CN110411524B - PWM (pulse-width modulation) fertilizer suction pipeline flow detection system and control method - Google Patents

PWM (pulse-width modulation) fertilizer suction pipeline flow detection system and control method Download PDF

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CN110411524B
CN110411524B CN201910698517.5A CN201910698517A CN110411524B CN 110411524 B CN110411524 B CN 110411524B CN 201910698517 A CN201910698517 A CN 201910698517A CN 110411524 B CN110411524 B CN 110411524B
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fertilizer
pulse
pwm
fertilization
pipeline
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CN110411524A (en
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金永奎
周良富
薛新宇
张玲
周立新
丁素明
张宋超
秦维彩
孔伟
孙竹
顾伟
蔡晨
崔龙飞
王宝坤
陈晨
杨风波
周晴晴
张学进
乐飞翔
孙涛
徐阳
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Nanjing Research Institute for Agricultural Mechanization Ministry of Agriculture
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Nanjing Research Institute for Agricultural Mechanization Ministry of Agriculture
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    • A—HUMAN NECESSITIES
    • A01—AGRICULTURE; FORESTRY; ANIMAL HUSBANDRY; HUNTING; TRAPPING; FISHING
    • A01C—PLANTING; SOWING; FERTILISING
    • A01C23/00—Distributing devices specially adapted for liquid manure or other fertilising liquid, including ammonia, e.g. transport tanks or sprinkling wagons
    • A01C23/04—Distributing under pressure; Distributing mud; Adaptation of watering systems for fertilising-liquids
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
    • G01F1/00—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow
    • G01F1/56—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by using electric or magnetic effects
    • G01F1/58—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by using electric or magnetic effects by electromagnetic flowmeters
    • G01F1/582—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by using electric or magnetic effects by electromagnetic flowmeters without electrodes
    • G—PHYSICS
    • G05—CONTROLLING; REGULATING
    • G05B—CONTROL OR REGULATING SYSTEMS IN GENERAL; FUNCTIONAL ELEMENTS OF SUCH SYSTEMS; MONITORING OR TESTING ARRANGEMENTS FOR SUCH SYSTEMS OR ELEMENTS
    • G05B19/00—Programme-control systems
    • G05B19/02—Programme-control systems electric
    • G05B19/04—Programme control other than numerical control, i.e. in sequence controllers or logic controllers
    • G05B19/05—Programmable logic controllers, e.g. simulating logic interconnections of signals according to ladder diagrams or function charts
    • G05B19/054—Input/output

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  • Engineering & Computer Science (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • General Physics & Mathematics (AREA)
  • Water Supply & Treatment (AREA)
  • Soil Sciences (AREA)
  • Environmental Sciences (AREA)
  • Automation & Control Theory (AREA)
  • Electromagnetism (AREA)
  • Fluid Mechanics (AREA)
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Abstract

The invention discloses a PWM (pulse-width modulation) type fertilizer suction pipeline flow detection system and a control method, which comprise a main water pipe, a mixing cavity, an EC/PH sensor, a pressure reduction electromagnetic valve, a first fertilization pipeline, a second fertilization pipeline, a Venturi fertilizer suction device, a fertilizer liquid barrel, a filter, a flowmeter, a fertilizer suction electromagnetic valve, a fertilization pump, a one-way valve and a control system. According to the invention, a PWM (pulse-width modulation) type fertilizer suction pipeline flow detection system is constructed according to the requirement that the flow among channels needs to be accurately measured, and flow detection and calculation methods in different time periods are designed according to the pulse characteristics of a Venturi fertilizer suction device, an electromagnetic valve and a Hall flowmeter in a PWM control mode, so that an accurate flow value in each period is obtained. The detection system has the advantages of novel design, accurate and reliable control system, quick detection, better economic value and social value and good application prospect.

Description

PWM (pulse-width modulation) fertilizer suction pipeline flow detection system and control method
Technical Field
The invention belongs to the technical field of water and fertilizer integration, and particularly relates to a PWM (pulse width modulation) mode fertilizer suction pipeline flow detection system and a detection control method.
Background
In recent years, micro-irrigation has the advantages of water conservation, high irrigation uniformity, labor conservation, fertilizer conservation, yield increase and the like, is developed rapidly, is widely used, becomes an important technical means in agricultural production, and has the application area reaching more than 5000 and ten thousand mu in national micro-irrigation at present. The micro-irrigation is an irrigation method which is characterized in that water and nutrients are conveyed to the roots of crops at a small flow rate through a pipeline system and special irrigation devices (drippers, micro-nozzles, infiltrating irrigation pipes, micro-pipes and the like) arranged at the tail part (a final-stage pipeline) so as to keep the soil in the optimal water, fertilizer and gas states. Since the micro-irrigation directly conveys water and nutrients to the roots of crops, the application of fertilizer by using the micro-irrigation system has great advantages, so that the integration of water and fertilizer is also commonly used.
