CN100470207C - Low-power consumption two-wire system vortex flowmeter - Google Patents
Low-power consumption two-wire system vortex flowmeter Download PDFInfo
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- CN100470207C CN100470207C CNB2007101620745A CN200710162074A CN100470207C CN 100470207 C CN100470207 C CN 100470207C CN B2007101620745 A CNB2007101620745 A CN B2007101620745A CN 200710162074 A CN200710162074 A CN 200710162074A CN 100470207 C CN100470207 C CN 100470207C
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Abstract
The present invention relates to the flow detection field, in particular to a low power consumption two-wire system vortex street flowmeter which consists of a piezoelectric transducer, a charge amplifier, a voltage amplifier, a program-controlled amplifier, a lowpass, a voltage follower, a peak detection circuit, a band-pass filter set, a multiway switch gate circuit, a wave shaping circuit, a singlechip, a man-machine interface circuit and a 4-20 mA output and power management circuit, wherein, the singlechip detects the peak value and the frequency of the vortex street signal to amplify and filter the vortex flow signals by controlling the program-controlled amplifier and the band-pass filter. The technology overcomes the problems that the prior art can not achieve low power consumption while measuring small flow, expanding measuring range rate and improving measuring precision effectively. While ensuring measuring small flow, expanding measuring range rate and improving measuring precision effectively, the invention achieves low power consumption of outputting the direct current of 4-20 mA and the operating current less than 4mA and achieves the two-wire system operation.
Description
Technical field
The present invention relates to field of flow detection, be a kind of low-power and two-wire vortex shedding flowmeter, particularly a kind of is low-power consumption, the two-wire system vortex flowmeter signal processing system that core, power spectrum analysis combine with the hardware band-pass filter group with single-chip microcomputer (MCU).
Background technology
Vortex shedding flow meter has the many characteristics of measuring media kind, is widely used in the measurement of fluid flow field.But, conventional signal processing method, i.e. amplification, shaping, filtering and counting can not be measured low discharge effectively, range ratio is limited and can not guarantee the in-site measurement precision.Simultaneously, low-power consumption, the two-wire system instrument of 4～20mA DC current need be exported in some application scenarios, promptly from the angle of electricity, instrument has only two lines with outside being connected, power lead and signal wire are multiplexing, by 24V (perhaps 12V) DC power supply, direct supply is contacted mutually with sampling (load) resistance.4mA represents the minimum value of instrument output, and 20mA represents the maximal value of instrument output, so the working current of instrument itself must could guarantee low-power consumption less than 4mA.
Summary of the invention
The technical problem to be solved in the present invention provide a kind of can effectively measure low discharge with expanded range than, guarantee measuring accuracy, be output as 4～20mA DC current, working current is less than the low-power and two-wire vortex shedding flowmeter of 4mA.
The technical solution adopted in the present invention is: low-power and two-wire vortex shedding flowmeter comprises piezoelectric sensor, charge amplifier, voltage amplifier, programmable amplifier, low-pass filter, voltage follower, peak detection circuit, bandpass filter group, multi-way switch gating circuit, shaping circuit, single-chip microcomputer, man-machine interface circuit and 4～20mA output and electric power management circuit.
The charge signal of piezoelectric sensor output changes voltage signal into through charge amplifier, again through being divided into 3 the tunnel behind voltage amplifier, programmable amplifier, the low-pass filter, the 1 road signal is delivered to the ADC input end of single-chip microcomputer through voltage follower, the ADC sampling and the conversion that are carried by single-chip microcomputer become digital quantity, and single-chip microcomputer is to the signal fast Fourier transform (FFT) of counting less, do power spectrum analysis, obtain the frequency values of signal, come the passage of select tape bandpass filter group, carry out filtering; The 2 road signal is delivered to peak detection circuit, and the peak value of peak detection circuit detection signal is also delivered to the ADC input end of single-chip microcomputer, and single-chip microcomputer is sampled to the peak value of signal and changed, and adjusts the enlargement factor of programmable amplifier; The 3 road signal is through voltage follower, deliver to the bandpass filter group and carry out filtering, decide by the spectrum analysis result of single-chip microcomputer certain road filtering signal is carried out shaping, signal after the shaping is delivered to the timer input end of single-chip microcomputer, count, single-chip microcomputer is presented at flow information on the LCD according to count results, and, deliver to 4～20mA output and convert the output of 4～20mA current signal to through V/I with electric power management circuit by self DAC conversion.
Charge amplifier is made up of amplifier U4A, capacitor C 1, C2, C3, C4, C5, C6, C41, resistance R 2, R3, capacitor C 1 is connected in reverse input end, capacitor C 2 is connected in positive input, capacitor C 5, C6, resistance R 3 are parallel between reverse input end and the output terminal, are connected in positive input after capacitor C 3, C4, resistance R 2 parallel connections.
Voltage amplifier is made up of amplifier U5B, capacitor C 29, resistance R 4, R5, R6, and resistance R 4 is connected in reverse input end, and resistance R 5 is connected in positive input, and resistance R 6 and capacitor C 29 are parallel between reverse input end and the output terminal.
Programmable amplifier is made up of amplifier U3A, digital regulation resistance U8, capacitor C 42, resistance R 7, R8, R9, the output of digital regulation resistance U8 is connected with the reverse input end of amplifier through resistance R 8, resistance R 7 also is connected in reverse input end, resistance R 9 is connected in positive input, the chip select line of digital regulation resistance, clock line and data line link to each other with the universal I/O port of single-chip microcomputer, by the resistance value of Single-chip Controlling digital regulation resistance, thus the enlargement factor of adjustment amplifier.
Low-pass filter is made up of amplifier U3B, capacitor C 8, C9, resistance R 10, R11, R12, R13, the output of programmable amplifier is connected in the amplifier reverse input end through resistance R 10, R11, node between resistance R 10, the R11 is by capacitor C 8 ground connection, be connected with amplifier out by resistance R 12, also be connected capacitor C 9 between the reverse input end of amplifier and the output terminal, resistance R 13 is connected in positive input, and the output terminal of amplifier U3B connects current-limiting resistance R15, schottky diode D7.
Voltage follower is made up of amplifier U3C and amplifier U3D, and two amplifiers are relation in parallel, and positive input receives the output signal that described low-pass filter is sent here through resistance R 15, reverse input end and output terminal short circuit.
Peak detection circuit is by amplifier U6A, U6B, diode D1, field effect transistor Q1, capacitor C 10, C43, resistance R 14 is formed, the positive input of amplifier U6A receives the output signal that described low-pass filter is sent here through resistance R 15, its output terminal is through resistance R 14, diode D1 is connected with amplifier U6B positive input, amplifier U6B positive input is also by field effect transistor Q1, capacitor C 10 ground connection, the output terminal of amplifier U6B and reverse input end short circuit, simultaneously also with the reverse input end short circuit of amplifier U6A, the grid of the field effect transistor in the peak detection circuit links to each other with the universal I/O port of single-chip microcomputer, and the output of peak detection circuit is connected to the ADC input end of single-chip microcomputer; The break-make of Single-chip Controlling field effect transistor, thereby the discharging and recharging of control capacitance make the peak value of peak detection circuit output in ought be for the previous period; Single-chip microcomputer is sampled to the peak signal of peak detection circuit output and is changed, and goes to adjust the resistance value of digital regulation resistance again according to peak value.
