Method of and apparatus for automatic measurement of impedance or other parameters with microprocessor calculation techniques

• US 4,196,475 A
• Filed: 09/02/1976
• Issued: 04/01/1980
• Est. Priority Date: 09/02/1976
• Status: Expired due to Term

• Current Assignee: Genrad Incorporated (Teradyne Incorporated)
• Original Assignee: Genrad Incorporated (Teradyne Incorporated)
• Inventors: Hall, Henry P.
• Primary Examiner(s): Krass, Errol A.
• Application Number:
  US05/719,810
• Time in Patent Office: 1,307 Days
• Field of Search: 235/151.3, 235/151.31, 324/57 R, 324/57 N, 324/73 AT, 338/320, 340/347 AD, 323/121, 364/480, 364/482, 364/606, 364/570, 364/559, 364/551, 364/525, 364/602
• US Class Current: 702/65
• 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

This disclosure is concerned with a new technique for automatically measuring impedance (though the process is also applicable to other parameters and characteristics as well) wherein a series of voltages are sequentially presented to a common detector and analog-to-digital converter, the numerical values of which voltages are of themselves meaningless, but from which, with the aid of microprocessor calculating equipment, ratios may be calculated that indicate impedance (or other parameters).

Claims

1. A method of automatic instrument measurement of impedance, that comprises, measuring voltages across an unknown impedance element and a standard element connected to receive the same a.c. current to produce voltage signals the values of which are meaningless of themselves in terms of impedance values but that have theoretical ratio formulae relationship to the impedance values;

converting the voltage signal values into corresponding digital quantities;

employing a microprocessor to automatically electronically calculate the ratio of said quantities in accordance with said formulae; and

indicating the calculated ratios to provide impedance measurement of said unknown element.

2. A method as claimed in claim 1 and in which said measuring is effected successively, with an initial measured voltage signal stored for presentation with a successive measured voltage signal to enable the said ratio calculation.

3. A method as claimed in claim 2 and in which the successive measuring of the voltages across the said elements is effected for 90 degree-displaced a.c. reference voltages, and said converting steps comprise the phase-detecting of the successively measured voltages and analog-to-digital converting of the phase-detected voltages.

4. A method as claimed in claim 3 and in which zeroing measurements are effected to produce measured values representing fixed and offset voltages and currents associated with said phase-detecting and converting, and said measured values are subtracted from each of the voltage signal values prior to calculating said ratios.

5. A method as claimed in claim 3 and in which the fixed and offset voltages and currents associated with said phase-detecting and converting are removed by making two phase-sensitive measurements of each signal using detecting references that are opposite in phase, and subtracting the results.

6. A method as claimed in claim 1 and in which said measuring comprises determining the voltages E_xp1 and E_sp1 appearing across the unknown impedance element (X_x +R_x) and the standard element R_s, respectively, that are in phase with a reference signal E₁, and the voltages E_xp2 and E_sp2 appearing accross the unknown impedance element (X_x +R_x) and the standard element R_s, respectively, that are in phase with a 90 degree phase-displaced signal E₂, where X_x and R_x are the reactive and resistive components, respectively, of the unknown impedance, and the said ratio calculating is effected in accordance with the formulae:

##EQU1##

7. A method as claimed in claim 6 and in which said calculating further includes the step of multiplying the ratios of equations (I) and (II) by R_s.

8. A method of automatic instrument measurement of impedance values, that comprises, generating an electric current in an instrument, producing, in response to that current, and measuring a plurality of voltages the voltage values of which of themselves do not measure desired impedance values, but that are theoretically related by formulae to such impedance values;

converting the voltages into corresponding digital signals;

employing a microprocessor to automatically electronically calculate said impedance values from said digital signals in accordance with said formulae; and

indicating the calculated impedance values.

9. A method as claimed in claim 8 and in which said measuring step comprises effecting successive measured voltages and storing initial measurements to await successive measured voltages prior to said calculating step.