The fertilization equipment in the present liquid manure integration system mainly comprises a pressure difference type fertilization tank, a high-pressure fertilization pump, a Venturi fertilizer absorber, a hydraulic fertilization pump and the like, the equipment realizes the purpose of applying fertilizer into a pipeline, but the concentration and the proportion of the fertilizer can not be accurately controlled, the automatic control can not be realized, the requirement of accurate fertilization can not be met, the problem is solved by the appearance of an automatic precise fertilizer applicator, and the rapid development is realized. The automatic precision fertilizer applicator is controlled by a computer or a small-sized controller to realize precise fertilizer application, the solution is continuously and quantitatively injected into the micro-irrigation pipeline by the aid of a pump, each path is provided with a Venturi fertilizer absorber and an electromagnetic valve, and the fertilizer application concentration, EC and PH value are automatically adjusted by a PWM (pulse-width modulation) mode.
At present, the fertilizing amount of each path of the automatic precision fertilizer applicator is automatically adjusted by a controller according to feedback values of EC and PH sensors, the flow rate is determined by calibration, and the accurate flow rate of each fertilizer suction cannot be obtained by measurement. The fertilizer suction flow is not a definite value because of the influence of a plurality of factors such as the main pipe pressure, the main pipe flow, EC, PH set values, Venturi inlet and outlet pressure and the like, so that the fertilizer suction flow at each time needs to be accurately measured and can be controlled more accurately.
Disclosure of Invention
The invention aims to construct a PWM (pulse-width modulation) type fertilizer suction pipeline flow detection system, and simultaneously provide a corresponding detection method to obtain an accurate flow value, thereby providing a foundation for accurate control of an automatic precision fertilizer applicator
The invention is realized by the following technical scheme:
a PWM mode fertilizer suction pipeline flow detection system comprises a main water pipe, a mixing cavity, an EC/PH sensor, a pressure reduction electromagnetic valve, a first fertilization pipeline, a second fertilization pipeline, a Venturi fertilizer suction device, a fertilizer liquid barrel, a filter, a flowmeter, a fertilizer suction electromagnetic valve, a fertilization pump, a one-way valve and a control system;
the mixing cavity is connected with the main water pipe in series, is positioned in the middle of the main water pipe and is used for fully mixing irrigation water and fertilizer liquid;
the water outlet of the main water pipe is connected with a first fertilization pipeline through a pressure reduction solenoid valve, a plurality of Venturi fertilizer absorbers are arranged on the first fertilization pipeline, each Venturi fertilizer absorber comprises an inflow section and an outflow section, the water outlet of the first fertilization pipeline is connected with the inflow section of the Venturi fertilizer absorber, a second fertilization pipeline is arranged below the Venturi fertilizer absorbers, the outflow section of the Venturi fertilizer absorbers is connected with the water inlet of the second fertilization pipeline, and the second fertilization pipeline is connected with the water inlet of the main water pipe sequentially through a fertilization pump and a check valve; the middle part of the Venturi fertilizer absorber is also provided with a fertilizer absorbing opening, the fertilizer absorbing opening is connected with a fertilizer liquid barrel through a fertilizer liquid pipe, the fertilizer liquid pipe is provided with a fertilizer absorbing electromagnetic valve, a flowmeter and a filter, and the Venturi fertilizer absorber, the fertilizer absorbing electromagnetic valve, the flowmeter, the filter and the fertilizer liquid barrel are sequentially connected;
the EC/PH sensor is positioned between the pressure reducing solenoid valve and the Venturi fertilizer absorber, is connected with the first fertilization pipeline through a three-way pipe and is used for acquiring an EC value and a PH value in the first fertilization pipeline;
the control system is arranged on one side of the fertilizer liquid barrel, is respectively and electrically connected with the fertilizer suction electromagnetic valve, the EC/PH sensor, the flowmeter, the fertilizer pump and the pressure reduction electromagnetic valve, and is used for controlling the operation of the fertilizer system.
The technical scheme of the invention is that the control system comprises an operation table box body, a touch screen, a PLC (programmable logic controller), a fertilizer pump frequency converter and an irrigation pump frequency converter; the utility model discloses a fertilizer applying machine, including operation panel box, PLC controller, fertilization pump converter and irrigation pump converter, the front installation touch-sensitive screen of operation panel box, install PLC controller, fertilization pump converter and irrigation pump converter in the operation panel box, the signal input part of PLC controller respectively with EC/PH sensor, flowmeter's signal output part signal connection, the signal output part of PLC controller respectively with the touch-sensitive screen, inhale fertile solenoid valve and decompression solenoid valve signal connection, the signal output part and the fertilization pump signal connection of fertilization pump converter.