The bandpass filter group is made up of 8 bandpass filter, is respectively amplifier U1A, capacitor C 11, C12, resistance R 21, R22, R23, R24, decoupling capacitance C45; Amplifier U1B, capacitor C 13, C14, resistance R 25, R26, R27, R28; Amplifier U1C, capacitor C 15, C16, resistance R 29, R30, R31, R32; Amplifier U1D, capacitor C 17, C18, resistance R 33, R34, R35, R36; Amplifier U2A, capacitor C 19, C20, resistance R 37, R38, R39, R40, decoupling capacitance C46; Amplifier U2B, capacitor C 21, C22, resistance R 41, R42, R43, R44; Amplifier U2C, capacitor C 23, C24, resistance R 45, R46, R47, R48; Amplifier U2D, capacitor C 25, C26, resistance R 49, R50, R51, R52, the circuit structure of these 8 bandpass filter is identical, parameter is different, thereby passband is different, but interconnects, cover the frequency band range of vortex shedding flow meter, and have certain overlapping between adjacent passband;
Wherein, input is connected in the reverse input end of amplifier U1A through resistance R 21, capacitor C 11, node between resistance R 21, the capacitor C 11 is connected with output terminal by capacitor C 12, by resistance R 22 ground connection, resistance R 23 is connected between reverse input end and the output terminal, resistance R 24 connects and positive input, and the connection of all the other seven bandpass filter is consistent with said structure.
The multi-way switch gating circuit is made up of U13, and its 8 input ends link to each other with 8 passages of bandpass filter group respectively, and common port links to each other with the input end of Schmidt trigger U14A, and 3 control line A, B, C link to each other with single-chip microcomputer respectively.
Shaping circuit is made up of Schmidt trigger U14A, and its input end is connected with the common port of multi-way switch gating circuit, and output terminal is connected with single-chip microcomputer.
The single-chip microcomputer model is MSP430F1611.
In 4～20mA output and the electric power management circuit, 4～20mA output circuit is by 4～20mA electric current loop transmitter XTR115, diode D2, D3, D4, D5, stabilivolt D6, triode Q2, reference source U7, amplifier U5A, resistance R 61, R62, R63, R64, capacitor C 31, C33, C34, C44, magnetic bead L1 forms, the voltage signal of single-chip microcomputer DAC output is through resistance R 61, R62 and R63 deliver to the 2nd pin of XTR115, XTR115 produces corresponding 4～20mA current signal and exports from the 4th pin, D2, D3, D4, D5 forms electric bridge, C34 is a filter capacitor, stabilivolt D6 plays pressure stabilization function, the difference part of triode Q2 compensation XTR115 output current and system consumption electric current, the 8th pin output 5V DC voltage of XTR115 links to each other with the 2nd pin of U9 in the electric power management circuit, raise the output level of U9,5V is provided power supply, U8 provides power supply for digital regulation resistance, R64, U7, C31 and U5A form reference power source, 1.235V is provided reference voltage Vref, C44 is a decoupling capacitance, and magnetic bead L1 connects simulation ground and digitally.
Electric power management circuit is by DC/DC converter U11, three terminal regulator U9, resistance R 65, R66, R67, R70, capacitor C 38, C39, C51, C37, C48, inductance L 2 is formed, outside 24V supply voltage is added in the 1st pin of three terminal regulator U9, after voltage stabilizing, export by the 3rd pin of U9, the output voltage of the 3rd pin is added in the 1st pin and the 8th pin of DC/DC transducer U11, respectively as input and the enable signal of U11, R70 and C48 form charging circuit, the 5V voltage that is provided by U10 the 8th pin charges to charging circuit, realizes each power supply chip U9 by low-voltage monitoring and charging circuit, U10, the electric sequence of U11.
The 9th pin SW of U11 is the voltage output pin, and output voltage is exported through after the filtering of inductance L 2, and C38 is a filter capacitor, and C39 is a storage capacitor, and the 4th pin of U11 links to each other with the 23rd pin P2.3 of single-chip microcomputer, monitors as system low-voltage.
The man-machine interface circuit is made up of keyboard circuit and LCD display circuit, is connected with single-chip microcomputer respectively.
Advantage of the present invention is: the present invention has overcome the existing in prior technology weak point, and the present invention adopts low-power scm, by the fast Fourier transform (FFT) of counting less, carries out power spectrum analysis, determines the frequency of vortex signal; Design one group of hardware band-pass filter, its passband covers the frequency band of vortex signal, selects concrete bandpass filter according to the analysis of spectrum result, carries out auto adapted filtering, eliminates on-the-spot noise to greatest extent, improves measuring accuracy.Simultaneously, the programmable amplifier that design digital regulation resistance and operational amplifier are formed is by the amplitude of peak detection circuit measurement vortex signal, determine the enlargement factor of programmable amplifier, make signal amplitude be in optimum range, realize the measurement of low discharge, the expanded range ratio.
Compared with prior art, it is very wide to have overcome conventional filter transmission band, the problem of noise removing ability; Under the limited condition of single-chip microcomputer arithmetic speed and memory capacity, realized digital signal processing, and guaranteed the real-time handled; Adopt low-power scm and output circuit, the working current that makes instrument is less than 4mA, and output current is 4-20mA, has realized two-wire system work.
Description of drawings
Fig. 1 is the hardware block diagram of system of the present invention.
Fig. 2 is the circuit theory diagrams of charge amplifier and voltage amplifier in the system of the present invention.
Fig. 3 is the circuit theory diagrams of programmable amplifier, low-pass filter, voltage follower and peak detection circuit in the system of the present invention.
Fig. 4 is a singlechip chip pin wiring schematic diagram in the system of the present invention.
Fig. 5 is the circuit theory diagrams of bandpass filter group in the system of the present invention
Fig. 6 is the circuit theory diagrams of 4～20mA output and electric power management circuit in the system of the present invention.
Fig. 7 is the circuit theory diagrams of multi-way switch and shaping circuit in the system of the present invention.
Fig. 8 is a keyboard wiring schematic diagram in the system of the present invention.
Fig. 9 is a LCD display chip wiring schematic diagram in the system of the present invention.
Figure 10 is a system software block diagram of the present invention.
Figure 11 is a master monitor process flow diagram in the system of the present invention.
Figure 12 is a programmable amplifier adjusting module process flow diagram in the system of the present invention.
Figure 13 is a computing module process flow diagram in the system of the present invention.
Figure 14 is a hardware timer interrupt service routine process flow diagram in the system of the present invention.
Figure 15 triggers ADC sample clock generator interrupt service routine process flow diagram in the system of the present invention.
Embodiment
The present invention is further illustrated below in conjunction with accompanying drawing.
