CN104596598A - Digital-analog hybrid filtering low-flow-velocity electromagnetic flowmeter - Google Patents
Digital-analog hybrid filtering low-flow-velocity electromagnetic flowmeter Download PDFInfo
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- CN104596598A CN104596598A CN201510045963.8A CN201510045963A CN104596598A CN 104596598 A CN104596598 A CN 104596598A CN 201510045963 A CN201510045963 A CN 201510045963A CN 104596598 A CN104596598 A CN 104596598A
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Abstract
The invention relates to a digital-analog hybrid filtering low-flow-velocity electromagnetic flowmeter and a filtering method. When the flow velocity of fluid is lower, the electromagnetic flowmeter is complex in flow signal processing, low in signal to noise ratio and low in resolution ratio. The digital-analog hybrid filtering low-flow-velocity electromagnetic flowmeter comprises a shell (1), wherein a control main board (2) is arranged in the shell; a microcontroller (3) is mounted on the control main board; the microcontroller is respectively connected with an A/D (analog-digital) converting circuit (4), an exciting control circuit (5), an LCD (liquid crystal display) control circuit (6), a key control circuit (7), a storage (8) and a communication interface (9); the A/D converting circuit is connected with a signal processing circuit (10); the exciting control circuit is connected with an exciting driving circuit (11); the exciting driving circuit is connected with a low-flow-velocity electromagnetic flow sensor (12); the LCD control circuit and the key control circuit are respectively connected with a man-machine interaction device (13). The filtering method is fit for the electromagnetic flowmeter.
Description
Technical field:
The present invention relates to a kind of numerical model analysis filtering low flow velocity electromagnetic flowmeter.
Background technology:
Electromagnetic flowmeter, as the main instrument of measuring flow, is widely used in industrial processes, carries out Measurement accuracy to the flow of various pipes inner fluid, flow velocity.The development of electromagnetic flowmeter and application are exactly the development of its Anti-Jamming Technique, and particularly when the velocity ratio of fluid is lower, the process of flow signal is very complicated.Due to its weak output signal, interference and noise large, and the modulate circuit of process low flow velocity flow signal cuts both ways, cause signal to noise ratio (S/N ratio) low, differentiate rate variance, the accuracy of measurement of low flow velocity flow is difficult to raising.Therefore, development and the application of low flow velocity electromagnetic flowmeter is limited.
Summary of the invention:
The object of this invention is to provide a kind of numerical model analysis filtering low flow velocity electromagnetic flowmeter.
Above-mentioned object is realized by following technical scheme:
A kind of numerical model analysis filtering low flow velocity electromagnetic flowmeter, its composition comprises: housing, control mainboard is had in described housing, described control mainboard is provided with microcontroller, described microcontroller respectively with A/D change-over circuit, excitation control circuit, LCD control circuit, key control circuit, storer, communication interface connects, described A/D change-over circuit is connected with signal conditioning circuit, described excitation control circuit is connected with excitatory driving circuit, described excitatory driving circuit is connected with low flow velocity electromagnetic flow transducer, described LCD control circuit, described key control circuit is connected with human-computer interaction device respectively.
Described numerical model analysis filtering low flow velocity electromagnetic flowmeter, described microcontroller comprises single-chip microcomputer, timer, Power supply detector, and the model of described single-chip microcomputer is TMS320F2812PGFA.
Described numerical model analysis filtering low flow velocity electromagnetic flowmeter, described signal conditioning circuit comprises differential amplifier circuit, and described differential amplifier circuit is connected with numerical model analysis wave filter; Described numerical model analysis wave filter comprises multiplying-type digital to analog converter, and described multiplying-type digital to analog converter is connected with low-pass filter, Reference waveform generator ROM respectively, and described Reference waveform generator ROM and address occur to be connected with control circuit.
Described numerical model analysis filtering low flow velocity electromagnetic flowmeter; described hull outside is equipped with human-computer interaction device; described human-computer interaction device comprises LCD display, operation push-button; described LCD display is connected with LCD control circuit, and described operation push-button and LCD control to be connected with described key control circuit.
