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Drift Indicator

IP.com Disclosure Number: IPCOM000075135D
Original Publication Date: 1971-Aug-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 2 page(s) / 22K

Publishing Venue

IBM

Related People

Frankeny, RF: AUTHOR

Abstract

Drift of a circuit from predetermined conditions is visually indicated. The input is connected to a circuit to be tested and resistor R1 is adjusted to turn both light-emitting diodes LED out. Voltage drift in the monitored circuit causes one of the LED's, depending on drift polarity, to light.

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Drift Indicator

Drift of a circuit from predetermined conditions is visually indicated. The input is connected to a circuit to be tested and resistor R1 is adjusted to turn both light- emitting diodes LED out. Voltage drift in the monitored circuit causes one of the LED's, depending on drift polarity, to light.

The LED's, operational amplifier A1, and emitter followers Q1 and Q2 form a closed loop circulating a current responsive to the value of R1 and input voltage Vin. Operational amplifier A1 is connected as a positive voltage follower with gain. Q1 and Q2 are complementary emitter followers used in the feedback loop as current drivers. Resistors R2, R3, R4 are current limiting resistors and R1 is the resistor that establishes the sensitivity of indicating diodes D1 and D2.

If the input is zero volts, the amplifier "servo's" to keep the difference between its input terminals 1 and 2 at zero volts, which means I=0 or both lights out. As soon as the input differs from zero Vin=Vt, the amplifier "servo's" to bring terminal 1 to the same potential, thus causing current Vt/R to flow through diode D1. The LED units give off light proportional to the current through them. At small currents, the light glows dimly and at high currents, fairly brightly. By observing the light brightness, zero input voltage can be set or indicated. R1 determines the amount of deviation from zero which will cause visible illumination from the diodes. If Vin goes negative, diode D2 will li...