Design and Testing of a Remote Control-Based Integrated Flow Regulation and Measurement Device

Abstract

In order to maintain sustainable agriculture, the flow in irrigation systems needs to be managed remotely and finely to achieve efficient use of water resources. This research develops a flow measuring device that integrates measurement and control to achieve precise flow regulation under remote control. The device chooses the angular regulating valve as the actuation component to control the flow. By the experimental study of the valve body working characteristics, this paper (1) establishes the relationships among the pressure in front of the valve, the valve body opening and the pipeline flow; (2) establishes the relationship between the valve opening degree and the number of driving pulses of the stepper motor, and (3) designs the opening decision and flow measurement software. The experiment shows that the flow coefficient of the valve body is 84.61, and there is no leakage loss when closed. It also shows that the regulation curve matches the law of fast-opening features. The established relationship and the correlation coefficient between the performance parameters and the measured value are both greater than 0.99, indicating a decent performance of fitness. In a test where the pipeline pressures were 0.10, 0.20, and 0.30 MPa, the average duration of flow regulation was 62.48 s, with a maximum overshoot of 5%, and a maximum steady-state error of 6%. The experiment also showed that the higher the pressure is, the better the regulation effect is. The flow measurement error under varied pressure is below 3%. With its simple structure, fast flow regulation time, and high accuracy, this device meets the requirements of flow management in irrigation systems. It can be used in a variety of flow rate remote monitoring and control scenarios.

1. Introduction

In order to maintain sustainability, intelligent agriculture and precision agriculture have become an important research direction of modern agriculture [1,2]. Variable adjustment technology of flow rate in irrigation pipelines helps the irrigation and fertilization operation match the actual needs of crops and, therefore, achieves the goal of water saving, fertilizer saving, and production increment [3,4,5].

Research on flow regulation in the field of agricultural irrigation focuses on three main areas. (1) PWM (Pulse Width Modulation) variable technique: Mo Jinqiu [6] and Ramon Salcedo [7] analyze pressure pulses and propose mitigation measures for large PWM variable sprinkler physical systems. Li Jianian [8] and Chang Chen [9] apply PWM variable technique combined with Venturi fertilizer applicator to fertilizer application control of the fertilizer applicator. (2) H Zhu [10], Wang Lixai [11] regulate the flow rate by adjusting the line pressure with a frequency converter and apply it to water-fertilizer-pharmacy integration systems and variable spraying systems. (3) Applying flow control by flow control valves, Sun Caizhen [12] designs a valve-regulated proportional valve fertilizer applicator to achieve control of the fertilizer supply flow.

Using flow control valves to regulate flow may make the regulation more stable and continuous. Flow control and valve control techniques are categorized as follows. (1) An intelligent control strategy based on PID control combined with multiple algorithms. For example, Song Lepeng [13,14] uses the variable theory domain adaptive fuzzy PID control algorithm to regulate electromechanical flow control valves, and Young-Rae Ko [15,16] directly uses PID closed-loop controllers as the control strategy. (2) Combined with the mathematical model control strategy of valve regulation law, Li Jinyang [17] uses BP neural networks to establish the relationship between valve opening and flow, Do-Hun Chin [18] and Zaryankin, A. E. [19] use simulation to obtain the operating characteristics of the regulating valve, and Rezazadeh [20] utilizes the flow equation for the flow and differential pressure relationship of MCOP, and uses for flow control. Additionally, the flow rate can also be estimated by modeling the regulation law of the valve body. Zhang [21] uses parameters including oil temperature, differential pressure, and spool displacement as input and flow rate as output with the help of neural networks to achieve the prediction of flow rate as a feedback signal to the flow controller.

IoT-based remote control enhances system automation and production efficiency [22]. Remote flow control technology is becoming increasingly used in modern agriculture [23]. Tu lv [24] and H. Ruan [25] have implemented remote control of the flow with the help of PWM technology and variable frequency pump technology. However, its implementation is relatively complex, which has led to most of the research on remove control methods for regulating valves staying in the laboratory and making it difficult to promote them on a large scale. Compared with other developed agricultural economies, the penetration rate of such technology in China is much lower [26]. Therefore, achieving acceptable flow control accuracy and responsiveness with simpler structures and control methods has become a crucial issue.

