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Bridge Reading Circuit

IP.com Disclosure Number: IPCOM000095667D
Original Publication Date: 1964-May-01
Included in the Prior Art Database: 2005-Mar-07
Document File: 2 page(s) / 30K

Publishing Venue

IBM

Related People

Abramson, P: AUTHOR [+3]

Abstract

The bridge circuit is for determining when the value of a resistance RX drops below a predetermined threshold.

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Bridge Reading Circuit

The bridge circuit is for determining when the value of a resistance RX drops below a predetermined threshold.

Resistor RX forms one leg of a resistance bridge. The other legs are resistors R1, R2 and R3. The bridge is calibrated by use of variable resistor R4. The center tap of R4 is connected to the emitter of NPN transistor 10. The bridge junction between R1 and RX is connected to the base of transistor 10. The emitter of transistor 10 is connected to the base of PNP transistor 12. The bridge junction between R1 and R3 is connected to ground. An input pulse applied to the circuit is applied through line 14 to the emitter of transistor 12 and to the junction of the bridge between R2 and RX. The collector of transistor 12 is connected to output line 16.

In operation, the bridge is sampled by applying a positive pulse to line 14. If the value of RX is above the predetermined threshold, the voltage drop in RX is sufficient to prevent transistor 10 from becoming conductive. Transistor 12, therefore, remains cut off, preventing an output signal from appearing on line 16. If, however, the value of RX is below the predetermined threshold when a pulse is applied to line 14, the potential drop across RX is less than the potential drop across R2 and R4. Transistor 10 becomes conductive, causing a potential which is more negative than the input pulse to be applied to the base of transistor 12. This causes transistor 12 to likewise be conductive, all...