CN100451561C - Low power consumption digital vortex street flower - Google Patents

Abstract

The present invention relates to an embedded system and a digital signal processing technology in the technical field of instruments and meters. A digital vortex street flow meter with low power consumption is mainly composed of a vortex street sensing head, a charge amplifier, a differential amplifier, an anti-aliasing filter, an embedded microcontroller, a digital signal processor (DSP), etc., wherein the embedded microcontroller and DSP form into a double-core central processing unit. Signals are input into DSP via a host interface after being converted from analog to digital in the microcontroller; processed data is transferred back to the microcontroller via an HPI interface. The microcontroller finishes the functions of display, control, storage and far transmission. The flow meter can finish precise vortex street frequency information extraction in strong noise background, and changes the contradiction that the existing vortex street flow meters need to replace circuits according to caliber, gas and liquid. The present invention can accurately measure vortex street signals whose flow speed is from 0.18 m/s to 6.22 m/s to make the measuring range ration reach 1:35, and can accurately measure vortex street signals whose Reynold number is 4.90*10 basically approaching to a theoretical lower limit value.

Description

Low power consumption digital formula vortex shedding flow meter

Technical field

The invention belongs to the technology of instrument and meter field, be specifically related to embedded system and Digital Signal Processing.

Technical background

Vortex shedding flow meter generally adopts pressure-sensing device that the horizontal alternation lift effect that is subjected on the vortex shedding flow meter vortex generation body is converted to electric signal, extracts the vortex street frequency from electric signal, and then obtains measured flux according to the relation of vortex street frequency and fluid flow.Although vortex shedding flow meter has various advantages, some practical problemss of Chu Xianing have influence on the application and the popularization of this flowmeter in actual applications.Problem mainly comprises: the lower limit range of (1) vortex shedding flow meter is higher than possible in theory minimum value far away; (2) vibration resistance of flowmeter is relatively poor, power-equipment such as the ubiquitous valve of industry spot, pump, compressor and the on-the-spot various strong vibrations source that occurs at random all may make measurement result very big error occur, even causing flowmeter to be difficult to operate as normal, it is particularly evident that these situations show in the lower range scope of flowmeter.The scene installation of the structural design of the existence of foregoing problems and the measuring principle of vortex shedding flow meter, vortex generation body, detecting element performance and structure, flowmeter etc. all has relation, but the topmost factor of limited flow meter performance then is the signal processing method of vortex shedding flow meter.

Under the signal to noise ratio (S/N ratio) condition with higher, the effect that analog signal processing method is handled the flowmeter detection signal is good.But when having comprised bigger periodicity of amplitude or impact noise in, the detection signal lower when signal to noise ratio (S/N ratio), analog signal processing method is the filtering noise composition effectively, and the false triggering when causing shaping easily produces wrong measurement result.The more important thing is, the peak value of useful signal waveform roughly with square being directly proportional of flow velocity (vortex street frequency), therefore when hanging down fluid-velocity survey, the vortex street frequency is lower, signal amplitude is less, signal to noise ratio (S/N ratio) reduces, and the amplitude of regular noise (as hydrodynamic noise) then strengthens relatively, to such an extent as to flood useful signal; Because these situations mainly appear at the lower range section of measurement, the deficiency of signal processing method has directly caused the dwindling of range of flowmeter.In the reality, noise generally will add the low-frequency range that the high pass link is measured with excision to having a strong impact on that measurement result produces in the circuit when removing low discharge; And since different pipe diameters, fluid type to signal band difference in requisition for excision, the element of support circuit can be adjusted accordingly; Above-mentioned situation is artificial has caused that the vortex shedding flow meter measurement range is narrow, product type is complicated, the shortcoming of vibration resistance and interchangeability difference.

At present vortex street flowmeter digital signal is handled and is used still rarely, and the general treatment scheme that adopts of the known vortex shedding flow meter with digital signal processing function is: measuring-signal is sampled and sample sequence is passed to computing machine or digital signal processor; Utilize the frequency domain character of the spectrum analysis software analysis sample sequence of establishment; From analysis result, infer the vortex street frequency.Wherein, the signal processing method of spectrum analysis software employing is the key of whole signal processing flow.But the disposal route that adopts at present shortage is set up signal model and definite simulating scheme at the characteristics of signal and the needs of signal Processing.Owing to comprise the multiple periodic noise composition that is difficult to remove in the vortex shedding flow meter detection signal, can estimate accurately that therefore this algorithm of a plurality of cyclical component parameters in the random signal has great importance for the vortex street frequency information in effective extraction noise background, raising signal processing quality.

