CN101451864A - Improved low power consumption two-wire system vortex shedding flowmeter - Google Patents
Improved low power consumption two-wire system vortex shedding flowmeter Download PDFInfo
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Abstract
The invention relates to the field of flow detection, as an advanced low power consumption two-wire system vortex-shedding meter, comprising a piezo-electric transducer, a differential charge amplifier, a voltage amplifier, a programmable amplifier, a low pass filter, a voltage follower, a band-pass filter set, a band-pass select switch circuit, a peak detection circuit, a wave shaping circuit, a singlechip, a human-computer interface circuit, a 4-20mA output and power management circuit, a constant flow source, a temperature sensor, a pressure sensor, a differential amplifier and a 16-bit analog-to-digital converter. Mini FFT spectral decomposition is used to be combined with the analog band-pass filter set to process signals of a vortex sensor and a multicycle frequency measurement method of precision is used, thereby having temperature and pressure compensating circuit and function, outputting 4-20mA direct current and having two-wire system work. The advanced low power consumption two-wire system vortex-shedding meter has greatly improved measure ratio, measurement precision and capacity of resisting disturbance.
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
Chinese invention patent announced a kind of low-power and two-wire vortex shedding flowmeter (Xu Kejun, Ceng Xianjun, Zhu Zhihai, Liu Sanshan etc. low-power and two-wire vortex shedding flowmeter, the application patent of invention, 200710162074.5, the applying date: 2007.11.14.).This flowmeter is made up of with electric power management circuit 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, single-chip microcomputer detects the peak value and the frequency of vortex signal, and controls programmable amplifier in view of the above and bandpass filter is amplified and filtering vortex flowmeter signals.This technology overcome prior art can not effectively measure low discharge, expanded range than, realize the problem of low-power consumption when improving measuring accuracy.When the guarantor levies effective measurement low discharge, expanded range ratio and improves measuring accuracy, realized low-power consumption, be output as 4～20mA DC current, working current, realized two-wire system work less than 4mA.But this low-power and two-wire vortex shedding flowmeter has the following disadvantages: what (1) paired pulses frequency computation part adopted is that a pulse may be counted or be counted less to rapid pulse more towards the mode of number in 2 seconds, causes the frequency computation part error of 0.5Hz; (2) use Schmidt trigger as shaping circuit, its threshold level and triggering amplitude are unadjustable, are unfavorable under the situation that noise and small-signal amplitude are arranged signal being carried out shaping; (3) She Ji bandpass filter can only be applicable to a kind of liquid of bore or a kind of gas meter of bore, and applicable surface is narrow; (4) directly connect to the simulation of circuit meter case to realize shielding, still, such connection can't be passed through safety feature test.
Summary of the invention
The key technology problems that exists during the present invention will solve and apply for a patent provides the low-power and two-wire vortex shedding flowmeter that a kind of scope of application is wideer, precision is higher, antijamming capability is stronger, power consumption is lower.
The technical solution adopted in the present invention is: adopt the differential charge amplifier, replace original charge amplifier, to improve the ability of extracting vortex signal, simultaneously, strengthen antijamming capability; The bandpass filter that the single operational amplifier of former cause is formed makes into to become bandpass filter by Hi-pass filter with the low-pass filter cascaded series, to obtain better pass-band performance; Peak detection circuit is placed on after the bandpass filter, to improve the precision that peak value detects; Become trigger that vortex signal is carried out shaping comparator arrangement, utilize the timer acquisition mode, adopt the frequency measurement method of precision such as multicycle, improve measuring accuracy; Do not connect meter case to the simulation of circuit, but by a shielding box is set outside charge amplifier, simultaneously,, be connected to meter case, to realize shielding and to pass through safety feature test with the simulation ground of circuit mode by series capacitance and inductance; At two kinds of measured medium modelled signals of liquids and gases disposal system, strengthened the versatility of instrument respectively; Increase temperature and pressure compensating circuit and function, for use in the measurement of gas flow; Design is power module more effectively, and the 24V DC voltage that the outside provides is transformed into 3.3V voltage by DC/DC (DC to DC converter), becomes 3V voltage through LDO (low pressure difference linear voltage regulator), as the power supply of numerical portion; 3.3V be transformed into 3V voltage by another road LDO again, as the power supply of artificial circuit part, simulation ground and digitally between connect by magnetic bead; 24V voltage is transformed into 7V voltage by another sheet LDO, as the power supply of temperature and pressure compensating circuit part.
Low-power and two-wire vortex shedding flowmeter after the improvement comprises piezoelectric sensor, differential charge amplifier, voltage amplifier, programmable amplifier, low-pass filter, voltage follower, bandpass filter group, the logical selected on-off circuit of band, peak detection circuit, shaping circuit, single-chip microcomputer, man-machine interface circuit, 4～20mA output and electric power management circuit, constant current source, temperature sensor, pressure transducer, differential amplifier, 16 analog to digital converters (ADC).
The charge signal of piezoelectric sensor output changes voltage signal into through the differential charge amplifier, again through being divided into 2 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 the filtering of bandpass filter group; Through after the bandpass filter, signal is divided into 2 the tunnel again, and the 1 the road delivers to peak detection circuit, and peak detection circuit detects peak value, delivers 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 2 road signal is delivered to shaping circuit and is carried out shaping, signal after the shaping is delivered to the timer input end of single-chip microcomputer, count, single-chip microcomputer is according to the frequency computation part result, flow information is presented on the LCD, 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.
The differential charge amplifier is made up of amplifier U1A, U1B, capacitor C 1, C2, C7, C9, C11, C12, C13, resistance R 2, R9, R10, R11, R16, and wherein, C1, C2, C12, C13 are feedback capacities, have determined the enlargement factor of charge amplifier.
