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# Detector Circuit for Continuity and Shorts Testing

IP.com Disclosure Number: IPCOM000074332D
Original Publication Date: 1971-Apr-01
Included in the Prior Art Database: 2005-Feb-23
Document File: 2 page(s) / 49K

IBM

## Related People

Malin, JR: AUTHOR

## Abstract

Testing for shorts, continuity and resistances in cables is simplified by this circuit in which the output of a DC bridge varies according to the input from the circuit under test. This output is compared with reference voltages in a plurality of comparators and they, by means of an Exclusive OR provides an indication of the condition of the circuit under test.

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Detector Circuit for Continuity and Shorts Testing

Testing for shorts, continuity and resistances in cables is simplified by this circuit in which the output of a DC bridge varies according to the input from the circuit under test. This output is compared with reference voltages in a plurality of comparators and they, by means of an Exclusive OR provides an indication of the condition of the circuit under test.

As shown the circuit includes a voltage regulator 1 for supplying a positive voltage to an unbalanced bridge composed of resistors R1, R2, R3, and R4. The resistor values are such that the voltage at sensing point A with nothing connected to it is 80% of the supply voltage. The voltage at sensing point B under the same conditions is at 40% of the supply voltage. When continuity exists between points A and B, due to an unbroken cable the voltage level at point A will drop to 56% of the input voltage. Point B will rise to 56% of the input voltage. If a 90 ohm terminating resistor is present at either level, the voltage level at point A will drop to 27% of the input voltage without continuity, and only 31% if continuity is present. Likewise, point B also exhibits similar stratification of voltage levels. A complete list of voltages is shown in Table 1. TABLE 1

Sensing Point A Sensing Point B % of supply voltage % of supply voltage
80.2% open circuit 56.4% continuity to point A
56.4% continuity to point B 40% open circuit
31.4% continuity + one 31.4% continuit...