10. A method as claimed in claim 8 and in which said formulae involve ratios of said voltages.

11. A method of automatic instrument measurement of parameters, that comprises, measuring a plurality of voltages in a circuit the voltage values of which of themselves do not measure desired, meaningful quantities, but that are theoretically related by formulae to such quantities;

converting the voltages into corresponding digital signals;

employing a microprocessor to automatically electronically calculate said quantities from said digital signals in accordance with said formulae; and

indicating the calculated quantities to provide measures of the desired parameters, said measuring comprising measuring 90 degrees phase-displaced components of voltages developed across an unknown impedance element and a standard element; and

said calculating comprising obtaining ratios of digital signals corresponding to the measured voltages that determine the impedance components of said unknown element.

12. A method as claimed in claim 11 and in which, prior to said calculating, measurement is made of the effect of fixed and offset voltages associated with said converting, and the measurement value resulting from said measurement is substracted from each of the measured voltages.

13. A method of automatic instrument measurement of impedance values, that comprises, measuring a plurality of voltages in a circuit the voltage values of which of themselves do not measure desired impedance values, but that are theoretically related by formulae to such impedance values;

converting the voltages into corresponding digital signals;

employing a microprocessor to automatically electronically calculate said impedance values from said digital signals in accordance with said formulae; and

indicating the calculated impedance values;

said converting step comprising phase-detecting of the measured voltages and analog-to-digital converting of the phase-detected voltages.

14. A method of automatic instrument measurement of impedance values, that comprises, measuring a plurality of voltages in a circuit the voltage values of which of themselves do not measure desired impedance values, but that are theoretically related by formulae to such impedance values;

converting the voltages into corresponding digital signals;

employing a microprocessor to automatically electronically calculate said impedance values from said digital signals in accordance with said formulae; and

indicating the calculated impedance values;

said measuring step comprising effecting successive measurements and storing initial measured voltages to await successive measured voltages prior to said calculating step;

said converting step comprising phase-detecting the successive measured voltages in a single circuit followed by analog-to-digital converting of the phase-detected voltages.

15. A method of measuring impedance and other electrical parameters without employing multiple-arm ratio bridge circuits requiring balancing variable impedance elements contained therein and null detection, which method comprises employing only a single arm containing an unknown impedance element and a standard element;

applying reference sinewave signals 90 degrees phase-displaced across said elements;

measuring the 90 degree phase-displaced voltages appearing across said elements, which voltages are meaningless in and of themselves but are related by theoretical ratio formulae to impedance;

phase-detecting said voltages and converting the phase-detected voltages to digital signals;

processing said digital signals in a microprocessor in accordance with said formulae and thereby electronically calculating ratios corresponding to impedance, in contradistinction to the technique of obtaining said ratios by the multiple bridge-arm variable impedance null-balancing detection.

16. A method as claimed in claim 15 and in which said measuring step comprises successively measuring the voltages appearing across said unknown impedance and standard elements in phase with each of the respective 90 degree phase-displaced reference signals, said phase-detecting and digital converting steps being performed upon the successively measured voltages.

17. A method of automatic instrument measurement of desired impedance values without requiring analog instrument measuring circuits wherein impedance values are measured and indicated by analog steps, which method comprises, providing an analog instrument measuring circuit with an input circuit restricted to those elements that are necessary to develop voltages at predetermined points thereof that, while meaningless in and of themselves, are related by theoretical formulae to impedance values that it is desired to measure;

generating an electric current in the input circuit;

producing said voltages in response to such current;

converting the voltages to digital signals; and

processing said digital signals in a microprocessor in accordance with said formulae and thereby electronically calculating the desired impedance values without the need of further analog circuits.

18. Apparatus for automatic instrument measurement of impedance having, in combination, an analog input circuit comprising an a.c. generator connected to a network containing an unknown impedance element and a standard element, and means for measuring the voltages produced across said elements by said generator, with the values of such voltages meaningless of themselves except as theoretically related by ratio formulae to impedance;

means responsive to said voltages for converting the same into digital signals;

microprocessor means provided with control logic and connected to said converting means for automatically electronically calculating impedance value ratios from said digital signals in accordance with said formulae; and

means connected to said microprocessor means for indicating the calculated impedance value ratios to provide a measure of the impedance of said unknown element.