Voltage amplifier is made up of amplifier U2B, capacitor C 3, resistance R 3, R5, R12, R13.
Programmable amplifier is made up of amplifier U3A, digital regulation resistance U4, capacitor C 4, C6, C10, resistance R 1, R6, R14, and output terminal L, the H of digital regulation resistance U4 connects with resistance R 1, as the feedback resistance of U3A.Wherein, the chip select line of digital regulation resistance U4, clock line and data line link to each other with the universaling 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 5, C8, resistance R 4, R7, R8, R15.
Voltage follower is made up of amplifier U3C and amplifier U3D, and two amplifiers are relation in parallel, and in-phase input end receives the output signal that described low-pass filter is sent here.
The bandpass filter group is made up of 1 low-pass filter and 7 bandpass filter.Wherein, low-pass filter is made up of amplifier U6A, capacitor C 17, C22, resistance R 18, R21, R22, R25, decoupling capacitance C24; The 1st bandpass filter is by amplifier U6D, capacitor C 32, C33, C30, resistance R 31, R37, R41, and amplifier U6B, capacitor C 28, C36, resistance R 29, R33, R34, R38 form; The 2nd bandpass filter is by amplifier U7A, capacitor C 42, C43, C40, resistance R 45, R51, R55, decoupling capacitance C26, and amplifier U7B, capacitor C 38, C46, resistance R 43, R47, R48, R52 form; The 3rd bandpass filter is by amplifier U7D, capacitor C 50, C52, C53, resistance R 59, R65, R69, and amplifier U7C, capacitor C 48, C56, resistance R 57, R61, R62, R66 form; The 4th bandpass filter is by amplifier U9A, capacitor C 51, C54, C55, resistance R 60, R68, R70, decoupling capacitance C27, and amplifier U9B, capacitor C 49, C57, resistance R 58, R63, R64, R67 form; The 5th bandpass filter is by amplifier U9D, capacitor C 41, C45, C44, resistance R 46, R54, R56, and amplifier U9C, capacitor C 39, C47, resistance R 44, R49, R50, R53 form; The 6th bandpass filter is by amplifier U8C, capacitor C 31, C34, C35, resistance R 32, R40, R42, and amplifier U8D, capacitor C 29, C37, resistance R 30, R35, R36, R39 form; The 7th bandpass filter is by amplifier U8B, capacitor C 19, C20, C21, resistance R 20, R27, R28, and amplifier U8A, capacitor C 18, C23, resistance R 19, R23, R24, R26, decoupling capacitance C25 form; The circuit structure of these 7 bandpass filter is identical, all is to become with 1 low-pass filter cascaded series with 1 Hi-pass filter, still, the parameter difference, thus passband is different, interconnects again, cover the frequency band range of vortex shedding flow meter, and have certain overlapping between adjacent passband.
Wave filter selects circuit to be made up of U11, and its 8 input ends link to each other with 8 passages of bandpass filter group respectively, and U11 output terminal the 3rd pin links to each other with the input end of shaping circuit U12 by resistance R 74.Shaping circuit U12 is made up of comparer, compares with common Schmidt trigger, and the comparer has here added a threshold, and waveform will surpass threshold value ability trigger pulse, has stronger antijamming capability.After signal carries out shaping, be output as the square wave of rule, send into the 12nd pin of single-chip microcomputer U3 again, promptly the P1.0 mouth is counted.Here adopt acquisition mode, utilize multicycle equal precision measurement method, paired pulses is counted, and has improved measuring accuracy.
The model of single-chip microcomputer U3 is MSP430F1611.
Peak detection circuit is made up of amplifier U10A, U10B, diode D1, D2, field effect transistor Q1, capacitor C 58, C59, C60, resistance R 71, R72, R73.The positive input of amplifier U10A receives the output signal of described multi-way switch U11.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.
4～20mA output and power management module are made up of 4～20mA current transducer XTR115, DC/DC, three LDO and magnetic bead BEAD.The 24V DC voltage becomes 3.3V through DC/DC by 24V earlier, become 3V voltage through LDO, power supply as numerical portion, 3.3V be transformed into 3V voltage by another road LDO again, power supply as artificial circuit part, simulation ground and digitally between connect by magnetic bead, numerical portion is with simulating the part level match like this, and single-chip microcomputer current sinking under 3V voltage is littler.Simultaneously, become 7V through one-level LDO, for the work of temperature and pressure compensation part constant current source by the 24V DC voltage.The electric current of system consumption is detected and is adjusted output current by XTR115.Because system power supply is not with isolating between the input, with watchcase (the earth) and systematically isolate to satisfy the requirement (promptly floatingly) of insulation between (simulation ground, digitally).
Constant-current source circuit is made up of 2.5V reference power supply U14, operational amplifier U15B, triode Q2, Q3, resistance R 77, R78, R88, R83, R90, for temperature sensor R86 and pressure transducer R87 provide constant current source.Temperature sensor R86 is platinum resistance, and two ends Temp+ and Temp-are connected to the input end of ADC U16.Pressure transducer R87, form by Ra, Rb, Rc, Rd, output signal is Press+ and Press-, amplify by the differential amplifier that operational amplifier U13A, U13B, resistance R 76, R79, R81, R84, R85, R89, potentiometer R82, capacitor C 66, C68, decoupling capacitance C63 form through one-level earlier, then, be connected to the input end of 16 analog to digital converter U16.
U16 is an ADC of 16, and the analog signal conversion of temperature sensor and pressure transducer output is become digital signal, delivers to single-chip microcomputer by the I2C bus, for the temperature and pressure compensation of flow signal provides information.