A filtering method for numerical model analysis filtering low flow velocity electromagnetic flowmeter described in claim 1-4, this filtering method comprises the steps:
If the input signal of wave filter is
, wherein
useful signal pulse,
it is channel
Noise, filter output signal
, wherein
useful signal component,
it is noise component;
If the transfer function of wave filter is
, wish at a time
(carrying out decision instant) makes signal to noise ratio (S/N ratio) be maximum, gets
with
ratio, with
represent, namely
（1）
If
fourier transform be
, then
（2）
?
moment
（3）
If
for white noise, its power spectrum is constant
, output noise
power spectrum be
, can obtain thus
（4）
Formula (4) and formula (3) are substituted into formula (1),
（5）
By Cauchy-Schwartz inequality,
（6）
So the maximum value possible of filter output signal to noise ratio (S/N ratio) is
（7）
The condition reaching maximal value is
（8）
Or
（9）
；
Signal
duration be limited, can realize for making matched filter and the response time short as far as possible, get
, namely
（10）
Reach a conclusion thus: the impulse response of matched filter is desired signal
to Z-axis mirror image and to right translation
.
The filtering method of described numerical model analysis filtering low flow velocity electromagnetic flowmeter, described
regard the impulse response of system as,
for system input,
with
again by low-pass filter filtering after being multiplied in multiplier, its result is equivalent to the filtering of system in claim 5 just, namely
（11）
Optimal filtering result
it is peak value; Numerical model analysis optimal filtering result
it is the maximal value of mean value;
The filtering method of described numerical model analysis filtering low flow velocity electromagnetic flowmeter, the process of described numerical model analysis optimal filtering, numerical model analysis optimal filtering set measured signal as
, have and signal in Reference waveform generator ROM
the reference signal that similar shape is synchronous
, simulating signal
be input to the reference voltage input terminal of multiplying-type digital to analog converter, with benchmark digital signal
in multiplying-type digital to analog converter, realize the multiplying of analog and digital signal, low-pass filter completes integration and to average computing, and the output of low-pass filter is direct current signal
（12）
From analyzing above, this measuring principle can effective restraint speckle to the full extent.
The filtering method of described numerical model analysis filtering low flow velocity electromagnetic flowmeter, the benchmark digital signal synchronous with the induced signal similar shape of sensor output is deposited in advance in described Reference waveform generator ROM, while induced signal sends into the reference voltage input terminal of multiplier and multiplying-type digital to analog converter after amplifying circuit amplifies, reference digital signal in Reference waveform generator ROM is also admitted to multiplier data input pin, and the now output of multiplying-type digital to analog converter is the result that this moment analog quantity and digital quantity carry out product calculation; The benchmark digital reference signal stored in Reference waveform generator ROM is controlled by the address control circuit synchronous with induced signal, be updated periodically data and send into multiplying-type digital to analog converter, realizing the digital analog multiplication computing of benchmark digital signal and actual sensed signal;
The simulating signal that multiplier exports sends into last link-low-pass filter of signal condition, for avoiding the impact of industrial frequency noise, requires that the odd harmonic of the cutoff frequency of this wave filter should avoid 50Hz power frequency.The second order active low-pass filter that design cutoff frequency is 0.5Hz, decays at 3dB place is determined after considering according to characteristics of signals and designing requirement;
The general type of the transport function of second order active low-pass filter is
（13）
When choosing 3dB, have
, wherein, characteristic frequency
, ratio of damping
, gain
;
The output of low-pass filter is the d. c. voltage signal be directly proportional to flow velocity, the incremental noise contained in the induced signal that sensor exports, flow noise and with phase noise etc. all by suppression by a relatively large margin or elimination, improve the accuracy of measurement of signal to noise ratio (S/N ratio) and electromagnetic flowmeter, also extend the range ratio of electromagnetic flowmeter simultaneously.
Beneficial effect:
1. the present invention is due to when flow velocity is lower; the induced voltage signal that flow sensor produces is faint and along with multiple interference and noise; and the amplitude of interference and noise signal is even also large than the amplitude of induced signal itself; by numerical model analysis filtering technique, signal condition is carried out to it; also good inhibiting effect is had on the impact of other interference and noise while effectively eliminating incremental noise; thus obtain the flow signal of more high s/n ratio; accuracy of measurement is high; reliability is strong, good stability, greatly improves the performance index of low flow velocity electromagnetic flowmeter.
Numerical model analysis wave filter of the present invention, be with multiplying-type digital to analog converter for core devices, realize the computing of analog quantity and digital quantity four-quadrant multiplication.Adopt the optimal filtering principle in measurement of correlation, there is the maximum signal to noise ratio under minimum variance meaning and stronger antijamming capability, thus comparatively ideally overcome interference.
Amplifier of the present invention adopts differential amplifier circuit, input impedance is large, have higher common-mode rejection ratio, high-amplification-factor, Low Drift Temperature, low nonlinearity etc., the very faint low-frequency ac signal that can export sensor (usually only have mV level even lower) effectively amplifies simultaneously.