This paper (1) designed an electric flow regulator, (2) established mathematical relationships between valve parameters through performance tests, and (3) developed a control program and flow measurement program to operate at a remote terminal. The aim is to achieve remote and accurate control and measurement of the flow rate.

2. Actuating Component Design

The integrated flow rate regulation device consists of a local actuating component and a remote control system. The actuating component consists of two parts: the valve body structure and the driver module.

2.1. Valve Body Structure

The valve body is angularly structured. Its flow path is simple and resistant to precipitation blockage. The valve body adapts well to the agricultural irrigation system to transport fertilizer, liquid, and other viscous media and contains suspended matter and other conditions. Its vertical installation also has a certain self-cleaning function. The spool is made of elastic material so that the valve has the ability to close when the opening degree is zero, eliminating leakage losses.

The structure of the body is shown in Figure 1. The main components are plunger, rubber cushion, inlet shrinkage tube, and valve body shell; four parts. The plunger is used to drive the radial action of the adjustment and the outlet section of the inlet shrinkage tube to control the shape of the flow channel together. The rubber gasket is used to seal the gap between the plunger and the inlet shrinkage outlet when the valve body is closed and fixed by the nut on the water ward side of the plunger. The inlet shrinkage tube consists of two parts, the inlet shrinkage section and the outlet section, which are used to gather the fluid entering the valve body with an inner diameter of 32 mm at the outlet. The valve body shell is a three-way structure, and consists of three parts: water inlet, chamber, and water outlet. The valve body fixes the internal structure of the valve body. The inlet shrinkage section and the valve body shell are made of PVC (polyvinyl chloride).

2.2. Driver Module

The driver module of the device is powered by a stepper motor. The power output shaft of the stepper motor is connected to the screw through a coupling to transmit the torque, and the radial movement of the plunger is ensured by the limitation of the plunger’s degrees of freedom by the plunger guide to adjust the valve opening, as shown in Figure 1.

To ensure that the motor drives the torque in the working pressure range of the valve body, it is necessary to calculate the motor output shaft torque and the screw torque, and then compare. Screw the driven plunger with a screw drive, which is mainly subject to resistance to the action of the plunger face level before and after the pressure difference. The required screw torque Tn can be obtained from the following formula [27].

$$T_n=\mathsf{\pi }\Delta p{D}^{2}d\tan \left(\arctan \left(nS/\pi d\right)+\arctan \left(f/\cos 0.5\alpha \right)\right)/800$$

(1)

where D is the diameter of the plunger facing the horizontal surface in mm, Δp is the maximum pressure difference of the valve standard working condition in MPa, n is the number of threads, S is the thread lead in mm, d is the thread middle distance in mm, f is the friction coefficient of the bolt (it is also a dimensionless number and can be checked in the spiral sub by material), α is the thread tooth angle in °.

Because of the existence of mechanical losses in the device, the motor torque selected should be greater than the requested torque Tn. It follows that the final choice of 42HS6315B4 type stepper motor with DV542C two-phase digital stepper motor driver. Both devices can be driven by 12 to 24 V DC.

Commands are sent to the stepper motor driver by the controller, including the rotational direction, number of pulses, and pulse frequency. The stepper motor’s angular displacement is controlled by the number of pulses, and the frequency of the pulses determines how quickly the motor rotates. This enables precise positioning of the opening of the regulating valve and control of the regulating speed.

3. Experimental Study

The development of the device control system is based on the hydraulic performance relationship of the valve body, and the opening-pulse relationship of the drive module, so the performance relationship between these two modules should be investigated through experimental studies.

3.1. Testing Device

The structure of the test device is shown in Figure 2a. The test device consists of a constant pressure water supply module, a flow regulation module, and a field control device. The constant pressure water supply module provides constant water pressure using variable frequency pumps, the flow regulation module includes the regulating valve body and its driving module, and the control device consists of electromagnetic flow meter, pressure transmitter, gate valve, field controller and field control terminal. A physical diagram of the flow regulation module and pressure transmitter installation is shown in Figure 2b.