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: designed the differential charge amplifier, replaced original single charge amplifier, improved the extractability of vortex signal, simultaneously, strengthened interference free performance; Designed by Hi-pass filter and become bandpass filter, replaced the bandpass filter that the single operational amplifier of former cause is formed, obtained better pass-band performance with the low-pass filter cascaded series; Peak detection circuit is placed on after the bandpass filter group, to improve the precision that peak value detects; Utilize the timer acquisition mode, adopt the frequency measurement method of precision such as multicycle, the pulse of shaping is counted, overcome that used timer counting mode in the past may exist ± counting error of 1 pulse, improved measuring accuracy; Outside charge amplifier, be provided with a shielding box,, simultaneously,, be connected to the shell of instrument, to meet the requirement of instrument safety performance test with the simulation ground series capacitance and the inductance of circuit to strengthen the ability of anti-electromagnetic interference (EMI); At two kinds of measured medium modelled signals of liquids and gases disposal system, strengthened the versatility of instrument respectively; Increase temperature and pressure compensating circuit and function, instrument can be used for the measurement of gas flow; Designed effective power management module more, even outside supply voltage drops to 14V, instrument also can operate as normal.
Description of drawings
Fig. 1 is the hardware block diagram of system of the present invention.
Fig. 2 is the circuit theory diagrams of differential charge amplifier and voltage amplifier in the system of the present invention.
Fig. 3 is the bias voltage circuit schematic diagram.
Fig. 4 is the circuit theory diagrams of programmable amplifier and digital regulation resistance wherein in the system of the present invention.
Fig. 5 is the circuit theory diagrams of low-pass filter and voltage follower in the system of the present invention.
Fig. 6 is a singlechip chip pin wiring schematic diagram.
Fig. 7 is the circuit theory diagrams of 4 wave filters in the bandpass filter group in the system of the present invention
Fig. 8 is the circuit theory diagrams of other 4 wave filters in the bandpass filter group in the system of the present invention
Fig. 9 is the circuit theory diagrams that system of the present invention median filter is selected circuit.
Figure 10 is the circuit theory diagrams of shaping circuit in the system of the present invention.
Figure 11 is the circuit theory diagrams of peak detection circuit.
Figure 12 is the circuit theory diagrams of 4～20mA output and electric power management circuit.
Figure 13 is constant current source, temperature sensor and pressure transducer schematic diagram.
Figure 14 is a pressure transducer differential amplifier circuit schematic diagram
Figure 15 is the circuit theory diagrams of 16 analog to digital converters (ADC).
Figure 16 is a keyboard input circuit synoptic diagram in the system of the present invention.
Figure 17 is a LCD display chip wiring schematic diagram in the system of the present invention.
Figure 18 is a system software block diagram of the present invention.
Figure 19 is a master monitor process flow diagram in the system of the present invention.
Figure 20 is a system of the present invention pulse capture theory diagram.
Figure 21 is the interrupt service routine process flow diagram of system timer B of the present invention.
Figure 22 is a system frequency estimation process flow diagram of the present invention.
Figure 23 is a bandpass filter group median filter channel selecting process flow diagram in the system of the present invention.
Figure 24 is that programmable amplifier is adjusted process flow diagram in the system of the present invention.
Figure 25 is a flow rate calculation 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 optimum 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 by piezoelectric sensor, differential charge amplifier, voltage amplifier, programmable amplifier, low-pass filter, voltage follower, bandpass filter group, the logical selected on-off circuit of band, peak detection circuit, shaping circuit, single-chip microcomputer, man-machine interface circuit, 4～20mA output and electric power management circuit, constant current source, temperature sensor, pressure transducer, differential amplifier, 16 analog to digital converters (ADC).
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 2 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 the bandpass filter group, carries out filtering; Spectrum analysis result by single-chip microcomputer decides the filtered signal in certain road of output.Output signal through the bandpass filter group is divided into 2 the tunnel.The 1 the road delivers 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 2 the road delivers to the shaping circuit of being made up of comparer carries out shaping, and the signal after the shaping is delivered to the timer input end of single-chip microcomputer, adopts acquisition mode, utilizes precision methods such as multicycle to carry out frequency computation part.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, the charge signal that is piezoelectric sensor output amplifies via the differential charge amplifier that amplifier U1A, U2B, capacitor C 1, C2, C7, C9, C11, C12, C13, resistance R 2, R9, R10, R11, R16 form, wherein, C1, C2, C12, C13 are feedback capacities, have determined the enlargement factor of charge amplifier; Then, the voltage amplifier of forming via amplifier U2B, capacitor C 3, resistance R 3, R5, R12, R13 amplifies.Bias voltage Vref among Fig. 2 and other figure is provided by biasing circuit shown in Figure 3.Biasing circuit is made up of U5, operational amplifier U2A, resistance R 17 and capacitor C 16, C17, and 1.235V is provided DC voltage.
By capacitance C9, after the removal flip-flop, deliver to the programmable amplifier of forming by amplifier U3A, digital regulation resistance U4, capacitor C 4, C6, C10, resistance R 1, R6, R14, as shown in Figure 4 through the signal after amplifying.Among the figure, output terminal L, the H of digital regulation resistance U4 connects with resistance R 1, as the feedback resistance of U3A; The chip select line of digital regulation resistance U4, 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.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, cost is low, and is low in energy consumption.
Deliver to low-pass filter and voltage follower through the signal behind the programmable amplifier, as shown in Figure 5.Low-pass filter is made up of amplifier U3B, capacitor C 5, C8, resistance R 4, R7, R8, R15.Voltage follower is made up of amplifier U3C and amplifier U3D, and two amplifiers are relation in parallel, and in-phase input end receives the output signal that described low-pass filter is sent here.
The output signal of voltage follower is divided into 2 the tunnel.The 1 the tunnel is Signal, delivers to the 59th pin P6.0/A0 of single-chip microcomputer, as shown in Figure 6, and for the laggard line period atlas analysis of Chip Microcomputer A C sample conversion.The 2 the tunnel is BPF, delivers to the bandpass filter group and carries out filtering, as shown in Figure 7 and Figure 8.