The technical scheme of the invention is that the flowmeter adopts a Hall flowmeter, the Hall flowmeter comprises a shell, an impeller, a screw, a magnetic element, a Hall element and an acquisition system, and the screw is fixedly arranged in the middle of the shell and is parallel to a fluid inlet of the shell; the screw is provided with an impeller, the upper side of the impeller is provided with a magnetic element, and the magnetic element is coaxial with the impeller; and one side of the magnetic element is provided with a Hall element, the signal input end of the Hall element is in signal connection with the signal output end of the acquisition system, and the signal output end of the Hall element is in signal connection with the signal input end of the PLC of the control system.
The technical scheme of the invention is that the multiple Venturi fertilizer absorbers are connected in parallel.
The invention further solves the technical scheme that the filter adopts a laminated filter, and the filtering precision is not less than 80 meshes.
The invention further solves the technical scheme that the fertilizer suction electromagnetic valve adopts a high-frequency electromagnetic valve.
The invention also protects a control method of the PWM fertilizer suction pipeline flow detection system, which takes the preset valve opening time as the whole PWM period, the control system generates PWM pulse waveforms, the switch of the fertilizer suction electromagnetic valve is adjusted through the duty ratio of the output PWM waveforms, and then the fluid flow passing through the flowmeter is adjusted, the flowmeter outputs corresponding pulse signals according to the change of the flow, the corresponding pulse signals are fed back to the control system, and the fertilizer suction flow in the PWM period is obtained through calculation, and the specific calculation steps are as follows:
step one, recording all pulse quantities and the time of each pulse in a period from opening of the fertilizer suction electromagnetic valve to closing of the fertilizer suction electromagnetic valve in a PWM period;
step two, calculating the first pulse flow according to the time of the first pulse, wherein the calculation formula is as follows:
Figure GDA0002553934650000031
wherein, V1Indicating the quantity of water of the first pulse, V0Representing a single pulse of water, t1Representing the time elapsed for the first pulse, t2Representing the time elapsed for the second pulse;
step three, correcting the flow of the last pulse according to the time of the last pulse and the time of the last pulse, wherein the correction formula is as follows:
Vn＝V0*tn/tn-1，
wherein, VnIndicating the water quantity, V, of the last pulse0Representing a single pulse of water, tn-1Representing the time elapsed by the penultimate pulse, tnRepresents the time elapsed for the last pulse;
step four, calculating the flow in one PWM period according to the results obtained in the step two and the step three, wherein the calculation formula is as follows:
Figure GDA0002553934650000032
wherein q represents the fertilizer suction flow of one PWM period, V1Indicating the quantity of water of the first pulse, V0Indicating a single pulse of water, VnRepresenting the amount of water of the last pulse, tiRepresents the time elapsed for the ith pulse;
and step five, weighing the reduced amount of the weight of the fertilizer liquid barrel in one PWM period by using an electronic scale, recording the reduced amount as the actual fertilizer suction amount of the Venturi fertilizer applicator, and comparing the actual fertilizer suction amount with the fertilizer suction amount obtained by calculation in the step four.
Further, the valve opening time is in the range of 0.05 to 2 seconds.
The invention has the beneficial effects that:
according to the invention, a PWM (pulse-width modulation) type fertilizer suction pipeline flow detection system is constructed according to the requirement that the flow among channels needs to be accurately measured, and flow detection and calculation methods in different time periods are designed according to the pulse characteristics of a Venturi fertilizer suction device, an electromagnetic valve and a Hall flowmeter in a PWM control mode, so that an accurate flow value in each period is obtained. The detection system has the advantages of novel design, accurate and reliable control system, quick detection, better economic value and social value and good application prospect.
Drawings
Fig. 1 is a schematic view of the overall structure of the present invention.
Fig. 2 is a single channel fertilizer absorption schematic diagram of the invention.
Fig. 3 is a structural view of a hall sensor of the present invention.
Fig. 4 is a schematic diagram showing the state of the hall sensor when the valve is opened according to the present invention.
Fig. 5 is a schematic diagram of the state of the hall sensor when the valve is closed.
Fig. 6 is a graph of pulse versus time for the present invention.
Fig. 7 is a schematic structural diagram of a control system of the present invention.
