Resistance measuring arrangement
First Claim
1. The method of measuring the resistance of an unknown resistor which comprises the steps of measuring the voltage VR across a known resistor when said known resistor is connected to a source of voltage, measuring the voltage V'"'"'R across said known resistor when said known resistor is connected in series with an unknown resistor to said source of voltage, computing the quantity (VR/V'"'"'R)-1, and developing an output signal proportional to said computed quantity which corresponds to the resistance value of said unknown resistor.
1 Assignment
0 Petitions
Accused Products
Abstract
The invention employs a pair of known resistors which are permanently connected to the input terminals to which the unknown resistor may be connected. A source of d.c. voltage is connected to one input terminal and the voltage drops produced across each known resistor are alternately sampled and supplied to an A/D converter which converts these voltage drops into corresponding digital signals. A microprocessor computes the quantity VR1/VR2-1 where VR1 is the voltage drop across one known resistor and VR2 is the voltage drop across the other known resistor. The computed quantity is a linear function of the value of the unknown resistance. This computed quantity may then be converted to a corresponding analog signal and supplied to a meter. Since no switches are connected across the unknown resistor, leakage problems normally associated with extremely high resistance measurements are virtually eliminated and very high resistances in the order of 5000-10,000 megohms may be accurately measured and displayed.
290 Citations
39 Claims
- 1. The method of measuring the resistance of an unknown resistor which comprises the steps of measuring the voltage VR across a known resistor when said known resistor is connected to a source of voltage, measuring the voltage V'"'"'R across said known resistor when said known resistor is connected in series with an unknown resistor to said source of voltage, computing the quantity (VR/V'"'"'R)-1, and developing an output signal proportional to said computed quantity which corresponds to the resistance value of said unknown resistor.
- 5. A high resistance measuring circuit, comprising a pair of terminals across which an unknown resistance may be connected, a source of voltage connected to one of said terminals, a first known resistor R1, means permanently connecting said first known resistor to said one terminal so that a voltage drop VR1 is produced thereacross, a second known resistor R2, means permanently connecting said second known resistor to said other terminal so that a voltage drop VR2 is produced thereacross, means for computing the quantity (VR1/VR2)-1, and means for developing an output signal proportional to said computed quantity which varies linearly with the value of said unknown resistance.
- 19. A high resistance measuring circuit, comprising a pair of terminals across which an unknown resistance may be connected, a source of voltage connected to one of said terminals, a first known resistor, means permanently connecting said first known resistor to said one terminal, a second known resistor, means permanently connecting said second known resistor to said other terminal, and means controlled by the voltages produced across said first and second known resistors for developing an output signal which varies as a function of the value of said unknown resistance.
- 24. A high resistance measuring circuit, comprising a pair of terminals across which an unknown resistance may be connected, means for selectively supplying voltages of different magnitudes to one of said terminals, a first series of resistors connected to said one terminal, a second series of resistors connected to said other terminal, a first pair of semiconductor analog switches connected to different resistors in said first series, a second pair of semiconductor analog switches connected to different resistors in said second series, A/D converter means having an input connected to the outputs of said first and second pairs of analog switches, means connected to the output of said A/D converter means for developing an output signal which varies linearly with the value of said unknown resistance, and means controlled at least in part by said selective voltage supply means for selectively controlling said first and second pairs of analog switches.
- 27. A resistance measuring circuit, comprising a pair of input terminals across which an unknown resistance may be connected, resistance measuring means connected to said input terminals and arranged to provide an output signal corresponding to the value of said unknown resistance, means connected to one of said input terminals for detecting the presence of an AC voltage between said one terminal and a reference potential, and microprocessor means programmed to first enable said AC voltage detecting means and then to enable said resistance measuring means only in the event that said AC voltage detecting means does not detect the presence of an AC voltage of predetermined magnitude between said one terminal and said reference potential.
- 32. A portable resistance measuring unit, comprising a housing having a front panel which includes a pair of input terminals to which an unknown resistance may be connected, a battery contained within said housing, a read switch on said panel, an oscillator contained within said housing, means for rectifying the output of said oscillator and supplying a unidirectional voltage to one of said terminals, resistance measuring means connected to said input terminals and arranged to provide an output signal which varies linearly with changes in said unknown resistance, and means operative only during periods when said read switch is actuated for supplying power from said battery to said oscillator and said resistance measuring means.
- 35. A resistance measuring circuit, comprising a pair of input terminals across which an unknown resistance may be connected, resistance measuring means connected to said input terminals and arranged to provide an output signal corresponding to the value of said unknown resistance, a read push button, means operative when said push button is depressed for enabling said resistance measuring means, and means operative as said push button is released for connecting a resistor of low resistance value across said input terminals to discharge any capacity associated with the unknown resistance connected to said input terminals.
Specification