3.2. Experimental Design

Characteristic flow coefficient test: The differential pressure Δp before and after the valve body is maintained at an average of 15 levels in 0.02–0.30 Mpa, and the pipeline flow q, pre-valve pressure p1 with the valve body fully open is measured.

Performance parameter test: Keep the differential pressure Δp before and after the valve body at 5 levels in 0.05–0.25 MPa. The valve opening is selected uniformly at 25 levels in 0–50% and 12 levels uniformly in 50–100%. The flow rate, pre-valve pressure, and back-end pressure are q, p₁ and p₂, respectively.

Opening and pulse relationship test: The valve opening is selected uniformly at 25 levels in 0–50% and 12 levels uniformly in 50–100%. Then, measure the actual opening of the valve body la and record the cumulative number of pulses np.

During the test, the test level is adjusted continuously, and the pressure and flow rate under the current test level is stabilized for 15 s before switching to the next test level, the data is collected every 5 s, the measured data is obtained by averaging the 3 data before switching the level after the test, and each group is repeated for 3 times.

3.3. Test Index

Pressure head: Pressure transmitter (model: PCM300, accuracy 0.5%) is used before and after the flow adjustment module to monitor.

Flow rate: The pipeline flow rate is monitored by the electromagnetic flow meter (EMF5000, accuracy 0.5%).

Cumulative number of pulses: The sum of the number of pulses of the stepper motor action is monitored and recorded by the controller.

Valve body relative opening: Expressed by the ratio of the accumulated number of pulses of the stepper motor action and the total number of pulses of its full stroke, which is monitored and recorded by the controller.

The actual opening of the valve body: Measured by the vernier calipers, the spool is in the fully closed position and recorded as 0 mm.

3.4. Analysis of Test Results

3.4.1. Valve Body Hydraulic Characteristics

The flow path of the valve body will make the medium subject to local pressure loss. By adjusting the opening of the valve body, one can change this loss, and thus regulate the flow. When the regulating valve is in operation, the relationship between the lead pressure p₁, the relative opening l_re, and the flow rate q through the valve body can be obtained from the following formula [28].

$$q=K_V\sqrt{\left[\left(1-C_{PP}\right)p_1\right]/\left\{\rho \left[1+C_{PP}\left(k_L^{-2}-1\right)\right]\right\}}$$

(2)

where q is the flow rate through the valve body, m³/h; K_V is the dimensionless characteristic flow coefficient obtained through tests; C_PP is the post-valve pressure prediction coefficient, a dimensionless number; k_L is the relative flow coefficient, which is only related to the relative opening lre; p₁ is the pre-valve pressure, MPa; ρ is the density of the medium in kg∙L⁻¹ (the test uses clear water, the density is about 1 kg∙L⁻¹)

The valve body characteristic flow coefficient K_V is determined by using the relationship between flow and pressure at the full start of the valve body, and is calculated by using the following formula [28].

$$K_V=({{\displaystyle \sum }}_{i=1}^n{q}_i\sqrt{\rho /\Delta p_i})/n$$

(3)

where Δp is the differential pressure Δp before and after the valve body, MPa; n is the number of data groups, (the number of levels in this study is 15, with 3 replication groups, so n is 45, and its calculation table (

Table 1. Calculation table of characteristic flow coefficient.

No.	Pressure Difference Δp (MPa)	Measured Flow qa (m3∙h−1)	Flow Coefficient KV
1	0.020	11.655	82.413
2	0.040	16.620	83.100
3	0.060	20.620	84.181
4	0.080	23.970	84.747
5	0.100	26.755	84.607
6	0.120	29.380	84.813
7	0.140	31.545	84.308
8	0.160	33.905	84.763
9	0.180	36.075	85.030
10	0.200	38.065	85.116
11	0.220	40.000	85.280
12	0.240	41.830	85.385
13	0.260	43.530	85.369
14	0.280	45.050	85.136
15	0.300	46.480	84.860

) is as follows). Then, K_V = 84.61.