In the figure, the serial numbers of 1-a main water pipe, 2-a mixing cavity, 3-an EC/PH sensor, 4-a pressure reducing solenoid valve, 5-a first fertilization pipeline, 6-a Venturi fertilizer absorber, 7-a fertilizer liquid barrel, 8-a filter, 9-a flowmeter, 10-a fertilizer absorbing solenoid valve, 11-a fertilization pump, 12-a one-way valve, 13-a control system and 14-a second fertilization pipeline, 61-inflow section, 62-outflow section, 63-fertilizer sucking port, 91-shell, 92-Hall element, 93-acquisition system, 94-magnetic element, 95-impeller, 96-screw, 131-operation table box, 132-touch screen, 133-PLC controller, 134-fertilizer pump frequency converter and 135-irrigation pump frequency converter.
Detailed Description
The invention will be further described with reference to the accompanying drawings and examples.
Referring to fig. 1-2, the PWM-mode fertilizer suction pipeline flow detection system includes a main water pipe 1, a mixing chamber 2, an EC/PH sensor 3, a pressure reducing solenoid valve 4, a first fertilization pipeline 5, a second fertilization pipeline 14, a venturi fertilizer suction device 6, a fertilizer liquid barrel 7, a filter 8, a flowmeter 9, a fertilizer suction solenoid valve 10, a fertilization pump 11, a check valve 12, and a control system 13;
the main water pipe 1 is used for conveying water and fertilizer liquid required by irrigation and is provided with a water inlet and a water outlet, and the water flow direction moves according to the direction shown in the figure; the mixing cavity 2 is connected with the main water pipe 1 in series, is positioned in the middle of the main water pipe 1, and is internally provided with a spiral water guide structure for fully mixing irrigation water and fertilizer liquid;
the water outlet of the main water pipe 1 is connected with a first fertilization pipeline 5 through a pressure reduction electromagnetic valve 4, the pressure reduction electromagnetic valve 4 is connected with the main water pipe 1 through a tee joint and is positioned at the water outlet of the main water pipe 1, the pressure of the first fertilization pipeline 5 can be controlled to be not higher than a set value, and the pressure reduction electromagnetic valve 4 is also electrically connected with a control system 13 and can be opened or closed through the control system; the first fertilization pipeline 5 is provided with a plurality of Venturi fertilizer absorbers 6, each Venturi fertilizer absorber 6 comprises a flow inlet section 61 and a flow outlet section 62, the water outlet of the first fertilization pipeline 5 is connected with the flow inlet section 61 of each Venturi fertilizer absorber 6, a second fertilization pipeline 14 is arranged below each Venturi fertilizer absorber 6, the flow outlet section 62 of each Venturi fertilizer absorber 6 is connected with the water inlet of the corresponding second fertilization pipeline 14, each second fertilization pipeline 14 is connected with the water inlet of the corresponding main water pipe 1 through a fertilization pump 11 and a one-way valve 12 in sequence, each fertilization pump 11 is a multi-stage corrosion-resistant centrifugal pump and is electrically connected with a control system, and each one-way valve 12 is located between each fertilization pump 11 and the corresponding main water pipe 1 to enable water to flow back to the water inlet of the corresponding main water pipe 1 from the water outlet of the corresponding main water pipe 1 through the fertilization pipeline; the middle part of the Venturi fertilizer absorber 6 is also provided with a fertilizer absorbing opening 63, the fertilizer absorbing opening 63 is connected with a fertilizer liquid barrel 7 through a fertilizer liquid pipe 64, the fertilizer liquid barrel 7 contains fertilizer liquid, and the barrel is made of plastic materials and can prevent corrosion; the fertilizer liquid pipe 64 is provided with a fertilizer suction electromagnetic valve 10, a flowmeter 9 and a filter 8, and the Venturi fertilizer suction device 6, the fertilizer suction electromagnetic valve 10, the flowmeter 9, the filter 8 and the fertilizer liquid barrel 7 are sequentially connected;
the EC/PH sensor 3 is positioned between the pressure reducing electromagnetic valve 4 and the Venturi fertilizer absorber 6, is connected with the first fertilization pipeline 5 through a three-way pipe, and is simultaneously connected with the control system 13 through a signal line for acquiring an EC value and a PH value in the first fertilization pipeline 5 and feeding back the EC value and the PH value to the control system 13, preferably, the EC/PH sensor adopted in the embodiment is of a type S-EC/PH-A1 of Nanjing Qigrow science and technology Limited;
the control system 13 is arranged on one side of the fertilizer liquid barrel 7, is respectively and electrically connected with the fertilizer suction electromagnetic valve 10, the EC/PH sensor 3, the flowmeter 9, the fertilizing pump 11 and the pressure reduction electromagnetic valve 4, and is used for controlling the operation of the fertilizing system.