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, from 0.5Hz to 3.7KHz.In this frequency band range, may comprise vortex flowmeter signals frequency, mechanical vibration frequency, flow field turbulent noise frequency and other noise frequency.If this signal is directly carried out shaping and counting,, make measurement result bigger error occur because various The noise are easy to cause the false triggering of shaping circuit.At this problem, one group of analog band-pass filter of system design of the present invention comprises 1 low-pass filter and 7 bandpass filter, as shown in Figure 7 and Figure 8.Wherein, low-pass filter is amplifier U6A, capacitor C 17, C22, resistance R 18, R21, R22, R25, decoupling capacitance C24; The 1st bandpass filter is amplifier U6D, capacitor C 32, C33, resistance R 31, R37, R41, amplifier U6B, capacitor C 28, C36, resistance R 29, R33, R34, R38; The 2nd bandpass filter is amplifier U7A, capacitor C 42, C43, resistance R 45, R51, R55, decoupling capacitance C26, amplifier U7B, capacitor C 38, C46, resistance R 43, R47, R48, R52; The 3rd bandpass filter is amplifier U7D, capacitor C 50, C52, C53, resistance R 59, R65, R69, amplifier U7C, capacitor C 48, C56, resistance R 57, R61, R62, R66; The 4th bandpass filter is amplifier U9A, capacitor C 51, C54, C55, resistance R 60, R68, R70, decoupling capacitance C27, amplifier U9B, capacitor C 49, C57, resistance R 58, R63, R64, R67; The 5th bandpass filter is amplifier U9D, capacitor C 41, C45, C54, resistance R 46, R54, R56, amplifier U9C, capacitor C 39, C47, resistance R 44, R49, R50, R53; The 6th bandpass filter is amplifier U8C, capacitor C 31, C34, C35, resistance R 32, R40, R42, amplifier U8D, capacitor C 29, C37, resistance R 30, R35, R36, R39; The 7th bandpass filter is amplifier U8B, capacitor C 19, C20, C21, resistance R 20, R27, R28, amplifier U8A, capacitor C 18, C23, resistance R 19, R23, R24, R26, decoupling capacitance C25.The circuit structure of these 7 bandpass filter is identical, parameter is different, thereby passband is different, but interconnect, and covers the frequency band range of vortex shedding flow meter, and has certain overlapping between adjacent passband.Realize 1 bandpass filter by 1 Hi-pass filter and 1 low-pass filter, the amplitude versus frequency characte than single amplifier bandpass filter is good like this, and the amplitude versus frequency characte of the passband part that promptly forms like this is more smooth, and cut-off region is decayed sooner.Consider the scope of the frequency range of whole vortex signal, if go filtering, poor effect with one group of bandpass filter group at 0.5Hz to 3700Hz, so, design some groups of bank of filters at different situations, so both had certain versatility and interchangeability, guaranteed to have filter effect preferably again.For example, design the parameter of 1 group of bandpass filter group at the liquid flow measurement of 15mm to 200mm bore, its frequency of operation covers 1Hz to 500Hz; Design the parameter of 1 group of bandpass filter at the gas flow measurement of 25mm to 150mm bore, its frequency of operation covers 19Hz to 2300Hz.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 of the influence of various noises like this, avoid false triggering, guarantee the precision of counting vortex signal with the signal after which band-pass filter.
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 U11, as shown in Figure 9.8 input ends of this device link to each other with 8 passages of bandpass filter group respectively, and common port is that output switching terminal 3 links to each other with the input end 3 of comparer U12 by resistance R 74, as shown in figure 10.In Fig. 9,3 control line A, the B of U11, C link to each other with I/O mouth P5.3, P5.2, the P5.1 of single-chip microcomputer respectively, as shown in Figure 6.U11 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.By the signal of gating is the vortex signal that passes through filtering, contains minimum noise, sends into comparer U12 and carries out shaping, is output as the square wave of rule, sends into the P1.0 of single-chip microcomputer again, counts.Compare with common Schmidt trigger, the comparer here can be adjusted threshold voltage, and waveform will surpass threshold value ability trigger pulse, has stronger antijamming capability.
8 select the output of 1 multi-way switch U11 also to be connected to the input end of peak detection circuit, i.e. the in-phase input end 3 of U10A, as shown in figure 11.Peak detection circuit is made up of amplifier U10A, U10B, diode D1, D2, field effect transistor Q1, capacitor C 58, C59, C60, resistance R 71, R72, R73.The in-phase input end of amplifier U10A receives the output signal of described multi-way switch U11.The grid of the field effect transistor in the peak detection circuit links to each other with the universaling 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.Peak detection circuit is placed on after the bandpass filter, measures amplitude, can obtain result more accurately through signal after the filtering.
System of the present invention adopts the single-chip microcomputer MSP430F1611 of TI company for handling core, as shown in Figure 6.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.
4～20mA output and power management module are made up of 4～20mA current transducer XTR115, DC/DC, three LDO and magnetic bead BEAD.The 24V DC voltage becomes 3.3V through DC/DC by 24V earlier, become 3V voltage through LDO, power supply as numerical portion, 3.3V be transformed into 3V voltage by another road LDO again, power supply as artificial circuit part, simulation ground and digitally between connect by magnetic bead, numerical portion is with simulating the part level match like this, and single-chip microcomputer current sinking under 3V voltage is littler.Simultaneously, become 7V through one-level LDO, for the work of temperature and pressure compensation part constant current source by the 24V DC voltage.The electric current of system consumption is detected and is adjusted output current by XTR115.Because system power supply is not with isolating between the input, with watchcase (the earth) and systematically isolate to satisfy the requirement (promptly floatingly) of insulation between (simulation ground, digitally).
