Carrier frequency measuring method and apparatus

• US 6,223,138 B1
• Filed: 05/26/1998
• Issued: 04/24/2001
• Est. Priority Date: 05/27/1997
• Status: Expired due to Term

• Current Assignee: CARL Schenck AG (Durr AG)
• Original Assignee: CARL Schenck AG (Durr AG)
• Inventors: Sonnenschein, Roland, Raffius, Gerhard, Pitz, Juergen
• Primary Examiner(s): ASSOUAD, PATRICK J
• Application Number:
  US09/085,374
• Time in Patent Office: 1,064 Days
• Field of Search: 702/42, 702/76, 702/77, 702/189, 73/11.5, 737/60, 324/657, 324/666, 324/680, 324/706, 324/725, 327/92, 332/172
• US Class Current: 702/189
• CPC Class Codes: G01G 3/147 involving digital counting

Abstract

In a signal measuring method and apparatus, a digital signal processor (5) including a digital signal generator (5A) generates a digital signal, which is converted by a digital-to-analog converter (2) into a sinusoidal analog signal that is applied as a supply voltage to the transducers, such as load cell strain gages arranged in a bridge circuit (1). The analog supply voltage signal is modulated by the measurement voltage in the bridge circuit (1). The resulting modulated signal is amplified if necessary in an amplifier (3), and is then digitalized in an analog-to-digital converter (4) operating with a sampling frequency at least twice the carrier frequency and preferably corresponding to a whole number multiple thereof. The digital signal processor (5) carries out a Fourier transform of the digitalized signal to calculate the magnitude and phase of the measurement voltage, which may then be used for the complex calculation of zero point compensations and adjustment calibrations.

Claims

1. A method of obtaining and evaluating a measurement voltage provided by a bridge circuit including at least one measuring transducer, comprising the following steps:

a) applying, to at least one supply voltage input of said bridge circuit, an alternating carrier voltage having a carrier frequency;

b) modulating said alternating carrier voltage with a measurement value in said bridge circuit to form a modulated measurement voltage at at least one signal output of said bridge circuit;

c) converting said modulated measurement voltage into a digital measurement voltage, using an analog-to-digital conversion sampling rate of at least twice said carrier frequency; and

d) obtaining a magnitude and a phase of said measurement value from said digital measurement voltage by carrying out a Fourier transform on said digital measurement voltage.

2. The method according to claim 1, further comprising a step of amplifying said modulated measurement voltage between said steps b) and c), and carrying out no further processing of said modulated measurement voltage between said steps b) and c) other than said amplifying.

3. The method according to claim 2, wherein said sampling rate is a whole number multiple of said carrier frequency.

4. The method according to claim 1, wherein said step c) is carried out directly following said step b) with no additional processing of said modulated measurement voltage between said steps b) and c).

5. The method according to claim 4, wherein said sampling rate is a whole number multiple of said carrier frequency.

6. The method according to claim 1, wherein said sampling rate is a whole number multiple of said carrier frequency.

7. The method according to claim 1, wherein said step c) is carried out using an analog-to-digital converter, and said step d) is carried out using a digital signal processor circuit.

8. The method according to claim 1, further comprising a preliminary step of generating said alternating carrier voltage by generating a digital carrier signal and converting said digital carrier signal into said alternating carrier voltage by carrying out a digital-to-analog conversion thereof.

9. The method according to claim 1, further comprising a step of generating a digital reference signal by carrying out an analog-to-digital conversion of said alternating carrier voltage applied to said at least one supply voltage input of said bridge circuit, and wherein said step d) of obtaining said magnitude and said phase of said measurement value further comprises evaluating said digital reference signal.

10. The method according to claim 1, wherein said modulated measurement voltage has a signal magnitude of less than 10 millivolts.

11. The method according to claim 1, not including any demodulation step, and not including any narrow band filtering step.

12. The method according to claim 1, further comprising a step of applying a test condition to said at least one measuring transducer and carrying out a complex calibration of said bridge circuit using said magnitude and said phase of said measurement value determined in said step d).

13. An apparatus for obtaining and evaluating a measurement signal, comprising:

a bridge circuit including at least one measurement transducer, at least one supply voltage input, and at least one signal output,

a signal generator connected to said at least one supply voltage input,

an analog-to-digital converter having at least one analog input connected to said at least one signal output, and having at least one digital output, and

a digital signal processor connected to said at least one digital output.

14. The apparatus according to claim 13, further comprising at least one conductor, wherein said at least one analog input is directly connected by said at least one conductor to said at least one signal output without any interposed signal processing device.

15. The apparatus according to claim 13, further comprising an amplifier interposed between said at least one signal output and said at least one analog input, wherein said at least one analog input is directly connected through said amplifier to said at least one signal output.

16. The apparatus according to claim 15, wherein said bridge circuit includes two of said supply voltage inputs and two of said signal outputs and is connected to said signal generator and to said amplifier according to a four-wire connection technology comprising two supply conductors connecting said signal generator to said two supply voltage inputs and two signal conductors connecting said two signal outputs to said amplifier.

17. The apparatus according to claim 16, wherein said signal generator is a digital signal generator, and further comprising a digital-to-analog converter interposed between said signal generator and said supply voltage inputs.

18. The apparatus according to claim 15, further comprising an analog-to-digital reference converter having at least one digital output connected to said digital signal processor and having at least one analog input, wherein said bridge circuit includes two of said supply voltage inputs and two of said signal outputs and is connected according to a six-wire connection technology comprising two supply conductors connecting said signal generator to said two supply voltage inputs, two signal conductors connecting said two signal outputs to said amplifier, and two reference conductors connecting said two supply voltage inputs to said at least one analog input of said analog-to-digital reference converter.

19. The apparatus according to claim 18, wherein said signal generator is a digital signal generator, and further comprising a digital-to-analog converter interposed between said signal generator and said supply voltage inputs.

20. The apparatus according to claim 13, wherein said signal generator is a digital signal generator, and further comprising a digital-to-analog converter interposed between said signal generator and said at least one supply voltage input.

21. The apparatus according to claim 20, wherein said signal generator is incorporated in said digital signal processor.

22. The apparatus according to claim 20, further comprising an amplifier interposed between said at least one signal output and said at least one analog input, and a transducer housing in which said bridge circuit, said amplifier, said analog-to-digital converter, said digital-to-analog converter, and said digital signal processor are arranged and housed.

23. The apparatus according to claim 13, wherein said digital signal processor comprises and incorporates said signal generator, a microprocessor and a Fourier transform module.

24. The apparatus according to claim 13, not including any demodulator, and not including any narrow band filter.

25. The apparatus according to claim 13, wherein said bridge circuit is a Wheatstone bridge and said at least one measurement transducer comprises at least one strain gage.