19. Apparatus as claimed in claim 18 and in which said converting means comprises phase-sensitive detector means connected to receive the measured voltages from the input circuit and connected to analog-to-digital converter means for producing digital signals corresponding to the phase-detected measured voltages.

20. Apparatus as claimed in claim 19 and in which means is provided for the zero-measuring of fixed and offset voltage and current values in said detector and converter means and for subtracting the zero measurement values from each of the said measured voltages.

21. Apparatus as claimed in claim 20 and in which the zero-measuring means comprises means within the analog-to-digital converter means for producing a signal measuring the zeroing signal;

and there is further provided high-frequency signal means connected to counter means and gated in response to said zeroing signal to apply a count representative of the zeroing signal to the microprocessor means for subtraction from the digital signals corresponding to said measured voltages.

22. Apparatus as claimed in claim 21 and in which said a.c. generator, the 90 degree phase-displaced reference signals and said high-frequency signal are derived from a common stable source.

23. Apparatus as claimed in claim 19 and in which said a.c. generator comprises a source of 90 degrees phase-displaced reference signals, and said voltage measuring means includes means for measuring the 90 degree phase-displaced components of voltages developed across said unknown impedance and standard elements.

24. Apparatus as claimed in claim 23 and in which said voltage measuring means measures the said components of voltages developed across said unknown impedance and standard elements in successive measurements.

25. Apparatus as claimed in claim 24 and in which means is provided for storing first voltage measurement values to await successive voltage measurement values for subsequent calculation, and said phase-sensitive detector means is a single phase detector connected to receive all of the measured voltages from the input circuit.

26. Apparatus as claimed in claim 25 and in which said successive measurements are effected by alternatingly switching differential amplifier means connected across each of the unknown impedance and standard elements to said phase detector.

27. Apparatus as claimed in claim 26 and in which said phase detector comprises dual-slope integrator means.

28. Apparatus as claimed in claim 23 and in which the said formulae relating the measured voltage components E_xp1 and E_sp1 appearing across the unknown impedance element (X_x +R_x) and the standard element R_s, respectively, that are in phase with one of the reference signals E₁, and the voltage components E_xp2 and E_sp2 appearing across the unknown impedance element (X_x +R_x) and the standard element R_s, respectively, that are in phase with the 90 degree-displaced reference signal E₂ are:

##EQU2## where X_x and R_x are the reactive and resistive components, respectively, of the unknown impedance.

29. Apparatus as claimed in claim 28 and in which means is provided for multiplying each of the ratios of formulae (I) and (II) by R_s.

30. Apparatus as claimed in claim 29 and in which means is provided for displaying from said ratios at least one of CRL and D-Q.

31. Apparatus for automatic instrument measurement of impedance values having, in combination, input circuit means limited to those analog-operated circuit components necessary to develop voltages at predetermined points thereof that, while meaningless in and of themselves, are related by theoretical formulae to impedance values it is desired to measure;

means for generating an electric current in the input circuit means;

means for producing said voltages in response to that current;

means for converting the voltages to digital signals; and

microprocessing means connected to the converting means for processing said digital signals in accordance with said formulae and thereby electronically calculating the desired impedance values without the need of further analog circuits.

32. Apparatus as claimed in claim 31 and in which means is provided for presenting said voltages successively to said converting means, and means is provided for storing initial voltages while awaiting successive voltages prior to combining said voltages for the processing of the same.

33. Apparatus for automatic instrument measurement of parameters having, in combination, input circuit means limited to those analog-operated circuit components necessary to develop voltages at predetermined points thereof that, while meaningless in and of themselves, are related by theoretical formulae to parameters it is desired to measure;

means for converting the voltages to digital signals; and

microprocessing means connected to the converting means for processing said digital signals in accordance with said formulae and thereby electronically calculating the desired parameters without the need of further analog circuits;

said apparatus further having means for producing zeroing measurement values of fixed and offset voltages and currents, including those associated with said converting means;

means for digitizing said zeroing measurement values; and

means for subtracting the digitized zeroing measurement values from each of the digital signals corresponding to each of the said first-named voltages.