Summary of the invention

The purpose of this invention is to provide a kind of low power consumption digital formula vortex shedding flow meter that adopts embedded microcontroller MCU and DSP combination, this flowmeter can be in strong noise background, finishing accurate vortex street frequency information extracts, changing existing flux of vortex street instrument need be according to the contradiction of bore, Medium Replacement circuit component, and can expanded range, especially can be to the accurate measurement of tiny flow quantity signal and low signal-to-noise ratio signal.

Low power consumption digital formula vortex shedding flow meter mainly is made up of vortex street sensing head 1, charge amplifier 2, differential amplifier 3, anti-wave filter 4, embedded microcontroller 5 and the digital signal processor 6 of mixing repeatedly.The input end of flow signal first order charge amplifier 2 in vortex street sensing head 1 incoming analog signal pre-process circuit (Fig. 2) is converted to voltage signal and inserts differential amplifier 3 and the anti-repeatedly wave filter 4 (Fig. 2) that mixes that second level amplifier is formed.Pre-service becomes any one road P6.0 in eight road A/D translation interfaces of analog voltage signal input embedded microcontroller 5 (MCU).Form the double-core CPU (central processing unit) by microcontroller 5 and digital signal processor 6 (DSP), the two connects data line HD0～7 of DSP host interface HPI by one group of optional I/O interface P4 of MCU, any 7 mouth lines of P2 and P3 mouth are connected the control line (Fig. 4 and Fig. 5) of HPI, realize that on the one hand data pass between MCU and DSP mutually, the algorithm routine that will be stored in the MCU program space on the other hand imports among the DSP.Form serial and show (Fig. 5) for any 3 by all the other I/O interfaces of microcontroller 5, P1.1 interface by PWM output is formed the teletransmission circuit, and utilize in two groups of universal asynchronous serial interfaces (UART) of microcontroller 5 optional one group as communication interface 7 (Fig. 5), the work on the spot parameter is write by computing machine by communication interface 7 in the Flash ROM cell of microcontroller and stores.Hardware block diagram of the present invention as shown in Figure 1, the total system structure is mainly divided three parts: simulating signal pre-process circuit, digital signal processing circuit and man-machine Fabric Interface part.The signal of vortex street sensing head 1 output is the charge signal that contains various noises in the vortex shedding flow meter, and amplitude is very little.The simulating signal pre-process circuit is by carrying out the processing of three aspects to the charge signal that collects based on the mimic channel of operational amplifier: 1. the alternation charge signal of flowmeter piezoelectric detection element being exported by the charge amplifier 2 of input stage is converted to voltage signal; 2. realized the amplitude amplification of alternating signal by the enlarging function of differential amplifier 3 and subsequent conditioning circuit; 3. the anti-wave filter 4 that mixes repeatedly that constitutes by simulation low-pass filter has been realized signal mode number conversion filtering before.The simulating signal pre-process circuit is seen shown in Figure 2.Charge amplifier 2 (circuit that the first order amplifier among Fig. 2 is formed) will be imported the high-impedance preamplifier that charge signal converts voltage signal output to, and its output voltage is directly proportional with the input electric charge.Differential amplifier 3 amplifies the signal before the data acquisition sends into the anti-wave filter 4 (circuit that the second level amplifier among Fig. 2 is formed) that mixes repeatedly then.Pretreated signal input MSP430F149 microcontroller 5 one of them A/D translation interface, 12 integrated A/D converters of MSP430F149 are directly gathered the vortex signal after the low-pass filtering, use 3 optional general purpose I/O interface to connect the liquid crystal display device (LCD) of Serial Control, guarantee the low-power consumption of complete machine.The hardware UART interface of MSP430F149 is realized and external communication, is finished parameter management.Digital signal processor 6 also obtains data from single chip microcontroller MSP430F149, and result is sent back MCU as data processing core, and the approach that realizes data transmission is that the host interface (HPI) by DSP is connected with the I/O interface of MCU.Because DSP does not possess non-volatile program storage, the DSP program that the present invention's design utilizes the HPI interface will be stored in the MCU program space is imported among the DSP, and utilizes the operation of Bootloader function on DSP.Core algorithm among the DSP adopts lax trap period map method that signal is carried out digital signal processing, and this algorithm is introduced the maximal possibility estimation process with periodogram, is easy to realize real-time processing.

