Methods and systems for filtering unwanted noise in a material metering machine

• US 20040145502A1
• Filed: 01/08/2004
• Published: 07/29/2004
• Est. Priority Date: 01/09/2003
• Status: Active Grant

• Current Assignee: Process Control Corporation
• Original Assignee: Process Control Corporation
• Inventors: Thomson, Malcolm G.
• Granted Patent: US 7,126,504 B2
• Time in Patent Office: Days
• US Class Current: 341/61
• CPC Class Codes: H03H 17/025 Notch filters
• CPC Class Codes: H03H 17/0664 where the output-delivery frequency is lower than the input sampling frequency, i.e. decimation

Abstract

Methods and systems for filtering an analog signal sampled at a very high frequency and outputting a digital signal that has a very low sampling frequency to drive a material metering machine. The high frequency digital input signal is input to a first decimation element, which filters out the noise in the signal introduced by an analog-to-digital (A/D) converter and reduces the sampling frequency of the digital signal to a lower sampling frequency of 1200 hertz. The reduced rate digital signal is input into a second decimation element that contains several decimation filters, which reject the 60 hertz line noise and its harmonics while simultaneously reducing the sampling frequency of the digital signal to 10 hertz. The output of the second decimation element is then passed to a bank of selectable filters with sub-hertz cutoff frequencies to remove the machine noise from the material metering machine.

Claims

1. A system, comprising:

(A) a material metering machine having a load cell, the load cell being configured to generate an analog signal, the analog signal being indicative of a load on the load cell;

(B) an analog-to-digital converter configured to convert the analog signal into a digital signal, the digital signal having a sampling rate of 307.2 kHz;

(C) a preliminary decimation element comprising;

(C1) a first finite-impulse-response (FIR) filter having a decimation ratio of 16, the first FIR filter being configured to reduce the sampling rate of the digital signal from 307.2 kHz to 19.2 kHz; and

(C2) a second FIR filter serially coupled to the first FIR filter, the second FIR filter having a decimation ratio of 16, the second FIR filter being configured to reduce the sampling rate of the digital signal from 19.2 kHz to 1200 Hz;

(D) a primary decimation element serially coupled to the preliminary decimation element, the primary decimation element comprising;

(D1) a third FIR filter having a decimation ratio of 2, the third FIR filter being configured to reduce the sampling rate of the digital signal from 1200 Hz to 600 Hz;

(D2) a fourth FIR filter having a decimation ratio of 10, the fourth FIR filter being configured to reduce the sampling rate of the digital signal from 600 Hz to 60 Hz; and

(D3) a fifth FIR filter having a decimation ratio of 6, the fifth FIR filter being configured to reduce the sampling rate of the digital signal from 60 Hz to 10 Hz; and

(E) a filter bank serially coupled to the primary decimation element, the filter bank comprising;

(E1) selectable filters, each filter being configured to reduce the noise, the selectable filters including a filter having a sub-hertz 3-dB cutoff frequency, the selectable filters comprising a filter selected from the group consisting of;

(E1a) a SINC filter; and

(E1b) a raised cosine filter; and

(E2) a selectable filter switch configured to select a selectable filter, the selectable filter being selected as a function of operating criteria, the operating criteria being associated with the material metering machine, the operating criteria being determined through a closed feedback loop

2. A system, comprising:

a material metering machine comprising a decimation element; and

a filter bank, the filter bank comprising;

an input node adapted to receive a signal from the decimation element, the signal having noise from the material metering machine;

selectable filters, each selectable filter having a sub-hertz 3-dB cutoff frequency, each filter being configured to reduce the noise.

3. A system, comprising:

a filter bank input node -adapted to receive a signal having noise; and

selectable filters, each filter being configured to reduce the noise, the selectable filters including a filter having a sub-hertz 3-dB cutoff frequency.

4. The system of claim 3, wherein the selectable filters include a SINC filter.

5. The system of claim 4, wherein the SINC filter has a cutoff frequency, the cutoff frequency being selected from a group consisting of:

approximately 0.10 Hz;

approximately 0.12 Hz;

approximately 0.15 Hz;

approximately 0.20 Hz;

approximately 0.25 Hz;

approximately 0.32 Hz;

approximately 0.40 Hz;

approximately 0.50 Hz; and

approximately 0.70 Hz.

6. The system of claim 3, wherein the selectable filters include a raised cosine filter.

7. The system of claim 6, wherein the raised cosine filter has a cutoff frequency, the cutoff frequency being selected from a group consisting of:

approximately 0.20 Hz;

approximately 0.30 Hz; and

approximately 0.40 Hz.

8. The system of claim 3, further comprising:

a material metering machine that contributes to the noise in the signal.

9. The system of claim 8, wherein the material metering machine is adapted to measure a flow rate of material.

10. The system of claim 8, wherein the material metering machine is adapted to measure weight of material within the material metering machine.