Accompanying drawing illustrates:
Accompanying drawing 1 is structural representation of the present invention.
Accompanying drawing 2 is Part I circuit theory diagrams of single chip circuit in accompanying drawing 1.
Accompanying drawing 3 is Part II circuit theory diagrams of single chip circuit in accompanying drawing 1.
Accompanying drawing 4 is signal conditioning circuit and numerical model analysis Filter Principle block diagrams in accompanying drawing 1.
Accompanying drawing 5 is schematic diagrams of differential amplifier circuit in accompanying drawing 3.
Accompanying drawing 6 is circuit theory diagrams of multiplying-type digital to analog converter in accompanying drawing 3.
Accompanying drawing 7 is low-pass filter circuit schematic diagrams in accompanying drawing 3.
Accompanying drawing 8 is human-computer interaction device theory diagrams of the present invention.
In figure: between same circuits symbol, there is annexation.
Embodiment:
Embodiment 1:
A kind of numerical model analysis filtering low flow velocity electromagnetic flowmeter, its composition comprises: housing 1, have in described housing and control mainboard 2, described control mainboard is provided with microcontroller 3, described microcontroller respectively with A/D change-over circuit 4, excitation control circuit 5, LCD control circuit 6, key control circuit 7, storer 8, communication interface 9 connects, described A/D change-over circuit is connected with signal conditioning circuit 10, described excitation control circuit is connected with excitatory driving circuit 11, described excitatory driving circuit is connected with low flow velocity electromagnetic flow transducer 12, described LCD control circuit, described key control circuit is connected with human-computer interaction device 13 respectively.
Embodiment 2:
Numerical model analysis filtering low flow velocity electromagnetic flowmeter according to embodiment 1, described microcontroller comprises single-chip microcomputer, timer, Power supply detector, and the model of described single-chip microcomputer is TMS320F2812
PGFA。
Embodiment 3:
Numerical model analysis filtering low flow velocity electromagnetic flowmeter according to embodiment 1 or 2, described signal conditioning circuit comprises differential amplifier circuit 14, and described differential amplifier circuit is connected with numerical model analysis wave filter 15; Described numerical model analysis wave filter comprises multiplying-type digital to analog converter 16; described multiplying-type digital to analog converter is connected with low-pass filter 17, Reference waveform generator ROM18 respectively, and described Reference waveform generator ROM and address occur to be connected with control circuit 19.
Embodiment 4:
Numerical model analysis filtering low flow velocity electromagnetic flowmeter according to embodiment 1 or 2; described hull outside is equipped with human-computer interaction device; described human-computer interaction device comprises LCD display 20, operation push-button 21; described LCD display is connected with LCD control circuit, and described operation push-button and LCD control to be connected with described key control circuit.
Embodiment 5:
A filtering method for numerical model analysis filtering low flow velocity electromagnetic flowmeter described in claim 1-4, this filtering method comprises the steps:
If the input signal of wave filter is
, wherein
useful signal pulse,
it is channel
Noise, filter output signal
, wherein
useful signal component,
it is noise component;
If the transfer function of wave filter is
, wish at a time
(carrying out decision instant) makes signal to noise ratio (S/N ratio) be maximum, gets
with
ratio, with
represent, namely
（1）
If
fourier transform be
, then
（2）
?
moment
（3）
If
for white noise, its power spectrum is constant
, output noise
power spectrum be
, can obtain thus
（4）
Formula (4) and formula (3) are substituted into formula (1),
（5）
By Cauchy-Schwartz inequality,
（6）
So the maximum value possible of filter output signal to noise ratio (S/N ratio) is
（7）
The condition reaching maximal value is
（8）
Or
（9）
；
Signal
duration be limited, can realize for making matched filter and the response time short as far as possible, get
, namely
（10）
Reach a conclusion thus: the impulse response of matched filter is desired signal
to Z-axis mirror image and to right translation
.