Design philosophy of the present invention is: both adopted digital signal processing method, guaranteed that again instrument is low-power consumption work, so, adopting the low-power scm fast Fourier transform (FFT) of counting less, performance period, atlas analysis was determined the frequency values of vortex signal; Design one group of hardware band-pass filter, its passband covers the frequency band at vortex signal place, selects concrete bandpass filter according to the analysis of spectrum result, carries out auto adapted filtering, eliminate the influence of various harmonic waves and on-the-spot noise to greatest extent, improve measuring accuracy measuring.Adopt digital regulation resistance and operational amplifier to form programmable amplifier, detect the amplitude of determining vortex signal by peak value, adjust the enlargement factor of programmable amplifier, make the amplitude of signal reach optimum range, the needs that adapt to the measurement of big flow and low discharge, the expanded range ratio.Select the singlechip chip of low-power consumption for use, and supporting with it output circuit and the electric power management circuit of design, guaranteeing the instrumentation electric current less than 4mA, output current is 4-20mA, realizes two-wire system work.
The general structure of system of the present invention as shown in Figure 1.System of the present invention is made up of with electric power management circuit charge amplifier, voltage amplifier, programmable amplifier, low-pass filter, voltage follower circuit, peak detection circuit, bandpass filter group, multi-way switch, shaping circuit, single-chip microcomputer MSP430F1611 and peripheral chip, man-machine interface circuit and 4～20mA output.
The course of work of system of the present invention is: from the faint charge signal of piezoelectric sensor output, at first change it into voltage signal through charge amplifier, because amplitude is very little, so, again through one-level fixing voltage amplifier and one-level programmable amplifier.Signal after the amplification is through low-pass filter, and the high frequency interference in the filtered signal is divided into 3 the tunnel then.The 1 road signal is by voltage follower (impact damper) output, and ADC sampling and conversion by single-chip microcomputer carries become digital quantity.The FFT that single-chip microcomputer is counted less to signal does power spectrum analysis, obtains the frequency values of signal, comes the passage of select tape bandpass filter group.The 2 road signal is delivered to peak detection circuit; Peak detection circuit is delivered to the peak value of signal the input end of Chip Microcomputer A C; Single-chip microcomputer is sampled to the peak value of signal and is changed, and adjusts the enlargement factor of programmable amplifier according to peak value, makes the amplitude of signal reach optimum range.The 3 road signal is delivered to the bandpass filter group through voltage follower, carries out filtering; Decide by the spectrum analysis result of single-chip microcomputer certain road filtering signal is carried out shaping; Come gating by selected that road filtering signal of single-chip microcomputer by the multi-way switch gating circuit, shaping circuit carries out shaping to this road signal, and the signal after the shaping is delivered to the timer input end of single-chip microcomputer, counts.Single-chip microcomputer is presented at flow information on the LCD according to count results, and passes through the DAC conversion of self, delivers to 4～20mA output and electric power management circuit, converts the output of 4～20mA current signal to through V/I.
As shown in Figure 2, vortex flow sensors, i.e. the charge signal of piezoelectric sensor output becomes voltage signal, and has reduced output impedance via the charge amplifier that amplifier U4A, capacitor C 1, C2, C3, C4, C5, C6, C41, resistance R 2, R3 form.By capacitance C7, remove the flip-flop in the signal.Single-stage enlargement factor for fear of programmable amplifier is excessive, so the mode that adopts classification to amplify promptly added the fixing voltage amplifier of one-level enlargement factor before programmable amplifier.This amplifying circuit is made up of amplifier U5B, capacitor C 29, resistance R 4, R5, R6, and essence is a single order low-pass filtering amplifying circuit.After the filtering and amplification of vortex signal through this circuit, deliver to the programmable amplifier of forming by amplifier U3A, digital regulation resistance U8 AD5162, capacitor C 42, resistance R 7, R8, R9, as shown in Figure 3.
Adopting programmable amplifier is the relation that the amplitude of considering the vortex flow sensors output signal becomes with frequency square, and the frequency range broad of vortex signal, so the signal amplitude variation range is very big.And during the flow of same sensor measurement different medium, the difference of signal amplitude is also very big.In order to guarantee that under different frequency and the different medium situation, it is equal that the amplitude of vortex street sensor signal keeps substantially, with the expanded range ratio, and make the voltage magnitude of delivering to Chip Microcomputer A C input end near full scale, guaranteeing enough resolution, so, programmable amplifier adopted.Form programmable amplifier by low consumed power operational amplifier and digital regulation resistance AD5162, cost is low, and is low in energy consumption.AD5162 is the digital regulation resistance that a binary channels, each passage have 256 taps, and power consumption is extremely low, and the quiescent current maximum has only 6 microamperes.The every passage of AD5162 three port: A are arranged, B, W, wherein, A, B are two stiff ends, resistance is R between two ends
AB=100k Ω; W is a tap terminals, and the position of tap is decided by the serial data that writes potentiometer: when writing 00H, W is connected with B; When writing FFH, W is connected with A.When W end and A short circuit, there is following relation between the serial data that writes and the resistance of digital regulation resistance:
Wherein, R
WB(D) be the resistance between W end and B end, the i.e. resistance of current digital regulation resistance; D is the serial data value that writes, and its scope is 00H～FFH, promptly 0～255; R
WBe the connection resistance between tap.By the ABC of inverting amplifier as can be known, the enlargement factor of programmable amplifying circuit is:
In system of the present invention, only use one of them passage of AD5162, another passage stay do standby.
The chip selection signal CS of AD5162 links to each other with the 28th pin P3.0 mouth of single-chip microcomputer MSP430F1611 (hereinafter to be referred as single-chip microcomputer), as shown in Figure 4; Serial data input end SDI links to each other with the 29th pin P3.1 mouth of single-chip microcomputer; Input end of clock CLK links to each other with the 31st pin P3.3 mouth of single-chip microcomputer.Come the size of control figure potentiometer resistance value like this by single-chip microcomputer, just adjust the enlargement factor of programmable amplifier.ADC uses the internal reference source, and the full scale voltage of input end is set at 2.5V.And the signal amplitude of charge amplifier output has only tens mV, differs far away with the reference voltage of ADC.Detect if directly it is carried out peak value, precision can be very low.So system of the present invention carries out peak value to the signal after amplifying through program-controlled voltage and detects; Then, extrapolate the amplitude of original signal, calculate only enlargement factor again, digital regulation resistance is adjusted according to current enlargement factor.Consider in the vortex flowmeter signals after electric charge amplification and program control amplification to be mixed with high frequency interference and other noise,, earlier signal is carried out low-pass filtering, carry out peak value again and detect in order to reduce measuring error.
As shown in Figure 3, the second order active low-pass filter circuit is made up of amplifier U3B, capacitor C 8, C9, resistance R 10, R11, R12, R13.R15 is a current-limiting resistance.D7 is a schottky diode, plays clamped effect, and the ADC of protection single-chip microcomputer is not damaged.
