Digital display ohmmeter

• US 4,636,715 A
• Filed: 07/08/1985
• Issued: 01/13/1987
• Est. Priority Date: 08/13/1984
• Status: Expired due to Fees

• Current Assignee: CIL Inc. (Nouryon BV)
• Original Assignee: CIL Inc. (Nouryon BV)
• Inventors: Borkowicz, Jerzy
• Primary Examiner(s): Krawczewicz, Stanley T.
• Application Number:
  US06/752,846
• Time in Patent Office: 554 Days
• Field of Search: 324/62, 324/57 R, 324/51, 324/65 CR, 324/65 R
• US Class Current: 324/718
• CPC Class Codes: F42D 1/05 Electric circuits for blasting
• CPC Class Codes: G01R 27/14 Measuring resistance by measuring current or voltage obtained from a reference source G01R27/16, G01R27/20, G01R27/22 take precedence

Abstract

An apparatus and method is provided for measuring the continuity and resistance of electric circuits, particularly electric wire circuits used in blasting, in the presence of spurious voltages due to galvanic currents. A constant current from a cell is passed through the electric circuit to be tested and through a reference resistor where the voltages are measured to derive the resistance of the circuit. The measured voltages are sensed with a converter converted to a resistance measurement and displayed. The presence of spurious voltages is compensated for by connecting a galvanic current storage capacitor in the circuit, passing a reference current through the reference resistor and the circuit and comparing the voltage across the reference resistor with the voltage across the circuit and storage capacitor to derive a resistance reading. The reading is converted to a digital display. The method and apparatus provides a quick, convenient means of testing blasting circuit continuity in the field in the presence of stray current caused by in-earth galvanic action.

Claims

1. In an apparatus for measuring the continuity and resistance of an electric wire blasting network of the type where a constant current is passed through the network and a reference resistor;

and the voltages across the reference resistor and the network are measured and compared to derive the resistance of the blasting circuits;

the apparatus including a converter for sensing the measured voltages and converting their values to display resistance of the blasting network directly, the improvement of means for compensating for the effect of voltages due to galvanic currents associated with the blasting network comprisng;

a reference resistor;

a storage capacitor for voltage due to galvanic currents associated with the blasting network;

an input terminal for supplying a test voltage;

terminals for connection to the electric wire blasting network;

switch means operable between two positions, the first position being one wherein said storage capacitor is connectible only to said blasting network to assume a charge proportional to the voltage across the blasting network due to galvanic currents in the location of the blasting network and the second one being one in which said input terminal is connectible to said blasting network through said reference resistor, and in which said reference resistor, blasting network, and voltage storage capacitor are connectible to said converter;

synchronizing means for cyclically moving said switch means between said first and said second positions at a frequency at which the voltage applied to the storage condenser is substantially constant; and

the time constant of said storage capacitor being adapted to fully charge when said switch means is in said first position.

2. Apparatus for measuring continuity and resistance of an electric wire blasting network as claimed in claim 1 in which said synchronizing means cyclically moves said switch means at a frequency of two to five cycles per second.

3. In a method for measuring the continuity and resistance of an electric wire blasting network wherein a constant current is cyclically passed through the network and a reference resistor;

and the voltages across the reference resistor and the network are measured and compared to derive the resistance of the blasting circuits;

the measured voltages are sensed with a converter and their values are converted to display resistance of the blasting network directly, the improvement of compensating for the effect of voltages due to galvanic currents associated with the blasting comprising the steps of;

connecting a storage capacitor to the blasting network to assume a charge proportional to the voltage across the blasting network due to only the flow of galvanic current through the network; and

simultaneously passing a reference current through the reference resistor and blasting network and, while the said reference current is passing through the reference resistor and blasting network, comparing the voltage across the reference resistor with the voltage across the blasting network and storage capacitor to derive a reading of the resistance of the blasting network; and

the steps of connecting the storage capacitor to the blasting network and comparing the voltage across the reference resistor with the voltage across the blasting network and storage capacitor being done within a time cycle wherein the voltage across the blasting network due to the flow of galvanic currents is substantially constant.

4. In a method for measuring the continuity and resistance of an electric wire blasting network wherein a constant current is cyclically passed through the network and a reference resistor;

and the voltages across the reference resistor and the network are measured and compared to derive the resistance of the blasting circuits;

the measured voltages are sensed with a converter and their values are converted to display resistance of the blasting network directly, the improvement of compensating for the effect of voltages due to galvanic currents associated with the blasting comprising the steps claimed in claim 3 wherein the time cycle of the steps of connecting the storage capacitor to the blasting network and comparing the voltage across the reference resistor with the voltage across the blasting network and storage condenser is between 1/3 and 1/5 of a second.