Referring to fig. 7, in the present embodiment, the control system 13 includes an operation console box 131, a touch screen 132, a PLC controller 133, a fertilizer pump frequency converter 134, and an irrigation pump frequency converter 135; the front of operation panel box 131 installs touch-sensitive screen 132, installs PLC controller 133, fertilization pump converter 134 and irrigation pump converter 135 in the operation panel box 131, PLC controller 133's signal input part respectively with EC/PH sensor 3, flowmeter 9's signal output part signal connection, PLC controller 133's signal output part respectively with touch-sensitive screen 132, inhale fertile solenoid valve 10 and decompression solenoid valve 4 signal connection, the signal output part and the fertilization pump 11 signal connection of fertilization pump converter 134.
Referring to fig. 3, in this embodiment, the flowmeter 9 is a hall flowmeter, different proportions need to be set between the fertilization channels, and since many factors affecting the fertilizer suction amount of each channel cannot accurately control the flow rate and the proportion, the flow rate is detected by installing the flowmeter in each channel, the hall flowmeter includes a housing 91, an impeller 95, a screw 96, a magnetic element 94, a hall element 92, and an acquisition system 93, the screw 96 is fixedly set in the middle inside the housing 91, and is parallel to the fluid inlet of the housing 91; an impeller 95 is arranged on the screw 96, a magnetic element 94 is arranged on the upper side of the impeller 95, and the magnetic element 94 is coaxial with the impeller 95; one side of the magnetic element 94 is provided with a hall element 92, a signal input end of the hall element 92 is in signal connection with a signal output end of the acquisition system 93, and a signal output end of the hall element 92 is in signal connection with a signal input end of the PLC controller 133 of the control system 13. After water enters the flowmeter, the impeller 95 is driven to rotate, the magnetic element 94 also rotates, the Hall element 92 senses the magnetic element 94, and the acquisition system 93 generates a pulse signal, wherein each pulse signal represents a certain flow rate. The rotating speed of the impeller 95 changes along with the change of the flow, the hall element 92 outputs a corresponding pulse signal, the pulse signal is fed back to the control system 13, and the control system 13 judges the flow.
In this embodiment, the plurality of venturi fertilizer absorbers 6 are connected in parallel.
In this embodiment, the filter 8 is a laminated filter, has a filtering precision of not less than 80 meshes, and is mainly used for filtering impurities in the fertilizer solution, so as to ensure that system components are not affected.
In this embodiment, the fertilizer suction solenoid valve 10 is a high-frequency solenoid valve, and is electrically connected to the control system 13, and is rapidly switched on and off according to a PWM duty ratio output by the control system 13 to control the fertilizer suction amount.
The working principle of the detection system is as follows: irrigation water source passes through the main water pipe, and when main water pipe pressure was greater than pressure solenoid valve set pressure, the pressure solenoid valve was opened, and water got into fertilization pipeline, and the fertilization pump operation, rivers passed through the venturi and inhale fertile ware, produced the negative pressure at inhaling fertile mouthful, when inhaling fertile solenoid valve and open, the fertile liquid in the fertile liquid bucket was inhaled fertilization pipeline to get into the main pipe, mix with water in mixing the fertile intracavity, give the crop with irrigation water accurate ration together. When the pressure at the throat part of the Venturi fertilizer absorber is stable and unchanged, the fertilizer absorbing flow is also stable and unchanged. Under the condition of continuous fertilizer suction, the Venturi fertilizer suction device generates stable negative pressure, the fertilizer suction flow is basically constant, and the flow collected by the flow meter is relatively consistent. The fertilizer suction amount is adjusted by the control system according to the set fertilizer application proportion or EC/PH value and by controlling the on-off time of the electromagnetic valve in a PWM mode.
Under the PWM control mode, the fertilizer suction is intermittent, when the electromagnetic valve is opened, the fertilizer liquid enters the fertilizer suction pipe and the Venturi tube under the action of negative pressure, the negative pressure is reduced from the maximum value and is converted into potential energy (height), kinetic energy (speed) and pipeline loss of the fertilizer liquid, under the condition, the negative pressure at the throat is changed, the maximum negative pressure at the throat is different during different valve opening and valve closing time, and the change amplitude is different; when the valve opening time is short, the negative pressure value is not reduced to 0, the valve is closed, when the valve opening time is long, the negative pressure value is reduced to 0 from the maximum value, and then a stable state is maintained; when the valve is closed for a short time, the maximum negative pressure is not generated at the throat, the valve is opened, the negative pressure value is reduced, and the fertilizer suction amount is also reduced; when the valve is closed for a long time, the maximum negative pressure is generated at the throat, and the fertilizer suction amount is large after the valve is opened.