Embodiment 6:
The filtering method of the numerical model analysis filtering low flow velocity electromagnetic flowmeter according to embodiment 5, described
regard the impulse response of system as,
for system input,
with
again by low-pass filter filtering after being multiplied in multiplier, its result is equivalent to the filtering of system in claim 5 just, namely
（11）
Optimal filtering result
it is peak value; Numerical model analysis optimal filtering result
it is the maximal value of mean value;
Embodiment 7:
The filtering method of the numerical model analysis filtering low flow velocity electromagnetic flowmeter according to embodiment 5 or 6, the process of described numerical model analysis optimal filtering, numerical model analysis optimal filtering set measured signal as
, have and signal in Reference waveform generator ROM
the reference signal that similar shape is synchronous
, simulating signal
be input to the reference voltage input terminal of multiplying-type digital to analog converter, with benchmark digital signal
in multiplying-type digital to analog converter, realize the multiplying of analog and digital signal, low-pass filter completes integration and to average computing, and the output of low-pass filter is direct current signal
（12）
From analyzing above, this measuring principle can effective restraint speckle to the full extent.
Embodiment 8:
The filtering method of the numerical model analysis filtering low flow velocity electromagnetic flowmeter according to embodiment 5 or 6,
The benchmark digital signal synchronous with the induced signal similar shape of sensor output is deposited in advance in described Reference waveform generator ROM, while induced signal sends into the reference voltage input terminal of multiplier and multiplying-type digital to analog converter after amplifying circuit amplifies, reference digital signal in Reference waveform generator ROM is also admitted to multiplier data input pin, and the now output of multiplying-type digital to analog converter is the result that this moment analog quantity and digital quantity carry out product calculation; The benchmark digital reference signal stored in Reference waveform generator ROM is controlled by the address control circuit synchronous with induced signal, be updated periodically data and send into multiplying-type digital to analog converter, realizing the digital analog multiplication computing of benchmark digital signal and actual sensed signal;
The simulating signal that multiplier exports sends into last link-low-pass filter of signal condition, for avoiding the impact of industrial frequency noise, requires that the odd harmonic of the cutoff frequency of this wave filter should avoid 50Hz power frequency.The second order active low-pass filter that design cutoff frequency is 0.5Hz, decays at 3dB place is determined after considering according to characteristics of signals and designing requirement;
The general type of the transport function of second order active low-pass filter is
（13）
When choosing 3dB, have
, wherein, characteristic frequency
, ratio of damping
, gain
;
The output of low-pass filter is the d. c. voltage signal be directly proportional to flow velocity, the incremental noise contained in the induced signal that sensor exports, flow noise and with phase noise etc. all by suppression by a relatively large margin or elimination, improve the accuracy of measurement of signal to noise ratio (S/N ratio) and electromagnetic flowmeter, also extend the range ratio of electromagnetic flowmeter simultaneously.
Claims (9)
1. a numerical model analysis filtering low flow velocity electromagnetic flowmeter, its composition comprises: housing, it is characterized in that: in described housing, have control mainboard, described control mainboard is provided with microcontroller, described microcontroller respectively with A/D change-over circuit, excitation control circuit, LCD control circuit, key control circuit, storer, communication interface connects, described A/D change-over circuit is connected with signal conditioning circuit, described excitation control circuit is connected with excitatory driving circuit, described excitatory driving circuit is connected with low flow velocity electromagnetic flow transducer, described LCD control circuit, described key control circuit is connected with human-computer interaction device respectively.
2. numerical model analysis filtering low flow velocity electromagnetic flowmeter according to claim 1, is characterized in that: described microcontroller comprises single-chip microcomputer, timer, Power supply detector, and the model of described single-chip microcomputer is TMS320F2812PGFA.
3. numerical model analysis filtering low flow velocity electromagnetic flowmeter according to claim 1 and 2, it is characterized in that: described signal conditioning circuit comprises differential amplifier circuit, described differential amplifier circuit is connected with numerical model analysis wave filter; Described numerical model analysis wave filter comprises multiplying-type digital to analog converter, and described multiplying-type digital to analog converter is connected with low-pass filter, Reference waveform generator ROM respectively, and described Reference waveform generator ROM and address occur to be connected with control circuit.
4. numerical model analysis filtering low flow velocity electromagnetic flowmeter according to claim 1 and 2; it is characterized in that: described hull outside is equipped with human-computer interaction device; described human-computer interaction device comprises LCD display, operation push-button; described LCD display is connected with LCD control circuit, and described operation push-button and LCD control to be connected with described key control circuit.
