PORTABLE APPARATUS FOR MEASURING LOAD RESISTANCE

• US 3,816,812 A
• Filed: 04/19/1973
• Issued: 06/11/1974
• Est. Priority Date: 04/19/1973
• Status: Expired due to Term

• Current Assignee: Alber Engineering Incorporated
• Original Assignee: Carl H. Alber, Glenn Alber
• Inventors: Alber, Glenn, Alber, Carl H.
• Primary Examiner(s): Krawczewicz, Stanley T.
• Application Number:
  US05/352,611
• Time in Patent Office: 418 Days
• Field of Search: 324/62,64,3R
• US Class Current: 324/712
• CPC Class Codes: G01R 27/205 Measuring contact resistance of connections, e.g. of earth connections
• CPC Class Codes: H01H 1/0015 Means for testing or for inspecting contacts, e.g. wear indicator measuring circuits G01R31/3274

Abstract

Portable apparatus for measuring the resistance of a load including a current pulse power supply generating a current pulse to be supplied to the load, a digital voltmeter for detecting the voltage across the load and displaying a digital signal representative of the resistance of the load and a control circuit operating the digital voltmeter only when the current pulse has a predetermined amplitude. The portable apparatus is particularly advantageous for measuring the resistance of circuit breaker contacts with current pulses having an amplitude of 100 amps.

Claims

1. Apparatus for measuring the resistance of a load, comprising:

power supply means for generating a current pulse of a predetermined amplitude, wherein said pulse is applied to the load, means for detecting voltage across the load when The current pulse is applied to the load, said detecting means providing an output corresponding to the voltage, said detecting means including means for translating said output and displaying a signal representative of the resistance of the load; and

means for controlling display of the signal, wherein said control means includes means for providing a test signal, timing means responsive to said test signal to generate a timing signal after a predetermined period of time, and error means responsive to said test signal to indicate erroneous operation if said current pulse does not reach said predetermined amplitude within said predetermined period of time as tolled by the generator of said timing signal.

2. Apparatus for measuring the resistance of a load as recited in claim 1 and further comprising bias voltage means isolated from said power supply means for supplying bias voltage to said display means and said control means.

3. Apparatus for measuring the resistance of a load as recited in claim 1 wherein said power supply means includes a rechargeable DC battery and capacitance means connected across said battery to be charged thereby and to be discharged to generate said current pulse.

4. Apparatus for measuring the resistance of a load as recited in claim 1 wherein said power supply means includes means for regulating the amplitude of said current pulse.

5. The apparatus of claim 1, wherein the load of which the resistance is being measured includes an inductance and wherein the predetermined period of time provided by said timing means is sufficient to overcome any effects on the signal representative of the resistance of the load due to the existance of said inductance.

6. Apparatus for measuring the resistance of a load as recited in claim 1, further including rechargeable battery means for generating said current pulse and for providing bias voltage for said control means and said detecting means.

7. Apparatus for measuring the resistance of a load as recited in claim 1 wherein said detecting means includes means for providing a digital visual display representative of the resistance of the load.

8. Apparatus for measuring the resistance of a load, comprising:

power supply means for generating a current pulse of a predetermined amplitude, wherein said pulse is applied to the load;

means for detecting voltage across the load when the current pulse is applied to the load, said detecting means providing an output corresponding to the voltage, said detecting means including means for translating said output and displaying a signal representative of the resistance of the load; and

control means, wherein said control means includes means for sensing the amplitude of said current pulse generated by said power supply means and providing a signal corresponding thereto, means for comparing said signal corresponding to said current pulse with a reference signal corresponding to said predetermined amplitude, and means for generating a command signal once said signal corresponding to said current pulse substantially equals said reference signal, wherein said command signal is applied to said detecting means to cause said detecting means to display the signal representative of the resistance of the load.

9. Apparatus for measuring the resistance of a load as recited in claim 1 wherein said means for generating a command signal includes timing means for delaying the generating of said command signal such that said detecting means operates after a delay to supply said output corresponding to the voltage across the load.

10. Apparatus for measuring the resistance of a load, comprising:

power supply means for generating a current pulse of a predetermined amplitude, wherein the pulse is applied to the load, said power supply means including a first timing means for controlling the generation of said current pulse for a first time period and comparator means providing an output signal when said current pulse has attained said predetErmined amplitude;

means for detecting voltage across the load when the current pulse is applied to the load, wherein said detecting means provides an output corresponding to the voltage, said detecting means including means for translating said output and displaying a signal representative of the resistance of the load; and

control means for providing a test signal, wherein said control means includes second timing means responsive to said test signal to provide a timing signal for a second time period shorter than said first time period, AND gating means responsive to said timing signal and said comparator means output signal for supplying a command signal to said detecting means to cause said detecting means to display a signal representative of the resistance of the load only after said first time period elapses and prior to lapse of said second time period.

11. Apparatus for measuring the resistance of a load as recited in claim 10 wherein said detecting means includes an analog-to-digital converter responsive to said command signal for detecting the voltage across the load and a storage and readout circuit for storing and displaying a digital signal from said analog-to-digital converter representative of the resistance of the load.

12. Apparatus for measuring the resistance of a load as recited in claim 11 wherein said control means includes third timing means responsive to said test signal to provide a bias timing signal for a third time period longer than said first time period and further comprising bias voltage means for providing bias voltage for said storage and readout circuit and means responsive to said bias timing signal for supplying said bias voltage to said storage and readout circuit for said third time period.

13. Apparatus for measuring the resistance of a load as recited in claim 12 wherein said bias voltage means includes switch means manually operable to supply said bias voltage to said storage and readout circuit to refresh said displayed digital signal.

14. Apparatus for measuring the resistance of a load, comprising:

power supply means for generating a current pulse of a predetermined amplitude, wherein said pulse is applied to the load, said power supply means including a rechargeable battery having first and second terminals, a resistor and capacitor connected series between said first and second terminals, a control rectifier connected to the junction of said resistor and said capacitor, a sensing resistor connected in series with said control rectifier and said battery, and means for triggering said control rectifier to discharge said capacitor through said control rectifier, the load and said sensing resistor;

means for detecting voltage across the load when the current pulse is applied to the load, said detecting means providing an output corresponding to the voltage, said detecting means including means for translating said output and displaying a signal representative of the resistance of the load; and

means for controlling display of the signal, wherein said control means includes comparator means responsive to the current passing through sensing resistor to operate said detecting means when said current pulse has said predetermined amplitude.

15. Apparatus for measuring the resistance of a load as recited in claim 14 wherein said detecting means is a digital voltmeter providing an end of conversion pulse after the resistance of the load has been measured, and said control means includes means responsive to said end of conversion pulse to render said controlled rectifier non-conductive to permit said capacitor to be recharged.