The post-valve pressure prediction coefficient C_PP is the proportionality coefficient between the pre-valve pressure p₁ and the post-valve pressure p_2,100 under the same p₁ when the valve body is fully open, which is a constant in the same pipeline. The C_PP under this device is 0.375, and the measured data and the calculated data will use Pearson correlation analysis to get R² of 0.999, indicating an ideal fitting performance.

The relative flow coefficient k_L is measured experimentally by performance parameters. The relative flow coefficients at different pressures with relative openings are shown in Figure 3. It is observed that the relative flow coefficient k_L varies less at different pressures, and increases with the relative opening l_re at the same pressure. In the case of a small relative opening (0% to 5%), the relative flow coefficient at different pressures does not change immediately with the increase in opening, and the greater the pressure, the faster the relative flow coefficient changes. The main reason is the anti-leakage design of the valve body. The existence of the pre-closing volume when the spool is closed and greater water pressure can make the spool and the valve seat separate more quickly.

A polynomial was fitted to the test data to establish the relationship between opening and flow. The relationship established is as follows.

$$k_L=\{\begin{array}{c}-0.1893l_{re}^3-0.7487l_{re}^2+1.970l_{re}-0.045\\ l_{re}>-0.3\Delta p+0.1\\ 0 l_{re}\le -0.3\Delta p+0.1\end{array}$$

(4)

The correlation coefficient R² between the fitted and measured values at all five pressure levels is above 0.996, which is a good fit.

3.4.2. The Relationship between the Valve Opening and the Number of Pulses of the Stepper Motor

In order to verify the feasibility of using the ratio of the accumulated number of pulses from the stepper motor action to the total number of pulses from its full stroke as the relative opening of the valve body, a relationship between the actual opening of the valve and the number of pulses from the stepper motor is established.

The opening degree l of the control valve is proportional to the number of driving pulses n_p of the stepper motor, and its proportionality factor k can be calculated by the number of threads n, thread guide S, and the number of steps divided by the driver n_c. Its relationship is shown in Equation (5) [27].

$$k=S·n/n_c$$

(5)

If the driver divides one revolution into 25,600 steps, substituting the parameters yields a proportionality factor k of approximately 1.142 × 10⁻⁴.

The theoretically calculated value is close to the measured value, R² is 0.999, and the proposed relationship is reliable. It is shown that the method of characterizing the relative opening by the ratio of the number of pulses is reliable (Figure 4).

4. Control System Design

4.1. Hardware Design

The control system is composed of a field acquisition and execution subsystem, IOT cloud box, and remote monitoring subsystem. The overall framework is shown in Figure 5. The field acquisition and execution subsystem takes a programmable logic controller as the core, and connects pressure transmitter, motor driver, and other devices respectively. The remote monitoring subsystem takes cloud platform as the core, which can realize the monitoring of the acquisition data through remote management software and process the acquired data and output the valve opening size synchronously by running the opening decision algorithm, as well as the control command issuance. As the core hub, the IOT connects the site monitoring subsystem and remote decision monitoring subsystem through RS-232 serial port and 4G network, respectively, and realize the communication between data information and control signal at the local end and the cloud platform.

4.2. Software Design

The device control software is developed based on the relationship among the pressure in front of the valve, the valve opening, the pipeline flow, the accumulated pulses, and the actual opening. Its operation flow is shown in Figure 6. The steps are as follows.

(1) Configure initialization parameters such as target flow rate and allowable error. (2) Read the pressure before the valve and the number of opening pulses to calculate the current flow rate. (3) Judge whether the current flow rate is in the range of a reasonable flow rate interval; if it is within the range, the program ends; if it is not within the range, calculate the target opening pulse number. (4) Calculate a difference between the target opening pulse number and the current pulse number, and adjust the opening to the target opening based on its positive or negative value to drive the motor rotation direction. (5) Update the adjusted number of pulses to the current number of pulses. (6) The program jumps back to step 2 until the end of the program.

The measurement of the flow rate can be calculated directly into Equation (2). The calculation of its opening is the reverse of the former: The target flow rate as q with other parameters into Equation (2) to get the corresponding flow coefficient k_L, then its inverse function l_re = f_(kL) into Equation (3) to obtain the relative opening l_re, multiplied by the number of pulses corresponding to the full stroke of the stepper motor to obtain the number of pulses n_p1 corresponding to the target flow rate q₀.

