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Determination Of Circuit Continuity Beyond A Low Pass Filter

IP.com Disclosure Number: IPCOM000097345D
Original Publication Date: 1962-Oct-01
Included in the Prior Art Database: 2005-Mar-07
Document File: 2 page(s) / 38K

Publishing Venue

IBM

Related People

Mantey, JP: AUTHOR

Abstract

Continuity tests on thermocouples used to monitor processes under automatic control are desirable. Usually, each thermocouple is connected to a group of multiplexing relays 2 by means of a low pass filter 3. Each filter includes a pair of resistors 4 and 5 and a shunt capacitor 6. The relatively long time constant of filter 3 makes it very difficult to automatically measure thermocouple continuity.

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Determination Of Circuit Continuity Beyond A Low Pass Filter

Continuity tests on thermocouples used to monitor processes under automatic control are desirable. Usually, each thermocouple is connected to a group of multiplexing relays 2 by means of a low pass filter 3. Each filter includes a pair of resistors 4 and 5 and a shunt capacitor 6. The relatively long time constant of filter 3 makes it very difficult to automatically measure thermocouple continuity.

Under the control of a continuity tester 7, a reference voltage source 8 is selectively connected to the various thermocouple lines by means of relay 9, scanning control 10 and multiplexing relays 2. After a period of time determined by timer 11, analog to digital converter 12 is connected to the various thermocouple lines to measure the charge remaining on capacitor 6.

Where the thermocouple 1 presents a current path to the voltage across the capacitor 6, the voltage rapidly decays to a low value. In the case where the thermocouple line is open, the voltage across the capacitor 6 remains at a high value since it can discharge only through the leakage resistance of the circuit.

The analog to digital converter 12 is overloaded or recognizes this abnormally high voltage by limit testing to produce an open thermocouple signal at terminal 12 from the continuity tester 7.

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