As shown in figure 13, constant-current source circuit is made up of 2.5V reference power supply U14, operational amplifier U15B, triode Q2, Q3, resistance R 77, R78, R88, R83, R90, for temperature sensor R86 and pressure transducer R87 provide constant current source.Temperature sensor R86 is platinum resistance, and two ends Temp+ and Temp-are connected to the input end of ADC U16.Pressure transducer R87, form by Ra, Rb, Rc, Rd, output signal is Press+ and Press-, amplify by the differential amplifier that operational amplifier U13A, U13B, resistance R 76, R79, R81, R84, R85, R89, potentiometer R82, capacitor C 66, C68, decoupling capacitance C63 form through one-level earlier, as shown in figure 14; Then, be connected to the input end of 16 analog to digital converter U16, as shown in figure 15.U16 is an ADC of 16, and the analog signal conversion of temperature sensor and pressure transducer output is become digital signal, delivers to single-chip microcomputer by the I2C bus, for the temperature and pressure compensation of flow signal provides information.
The man-machine interface circuit of system of the present invention is made up of keyboard circuit and LCD display circuit, as Figure 16 and shown in Figure 17.Keyboard circuit adopts simple nonencoded keyboard design, has arranged quadruple linkage altogether: set, be shifted, increase progressively and confirm, as shown in figure 16.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 line is a high level when key is pressed.The LCD circuit of system of the present invention as shown in figure 17.Select the LCD of customization 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.
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 18.Wherein, initialization module comprises LCD initialization, fluid media (medium) and the initialization of instrument bore, peak detection block initialization, the initialization of 4-20mA electric current output module, the initialization of temperature and pressure compensating module, power down protection module initialization, flow rate calculation module initialization, bandpass filter selection initialization.
Master monitor module among Figure 18 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 19.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 the whether set of FFT calculation flag position, if set, then call the FFT computing module, to doing FFT calculating, spectrum analysis and correction through the vortex street sensor signal behind electric charge amplification, voltage amplification, low-pass filtering and the voltage follow, estimate the frequency at ceiling capacity place, come the select tape bandpass filter according to this frequency, and the peak value interval of detection time is set, the clear flag position, back of finishing dealing with; Then, inquiry send out to trigger the whether set of zone bit of lock-on signal.
In order to carry out the multicycle equal precision measurement, we are provided with timer A (TA) is the vortex signal impulse meter, it is the filler pulse counter that timer B (TB) is set, allow the PWM module (TA1) of TA regularly send out triggering lock-on signal (timing is decided by the lower limit of survey frequency), TA and TB are according to the time interval between adjacent twice triggering lock-on signal, catch the number and the filler pulse number of vortex signal pulse respectively, the working clock frequency of catching the umber of pulse that obtains and TB according to TA and TB calculates the frequency of vortex signal, as shown in figure 20.The work clock of timer A is provided by the outside, in other words the every increase of external pulse once, timer A rolling counters forward value will increase once, promptly timer A is used for external pulse is counted.Timer B is used for generation time at interval, and each timing triggers lock-on signal to just sending out.According to this lock-on signal, the PWM unit (TA1) of timer A just produces rising edge, the capturing unit of timer A (TA2) and timer B capturing unit (TB2) are caught into its Counter Value separately according to this rising edge, calculate the count difference value N of the TA of adjacent twice signal
xCount difference value N with TB
s, then
In the formula, F
sBe the working clock frequency of timer B, F
xBe the working clock frequency of timer A, i.e. the frequency of tested vortex flowmeter signals.
Among Figure 19,, TA1 then is set sends out the triggering lock-on signal, distribute clear flag position, back if send out the zone bit set that triggers lock-on signal; Then, change the sampling channel of ADC, gather peak value through the vortex street sensor signal behind electric charge amplification, voltage amplification, low-pass filtering, the bandpass filtering; And the control procedure that peak value detects is: the whether set of inquiry discharge zone bit, if set, then at first whether inquiry is discharge for the first time, if then directly discharge, if not discharge for the first time, then start the peak value that ADC goes sampled signal, start back time-delay a period of time, discharge again, the clear flag position, back of finishing dealing with; Next, the whether set of enlargement factor zone bit is adjusted in inquiry, if set calls and adjusts the enlargement factor module, and after finishing dealing with, the clear flag position; Then, the whether set of inquiry calculated flow rate zone bit, if the flow rate calculation module is then called in set, the clear flag position, back of finishing dealing with; The sample frequency zone bit is reset in inquiry, if set is then called the sample frequency module is set, according to fluid media (medium) and instrument bore sample frequency is set, the clear flag position, back of finishing dealing with; Inquiry LCD refreshes whether set of zone bit, if the LCD refresh module is then called in set, refreshes LCD, after finishing dealing with, removes LCD and refreshes zone bit; At last, the whether set of integrated flow zone bit is preserved in inquiry, if integrated flow is then preserved in set, and after finishing dealing with, the clear flag position.After finishing above-mentioned inquiry, processing capacity, master monitor returns, and restarts the next round inquiry, handles, constantly circulation.
Interrupt time reference as system with the timing of TB, each module is carried out work with reference to this benchmark in the system.Specifically, the crystal oscillator frequency of single-chip microcomputer is 8MHz, through frequency division, obtains the SMCLK of 1MHz, again through 4 frequency divisions, obtains the work clock of 250KHz, sends into TB.TB is according to this work clock, and the timing that produces 0.1 second is as the time reference of system works.According to this time reference, in program, set the time of the starting and ending work of each module.The timing of total system work is: set the ADC first passage, gather the data of vortex street sensor; Carry out FFT and calculate, obtain power spectrum, estimate frequency, the passage of select tape bandpass filter; Set the ADC second channel, gather the data of vortex street sensor, calculate peak value, adjust the enlargement factor of programmable amplifier; Send out and trigger lock-on signal; Carry out flow rate calculation.For example, the total system working cycle is set at 2s 1 time.Need the 0.426s time if image data and FFT calculate, so, setting program begins image data when 0.1s; When 0.6s, establish to send out and trigger lock-on signal; To acquired signal between the 1.8s, calculate peak value at 0.7s, carry out the adjustment of programmable amplifier enlargement factor; When 1.9s, begin calculated flow rate.