When the electromagnetic valve is opened, water enters the fertilizer suction pipe and flows into the Hall flowmeter to drive the impeller and the magnetic unit to rotate, the acquisition circuit generates a pulse signal, the flow rate of the fertilizer liquid is increased to a stable value from 0, the frequency of the pulse signal is changed, and the time of each pulse is different. When the electromagnetic valve is closed, the negative pressure in the pipeline disappears, but partial fertilizer liquid still flows forwards at a speed to generate a water hammer effect, the impeller in the flowmeter still continues to roll to generate pulse signals, the acquisition system still acquires and calculates the flow, and the pulse signals are invalid in practice, so that the pulse signals need to be distinguished and removed. The effective pulse of the flow calculation is therefore from the opening of the solenoid valve to the end of the closing of the solenoid valve.
Referring to fig. 4, the hall flow meter detection process during one PWM cycle: when the valve is opened, 3 states exist, the Hall element immediately generates a pulse at the induction position (a), the error is the largest, and the pulse is more than 1 pulse; the Hall element just passes the induction part (b), and generates a pulse after rotating for one circle, the error is 0, and the pulse is just 1 pulse after rotating for one circle; the Hall element is located at the middle position (c), and the error is more than 0-1 pulse. Referring to fig. 5, there are 3 states when the valve is closed, the hall element generates a pulse immediately just reaching the sensing position (a), and the error is 0; the Hall element just reaches the induction part (b), the error is maximum, and 1 pulse is reduced; the Hall element is in the middle position (c), and the error is less by 0-1 pulse.
It can be seen that the positions of the Hall elements are different when the valve is opened and closed, the detection errors are different, the errors are more or less 0-1 pulse when the flow is detected, and the fluctuation range is 2 pulses. In the PWM mode, the valve opening time is generally 0.05 s-2 s, the pulse number is 1-40 pulses, and 2 pulses have great influence on the measurement accuracy.
From the above analysis and the pulse-time curves, it can be seen that the 2 nd to the n-1 th pulses all represent a complete pulse, whereas the 1 st and the n-th pulses vary considerably, with flow rates from 0 to a maximum being possible and therefore requiring correction. As can be seen in fig. 6, the 1 st pulse has the longest elapsed time (maximum elapsed time) indicating a small flow rate, the 2 nd pulse has the smallest elapsed time indicating a large flow rate, and then the time gradually increases until it levels off, and the last pulse (maximum elapsed time) substantially coincides with the previous pulse.
Based on the above test requirements, the control method of the PWM-based fertilizer suction pipeline flow rate detection system according to the present invention uses a predetermined valve opening time as the whole PWM cycle, uses the control system 13 to generate PWM pulse waveforms, adjusts the on/off of the fertilizer suction solenoid valve 10 according to the duty ratio of the output PWM waveforms, and further adjusts the fluid flow rate passing through the flow meter 9, and the flow meter 9 outputs corresponding pulse signals according to the change of the flow rate, and the pulse signals include the number of pulses and the elapsed time of each pulse, and then feeds back the pulse signals to the control system 13, and calculates the fertilizer suction flow rate in the PWM cycle, and specifically includes the following steps:
step one, recording all pulse quantities and the time of each pulse in a period from opening of the fertilizer suction electromagnetic valve to closing of the fertilizer suction electromagnetic valve in a PWM period;
step two, calculating the first pulse flow according to the time of the first pulse, wherein the calculation formula is as follows:
Figure GDA0002553934650000071
wherein, V1Represents the water volume of the first pulse, L; v0Represents a single pulse of water volume, L; t is t1Represents the time, s, elapsed for the first pulse; t is t2Represents the time, s, elapsed for the second pulse;
step three, correcting the flow of the last pulse according to the time of the last pulse and the time of the last pulse, wherein the correction formula is as follows:
Vn＝V0*tn/tn-1，
wherein, VnRepresents the water volume of the last pulse, L; v0Represents a single pulse of water volume, L; t is tn-1Represents the time, s, elapsed for the penultimate pulse; t is tnRepresents the time elapsed for the last pulse, s;
step four, calculating the flow in one PWM period according to the results obtained in the step two and the step three, wherein the calculation formula is as follows:
Figure GDA0002553934650000072
wherein q represents the fertilizer suction flow of a PWM period, L/s; v1Represents the water volume of the first pulse, L; v0Represents a single pulse of water volume, L; vnRepresents the water volume of the last pulse, L; t is tiRepresents the time, s, elapsed for the ith pulse;
and step five, weighing the reduced amount of the weight of the fertilizer liquid barrel in one PWM period by using an electronic scale, recording the reduced amount as the actual fertilizer suction amount of the Venturi fertilizer applicator, and comparing the actual fertilizer suction amount with the fertilizer suction amount obtained by calculation in the step four.
