Self-checking ohmmeter that checks for contact resistance of its probes
First Claim
1. Apparatus for providing accurate information pertaining to the resistance of means under test, said apparatus comprising:
- ohmmeter means for providing a resistance reading,connecting means coupled to said ohmmeter means and manually operable for establishing connection with said means under test, wherein said connection is characterized as resistive, andmeans coupled to said connecting means for determining the acceptability of the resistance of said connection between said ohmmeter means and said means under test for indicating the accuracy of the ohmmeter reading, the relative resistance of said connection being determined relative to reference resistance of said ohmmeter means and separately from said ohmmeter reading.
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Accused Products
Abstract
A four terminal ohmmeter apparatus includes circuitry for blanking the meter read-out in the event one or more connections to a device or structure under test have been improperly made. The voltage drop between current terminals is determined and compared with a threshold value. The voltage drop between potential terminals or between potential and current terminals, as caused by a separate a.c. source, is also determined and compared with a standard. Individual indicators inform the operator of the validity of each connection in order that corrective action can be taken if necessary. Voltage inputs are also utilized for ascertaining whether a correct meter range is being used and for changing the range if it is improper.
47 Citations
19 Claims
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1. Apparatus for providing accurate information pertaining to the resistance of means under test, said apparatus comprising:
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ohmmeter means for providing a resistance reading, connecting means coupled to said ohmmeter means and manually operable for establishing connection with said means under test, wherein said connection is characterized as resistive, and means coupled to said connecting means for determining the acceptability of the resistance of said connection between said ohmmeter means and said means under test for indicating the accuracy of the ohmmeter reading, the relative resistance of said connection being determined relative to reference resistance of said ohmmeter means and separately from said ohmmeter reading. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15)
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16. Apparatus for providing accurate information pertaining to the resistance of means under test, said apparatus comprising:
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ohmmeter means for providing a resistance reading, said ohmmeter means including a reference resistance in series with a source of voltage, means for determining the voltage across said reference resistance and current terminal means terminating the series circuit including said source of voltage and said reference resistance, hand held connecting means coupled to said current terminal means of said ohmmeter means and manually engagable with said means under test for establishing connection with said means under test, wherein said connection is characterized as resistive, means concurrently operable with said ohmmeter means and coupled to said connecting means for determining, substantially simultaneously with said reading, the acceptability of the resistance of said connection between said ohmmeter means and said means under test for indicating, substantially simultaneously with the ohmmeter reading, the relative accuracy of the ohmmeter reading by determining the voltage at said connecting means to be very low, said acceptability of the resistance of said connection being determined separately from said ohmmeter reading, and means providing an immediate indication of said acceptability to the user of said apparatus, including means responsive to said concurrently operable means coupled to said connecting means for inhibiting read out of said ohmmeter means when said voltage at said connecting means is not within predetermined acceptable limits. - View Dependent Claims (17, 18)
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19. An ohmmeter apparatus including a source of voltage, a reference resistance in series with said source of voltage, means for determining the voltage across said reference resistance, and current terminal means terminating the series circuit including said source of voltage and said reference resistance, said current terminal means being provided with hand operable current connecting means, wherein said current connecting means are adapted to provide conductive connection with means under test, said connection being characterized as resistive, said ohmmeter apparatus further comprising:
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means coupled to said current terminal means for determining the voltage thereacross when said connecting means are applied to means under test, and indicating means for providing notification when the voltage across said current terminal means is within predetermined acceptable limits indicative of a very low resistance on the order of a million across said connecting means, wherein the voltage across said current terminal means is determined relative to voltage across said reference resistance for determining said acceptability.
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Specification