Filtered signal is divided into 3 the tunnel.The voltage follower that the 1 tunnel process is made up of amplifier U3C is output as Signal, delivers to the 59th pin P6.0/A0 of single-chip microcomputer, as shown in Figure 4, and for the laggard line period atlas analysis of Chip Microcomputer A C sample conversion.The voltage follower that the 2 tunnel process is made up of amplifier U3D is output as Vol, delivers to the bandpass filter group and carries out filtering, as shown in Figure 5.The 3 the tunnel receives the peak detection circuit of being made up of amplifier U6A, U6B, diode D1, field effect transistor (MOSFET) Q1, capacitor C 10, C43, resistance R 14, carries out peak value and detects.
Bias voltage Vref in foregoing charge amplifier, voltage amplifier, programmable amplifier and the low-pass filter provides by the U5A in 4～20mA output and the electric power management circuit, as shown in Figure 6.
In peak detection circuit, the effect of R14 is the charging current that limits when field effect transistor Q1 discharges capacitor C 10; The effect of diode D1 is to guarantee can only carry out unidirectional charging to capacitor C 10; Capacitor C 10 remains the maximal value of signal amplitude.The effect of Q1 is to capacitor discharge, the 40th pin of its grid G and single-chip microcomputer, and promptly universaling I/O port P4.4 links to each other.The break-make of Single-chip Controlling field effect transistor, thereby the discharging and recharging of control capacitance, promptly when this I/O mouth is high level, Q1 conducting, capacitor C 10 discharges; When this I/O mouth was low level, Q1 disconnected, capacitor C 10 chargings, and the peak value of holding signal is for Chip Microcomputer A C sampling.The output of peak detection circuit, promptly the 7th pin Peak of U6B is connected to single-chip microcomputer the 60th pin P6.1/A1.Single-chip microcomputer is sampled to peak value and is changed, and goes to adjust the resistance value of digital regulation resistance again according to peak value, realizes the adjustment to the programmable amplifier enlargement factor.
Though the vortex flow sensors signal has passed through foregoing low-pass filter, some high-frequency signals are eliminated.But because the variation range broad of vortex signal frequency, for example, establishing range ratio is 20:1, roughly is 70Hz～1400Hz for the frequency range of the vortex shedding flow meter measurement gas flow of 40mm bore.So the cutoff frequency of low-pass filter must be established than higher, in general, be greater than several times of 1400Hz.So, in this frequency band range, may comprise first-harmonic, harmonic wave and the noise of vortex signal.If this signal is directly carried out shaping and counting,, make measurement result bigger error occur because harmonic wave and The noise are easy to cause the false triggering of Schmidt trigger.At this problem, one group of analog band-pass filter of system design of the present invention, for example, 8 bandpass filter.The circuit structure of these 8 bandpass filter is identical, parameter difference, i.e. passband difference.Their passband is interconnected, and the width of passband increases progressively step by step, and to a certain degree overlapping arranged between the frequency band, and frequency range 70Hz～1400Hz of vortex shedding flow meter is covered.The concrete output signal of which wave filter of selecting is carried out shaping and counting, by single-chip microcomputer vortex signal is carried out results of spectral and decides.Be that single-chip microcomputer carries out power spectrum analysis to the vortex street sensor signal that collects, determine the scope of vortex signal; In view of the above, determine to carry out shaping and counting, can farthest eliminate noise and harmonic wave like this, avoid false triggering, guarantee the precision of counting the influence of vortex signal with the signal after which band-pass filter.
As shown in Figure 5, but the analog band-pass filter group form by 8 different bandpass filter of the identical parameter of structure.They are respectively amplifier U1A, capacitor C 11, C12, resistance R 21, R22, R23, R24, decoupling capacitance C45; Amplifier U1B, capacitor C 13, C14, resistance R 25, R26, R27, R28; Amplifier U1C, capacitor C 15, C16, resistance R 29, R30, R31, R32; Amplifier U1D, capacitor C 17, C18, resistance R 33, R34, R35, R36; Amplifier U2A, capacitor C 19, C20, resistance R 37, R38, R39, R40, decoupling capacitance C46; Amplifier U2B, capacitor C 21, C22, resistance R 41, R42, R43, R44; Amplifier U2C, capacitor C 23, C24, resistance R 45, R46, R47, R48; Amplifier U2D, capacitor C 25, C26, resistance R 49, R50, R51, R52.Bias voltage Vref in the bandpass filter group is provided with electric power management circuit by 4～20mA output.
8 wave filters in the bandpass filter group all have output, and still, the output signal of having only a wave filter is to represent vortex flowmeter signals and be subjected to disturbing effect little.System of the present invention selects for use 8 to select 1 multi-way switch 74HC4051, shown in U13 among Fig. 7.8 input ends of this device link to each other with 8 passages of bandpass filter group respectively, common port is that switch output links to each other with the input end of Schmidt trigger U14A, 3 control line A, B, C link to each other with I/O mouth P4.5, P4.6, the P4.7 of single-chip microcomputer respectively, as shown in Figure 4.U13 comes the corresponding passage of gating according to the level of 3 tunnel control pins, promptly comes the corresponding passage of gating according to the single-chip microcomputer results of spectral.Is through filtering, contains the vortex signal of minimum noise by the signal of gating, send into Schmidt trigger U14A and carry out shaping, be output as the square wave of rule, send into again in the timer (the 39th pin P4.3) of single-chip microcomputer and count.
System of the present invention adopts the single-chip microcomputer MSP430F1611 of TI company for handling core.Because super low-power consumption will be accomplished by system of the present invention, simultaneously, system uses the FFT computing when signal Processing, needs jumbo SRAM, can increase system power dissipation greatly but extend out, and the MSP430F1611 single-chip microcomputer has the SRAM of 10KB.
MSP430F1611 is the high-end product in the MSP430 series, it except the arithmetic logic unit that possesses super low-power consumption, also integrated abundant peripheral module.It mainly realizes low-power consumption by following three kinds of forms: have activity pattern and 5 kinds of low-power consumption modes, can select according to different needs, to reach purpose least in power-consuming; It also has unique clock system design, comprises fundamental clock (high-frequency clock and low-speed clock) system and DCO (digital oscillator) clock system; In addition, it adopts vector to interrupt, and supports more than ten interrupt source, and waking CPU up with interrupt request only needs 6 μ s.So, by suitable hardware design and reasonably programming, both can reduce system power dissipation, can make quick response to external event again.
MSP430F1611 is 16 single-chip microcomputers, uses present most popular reduced instruction set computer (RISC) structure, and a clock period can be carried out an instruction.Simultaneously, MSP430F1611 has adopted architectures such as 16 hardware multipliers generally having only DSP just to have, DMA, has strengthened its data processing and arithmetic capability greatly, for realizing that digital signal processing algorithm provides assurance in the system of the present invention.