Lax notch algorithm is based on a kind of maximum likelihood estimate of period map method, promptly earlier the result is made "ball-park" estimate, makes the mistake of estimation reduce gradually to level off to true value until the result again.Consider that in periodogram the spectrum peak of strong harmonic wave always influences the resolution of more weak harmonic wave, in this case, lax notch algorithm highlights more weak harmonic wave by removing strong harmonic wave.Its functional expression is:

$X_M=X-\underset{m=1}{\overset{K-1}{\mathrm{\Σ}}}{\widehat{\mathrm{\α}}}_m\mathrm{\ω}\left({\hat{f}}_m\right)$

$C={\left|\right|X-\underset{m=1}{\overset{K}{\mathrm{\Σ}}}{\widehat{\mathrm{\α}}}_m\mathrm{\ω}\left({\hat{f}}_m\right)\left|\right|}^2$

Satisfy the local convergence condition: Δ C≤ε; ω (f _i)=[1, exp (j2 π f _i) ... exp[j2 π f _i(N-1)]] ^T

The X-frequency-region signal; M-trap number of times; K-harmonic wave sum; ε then be a constant determining according to actual conditions wherein multiple-harmonic frequency maximal possibility estimation formula as shown in the formula:

${\hat{f}}_k=\underset{f}{\max }\frac{1}{N}{\left|\underset{n=0}{\overset{N-1}{\mathrm{\Σ}}}\exp (-2\mathrm{\πfn})x_k\left(n\right)\right|}^2$

At this moment, the maximal possibility estimation of multiple amplitude is seen formula

${\widehat{\mathrm{\&alpha;}}}_k=\frac{1}{N}\underset{n=0}{\overset{N-1}{\mathrm{\&Sigma;}}}\exp (-\mathrm{<figure-callout\; id="2"\; label="j"\; filenames="C20041001900800091.png,C20041001900800092.png"\; state="\{\{state\}\}">j</figure-callout>}2\mathrm{\&pi;}{\hat{f}}_{k}n)x_k\left(n\right)$

Wherein: N---hits;

---the maximal possibility estimation of k subfrequency; F---each harmonic frequency; x _k(n)---discrete sample signals;

---the maximal possibility estimation of k subharmonic amplitude; N=0,1 ..., N-1.

Beneficial effect of the present invention is: the digital signal processor of selecting for use and 16 single chip microcontrollers have super low-power consumption, low-voltage, high anti-jamming capacity and high integration, wherein MCU is inner integrated timer, general purpose I/O, the A/D converter of 12 200kbps, 60KB flash ROM storer, the 2KB ram register, watchdog circuit, rich functions modules such as hardware serial line interface, the present invention utilizes these characteristics to reduce peripheral circuit just, finish powerful control function, and combine with the high-speed computational capability of dsp chip, realized the intellectuality of total system, the low-power consumption and the wide scope of application.Experimental data shows, interference such as the pipe vibration that the present invention can effectively suppress to exist during flowmeter is measured at the scene, flow velocity noise, thus realize that low discharge measures, the lower limit of range extension has had comparatively significantly the range ratio of vortex shedding flow meter and enlarges.Application example of the present invention accurately measurement flow rate makes range ratio arrive 1: 35 from the vortex signal of 0.18m/s～6.22m/s, promptly (on the pipeline of 25mm bore) can accurately to measure Reynolds number be 4.90 * 10 ³The vortex signal of (being that frequency is about 0.18m/s), basically near theoretic lower limit (Reynolds number is 3 * 10 ³).

Description of drawings

Accompanying drawing 1 is an entire system block diagram of the present invention.

Accompanying drawing 2 is simulating signal pre-process circuit figure.

Accompanying drawing 3 is failed to be sold at auction for discharge is real and is decided experiment device schematic diagram.

Accompanying drawing 4 is DSP (digital signal processor) module principle figure.

Accompanying drawing 5 is MCU (micro controller module) schematic diagram.

Accompanying drawing 6 is the 4-20mA power supply remote-transmission module schematic diagram of being made up of the AM402 chip.

Accompanying drawing 7 is the dsp software process flow diagram.

Accompanying drawing 8 is the MSP430 main program flow chart.

Embodiment

The present invention is described further below in conjunction with accompanying drawing 3～accompanying drawing 8 and by embodiment.