Figure 21 is timer B (TB) interruption subroutine process flow diagram.When TA captured the vortex signal pulse, the time reference number that will in the interrupt service routine of TA TB be captured was preserved, and simultaneously, a zone bit was set.In the TB interrupt service routine, inquire about this zone bit, if set, then the time reference number that TB captured of expression is preserved, at this moment, the time reference number zero clearing that just TB can be captured.Next,, judged whether time of predefined keyboard scan by the number of number time references, if arrive, keyboard scan then; If not to or surpassed, just by number time reference number, judged whether to preestablish and gathered the time that is used for the data that FFT calculates, if arrive, ADC then is set goes image data, simultaneously, DMA is set transmits the data of gathering and arrive internal memory; If not to or surpassed, just the number by the number time reference has judged whether predefined time of triggering lock-on signal, if arrive, a sign of triggering lock-on signal just is set; If not to or surpassed, just judged whether the time of peak value detection by number time reference number, as if arriving, then begin peak detection process; If not to or surpassed, just judge whether the flow rate calculation time arrives.
The process that peak value detects is: discharge earlier, and be 0.1s discharge time; Then, recharge, the duration of charging also is 0.1s; ADC is set again to the peak value sampling first time; After sampling is finished, begin discharge again; Behind the discharge 0.1s, recharge 0.1s; Be provided with again ADC to the second time peak value sample; After sampling is finished, discharge again; In this manner, after the sampling of 3 minor peaks, just carry out the adjustment of programmable amplifier enlargement factor.This process is achieved in that several time reference numbers in program, judge whether when having arrived the predefined time that the first time, peak value detected, if arrive, discharge sign for the first time is set then; If not to or surpassed, whether surpassed with regard to judgement time benchmark number and preestablished the time that peak value for the first time detects, if surpassed, then expression had been carried out once discharging; Then, judge for the first time that peak value detects and indicate whether set that if set, then expression discharge for the first time finishes, and the charging sign just being set this moment; If there is not set, then continue to judge the whether set of charging sign; If set continues then to judge whether that charging finishes; If charging finishes, the discharge sign is set then; If charging sign does not have set, perhaps charging indicates set, but charging do not finish, and continues then to judge that discharge indicates whether set; If set continues then to judge whether discharge finishes; If discharge off then is provided with the charging sign; If the discharge sign does not have set, the flag set of perhaps discharging, but do not have discharge off, then continue judgement time benchmark number and whether arrived the time that preset flow rate is calculated.If arrived preset flow rate computing time, the flow rate calculation sign then is set, if not to or surpassed, just continue the time whether judgement time benchmark number equals predefined working cycle end; If equal, then continue the time that has judged whether that integrated flux is preserved.When net cycle time is 2s, it is 3 minutes that integrated flux is preserved cycling time, then through after the circulation of 90 tasks, just should preserve integrated flux, so after each working cycle finishes, all will judge whether the time of preservation integrated flux; If do not arrive the time of preserving integrated flux, but arrived the time that working cycle finishes, then set the sign of resetting sample frequency earlier, the sign that refreshes liquid crystal has been set again.
Figure 22 is the frequence estimation process flow diagram.Signal is sampled, the calculated rate value, the passage of select tape bandpass filter group then is provided with the peak value sampling time interval again, and a bandpass filter in the promptly specifically selected bandpass filter group is provided with the peak value sampling process and discharges and recharges the time.System of the present invention adopts the FFT that counts less to estimate the frequency of vortex signal.At first the burst that sampling is obtained carries out the zero-mean processing, eliminates DC component; Then, sequence is carried out the FFT computing.The fast inadequately and limited problem of memory source for the arithmetic speed that overcomes single-chip microcomputer, we have taked following technical measures, on single-chip microcomputer real-time implementation the FFT computing, and guaranteed the precision of algorithm: (1) adopts assembly language establishment FFT program, fast operation; (2) uniform data uses the Q13 fixed-point number to represent, promptly represent 1 data, most significant digit (left side first) is-symbol position, the size of 15 remaining bit representation data with 16, wherein, high 2 (left side second and the 3rd) is used for representing the integral part in the data, in calculating as safeguard bit, the fraction part in minimum 13 (the right 13) expression data, the data that sampling comes are placed on low 12 earlier, then, move to left 1, can reduce the EMS memory occupation amount like this; (3) adopt fixed-point number to calculate, its radix point of data that promptly uses in multiplication and additional calculation process is all fixed, to improve computing velocity; (3) in the FFT calculating process, every calculating through the one-level dish factor, its as a result maximum possible can enlarge 3 times, along with the increase of calculating progression, the data of representing with the Q13 form are certain to overflow, so, in computation process, must be shifted to data (moving to right), to prevent overflowing of data, but, in actual computation, be not that every grade of result calculated all can be overflowed, if this moment the result is shifted, will reduce the FFT precision of calculation results, because displacement diminishes data, promptly reduced the significance bit of fraction part, for this reason, earlier judge that whether this one-level result of calculation is greater than 1, when greater than 1 the time, just displacement just is not shifted less than 1.Calculate the power spectrum of signal by the FFT operation result,,, estimate the frequency of vortex flowmeter signals according to the peak power spectrum peak according to the energy principle that is dominant; At last, utilize the center of gravity correction method to carry out frequency spectrum and proofread and correct, improve the precision of vortex flowmeter signals frequency measurement.According to the frequency of vortex flowmeter signals, by the Single-chip Controlling multiplexer circuit, select bandpass filter corresponding to current vortex flowmeter signals frequency, this bandpass filter is linked to each other with the shaping circuit of back.According to discharging and recharging the time interval in the vortex signal frequency configuration peak value sampling process.