Peripheral hardware in MSP430F1611 the is integrated very abundant sheet mainly contains following functional module: house dog, analog comparator A, 12 ADC of timer A, timer B, serial ports 0,1, hardware multiplier, 8 input channels, 12 DAC, I of 2 output channels
2C bus, direct memory access (DMA) (DMA), port one～port 6 (P1～P6) and basic timer.Though MSP430F1611 does not have integrated liquid crystal driver module,, add a slice liquid crystal driver module, can accomplish low-power consumption equally.
What MSP430F1611 single-chip microcomputer storer adopted is unified structure, the i.e. storage area that physically separates fully such as FLASH, RAM, peripheral module, special function register SFR etc., be arranged at same address space, like this, just can carry out byte or the visit of font formula to them with a group address, data bus, identical instruction.This organizational form and CPU adopt reduced instruction to coordinate mutually, the visit of peripheral module are not needed independent instruction, for the exploitation and the debugging of software are provided convenience.
Fig. 6 is 4～20mA output and electric power management circuit.Wherein, 4～20mA output circuit is made up of 4～20mA electric current loop transmitter XTR115, diode D2, D3, D4, D5, stabilivolt D6, triode Q2, reference source U7 (LM285Z-1.2), amplifier U5A, resistance R 61, R62, R63, R64, capacitor C 31, C33, C34, C44, magnetic bead L1.Electric power management circuit is made up of DC/DC converter U11 (TPS62051), three terminal regulator U9, resistance R 65, R66, R67, R70, capacitor C 38, C39, C51, C37, C48, inductance L 2.Need to prove, indicate in 4～20mA output circuit " 5VA " locate with electric power management circuit in indicate " 5VA " and locate to link to each other; Indicate in 4～20mA output circuit " V+ " locate with electric power management circuit in indicate " V+ " and locate also to link to each other.
In order to satisfy industry spot instrument is carried out remote monitoring and remote measurement, instrument needs the analog quantity output of standard, adopts the current signal of 4～20mA usually.The on-the-spot flow instrument that uses of process industrial requires to use the two-wire system power supply sometimes.Compare with three-wire system, the power lead of two-wire system and output signal line are multiplexing, so, require the power consumption of total system to be no more than 4mA.
The MSP430F1611 single-chip microcomputer itself is integrated with precision 0.1% with 12 interior DAC, and still, this DAC is the voltage output type.Also must be if will carry out the output of 4～20mA electric current through the V/I change-over circuit.Single-chip microcomputer can be delivered to DAC integrated on the sheet with commutation frequency for the corresponding digital amount according to predefined upper and lower limit frequency values after counting to get the vortex signal frequency, its computing formula is:
Wherein, E is the digital quantity of delivering on the DAC, and f is the frequency values that measures, f
H, f
LBe respectively predefined upper and lower limit frequency values.
After conversion becomes voltage signal through DAC, carry out the conversion of voltage by 4～20mA electric current loop transmitter again to electric current.Adopt the U.S. 4～20mA of Burr-Brown company electric current loop transmitter chip XTR115, this chip only needs an external precision resister can realize the V/I conversion of signal, by the final 4～20mA electric current output of the control of the current signal after the conversion.XTR115 is not only the 4～20mA electric current loop transmitter that can realize the V/I conversion; Simultaneously, also be a stabilized voltage supply.It provides the supply voltage of 5V for artificial circuit part in the system of the present invention.
Referring to 4～20mA output among Fig. 6, single-chip microcomputer the 5th pin P6.6, i.e. the voltage signal of the representative frequency of single-chip microcomputer DAC output is delivered to the 2nd pin of XTR115 through resistance R 61, R62 and R63.XTR115 produces corresponding 4～20mA current signal and exports from the 4th pin.The positive pole of 24V direct supply is connected to Vin1 (perhaps Vin2), and negative pole series connection sampling (load) resistance is connected to Vin2 (perhaps Vin1) again.D2, D3, D4, D5 form electric bridge, shield.C34 is a filter capacitor.Stabilivolt D6 plays pressure stabilization function.Triode Q2 plays offset current, and promptly Q2 provides the difference part of XTR115 output current and system consumption electric current.The 8th pin output 5V DC voltage of XTR115 links to each other with the 2nd pin of U9 in the electric power management circuit, raises the output level of U9; For all amplifiers of system of the present invention provide 5V power supply; U8 provides power supply for digital regulation resistance.R64, U7, C31 and U5A form reference power source, for system of the present invention provides 1.235V reference voltage Vref.C44 is a decoupling capacitance.Magnetic bead L1 connects simulation ground and digitally.
Though XTR115 can be the power supply of the artificial circuit part in the system of the present invention,, can not directly partly power for digital circuit, will surpass 4mA because do the power consumption of system like this.For example, when single-chip microcomputer moved under high-frequency clock, its power consumption can reach 250uA/MHz.Specifically, the major clock of single-chip microcomputer is 8.0MHz, and the kernel portion power consumption of single-chip microcomputer is just more than 2mA.Add the work of peripheral cells such as ADC, DAC, timer, the power consumption of whole single-chip microcomputer may reach 5mA.At above-mentioned situation, it is that digital circuit is partly powered that system of the present invention adopts DC/DC converter U11.Outside 24V power supply is transformed into 10V voltage via three terminal regulator U9, is added to the input end of DC/DC converter again.Through conversion, DC/DC converter output 3V voltage partly uses for digital circuit in the system of the present invention.Because
U
iI
iη＝U
oI
o (4)
Wherein, U
iBe the input voltage of DC/DC converter, I
iBe input current, U
oBe output voltage, I
oBe output current, the η conversion efficiency.So,
As seen, at efficiency eta=90% o'clock, input 1mA electric current will be exported the 3mA electric current.Even whole numerical portion power consumption about 5mA, but can not surpass 2mA from the electric current that power supply and output signal multiplexing line are asked for yet.
Referring to the power management part among Fig. 6, outside 24V supply voltage is added in the 1st pin of three terminal regulator U9, after voltage stabilizing, by the 3rd pin output of U9.Owing to added 5V voltage on the 2nd pin of U9, so, raised the output level of the 3rd pin, promptly be output as 10V voltage.This 10V voltage is added in the 1st pin and the 8th pin of DC/DC transducer U11, respectively as input and the enable signal of U11.C37 is a storage capacitor.The 6th pin LBI of U11 is the input pin of low-voltage monitoring, and the 2nd pin is the output pin of low-voltage monitoring, and promptly when the level of the 6th pin was lower than 1.21V, the 2nd pin output signal level will change; Simultaneously, U11 quits work.System of the present invention utilizes this low-voltage monitoring function, to realize the different electric sequence of each power supply chip (U9, U10, U11), promptly makes U10, U9 work earlier, allows U11 work again.If allow U9 and U11 work simultaneously, because the output voltage of U9 is not also set up fully at the beginning, this moment, U11 need get big electric current from U9, and this will cause the holding circuit action of U9 inside, promptly think output short-circuit by mistake, thereby caused the U9 can't operate as normal.For this reason, form charging circuit by R70 and C48, the 5V voltage that is provided by U10 the 8th pin charges to charging circuit, and when the voltage at C48 two ends during greater than 1.21V, U11 just starts working, and promptly after the output voltage of U10 and U9 was set up fully, U11 just worked.
