Method and ohmmeter for measuring very low electric resistances
First Claim
1. An ohmmeter for measuring a very low electric resistance, comprising:
- a source of electric energy for delivering a one-polarity measuring current flowing through an electrically conducting object presenting said very low resistance so as to create a voltage drop proportional both to the magnitude of the measuring current and to said very low electric resistance;
means for detecting said measuring current and for producing a signal representative of the magnitude of said measuring current;
first integration means for integrating with respect to time and from a given instant the signal representative of the magnitude of the measuring current in order to produce a first integration signal representative of the quantity of measuring current which has flowed through the electrically conducting object from said instant;
means for generating an interruption signal when said first integration signal reaches a predetermined amplitude, that is, when a predetermined quantity of measuring current has flowed through the electrically conducting object from said instant;
second integration means for integrating with respect to time said voltage drop proportional to the magnitude of the measuring current and to said very low electric resistance in order to produce a second integration signal;
means for controlling said first and second integration means so as to simultaneously start the integration of the signal representative of the magnitude of the measuring current carried out by the first integration means and the integration of said voltage drop carried out by the second integration means; and
means for stopping the integration of said voltage drop carried out by the second integration means in response to said interruption signal;
the second integration signal having upon stopping of the integration of said voltage drop carried out by the second integration means an amplitude which is related to said predetermined quantity of measuring current and which constitutes a measure of said very low electric resistance.
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Accused Products
Abstract
An ohmmeter for measuring very low electric resistances, for example the very low resistance of a very high current electric joint, which ohmmeter comprises a source for establishing a measuring current through the joint to thereby create a voltage drop proportional to the magnitude of the measuring current and to the resistance to be measured. A first integrator integrates a signal respresentative of the magnitude of the measuring current in order to produce a first integration signal, while a second integrator integrates the voltage drop proportional to the measuring current and to the very low resistance in order to produce a second integration signal. The two integrators are simultaneously reset to zero so that they both start their respective integrations at a same instant. The first integration signal is compared to a reference signal through a comparator. When the amplitude of the first integration signal reaches the amplitude of the reference signal, the comparator delivers a signal which stops the integration carried out by the second integrator. The second integration signal is then stored, this signal having an amplitude constituting a measure of the very low electric resistance. A display device receives the stored integration signal for displaying the value of the measured resistance.
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Citations
23 Claims
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1. An ohmmeter for measuring a very low electric resistance, comprising:
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a source of electric energy for delivering a one-polarity measuring current flowing through an electrically conducting object presenting said very low resistance so as to create a voltage drop proportional both to the magnitude of the measuring current and to said very low electric resistance; means for detecting said measuring current and for producing a signal representative of the magnitude of said measuring current; first integration means for integrating with respect to time and from a given instant the signal representative of the magnitude of the measuring current in order to produce a first integration signal representative of the quantity of measuring current which has flowed through the electrically conducting object from said instant; means for generating an interruption signal when said first integration signal reaches a predetermined amplitude, that is, when a predetermined quantity of measuring current has flowed through the electrically conducting object from said instant; second integration means for integrating with respect to time said voltage drop proportional to the magnitude of the measuring current and to said very low electric resistance in order to produce a second integration signal; means for controlling said first and second integration means so as to simultaneously start the integration of the signal representative of the magnitude of the measuring current carried out by the first integration means and the integration of said voltage drop carried out by the second integration means; and means for stopping the integration of said voltage drop carried out by the second integration means in response to said interruption signal; the second integration signal having upon stopping of the integration of said voltage drop carried out by the second integration means an amplitude which is related to said predetermined quantity of measuring current and which constitutes a measure of said very low electric resistance. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 10, 13, 14, 15, 16, 17, 18, 19, 20)
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9. An ohmmeter for measuring a very low electric resistance, comprising:
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a source of electric energy for delivering a measuring current flowing through an electrically conducting object presenting said very low resistance so as to create a voltage drop proportional both to the magnitude of the measuring current and to said very low electric resistance; means for detecting said measuring current and for producing a signal representative of the magnitude of said measuring current; first integration means for integrating with respect to time the signal representative of the magnitude of the measuring current in order to produce a first integration signal; second integration means for integrating with respect to time said voltage drop proportional to the magnitude of the measuring current and to said very low electric resistance in order to produce a second integration signal; means for controlling said first and second integration means so as to simultaneously start the integration of the signal representative of the magnitude of the measuring current carried out by the first integration means and the integration of said voltage drop carried out by the second integration means; and means for comparing said first integration signal with a reference signal having a predetermined amplitude, and for stopping the integration of said voltage drop carried out by the second integration means when the first integration signal reaches an amplitude equal to the predetermined amplitude of the reference signal; the second integration signal having upon stopping of the integration of said voltage drop carried out by the second integration means an amplitude which constitutes a measure of said very low electric resistance; wherein said second integration means comprises a circuit for amplifying said voltage drop proportional both to the magnitude of the measuring current and to said very low electric resistance so as to produce an amplified voltage drop and an integrator for integrating said amplified voltage drop; and wherein a parasitic electromotive force due to a thermoelectric effect is produced by connections of said ohmmeter to the electrically conducting object, this parasitic electromotive force being amplified through said amplifying circuit, said second integration means comprising switching means interposed between the amplifying circuit and said integrator which comprises a first input, a second input connected to a capacitor and means for integrating a voltage present between said first and second inputs, the switching means comprising means for transmitting, when the measuring current is not delivered from the source of electric energy, the amplifed parasitic electromotive force to said second input and therefore to the capacitor so that this capacitor stores said amplified parasitic electromotive force, the switching means also comprising means for transmitting, when said measuring current is delivered by the source of electric energy, the amplifed voltage drop to which is added the amplified parasitic electromotive force to the first input of said integrator.
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11. An ohmmeter for measuring a very low electric resistance, comprising:
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a source of electric energy for delivering a measuring current flowing through an electrically conducting object presenting said very low resistance so as to create a voltage drop proportional both to the magnitude of the measuring current and to said very low electric resistance; means for detecting said measuring current and for producing a signal representative of the magnitude of said measuring current; first integration means for integrating with respect to time the signal representative of the magnitude of the measuring current in order to produce a first integration signal; second integration means for integrating with respect to time said voltage drop proportional to the magnitude of the measuring current and to said very low electric resistance in order to produce a second integration signal; means for controlling said first and second integration means so as to simultaneously start the integration of the signal representative of the magnitude of the measuring current carried out by the first integration means and the integration of said voltage drop carried out by the second integration means; means for comparing said first integration signal with a reference signal having a predetermined amplitude, and for stopping the integration of said voltage drop carried out by the second integration means when the first integration signal reaches an amplitude means when the predetermined amplitude of the reference signal; the second integration signal having upon stopping of the integration of said voltage drop carried out by the second integration means an amplitude which constitutes a measure of said very low electric resistance; and means for storing a parasitic electromotive force caused by a thermoelectric effect produced by connections of the ohmeter to said electrically conducting object. - View Dependent Claims (12)
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21. A method for measuring a very low electric resistance comprising the following steps:
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producing a one-polarity measuring current flowing through an electrically conducting object presenting said very low resistance so as to create a voltage drop proportional both to the magnitude of the measuring current and to said very low electric resistance; producing a signal representative of the magnitude of said measuring current; integrating with respect to time and from a same instant the signal representative of the magnitude of said measuring current in order to produce a first integration signal representative of the quantity of measuring current which has flowed through the electrically conducting object from said instant, and said voltage drop proportional to the magnitude of the measuring current and to said very low electric resistance in order to produce a second integration signal; generating an interruption signal when said first integration signal reaches a predetermined amplitude, that is, when a predetermined quantity of measuring current has flowed through the electrically conducting object from said instant; and stopping the integration of the voltage drop proportional to the magnitude of the measuring current and to said very low electric resistance in response to said interruption signal; the second integration signal having upon stopping of the integration of said voltage drop proportional to the magnitude of the measuring current and to said very low electric resistance an amplitude which is related to said predetermined quantity of measuring current and which constitutes a measure of said very low electric resistance. - View Dependent Claims (22, 23)
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Specification