Setting the valve opening time to be 1s, adopting water to replace the fertilizer liquid, recording the effective pulse number and the time of each pulse, respectively calculating the flow according to a correction algorithm, simultaneously recording the fertilizer suction amount of each time by using an electronic scale, converting the fertilizer suction amount into the pulse number and comparing the pulse number.
In this embodiment, the above calculation method is adopted to calculate the actual water amount of the 2 groups of data in one PWM period, where V is0Is a performance parameter of the flowmeter, which is directly given by the manufacturer and has a value of 1/60L.
The data for the 2 sets of data recorded are as follows:
Figure GDA0002553934650000081
comparing the calculated flow with the measured flow in the 1 st group:
first according to t1/t25.83 ≧ 4, V is calculated1＝3V012.5L mL/4, then calculate V17＝V0*t17/t1614.8 mL; finally obtaining V1And V17And substituting the calculated q into the formula in the step four to obtain 277.3mL/s, so that the volume of water passing through the valve opening time of 1s is 277.3mL, the mass of the water is 277.3g according to the calculated density of the water, the reduced water amount in the actual fertilizer barrel is 273g, and the error percentage of the water amount obtained by calculation and the actually absorbed water amount is 1.6%.
Comparing the calculated flow with the measured flow in the group 2:
first according to t1/t25.88 ≧ 4, V is calculated1＝3V012.5 mL/4, then calculate V18＝V0*t18/t170.3 mL; finally obtaining V1And V18And substituting the formula in the step four to calculate that q is 279.5mL/s, therefore, the volume of water passing through the valve-opening time of 1s was 279.5mL, the mass of water calculated from the water density was 279.5g, and the amount of water reduced in the actual fertilizer bucket was 274g, so that the percentage error between the calculated amount of water and the actually absorbed amount of water was 2%.
In summary, the deviation between the detection system and the detection method adopted by the invention and the actual flow is less than 3%, which indicates that the detection system and the detection method are feasible.
The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various changes and modifications can be made without departing from the inventive concept of the present invention, and these changes and modifications are all within the scope of the present invention.

Claims (7)

1. A control method of a PWM (pulse-width modulation) fertilizer suction pipeline flow detection system is characterized by comprising the following steps of: the detection system comprises a main water pipe (1), a mixing cavity (2), an EC/PH sensor (3), a pressure reducing solenoid valve (4), a first fertilization pipeline (5), a second fertilization pipeline (14), a Venturi fertilizer absorber (6), a fertilizer liquid barrel (7), a filter (8), a flowmeter (9), a fertilizer absorbing solenoid valve (10), a fertilization pump (11), a one-way valve (12) and a control system (13);
the mixing cavity (2) is connected with the main water pipe (1) in series, is positioned in the middle of the main water pipe (1) and is used for fully mixing irrigation water and fertilizer liquid;
the water outlet of the main water pipe (1) is connected with a first fertilization pipeline (5) through a pressure reducing electromagnetic valve (4), the first fertilization pipeline (5) is provided with a plurality of Venturi fertilizer absorbers (6), each Venturi fertilizer absorber (6) comprises an inflow section (61) and an outflow section (62), the water outlet of the first fertilization pipeline (5) is connected with the inflow section (61) of each Venturi fertilizer absorber (6), a second fertilization pipeline (14) is arranged below each Venturi fertilizer absorber (6), the outflow section (62) of each Venturi fertilizer absorber (6) is connected with the water inlet of the corresponding second fertilization pipeline (14), and the corresponding second fertilization pipeline (14) is connected with the water inlet of the main water pipe (1) sequentially through a fertilization pump (11) and a one-way valve (12); the venturi fertilizer absorber (6) is characterized in that a fertilizer absorbing opening (63) is further formed in the middle of the venturi fertilizer absorber (6), the fertilizer absorbing opening (63) is connected with the fertilizer liquid barrel (7) through a fertilizer liquid pipe (64), a fertilizer absorbing electromagnetic valve (10), a flowmeter (9) and a filter (8) are arranged on the fertilizer liquid pipe (64), and the venturi fertilizer absorber (6), the fertilizer absorbing electromagnetic valve (10), the flowmeter (9), the filter (8) and the fertilizer liquid barrel (7) are sequentially connected;
the EC/PH sensor (3) is positioned between the pressure reducing solenoid valve (4) and the Venturi fertilizer absorber (6), is connected with the first fertilization pipeline (5) through a three-way pipe, and is used for acquiring an EC value and a PH value in the first fertilization pipeline (5);
the control system (13) is arranged on one side of the fertilizer liquid barrel (7), is respectively and electrically connected with the fertilizer suction electromagnetic valve (10), the EC/PH sensor (3), the flowmeter (9), the fertilizer pump (11) and the pressure reduction electromagnetic valve (4), and is used for controlling the operation of the fertilizer system;