The 9th pin SW of U11 is the voltage output pin, and output voltage is exported through after the filtering of inductance L 2.C38 is a filter capacitor.C39 is a storage capacitor.The 4th pin of U11 links to each other with the 23rd pin P2.3 of single-chip microcomputer, monitors as system low-voltage.R65 is a pull-up resistor.When the output voltage of U11 the 9th pin was lower than (95～98.5) % of rated output voltage 3V, the 4th pin output level of U11 will change, and sends look-at-me to single-chip microcomputer.The 5th pin FB of U11 is the feedback voltage input end.Determine the output voltage values of U11 by the resistance value of the 5th pin internal voltage value of U11 and R66, R67.When the output voltage of the 9th pin fluctuates, this voltage is added on the 5th pin after by R66 and R67 dividing potential drop, with the 5th pin inner setting voltage will be unequal, thereby make U11 adjust output voltage, make the output voltage stabilization on the 9th pin.C51 is a feed-forward capacitance.
The man-machine interface circuit of system of the present invention is made up of keyboard circuit and LCD display circuit, as Fig. 8 and shown in Figure 9.Keyboard circuit adopts simple nonencoded keyboard design, has arranged quadruple linkage altogether: set, be shifted, increase progressively and confirm, as shown in Figure 8.Key assignments is by the P1 mouth timing scan in the universaling I/O port of single-chip microcomputer, and quadruple linkage takies P1.4, P1.5, P1.6, P1.7 respectively.A corresponding mouthful of line is low level when key is pressed, and has the mechanical shaking of 10～30ms in key is pressed the process of contact stabilization, and this shake generally can be solved by hardware or software.Hardware can have trigger or RC low-pass filtering to realize, still, can increase hardware cost; Software then only needs scanning key assignments, counting time-delay to get final product.System of the present invention adopts software to go shake.The LCD circuit of system of the present invention as shown in Figure 9.Select the LCM141 LCD for use, be exclusively used in instrument such as flow, temperature, pressure, can 14 8 segmentation characters of double demonstration, and have alphabetical prompt and show.This display device power consumption is extremely low, and the maximum current that operating voltage consumes during for 3V only is 60 μ A, satisfies the low-power consumption requirement of native system.
System software The general frame of the present invention is made up of master monitor module, protection module, interrupt module, initialization module, programmable amplifier adjusting module, computing module, electric current output module, human-machine interface module as shown in figure 10.Wherein, initialization module comprises the initialization module of single-chip microcomputer and LCD (liquid crystal); Human-machine interface module comprises keyboard load module and LCD module.
Master monitor module among Figure 10 is the total activation program of whole software system, calls the subroutine in each module, realizes the desired function of system of the present invention.The flow process of master monitor as shown in figure 11.It is a loop program, and system one powers on, and master monitor moves automatically, enters continuous inquiry sign and carries out in the circulation of respective handling.Basic process is: after system powers on, carry out initialization immediately; After the initialization, at first inquire about peak value and detect whether set of zone bit, if set is then called peak value and detected and program control enlargement factor adjusting module, peak value detection zone bit is removed in the back of finishing dealing with; Secondly, the whether set of inquiry spectrum analysis zone bit, if computing module is then called in set, estimated signal frequency, and select tape bandpass filter passage, the spectrum analysis zone bit is removed in the back of finishing dealing with; Then, the whether set of inquiry output identification position, if set, then signal calculated frequency, flow, renewal DAC output, the output identification position is removed in the back of finishing dealing with; Next, the whether set of inquiry button zone bit, if respective keys is then handled in set, key flag bit is removed in the back of finishing dealing with; At last, inquiry LCD refreshes whether set of zone bit, if set then refreshes LCD output, the back of finishing dealing with is removed LCD and refreshed zone bit.After finishing above-mentioned inquiry, processing capacity, master monitor returns, and restarts the next round inquiry, handles, constantly circulation.
Initialization module among Figure 10 carries out initialization to single-chip microcomputer and LCD.Single-chip microcomputer is carried out the related register that initialization is exactly each functional module in the definition single-chip microcomputer, stipulate their initialization mode, these functional modules comprise clock module, general purpose timer (timer A is used for counting, and timer B is used for regularly) module, WatchDog Timer, ADC module, DAC module, universaling I/O port.Initialization is exactly to send the related command word by single-chip microcomputer to LCD to LCD, the working method of definition LCD, and when powering in system of the present invention, the information of preserving when directly showing correlative flow information or last time power down.
Programmable amplifier adjusting module among Figure 10 is adjusted the resistance value of digital regulation resistance according to detected vortex signal peak value, thereby realizes the adjustment of programmable amplifier enlargement factor.Owing to contain undesired signal in the vortex street sensor output signal in practice, cause the peak detection circuit level may be higher than the actual magnitude of signal, system of the present invention adopts and repeatedly samples, asks average method to come the peak information of picked up signal.According to peak information that obtains and current enlargement factor, extrapolate the signal amplitude before programmable amplifier, in conjunction with the reference voltage of ADC, calculate the enlargement factor that makes new advances again, upgrade the digital regulation resistance resistance, realize the adjustment of programmable amplifier enlargement factor.Its program circuit as shown in figure 12.
Computing module among Figure 10 is sampled to signal, the calculated rate value, and the passage of select tape bandpass filter group is promptly specifically selected a bandpass filter in the bandpass filter again, and its flow process is as shown in figure 13.System of the present invention adopts the real number FFT that counts less to estimate the frequency of vortex signal.At first the burst that samples is carried out zero-mean and handle, eliminate trend term; Then, sequence is carried out a yard bit-reversed, use butterfly computation to obtain the real number FFT operation result of sequence; The power spectrum of signal calculated again according to the energy principle that is dominant, goes out the frequency of signal according to a preliminary estimate; At last, utilize the center of gravity correction method to carry out frequency spectrum and proofread and correct, obtain high-precision signal frequency value.According to the frequency of vortex signal, by the Single-chip Controlling multi-way switch, select the residing bandpass filter of current demand signal, this bandpass filter passage is communicated with back level Schmidt trigger, as shown in Figure 7.For avoiding signal frequency to be in the edge of adjacency channel, cause frequent switching channel, reduce the error that switching channel brings, be provided with transitional zone at adjacency channel.
Interrupt module among Figure 10 comprises internal interrupt and and external interrupt.
