DEVICE AND METHOD FOR MEASURING A VALUE OF A RESISTOR

• US 20130249575A1
• Filed: 03/22/2013
• Published: 09/26/2013
• Est. Priority Date: 03/22/2012
• Status: Active Grant

• Current Assignee: Vitesco Technologies GmbH (Continental AG)
• Original Assignee: Continental Automotive GmbH (Continental AG)
• Inventors: HERTES, VOLKER
• Granted Patent: US 9,182,430 B2
• Time in Patent Office: Days
• US Class Current: 324/711
• CPC Class Codes: G01K 7/203 in an oscillator circuit
• CPC Class Codes: G01R 27/02 Measuring real or complex resistance, reactance, impedance, or other two-pole characteristics derived therefrom, e.g. time constant by measuring phase angle only G01R25/00
• 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

A device for measuring the value of a resistor has a first RC element with a first time constant and a second RC element with a second time constant. The first RC element has a first capacitor and a resistor. The second RC element has a second capacitor and the resistor to be measured. An evaluation circuit charges the first and second capacitors to a first and a second voltage, respectively, and initiates their discharge. The evaluation circuit measures the time that elapses from the start of the discharge to the instant at which the voltages across the capacitors are equal, and determines the value of the resistor from the values. In the event that the first time constant is larger than the second time constant, the first voltage is smaller than the second voltage, and vice versa.

Claims

1. A device for measuring a value of a resistor, comprising:

a first RC element having a first time constant, said first RC element including a first capacitor and a further resistor connected in parallel with said first capacitor;

a second RC element having a second time constant, said second RC element including a second capacitor and the resistor to be measured connected in parallel with said second capacitor;

an evaluation circuit connected to said first and second capacitors and being configured;

to charge said first and second capacitors to a first voltage and a second voltage, respectively, and to initiate a discharge thereof through only said further resistor or the resistor to be measured;

to measure a time that elapses from a start of a discharge of said first and second capacitors to an instant at which the voltages across said first and second capacitors are equal; and

to determine the value of the resistor to be measured from the values, wherein, in an event that the first time constant is greater than the second time constant, the first voltage is smaller than the second voltage, and vice versa.

2. The device according to claim 1, which further comprises a voltage divider connected between said first and second capacitors and a voltage source for charging said capacitors, and wherein said evaluation circuit is configured to connect one of said first and second capacitors to said voltage source via a first controllable switch and to connect the respectively other capacitor to said voltage source via said first switch and said voltage divider, and wherein said voltage divider is configured to draw no current while the first and second capacitors are discharging.

3. The device according to claim 2, which comprises a first switch connected at an input of said voltage divider and a second switch connected at an output of said voltage divider, wherein said first and second switches are connected to said evaluation circuit and said evaluation circuit is configured to open said switches during the discharge process.

4. A method of measuring a value of a resistor, which comprises:

providing a first RC element, formed of a first capacitor and a further resistor and having a first time constant, and charging the first capacitor to a first voltage;

providing a second RC element, formed of a second capacitor and the resistor to be measured and having a second time constant, and charging the second capacitor to a second voltage;

if the first time constant is greater than the second time constant, the first voltage is smaller than the second voltage, and vice versa, and a ratio of the first voltage to the second voltage is 1/K;

with an evaluation circuit, initiating a discharge of the capacitors and measuring a time interval that elapses from a start of the discharge of the capacitors to an instant at which the first and second voltages across the capacitors are equal, and determining a value of the resistor to be measured from the values of the first and second capacitors, of said further resistor, the ratio of the first voltage to the second voltage, and the measured time.

5. The according to claim 4, wherein said evaluation circuit is configured to determine the value of the resistor according to the formula