Figure 23 is that bandpass filter group median filter is selected process flow diagram.1 low-pass filter of design and the passband of 7 bandpass filter cover whole vortex signal frequency to be processed, simultaneously, between the passband of adjacent filter lap is arranged, to avoid when the vortex signal frequency is in adjacent passband edge, cause the frequent switching of bandpass filter, promptly avoid conversion bandpass filter continually.During the frequency range of the bandpass filter that exceeds last time and select when frequency, just search the wave filter that covers this frequency, select only wave filter.Concrete selection course is: when frequency does not surpass the bound of current filter transmission band, just still select current wave filter; When frequency just in time drops in the halved belt of two filter transmission bands, to select according to the point of crossing of these two filter transmission bands, promptly the joining of these two wave filter amplitude versus frequency charactes as a separatrix: when frequency is lower than the point of crossing, just select the wave filter of lower passband, be higher than the wave filter that upper passband is just selected in the point of crossing.
Figure 24 is the process flow diagram that programmable amplifier is adjusted.According to detected vortex signal peak value, adjust the resistance value of digital regulation resistance, thereby realize the adjustment of programmable amplifier enlargement factor.Because there is the nature relaxation phenomenon in the vortex street sensor output signal in practice, so amplitude fluctuates, we adjust the enlargement factor of programmable amplifier according to the peak value of minimum.For this reason, system of the present invention repeatedly samples to the output signal of peak detection circuit, and the result handles to peak value sampling, finds out minimum peak, according to this minimum value the programmable amplifier enlargement factor is set then, the vortex signal of small magnitude also can be triggered by reshaper.When peak value during, just programmable amplifier is not adjusted greater than the upper limit (2.3V) or less than lower limit (2.0V); And work as peak value within the bound scope, and just calculate the programmable amplifier enlargement factor according to peak meter, enlargement factor is converted to the quantized value of the digital regulation resistance in the programmable amplifier.If quantized value exceeds the upper limit 255 of digital regulation resistance quantized value, just quantized value is set to 255, is lower than the lower limit 1 of the quantized value of digital regulation resistance when quantized value, and it is 1 that quantized value just is set.At last, quantized value is write digital regulation resistance, upgrade the resistance value of digital regulation resistance.
Figure 25 is the flow rate calculation process flow diagram.The flow rate calculation module is the result that pulsed frequency is calculated, and after treatment, calculates instantaneous delivery, finally is converted to electric current output.According to the frequency computation part result, at first judge and whether calculate for the first time, if, be 0 with regard to the frequency of calculating is set, preserve frequency, deposit formation in; If not, judge that then the result that peak value detects is double less than by amplitude, if the frequency of calculating with regard to setting is 0, the preservation frequency deposits formation in; If not then whether determination frequency if frequency just be set be 0, preserves frequency less than cutoff frequency, deposits formation in; Then judge the whether double setpoint frequency fluctuation range that exceeds of the frequency calculated, if, with regard to the frequency of preserving in the clear 0 whole formation, preserve the double just now frequency resultant of calculating, deposit formation in; Then sort, find out the number of non-0 frequency, judge then whether the number of non-0 frequency surpasses 5, if non-0 frequency in the just direct average queue calculates the vortex signal frequency to being kept at the formation medium frequency; If not, just find out the maximal value in non-0 frequency in the formation, second largest value, minimum value, sub-minimum is removed these 4 in non-0 frequency values then, and average remaining non-0 frequency calculates the vortex signal frequency; Then select instrument coefficient, calculate instantaneous delivery, the instantaneous delivery that calculates is carried out the temperature and pressure compensation, calculate integrated flow, the decision circuitry test indicates whether set, if there is not set, just instantaneous delivery is converted into the current value of correspondence.If, transform with regard to not carrying out electric current, directly return.
Claims (9)
1, improved low-power and two-wire vortex shedding flowmeter comprises piezoelectric sensor, differential charge amplifier, voltage amplifier, programmable amplifier, low-pass filter, voltage follower, bandpass filter group, the logical selected on-off circuit of band, peak detection circuit, shaping circuit, single-chip microcomputer, man-machine interface circuit, 4～20mA output and electric power management circuit, constant current source, temperature sensor, pressure transducer, differential amplifier, 16 analog to digital converters; It is characterized in that:
The charge signal of piezoelectric sensor output changes voltage signal into through the differential 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 2 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 the FFT that the digital quantity single-chip microcomputer is counted less to signal, do power spectrum analysis, obtain the frequency values of signal, come the passage of select tape bandpass filter group; The 2 road signal is delivered to the bandpass filter group, carries out filtering; Spectrum analysis result by single-chip microcomputer decides the filtered signal in certain road of output; Output signal through the bandpass filter group is divided into 2 the tunnel; The 1 the road delivers 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 2 the road delivers to the shaping circuit of being made up of comparer carries out shaping, signal after the shaping is delivered to the timer input end of single-chip microcomputer, adopt acquisition mode, utilize precision methods such as multicycle to count single-chip microcomputer according to count results, flow information is presented on the LCD, and, deliver to 4～20mA output and electric power management circuit by self DAC conversion, convert the output of 4～20mA current signal to through V/I.
2, improved low-power and two-wire vortex shedding flowmeter as claimed in claim 1, it is characterized in that: the differential charge amplifier is made up of amplifier U1A, U1B, capacitor C 1, C2, C7, C9, C11, C12, C13, resistance R 2, R9, R10, R11, R16, wherein, C1, C2, C12, C13 are feedback capacities, have determined the enlargement factor of charge amplifier.
