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Automatic Diagnostic Method of a Multiplexed Analog Input System

IP.com Disclosure Number: IPCOM000082078D
Original Publication Date: 1974-Oct-01
Included in the Prior Art Database: 2005-Feb-28
Document File: 3 page(s) / 55K

Publishing Venue

IBM

Related People

Boinodiris, S: AUTHOR

Abstract

Vital sections of the analog input system for a computer are automatically analyzed online, through diagnostic routines set by software at desired intervals. The diagnostic software routines switch diagnostic switching hardware 10 in addition to controlling multiplexer 11 switching. The switching follows a pattern which determines whether the amplifier or the analog-to-digital converter (ADC) 12 is faulty, or a point or group switch is faulty. The ADC 12 at the same time performs a series of conversions giving indication of the potential read at input point 15. This potential changes by injection of various potentials through the combination of switching the multiplexer 11 and the diagnostic switching hardware 10.

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Automatic Diagnostic Method of a Multiplexed Analog Input System

Vital sections of the analog input system for a computer are automatically analyzed online, through diagnostic routines set by software at desired intervals. The diagnostic software routines switch diagnostic switching hardware 10 in addition to controlling multiplexer 11 switching. The switching follows a pattern which determines whether the amplifier or the analog-to-digital converter (ADC) 12 is faulty, or a point or group switch is faulty. The ADC 12 at the same time performs a series of conversions giving indication of the potential read at input point 15. This potential changes by injection of various potentials through the combination of switching the multiplexer 11 and the diagnostic switching hardware 10.

The diagnostic method described can be used for single-ended as well as for differential input systems. The method can be used for solid-state as well as relay switching and direct input or flying capacitor input. For simplicity, the single-ended case is described where i is a point switch indication from 1 to n and j is a group switch indication from 1 to m. Sij, therefore, is the point switch of the i point in the j group while Sj is the group switch of the j group.

The commands from CPU 30 to sensor controls 31 and diagnostic controls 32 are Diagnostic Zero Convert, Diagnostic Half-Scale Convert, Diagnostic Overload Convert with Group Switch Short Detect, Diagnostic Overload Convert with Point Switch Short Detect, and Diagnostic Unknown Convert with Source Impedance Detect.

In the circuit, resistors 21 and 22 are both of resistance value approximately equal (Rb) and equal to some value Rx. The RxCs time constant is much smaller than tm, where tm is the margin time from the time the switches are activated until the conversion actually starts. Cs is a stray multiplexer bus capacitance as shown in dotted lines. Vb is a voltage source of potential Vb = Vfs + V, where Vfs is the maximum input voltage that can be placed into the input of ADC 12 without causing a sensed overflow reading. V is a margin potential much smaller than Vfs. Vfs + V is a potential that causes an overflow when connected into the input...