At first the present invention adopts method of standard table to carry out on the discharge experimental provision that discharge is real fails to be sold at auction fixed (as shown in Figure 3).The flow experiment is carried out on the device of 25mm bore, and standard scale is the turbo flow meter of 10mm and 15mm bore.Flowmeter A is the vortex street that the present invention designs, and flowmeter B is exactly traditional analogue instrument, is used for comparison.Experimental data shows, thereby the effective lower limit of anti-interference range extension of the present invention has had comparatively significantly the range ratio of vortex shedding flow meter and enlarges.Flux of vortex street with the 25mm bore is counted example, and the vortex street range of traditional analogy method processing signals is generally 1.1m ³/ h～11m ³/ h (range ratio is 1: 10), this moment, the vortex street flow velocity was about 0.62m/s～6.22m/s, can only cover the vortex signal frequency band of a very little part like this.Experiment shows, the present invention accurately measurement flow rate makes range ratio arrive 1: 35 from the vortex signal of 0.18m/s～6.22m/s, promptly (on the pipeline of 25mm bore) can accurately to measure Reynolds number be 4.90 * 10 ³The vortex signal of (being that frequency is about 0.18m/s), basically near theoretic lower limit (Reynolds number is 3 * 10 ³), (Reynolds number is 15 * 10 and the vortex shedding flow meter of the analogy method of using simultaneously generally can only detect the vortex signal of flow velocity more than 0.62m/s ³About), so the present invention is being fruitful aspect the range ratio that enlarges vortex shedding flow meter.And because the chip of selecting for use is a super low-power consumption, module integrated level height so the power consumption of system can be controlled at below the 4mA, can be realized the teletransmission of 4～20mA two-wire system, has made things convenient for the installation and the signal transmission of field instrument.

The DSP of present embodiment selects TMS320C5416 (as Fig. 4) for use, and it is produced by TI company is 16 fixed-point DSP chip that are subordinated to TMS320C54x series.DSP is as data processing core, mainly obtain data from single chip microcontroller MSP430F149, and result sent back MCU, the approach that realizes data transmission is that the host interface (HPI) by DSP is connected with the I/O interface of MCU, because MSP430F149 has 6 groups of 8 I/O interfaces, select the HD0-7 of P4 mouth as data port connection DSP in the present embodiment, any 7 mouth lines of P2 and P3 mouth are connected the control signal wire of HPI.Because DSP does not possess non-volatile program storage, the DSP program of utilizing the HPI interface will be stored in the MCU program space is imported among the DSP, and utilizes the operation of Bootloader function on DSP.

Microcontroller 5 (MCU) is selected 16 single chip microcontroller MSP430F149 (as Fig. 5) of TI company for use.12 integrated A/D converters of MSP430F149 are directly gathered the simulation vortex signal after the low-pass filtering, have omitted the follow-up shaping circuit of traditional vortex street, have improved the versatility of circuit.Use 3 optional general purpose I/O interface to connect the LCD display part of Serial Control, guarantee the low-power consumption of complete machine.One group of hardware universal asynchronous serial interface (UART) of MSP430F149 is realized and external communication, finish parameter management, inner Flash ROM storage running data, WDT and DCOCLK circuit module guarantee the reliability of total system electrification reset, oscillator starting of oscillation, program run.In addition, system provides 3.3V operating voltage by AM402 and PS767D301 power supply chip to the interface circuit of micro controller system and DSP, provide 1.5V core voltage to dsp chip, and by connecting the P1.1 interface that MSP430F149 possesses PWM output, AM402 and its peripheral circuit have been formed the remote-transmission module (as shown in Figure 6) of 4-20mA signal, make that the automatic monitoring of industry spot and bus management are conveniently realized.

The present invention adopts host interface HPI to import program by the Flash ROM of MCU to DSP, the HPI initialization is finished by MCU, DSP finishes the interruption of self and the initial work of other work registers then, enter query State, wait for that MCU will adopt the data of coming and send into designated space, gather and transmit in case finish, the DSP computing of trap period map method that promptly begins to relax, and will calculate gained frequency f substitution following formula, finish final flow rate calculation, result of calculation is fetched processing such as carrying out follow-up demonstration, storage by MCU.The software design flow process of DSP part as shown in Figure 7.

$Q=3600\&times;\frac{f}{K}$ Q---fluid volume flow wherein, the instrument coefficient of K---demarcation.