5. a filtering method for the numerical model analysis filtering low flow velocity electromagnetic flowmeter described in claim 1-4, is characterized in that: this filtering method comprises the steps:
If the input signal of wave filter is
, wherein
useful signal pulse,
it is channel
Noise, filter output signal
, wherein
useful signal component,
it is noise component;
If the transfer function of wave filter is
, wish at a time
(carrying out decision instant) makes signal to noise ratio (S/N ratio) be maximum, gets
with
ratio, with
represent, namely
（1）
If
fourier transform be
, then
（2）
?
moment
（3）
If
for white noise, its power spectrum is constant
, output noise
power spectrum be
, can obtain thus
（4）
Formula (4) and formula (3) are substituted into formula (1),
（5）
By Cauchy-Schwartz inequality,
（6）
So the maximum value possible of filter output signal to noise ratio (S/N ratio) is
（7）
The condition reaching maximal value is
（8）
Or
（9）
；
Signal
duration be limited, can realize for making matched filter and the response time short as far as possible, get
, namely
（10）
Reach a conclusion thus: the impulse response of matched filter is desired signal
to Z-axis mirror image and to right translation
.
6. the filtering method of numerical model analysis filtering low flow velocity electromagnetic flowmeter according to claim 5, is characterized in that: described
regard the impulse response of system as,
for system input,
with
again by low-pass filter filtering after being multiplied in multiplier, its result is equivalent to the filtering of system in claim 5 just, namely
（11）
Optimal filtering result
it is peak value; Numerical model analysis optimal filtering result
it is the maximal value of mean value.
7. the filtering method of the numerical model analysis filtering low flow velocity electromagnetic flowmeter according to claim 5 or 6, is characterized in that: the process of described numerical model analysis optimal filtering, numerical model analysis optimal filtering set measured signal as
, have and signal in Reference waveform generator ROM
the reference signal that similar shape is synchronous
, simulating signal
be input to the reference voltage input terminal of multiplying-type digital to analog converter, with benchmark digital signal
in multiplying-type digital to analog converter, realize the multiplying of analog and digital signal, low-pass filter completes integration and to average computing, and the output of low-pass filter is direct current signal
（12）
From analyzing above, this measuring principle can effective restraint speckle to the full extent.
8. the filtering method of the numerical model analysis filtering low flow velocity electromagnetic flowmeter according to claim 5 or 6, it is characterized in that: in described Reference waveform generator ROM, deposit the benchmark digital signal synchronous with the induced signal similar shape of sensor output in advance, while induced signal sends into the reference voltage input terminal of multiplier and multiplying-type digital to analog converter after amplifying circuit amplifies, reference digital signal in Reference waveform generator ROM is also admitted to multiplier data input pin, the now output of multiplying-type digital to analog converter is the result that this moment analog quantity and digital quantity carry out product calculation, the benchmark digital reference signal stored in Reference waveform generator ROM is controlled by the address control circuit synchronous with induced signal, be updated periodically data and send into multiplying-type digital to analog converter, realizing the digital analog multiplication computing of benchmark digital signal and actual sensed signal,
The simulating signal that multiplier exports sends into last link-low-pass filter of signal condition, for avoiding the impact of industrial frequency noise, requires that the odd harmonic of the cutoff frequency of this wave filter should avoid 50Hz power frequency.
9. after considering according to characteristics of signals and designing requirement, determine the second order active low-pass filter that design cutoff frequency is 0.5Hz, decays at 3dB place;
The general type of the transport function of second order active low-pass filter is
（13）
When choosing 3dB, have
, wherein, characteristic frequency
, ratio of damping
, gain
;
The output of low-pass filter is the d. c. voltage signal be directly proportional to flow velocity, the incremental noise contained in the induced signal that sensor exports, flow noise and with phase noise etc. all by suppression by a relatively large margin or elimination, improve the accuracy of measurement of signal to noise ratio (S/N ratio) and electromagnetic flowmeter, also extend the range ratio of electromagnetic flowmeter simultaneously.
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN113340369A (en) * | 2021-04-16 | 2021-09-03 | 中国民用航空适航审定中心 | Signal processing method and device for turbine fuel mass flowmeter |
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| CN202994223U (en) * | 2012-12-30 | 2013-06-12 | 哈尔滨理工大学 | Micro-flow electromagnetic flow meter |
| CN204421980U (en) * | 2015-01-29 | 2015-06-24 | 哈尔滨理工大学 | Numerical model analysis filtering low flow velocity electromagnetic flowmeter |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN113340369A (en) * | 2021-04-16 | 2021-09-03 | 中国民用航空适航审定中心 | Signal processing method and device for turbine fuel mass flowmeter |
| CN113340369B (en) * | 2021-04-16 | 2022-05-03 | 中国民用航空适航审定中心 | Signal processing method and device for turbine fuel mass flowmeter |
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Application publication date: 20150506 |