3, improved low-power and two-wire vortex shedding flowmeter as claimed in claim 1 is characterized in that: the bandpass filter group is made up of 1 low-pass filter and 7 bandpass filter; Wherein, low-pass filter is made up of amplifier U6A, capacitor C 17, C22, resistance R 18, R21, R22, R25, decoupling capacitance C24; The 1st bandpass filter is by amplifier U6D, capacitor C 32, C33, C30, resistance R 31, R37, R41, and amplifier U6B, capacitor C 28, C36, resistance R 29, R33, R34, R38 form; The 2nd bandpass filter be by amplifier U7A, capacitor C 42, C43, C40, resistance R 45, R51, R55, decoupling capacitance C26, and amplifier U7B, capacitor C 38, C46, resistance R 43, R47, R48, R52 form; The 3rd bandpass filter is by amplifier U7D, capacitor C 50, C52, C53, resistance R 59, R65, R69, and amplifier U7C, capacitor C 48, C56, resistance R 57, R61, R62, R66 form; The 4th bandpass filter is by amplifier U9A, capacitor C 51, C54, C55, resistance R 60, R68, R70, decoupling capacitance C27, and amplifier U9B, capacitor C 49, C57, resistance R 58, R63, R64, R67 form; The 5th bandpass filter is by amplifier U9D, capacitor C 41, C45, C44, resistance R 46, R54, R56, and amplifier U9C, capacitor C 39, C47, resistance R 44, R49, R50, R53 form; The 6th bandpass filter is by amplifier U8C, capacitor C 31, C34, C35, resistance R 32, R40, R42, and amplifier U8D, capacitor C 29, C37, resistance R 30, R35, R36, R39 form; The 7th bandpass filter is amplifier U8B, capacitor C 19, C20, C21, resistance R 20, R27, R28, and amplifier U8A, capacitor C 18, C23, resistance R 19, R23, R24, R26, decoupling capacitance C25 form.The circuit structure of these 7 bandpass filter is identical, all is to become with 1 low-pass filter cascaded series with 1 Hi-pass filter, still, the parameter difference, thus passband is different, interconnects again, cover the frequency band range of vortex shedding flow meter, and have certain overlapping between adjacent passband.
4, improved low-power and two-wire vortex shedding flowmeter as claimed in claim 1, it is characterized in that: shaping circuit is made up of comparer, has added a threshold, waveform will surpass threshold value ability trigger pulse, after signal carries out shaping, is output as the square wave of rule, send into single-chip microcomputer again, count.
5. improved low-power and two-wire vortex shedding flowmeter as claimed in claim 1, it is characterized in that: adopt acquisition mode, utilize multicycle equal precision measurement method, paired pulses is counted, it is the vortex signal impulse meter that timer A (TA) promptly is set, it is the filler pulse counter that timer B (TB) is set, allow the PWM module (TA1) of TA regularly send out triggering lock-on signal (timing is decided by the lower limit of survey frequency), TA and TB are according to the time interval between adjacent twice triggering lock-on signal, catch the number and the filler pulse number of vortex signal pulse respectively, the working clock frequency of catching the umber of pulse that obtains and TB according to TA and TB calculates the frequency of vortex signal.
6, improved low-power and two-wire vortex shedding flowmeter as claimed in claim 1 is characterized in that: peak detection circuit is made up of amplifier U10A, U10B, diode D1, D2, field effect transistor Q1, capacitor C 58, C59, C60, resistance R 71, R72, R73; The positive input of amplifier U10A receives the output signal of described multi-way switch U11; 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; Peak detection circuit is placed on after the bandpass filter group, to improve the precision that peak value detects.
7, improved low-power and two-wire vortex shedding flowmeter as claimed in claim 1, it is characterized in that: real-time implementation FFT computing on single-chip microcomputer, and guaranteed the precision of algorithm, by adopting assembly language programming, uniform data to use that the Q13 fixed-point number is represented, fixed-point number calculates and determining whether the mode that is shifted, guarantee the requirement of amount in precision, real-time and the internal memory of algorithm according to every grade of operation result size.
8. the low-power and two-wire vortex shedding flowmeter after the improvement as claimed in claim 1, it is characterized in that: in the temperature and pressure compensating circuit, constant-current source circuit is made up of 2.5V reference power supply U14, operational amplifier U15B, triode Q2, Q3, resistance R 77, R78, R88, R83, R90, for temperature sensor R86 and pressure transducer R87 provide constant current source; Temperature sensor R86 is platinum resistance, and two ends Temp+ and Temp-are connected to the input end of ADC U16; Pressure transducer R87, form by Ra, Rb, Rc, Rd, output signal is Press+ and Press-, amplify by the differential amplifier that operational amplifier U13A, U13B, resistance R 76, R79, R81, R84, R85, R89, potentiometer R82, capacitor C 66, C68, decoupling capacitance C63 form through one-level earlier, then, be connected to the input end of 16 analog to digital converter U16;
U16 is an ADC of 16, and the analog signal conversion of temperature sensor and pressure transducer output is become digital signal, delivers to single-chip microcomputer by the I2C bus, for the temperature and pressure compensation of flow signal provides information.
9, as the low-power and two-wire vortex shedding flowmeter after the said improvement of claim 1, it is characterized in that: the simulation ground of circuit does not directly connect meter case, but, simultaneously the mode of the simulation of circuit ground by series capacitance and inductance is connected to meter case outside charge amplifier by a shielding box is set; Simulation ground and digitally between connect by magnetic bead.
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2008
- 2008-12-22 CN CN 200810246107 patent/CN101451864B/en not_active Expired - Fee Related
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