11. The system of claim 8, further comprising a selectable filter switch configured to select a selectable filter, the selectable filter being selected as a function of operating criteria, the operating criteria being associated with the material metering machine, the operating criteria being determined through a closed feedback loop.

12. The system of claim 3, further comprising a decimation element configured to provide the signal to the filter bank input node.

13. The system of claim 3, further comprising means for providing the signal to the filter bank input node.

14. A filtering method, comprising the steps of:

receiving a signal having noise;

selecting a filter, the filter being selected from a plurality of selectable filters, the plurality of selectable filters including a filter having a sub-hertz 3-dB cutoff frequency; and

filtering the signal using the selected filter to reduce the noise.

15. The method of claim 14, wherein the step of selecting the filter comprises the step of:

selecting a SINC filter.

16. The method of claim 15, wherein the step of selecting the SINC filter comprises the step of:

selecting a SINC filter having a sub-hertz 3-dB cutoff frequency.

17. The method of claim 14, wherein the step of selecting the filter comprises the step of:

selecting a raised cosine filter.

18. The method of claim 17, wherein the step of selecting the raised cosine filter comprises the step of:

selecting a raised cosine filter having a sub-hertz 3-dB cutoff frequency.

19. A filtering apparatus, comprising:

a primary input node configured to receive a digital signal, the digital signal having an initial sampling rate, the digital signal further having line noise; and

a primary decimation element having a decimation ratio, the primary decimation element further having a filter length, the primary decimation element being configured to reduce the line noise at 50 Hz, the primary decimation element further being configured to reduce the line noise at 60 Hz, the primary decimation element further being configured to reduce the initial sampling rate to a reduced sampling rate as a function of the decimation ratio.

20. The apparatus of claim 19, wherein the initial sampling rate is 1200 Hz.

21. The apparatus of claim 19, wherein the reduced sampling rate is 10 Hz.

22. The apparatus of claim 19, wherein the primary decimation element comprises:

a first filter having a decimation ratio of 2;

a second filter serially coupled to the first filter, the second filter having a decimation ratio of 10; and

a third filter serially coupled to the second filter, the third filter having a decimation ratio of 6.

23. The apparatus of claim 19, further comprising an analog-to-digital (A/D) converter, the A/D converter being configured to receive an analog signal, the A/D converter further being configured to convert the analog signal into the digital signal, the A/D converter further being configured to provide the digital signal to the primary input node.

24. The apparatus of claim 19, further comprising a preliminary decimation element having an input, the preliminary decimation element further having an output, the output of the preliminary decimation element being communicatively coupled to the primary input node, the preliminary decimation element comprising:

a first filter having a decimation ratio of 16; and

a second filter serially coupled to the first filter, the second filter having a decimation ratio of 16.

25. The apparatus of claim 24, further comprising an analog-to-digital (A/D) converter, the A/D converter being configured to receive an analog signal, the A/D converter further being configured to digitize the analog signal, the A/D converter further being configured to provide the digitized signal to the input of the preliminary decimation element.

26. A filtering method, comprising the steps of:

receiving a digital signal, the digital signal having an initial sampling rate, the digital signal further having line noise;

filtering the line noise at 50 Hz;

filtering the line noise at 60 Hz; and

reducing the initial sampling rate of the digital signal to a reduced sampling rate.

27. The method of claim 26, wherein the step of receiving the digital signal comprises the step of receiving a digital signal having a sampling rate of 1200 Hz.

28. The method of claim 26, wherein the step of filtering the line noise at 50 Hz comprises the step of cascading the digital signal through multiple filters.

29. The method of claim 26, wherein the step of filtering the line noise at 60 Hz comprises the step of cascading the digital signal through multiple filters.

30. The method of claim 26, wherein the step of reducing the initial sampling rate comprises the step of cascading the digital signal through multiple filters.

31. The method of claim 26, further comprising the step of cascading the digital signal through multiple filters.

32. The method of claim 31, wherein the step of cascading the digital signal through multiple filters comprises the step of directing the digital signal through a filter having a decimation ratio of 16.

33. The method of claim 31, wherein the step of cascading the digital signal through multiple filters comprises the step of directing the digital signal through a filter having a decimation ratio of 2.

34. The method of claim 31, wherein the step of cascading the digital signal through multiple filters comprises the step of directing the digital signal through a filter having a decimation ratio of 10.

35. The method of claim 31, wherein the step of cascading the digital signal through multiple filters comprises the step of directing the digital signal through a filter having a decimation ratio of 6.

36. The method of claim 26, further comprising the steps of:

receiving an analog data signal from a load cell, the load cell being located on a material metering machine; and

converting the analog signal into the digital signal.

37. The method of claim 26, wherein the step of converting the analog signal comprises the step of:

generating a digital signal having a sampling rate of 1200 Hz.