Method and circuit arrangement for current measurement

• US 7,242,177 B2
• Filed: 08/07/2003
• Issued: 07/10/2007
• Est. Priority Date: 08/14/2002
• Status: Expired due to Fees

• Current Assignee: Siemens AG
• Original Assignee: Siemens AG
• Inventors: Maier, Reinhard, Rupp, Ju
• Primary Examiner(s): PATEL, PARESH H
• Application Number:
  US10/524,561
• Publication Number:
  US 20060164069A1
• Time in Patent Office: 1,433 Days
• Field of Search: None
• US Class Current: 324/126
• CPC Class Codes: G01R 15/146 Measuring arrangements for current not covered by other subgroups of G01R15/14, e.g. using current dividers, shunts, or measuring a voltage drop if no voltage isolation is involved G01R1/203 or G01R19/0092
• CPC Class Codes: G01R 19/252 using analogue/digital converters of the type with conversion of voltage or current into frequency and measuring of this frequency
• CPC Class Codes: G01R 19/32 Compensating for temperature change

Abstract

A method with corresponding circuit arrangement is disclosed, whereby for evaluation of a measured signal arising as an analogue value with a potential greater than zero potential in a measuring device requiring a supply current, the measured information therefrom is transmitted as a digital signal to an analytical unit lying at earth potential after an A/D conversion. The generated digital signal thus provides the clock signal for a modulation of the supply current and thus also carries out the function of the carrier for the information content of the measured signal. Curved characteristic lines for compression/decompression of the signals are used. Suitable devices for temperature compensation may be similarly provided.

Claims

1. A method for current measurement through a conductor at a potential which is at a higher value than zero potential, comprising:

measuring the voltage drop across a shunt resistance to determine the current value in the form of an analog signal, the shunt resistance being formed by a section of the conductor in which the electrical resistance is increased locally by reducing the cross-section of the conductor;

converting the analog signal to a digital signal using an analog/digital converter;

supplying a reference voltage to the analog/digital converter to compensate for a temperature dependence of the shunt resistance, a temperature course of the reference voltage at least approximately corresponding to a temperature course of the shunt resistance; and

transmitting the digital signal to an evaluation unit which is at ground potential;

wherein the analog signal is subjected to compression based on a non-linear characteristic of the analog/digital converter, and the digital signal is subjected to expansion after transmission at ground potential.

2. The method as claimed in claim 1, wherein compression and expansion are effected logarithmically.

3. The method as claimed in claim 1, wherein compression and expansion are effected on the basis of the stipulation of root functions.

4. The method as claimed in claim 1, in which, in order to evaluate a measurement signal which, at a higher potential than zero potential, is in the form of an analog value in a measuring device that requires a supply current, having the following measures:

the compressed information content of the measurement signal is transmitted, after A/D conversion, in the form of a digital signal to the evaluation unit, which is at ground potential, and

after A/D conversion of the measurement signal, the digital signal produced provides the clock for modulating the supply current, with the result that the modulated supply current for the measuring device likewise performs the function of the carrier for the information content of the measurement signal.

5. A circuit arrangement for carrying out the method as claimed in claim 1 for use when measuring the current at a shunt, in which the voltage drop is evaluated as a measure of the current after amplification, said circuit arrangement comprising a shunt, an amplifier for the voltage signal that is tapped off at the shunt, an analog/digital converter, an evaluation unit, means for supplying the measuring components with current, and further means for signal compression and signal expansion.

6. The circuit arrangement as claimed in claim 5, further comprising means for temperature compensation.

7. The circuit arrangement as claimed in claim 6, wherein the means for temperature compensation includes a temperature-dependent reference voltage source.

8. The circuit arrangement as claimed in claim 5, wherein a unit for signal compression is connected upstream of the A/D converter.

9. The circuit arrangement as claimed in claim 5, wherein the means for signal expansion are integrated in the evaluation unit.

10. The circuit arrangement as claimed in claim 5, further comprising means for at least one of short-circuit disconnection and overload disconnection.

11. The circuit arrangement as claimed in claim 10, further comprising a first comparator, which compares the instantaneous value of the current with a first threshold value and produces a signal for short-circuit disconnection when said first threshold value is exceeded.

12. The circuit arrangement as claimed in claim 10, further comprising a second comparator, which compares the instantaneous temperature of the load with a second threshold value and outputs a signal for overload disconnection when said second threshold value is exceeded.

13. The circuit arrangement as claimed in claim 12, further comprising a thermal model of the load, said model being used to ascertain the instantaneous temperature of the load from the current measured.

14. The circuit arrangement as claimed in claim 5, wherein the means for signal expansion are integrated in the evaluation unit in the existing microcontroller, in the form of software.