the method comprises the following steps that a preset valve opening time is taken as a whole PWM period, a PWM pulse waveform is generated by a control system (13), the on-off of a fertilizer suction electromagnetic valve (10) is adjusted through the duty ratio of the output PWM waveform, the flow rate of fluid passing through a flow meter (9) is further adjusted, the flow meter (9) outputs a corresponding pulse signal according to the change of the flow rate, the corresponding pulse signal is fed back to the control system (13), and the fertilizer suction flow rate in the PWM period is obtained through calculation, wherein the specific calculation steps are as follows:
step one, recording all pulse quantities and the time of each pulse in a period from opening of the fertilizer suction electromagnetic valve to closing of the fertilizer suction electromagnetic valve in a PWM period;
step two, calculating the first pulse flow according to the time of the first pulse, wherein the calculation formula is as follows:
Figure FDA0002553934640000011
wherein, V1Indicating the quantity of water of the first pulse, V0Representing a single pulse of water, t1Representing the time elapsed for the first pulse, t2Representing the time elapsed for the second pulse;
step three, correcting the flow of the last pulse according to the time of the last pulse and the time of the last pulse, wherein the correction formula is as follows:
Vn＝V0*tn/tn-1，
wherein, VnIndicating the water quantity, V, of the last pulse0Representing a single pulse of water, tn-1Representing the time elapsed by the second last pulse, tnRepresents the time elapsed for the last pulse;
step four, calculating the flow in one PWM period according to the results obtained in the step two and the step three, wherein the calculation formula is as follows:
Figure FDA0002553934640000021
wherein q represents the fertilizer suction flow of one PWM period, V1Indicating the quantity of water of the first pulse, V0Indicating a single pulse of water, VnRepresenting the amount of water of the last pulse, tiRepresents the time elapsed for the ith pulse;
and step five, weighing the reduced amount of the weight of the fertilizer liquid barrel in one PWM period by using an electronic scale, recording the reduced amount as the actual fertilizer suction amount of the Venturi fertilizer applicator, and comparing the actual fertilizer suction amount with the fertilizer suction amount obtained by calculation in the step four.
2. The control method of the PWM fertilizer suction pipeline flow detection system according to claim 1, characterized in that: the control system (13) comprises an operation table box body (131), a touch screen (132), a PLC (programmable logic controller) controller (133), a fertilizer pump frequency converter (134) and an irrigation pump frequency converter (135); the utility model discloses a fertilizer applying machine, including operation panel box (131), front installation touch-sensitive screen (132) of operation panel box (131), install PLC controller (133), fertilization pump converter (134) and irrigation pump converter (135) in the operation panel box (131), the signal input part of PLC controller (133) respectively with EC/PH sensor (3), flowmeter (9) signal output part signal connection, the signal output part of PLC controller (133) respectively with touch-sensitive screen (132), inhale fertile solenoid valve (10) and decompression solenoid valve (4) signal connection, the signal output part and the fertilization pump (11) signal connection of fertilization pump converter (134).
3. The control method of the PWM fertilizer suction pipeline flow detection system according to claim 2, characterized in that: the flowmeter (9) adopts a Hall flowmeter, the Hall flowmeter comprises a shell (91), an impeller (95), a screw (96), a magnetic element (94), a Hall element (92) and an acquisition system (93), and the screw (96) is fixedly arranged in the middle of the inside of the shell (91) and is parallel to a fluid inlet of the shell (91); an impeller (95) is arranged on the screw (96), a magnetic element (94) is arranged on the upper side of the impeller (95), and the magnetic element (94) is coaxial with the impeller (95); one side of the magnetic element (94) is provided with a Hall element (92), the signal input end of the Hall element (92) is in signal connection with the signal output end of the acquisition system (93), and the signal output end of the Hall element (92) is in signal connection with the signal input end of the PLC (133) of the control system (13).
4. The control method of the PWM fertilizer suction pipeline flow detection system according to claim 1, characterized in that: the venturi fertilizer absorbers (6) are connected in parallel.
5. The control method of the PWM fertilizer suction pipeline flow detection system according to claim 1, characterized in that: the filter (8) adopts a laminated filter, and the filtering precision is not less than 80 meshes.
6. The control method of the PWM fertilizer suction pipeline flow detection system according to claim 1, characterized in that: the fertilizer suction electromagnetic valve (10) adopts a high-frequency electromagnetic valve.
7. The control method of the PWM fertilizer suction pipeline flow detection system according to claim 1, characterized in that: the valve opening time is in the range of 0.05 to 2 seconds.
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