards and systems. It provides accurate determination of bus/NET problems, saves considerable time over other methods, and reduces the number of cards that have to be scrapped. Having a meter that tells a tester, engineer or technician which node or element on a bus/NET is sinking or sourcing the current is often necessary when trying to determine why that bus/NET is not functioning properly at a certain point in time. Anytime two or more components are electrically connected, determining which component is erringly sinking or sourcing the current is a task which is very difficult. Since the sinking and sourcing components on a bus/NET are or may be constantly changing within the flow of data, it is very useful to have a meter which can be synchronized to the operation that can determine the active source or sink on the bus/NET at a specific time. The diagnostic meter disclosed herein is illustrated in Fig. 1. It employs the use of a one-point probe. Each node on the bus/NET is measured for voltage. In the case of a negative active net the node on the net with the highest measurement is the source of the current and the node with the lowest reading is the node sinking most of the current. The meter is triggered by some outside special condition which indicates the bus/NET is in error.

The meter is made of three simple parts: a DC voltmeter 1 with resolution to microvolts, a triggered sensor 2, and a constant current source 3. Upon receiving a triggered condition from trigger sensor 2, constant current source 3 is activated, thereby injecting a small current into the card being tested while, at a slightly later time, activating voltmeter 1 to precisely measure the voltage. The unique concept of this meter is this special small current injection, forcing a small voltage drop across the card's printed circuit land pattern and enabling the meter to detect the voltage difference at the different nodes on that bus/NET, thus determining the sinking or sourcing element on the bus/NET. It uses the small resistance of the printed circuit land pattern to develop this voltage drop. The meter can be used with either a plus or minus active logic state. If minus active is the condition being measured, then a plus constant current is injected and the lowest voltage reading is the sinking component.

If plus active is the condition being measured, then a minus constant current is injected and the highest voltage reading is the sourcing component. The operation of the meter is described using the NET configurations of Figs. 2 and 3. It will be assumed that printed circuit lands typ...