Internal interrupt comprises that timer interrupts and comparer interrupts.Because single-chip microcomputer MSP430F1611 has only 2 hardware timers, wherein 1 will be operated in count mode, is used for step-by-step counting, so only remaining 1 hardware timer can be used.But, in program, need 5 timings at least: regularly carry out peak value and detect; Regularly carry out spectrum analysis; Regularly carry out the output of flow rate calculation and electric current; Periodic refreshing LCD; Be the button operation timing.And these 5 timings have nothing in common with each other.For this reason, on the basis of hardware timer, 5 software timer time references are set.Select suitable hardware fixed time interval, making all software timing time is the integral multiple of hardware fixed time interval.With each software timer time reference zero clearing, in the timer interrupt service routine, software timer time reference Timebase is added 1 operation earlier; If certain software timer time reference reaches preset value, with this time reference zero clearing, and corresponding marker bit is set, so that the master monitor inquiry.Comparer interrupts being used for system's power down protection.In the comparer interrupt service routine, at first close other interruptions, prevent that the higher priority interruption from interrupting current interrupt service routine; Then, information such as present flow rate are stored in the user octet of FLASH storer.Hardware timer interrupt service routine flow process as shown in figure 14.
External interrupt is the I/O mouth and interrupts, and can be divided into button according to function and interrupt and trigger the ADC sampling interrupting.In the button interrupt service routine, key flag bit is set, carry out respective keys and handle, and the combined with hardware timer is finished to disappear and function such as trembled.Trigger ADC sampling interrupt service subroutine and finish burst sampling function.When master monitor inquires the spectrum analysis zone bit when being SM set mode, open the interrupt function of this I/O mouth, trigger by the ACLK clock signal and interrupt; In this interrupt service routine, use software mode to start the ADC sampling, and sampled result is kept at as a result in the array, when sample sequence satisfies regulation and counts, close this I/O mouth interrupt function.Trigger ADC sample clock generator interrupt service routine flow process as shown in figure 15.
Human-machine interface module among Figure 10 is made up of keyboard and LCD, and LCD is responsible for Displaying Meter measurement result and instrument parameter; Keyboard then cooperates LCD, revises the instrument parameter, switches the LCD duty.The button of system of the present invention has 4: setting key (SET), shift key (SHF), increase progressively key (INC) and acknowledgement key (ENTR).The function of 4 buttons is respectively: the SET key is used for determining the duty of LCD and the switching of the superior and the subordinate's menu; The SHF key is used for menu at the same level, numeral or radix point displacement; The INC key is used to revise data; The ENTR key is used for confirming to revise and switch the LCD show state.
System of the present invention selects serial line interface LCD LCM141 for use.This LCD is that segmentation shows, divides two row up and down, has prompting character and 14 prompting bar codes in addition.The select lines of LCD (CS), clock line (WR) and data line (DATA) link to each other with P4.2 with P4.0, the P4.1 of single-chip microcomputer respectively, by the software simulation clock LCD are carried out read-write operation.By software setting, LCD has two kinds of duties: show state and state is set; Switch two kinds of duties by the SET key.Show state is divided into two pages again: page shows flow information, wherein above delegation show instantaneous delivery, below delegation show integrated flux; Another display page display frequency and signal peak, wherein above the delegation display frequency, the acquiescence unit is Hz (hertz), below delegation's shows signal peak value, the acquiescence unit is V (volt).Be provided with under the state, the prompting letter of menu at the same level is simultaneously displayed on upper and lower two row of LCD, and the option that is in state of activation is the flicker shape; Change the activation option by the SHF key, enter the activation option by ENTR.After entering parameter options to be revised, delegation shows the prompting letter of this option above the LCD, below delegation's display digit, and the numeral activation for being the flicker shape; Change the activation digit order number by the SHF key, change activating position numerical value by the INC key.After the parameter values change, determine this modification by ENTR, cancel this modification by the SET key, and return the last layer menu.
Protection module among Figure 10 comprises power down protection and house dog timing reset.
Be integrated with analog comparator in single-chip microcomputer inside, this comparer can compare outside two input voltages, also can compare with inner different reference voltages the outside input.Comparative result can be exported to the outside by pin, also can produce to inside and interrupt.System of the present invention uses external input voltage and internal reference voltage to compare, and the output result produces internal interrupt.In interrupt service subroutine, call the erasable function of FLASH, current demand signal frequency, accumulative total umber of pulse, instantaneous delivery and integrated flux are kept in the user octet of FLASH storer; After system powers on once more, these information to be read, instrument continues operation during from the last time power down.In addition, system of the present invention can be provided with the instrument parameter by human-machine interface module, after setting is finished each parameter information is stored in the user octet of FLASH storer, can not lose after the power down.
Be integrated with house dog (Watchdog) module in single-chip microcomputer inside, a hardware timer is arranged in the module.After opening watchdog module, hardware timer is started working, and triggers to reset when arriving the setting fixed time interval.So, need in system software, remove the counting initial value of hardware counter in good time, the hardware timer that resets prevents that false triggering from resetting, this process is commonly called as " feeding dog ".Use house dog timing reset function, can make system cause crashing and restart, shield from software fault.
Claims (10)
1, two-wire system vortex flowmeter, comprise piezoelectric sensor, charge amplifier, voltage amplifier, programmable amplifier, low-pass filter, voltage follower, peak detection circuit, bandpass filter group, multi-way switch gating circuit, shaping circuit, single-chip microcomputer, man-machine interface circuit and 4～20mA output and electric power management circuit, it is characterized in that:
The charge signal of piezoelectric sensor output changes voltage signal into through charge amplifier, again through being divided into 3 the tunnel behind voltage amplifier, programmable amplifier, the low-pass filter, the 1 road signal is delivered to the ADC input end of single-chip microcomputer through voltage follower, the ADC sampling and the conversion that are carried by single-chip microcomputer become digital quantity, and single-chip microcomputer is to the signal fast Fourier transform (FFT) of counting less, do power spectrum analysis, obtain the frequency values of signal, come the passage of select tape bandpass filter group, carry out filtering; The 2 road signal is delivered to peak detection circuit, and the peak value of peak detection circuit detection signal is also delivered to the ADC input end of single-chip microcomputer, and single-chip microcomputer is sampled to the peak value of signal and changed, and adjusts the enlargement factor of programmable amplifier; The 3 road signal is through voltage follower, deliver to the bandpass filter group and carry out filtering, decide by the spectrum analysis result of single-chip microcomputer certain road filtering signal is carried out shaping, signal after the shaping is delivered to the timer input end of single-chip microcomputer, counts, and single-chip microcomputer is according to count results, flow information is presented on the LCD, and the conversion of the DAC by single-chip microcomputer, deliver to 4～20mA output and electric power management circuit, convert the output of 4～20mA current signal to through V/I.