MCU partly realizes functions such as data presentation, storage and teletransmission, and during operation, the MSP430F149 initialization is provided with clock frequency and liquid crystal driver earlier, hardware serial ports, A/D modular converter, general purpose I/O interface etc.MCU initialization HPI interface then, and the DSP program imported, the work of DSP started.After initialization was finished, MSP430F149 checked that serial ports has the printenv input, if there is not parameter to insert, then calls parameter in the past, and the down-stream parameter management passes through to interrupt realizing.After MCU enters major cycle, program was the cycle with 1 second, by A/D continuous acquisition data, per 256 data are imported among the DSP for one group, fetch last operation result again, compensate and correct, relatively bound is carried out data presentation and teletransmission and is handled, and then corresponding marker bit is carried out set, enter low-power consumption mode, return major cycle by withdrawing from low-power consumption mode after regularly interruption is returned again.Main program flow chart is seen shown in Figure 8.

Claims (2)

1. low power consumption digital formula vortex shedding flow meter is characterized in that the traffic figure Signal Processing uses lax notch algorithm and carry out, and its functional expression is:

$X_M=X-\underset{m=1}{\overset{K-1}{\mathrm{\&Sigma;}}}{\widehat{\mathrm{\&alpha;}}}_m\mathrm{\&omega;}\left({\hat{f}}_m\right)$

$C={\left|\right|X-\underset{m=1}{\overset{K}{\mathrm{\&Sigma;}}}{\widehat{\mathrm{\&alpha;}}}_m\mathrm{\&omega;}\left({\hat{f}}_m\right)\left|\right|}^2$

Satisfy the local convergence condition: Δ C≤ε; ω (f _i)=[1, exp (j2 π f _i) ... exp[j2 π f _i(N-1)]] ^T

In the formula: the X-frequency-region signal; M-trap number of times; K-harmonic wave sum; ε then is a constant of determining according to actual conditions, wherein the maximal possibility estimation of complex frequency and multiple amplitude formula as follows

${\hat{f}}_k=\underset{f}{\max }\frac{1}{N}{\left|\underset{n=0}{\overset{N-1}{\mathrm{\&Sigma;}}}\exp (-2\mathrm{\&pi;fn})x_k\left(n\right)\right|}^2$

${\widehat{\mathrm{\&alpha;}}}_k=\frac{1}{N}\underset{n=0}{\overset{N-1}{\mathrm{\&Sigma;}}}\exp (-j2\mathrm{\&pi;}{\hat{f}}_{k}n)x_k\left(n\right)$

In the formula: N---hits;

---the maximal possibility estimation of k subfrequency; F---each harmonic frequency; x _k(n)--discrete sample signals; ---the maximal possibility estimation of k subharmonic amplitude; N=0,1 ..., N-1.

2. according to the described low power consumption digital formula of claim 1 vortex shedding flow meter, mainly by vortex street sensing head (1), charge amplifier (2), differential amplifier (3), the anti-repeatedly wave filter (4) that mixes, embedded microcontroller (5) and digital signal processor (6) are formed, the input end that it is characterized in that the charge amplifier (2) of flow signal in vortex street sensing head (1) incoming analog signal pre-process circuit, be converted to voltage signal and insert the differential amplifier of forming by second level amplifier (3), insert the anti-repeatedly wave filter (4) that mixes then, pre-service becomes analog voltage signal to import any one tunnel in eight road A/D translation interfaces of embedded microcontroller (5), form the double-core CPU (central processing unit) by embedded microcontroller (5) and digital signal processor (6), the two connects the data line HD 0～7 of DSP host interface HPI by one group of optional I/O interface of embedded microcontroller (5), any 7 mouth lines of the P2 of embedded microcontroller (5) and P3 mouth are connected the control line of HPI, realize that data pass mutually between embedded microcontroller (5) and digital signal processor (6), and the algorithm routine that will be stored in embedded microcontroller (5) program space imports in the digital signal processor (6), form serial and show for any 3 by all the other I/O interfaces of embedded microcontroller (5), PWM output interface by embedded microcontroller (5) is formed the teletransmission circuit, and utilize in two groups of universal asynchronous serial interfaces of embedded microcontroller (5) optional one group as communication interface (7), the work on the spot parameter is write by computing machine by communication interface (7) in the Flash ROM cell of embedded microcontroller (5) and stores.

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