Communications: electrical – Condition responsive indicating system – Specific condition
Patent
1998-05-21
2000-06-13
Lieu, Julie
Communications: electrical
Condition responsive indicating system
Specific condition
340660, 340661, 340664, 324133, 324555, 324556, G08B 2100
Patent
active
060754486
ABSTRACT:
This invention solves the problem of differentiating between a short-circuit and a low resistance value. A multi-tester impresses voltage across an LED circuit in inverse correspondence with the resistance of a subject circuit. A low-resistance voltage divider, including a circuit under test having an unknown resistance R.sub.X as a first shoulder or voltage portion, causes a threshold voltage to be impressed across the LED, thereby causing the LED to emit light for circuit resistance values at or below a maximum detectable resistance R.sub.X1. Shorts are detected by switching a shunt resister defining a second shoulder or voltage portion into parallel relationship with the LED circuit. The shunt resister has a low resistance which decreases the sensitivity of the LED to such a point that the threshold voltage is impressed across the LED for a circuit resistance R.sub.X2 of near zero amount. When the shunt resister is switched into operation, the LED emits light if, and only if, there is a short in the subject circuit. In another embodiment, the multi-tester impresses a voltage across an LED circuit in correspondence with the resistance of a subject circuit. The LED circuit is connected in parallel with a battery. The subject electrical circuit having an unknown resistance R.sub.X shunts the LED circuit. For values of R.sub.X below a minimum amount, the LED does not emit light. For values of R.sub.X up to about a maximum detectable resistance, the LED emits light of greater intensity.
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Kosow, "Overvoltage and Undervoltage Protection," Electric Machinery and Control, 1964, pp. 480-481.
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