2, two-wire system vortex flowmeter as claimed in claim 1, it is characterized in that: charge amplifier is made up of amplifier U4A, capacitor C 1, C2, C3, C4, C5, C6, C41, resistance R 2, R3, capacitor C 1 is connected in reverse input end, capacitor C 2 is connected in positive input, capacitor C 5, C6, resistance R 3 are parallel between reverse input end and the output terminal, be connected in positive input after capacitor C 3, C4, resistance R 2 parallel connections
Voltage amplifier is made up of amplifier U5B, capacitor C 29, resistance R 4, R5, R6, and resistance R 4 is connected in reverse input end, and resistance R 5 is connected in positive input, and resistance R 6 and capacitor C 29 are parallel between reverse input end and the output terminal,
Programmable amplifier is made up of amplifier U3A, digital regulation resistance U8, capacitor C 42, resistance R 7, R8, R9, the output of digital regulation resistance U8 is connected with the reverse input end of amplifier through resistance R 8, resistance R 7 also is connected in reverse input end, resistance R 9 is connected in positive input, the chip select line of digital regulation resistance, clock line and data line link to each other with the universal I/O port of single-chip microcomputer, by the resistance value of Single-chip Controlling digital regulation resistance, thus the enlargement factor of adjustment amplifier
Low-pass filter is made up of amplifier U3B, capacitor C 8, C9, resistance R 10, R11, R12, R13, the output of programmable amplifier is connected in the amplifier reverse input end through resistance R 10, R11, node between resistance R 10, the R11 is by capacitor C 8 ground connection, be connected with amplifier out by resistance R 12, also be connected capacitor C 9 between the reverse input end of amplifier and the output terminal, resistance R 13 is connected in positive input, and the output terminal of amplifier U3B connects current-limiting resistance R15, schottky diode D7.
3, two-wire system vortex flowmeter as claimed in claim 1, it is characterized in that: voltage follower is made up of amplifier U3C and amplifier U3D, two amplifiers are relation in parallel, positive input receives the output signal that described low-pass filter is sent here through resistance R 15, reverse input end and output terminal short circuit.
4, two-wire system vortex flowmeter as claimed in claim 1, it is characterized in that: peak detection circuit is by amplifier U6A, U6B, diode D1, field effect transistor Q1, capacitor C 10, C43, resistance R 14 is formed, the positive input of amplifier U6A receives the output signal that described low-pass filter is sent here through resistance R 15, its output terminal is through resistance R 14, diode D1 is connected with amplifier U6B positive input, amplifier U6B positive input is also by field effect transistor Q1, capacitor C 10 ground connection, the output terminal of amplifier U6B and reverse input end short circuit, simultaneously also with the reverse input end short circuit of amplifier U6A, the grid of the field effect transistor in the peak detection circuit links to each other with the universal I/O port of single-chip microcomputer, and the output of peak detection circuit is connected to the ADC input end of single-chip microcomputer; The break-make of Single-chip Controlling field effect transistor, thereby the discharging and recharging of control capacitance make the peak value of peak detection circuit output in ought be for the previous period; Single-chip microcomputer is sampled to the peak signal of peak detection circuit output and is changed, and goes to adjust the resistance value of digital regulation resistance again according to peak value.
5, two-wire system vortex flowmeter as claimed in claim 1 is characterized in that: the bandpass filter group is made up of 8 bandpass filter, is respectively amplifier U1A, capacitor C 11, C12, resistance R 21, R22, R23, R24, decoupling capacitance C45; Amplifier U1B, capacitor C 13, C14, resistance R 25, R26, R27, R28; Amplifier U1C, capacitor C 15, C16, resistance R 29, R30, R31, R32; Amplifier U1D, capacitor C 17, C18, resistance R 33, R34, R35, R36; Amplifier U2A, capacitor C 19, C20, resistance R 37, R38, R39, R40, decoupling capacitance C46; Amplifier U2B, capacitor C 21, C22, resistance R 41, R42, R43, R44; Amplifier U2C, capacitor C 23, C24, resistance R 45, R46, R47, R48; Amplifier U2D, capacitor C 25, C26, resistance R 49, R50, R51, R52, the circuit structure of these 8 bandpass filter is identical, parameter is different, thus passband is different, but interconnect, cover the frequency band range of vortex shedding flow meter, and have certain overlapping between adjacent passband
Wherein, input is connected in the reverse input end of amplifier U1A through resistance R 21, capacitor C 11, node between resistance R 21, the capacitor C 11 is connected with output terminal by capacitor C 12, by resistance R 22 ground connection, resistance R 23 is connected between reverse input end and the output terminal, resistance R 24 connects and positive input, and the connection of all the other seven bandpass filter is consistent with said structure.
6, two-wire system vortex flowmeter as claimed in claim 1, it is characterized in that: the multi-way switch gating circuit is made up of U13, its 8 input ends link to each other with 8 passages of bandpass filter group respectively, common port links to each other with the input end of Schmidt trigger U14A, and 3 control line A, B, C link to each other with single-chip microcomputer respectively.
7, two-wire system vortex flowmeter as claimed in claim 1 is characterized in that: shaping circuit is made up of Schmidt trigger U14A, and its input end is connected with the common port of multi-way switch gating circuit, and output terminal is connected with single-chip microcomputer.
8, two-wire system vortex flowmeter as claimed in claim 1 is characterized in that: the single-chip microcomputer model is MSP430F1611.
9, two-wire system vortex flowmeter as claimed in claim 1, it is characterized in that: in 4～20mA output and the electric power management circuit, 4～20mA output circuit is by 4～20mA electric current loop transmitter XTR115, diode D2, D3, D4, D5, stabilivolt D6, triode Q2, reference source U7, amplifier U5A, resistance R 61, R62, R63, R64, capacitor C 31, C33, C34, C44, magnetic bead L1 forms, the voltage signal of single-chip microcomputer DAC output is through resistance R 61, R62 and R63 deliver to the 2nd pin of XTR115, XTR115 produces corresponding 4～20mA current signal and exports from the 4th pin, D2, D3, D4, D5 forms electric bridge, C34 is a filter capacitor, stabilivolt D6 plays pressure stabilization function, the difference part of triode Q2 compensation XTR115 output current and system consumption electric current, the 8th pin output 5V DC voltage of XTR115 links to each other with the 2nd pin of U9 in the electric power management circuit, raise the output level of U9,5V is provided power supply, U8 provides power supply for digital regulation resistance, R64, U7, C31 and U5A form reference power source, 1.235V is provided reference voltage Vref, C44 is a decoupling capacitance, magnetic bead L1 connects simulation ground and digitally
Electric power management circuit is by DC/DC converter U11, three terminal regulator U9, resistance R 65, R66, R67, R70, capacitor C 38, C39, C51, C37, C48, inductance L 2 is formed, outside 24V supply voltage is added in the 1st pin of three terminal regulator U9, after voltage stabilizing, export by the 3rd pin of U9, the output voltage of the 3rd pin is added in the 1st pin and the 8th pin of DC/DC transducer U11, respectively as input and the enable signal of U11, R70 and C48 form charging circuit, the 5V voltage that is provided by U10 the 8th pin charges to charging circuit, realize each power supply chip U9 by low-voltage monitoring and charging circuit, U10, the electric sequence of U11
The 9th pin SW of U11 is the voltage output pin, and output voltage is exported through after the filtering of inductance L 2, and C38 is a filter capacitor, and C39 is a storage capacitor, and the 4th pin of U11 links to each other with the 23rd pin P2.3 of single-chip microcomputer, monitors as system low-voltage.
10, two-wire system vortex flowmeter as claimed in claim 1 is characterized in that: the man-machine interface circuit is made up of keyboard circuit and LCD display circuit, is connected with single-chip microcomputer respectively.
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