5. Performance Test

The validation test was conducted with a remote control system attached to the performance test platform (Figure 2). The sensors used are consistent with the performance test platform. The control software was run on the remote control terminal to make decisions and give regulation commands. The test data were collected through the local control module, and the data is collected in the same way as above. Through several trial adjustments, the pulse frequency of the stepper motor driver is set to 400 HZ. This opening adjustment speed can make the flow adjustment take into account the adjustment speed and stability, and at the same time, the water hammer phenomenon will not occur. Our goal is to test the regulation performance of the flow rate, and the flow measurement performance, respectively.

The test is set up with multiple levels of test pressure p₁, target flow q₀, and target opening l_re. The flow measurement software output data q_m and the actual data q_a measured by the electromagnetic flowmeter are recorded once per second. The regulation time t_s is used to evaluate the regulation rapidity, the overshoot Δh to evaluate the regulation stability, and the steady-state error e_ss to evaluate the regulation accuracy. The relative error δ of q_a and q_m evaluate measurement accuracy. All tests are repeated 5 times.

The average values of q_s, t_s, Δh, e_ss, the mean values of q_a and q_m and δ of the measurement test for each working condition of the regulation experiment are calculated in

Table 2. Performance evaluation.

p1 (MPa)	Adjustment Performance Test					Measurement Performance Test
	qp (m3∙h−1)	qs (m3∙h−1)	ts (s)	Δh (%)	ess (%)	lre (%)	qa (m3∙h−1)	qm (m3∙h−1)	δ (%)
0.1	5	4.751	67.667	1.417	5.250	20	8.436	8.527	1.076
	10	10.113	67.333	3.500	1.111	50	16.278	16.396	0.729
	15	15.132	78.333	4.458	0.875	80	20.147	20.299	0.755
0.2	5	4.834	48.000	0.333	3.417	20	12.438	12.718	2.247
	15	15.458	60.667	0.000	2.958	50	24.263	24.887	2.571
	25	25.347	68.000	0.000	1.367	80	28.681	28.997	1.104
0.3	5	5.000	51.000	0.750	0.000	20	13.664	13.992	1.076
	15	15.215	55.333	2.250	1.417	50	26.884	27.682	2.967
	25	24.902	66.000	0.083	0.389	80	31.196	31.380	0.588

.

From the table, we can obtain the following information. In the regulation performance tests, the final steady-state flow rates achieved were all similar to the target flow rates, with steady-state errors within 6%, and in most cases within 2%. The higher the pressure and flow rate, the higher the regulation accuracy. This meets the requirements of flow regulation in production. The rapidity and stability of the flow rate regulation is also good. The regulation time decreases as the pressure increases, and increases as the target flow rate increases, with a maximum of 78 s. Overshoot is within 5%, with less overshoot at moderate pressures.

In the test performance tests, the measured flow rates were compared at multiple opening levels at multiple pressures, and it can be seen that the measured flow rates match the actual flow rates with an error of 3% or less. The accuracy of the measurement is higher at higher opening and flow levels, but the effect of pressure on the accuracy of the measurement is not significant.

6. Conclusions

(1)

A remote control-based integrated device for flow regulation and measurement is designed. The device has a stepper motor as the power input, an angular regulating valve as the actuating component, a pressure transmitter as the collecting component, a PLC and a cloud box as the signal transmission relay, and a remote control terminal as the data processing and human-computer interaction platform, enabling remote pipeline flow regulation and measurement.

(2)

The device’s regulation properties were studied. The flow coefficient K_V of the valve body is 84.61, and the regulation curve is in accordance with the law of fast-opening characteristics. There is no leakage loss when closed within 0.3 MPa of the pressure difference between the front and rear of the valve body. This paper also created the connection between the pressure before valve p₁, valve body opening l_re, pipe flow q, and the relationship between the valve opening degree l_re and the number of driving pulses n_p of the stepper motor. The correlation of the measured data under test circumstances is more than 0.99, indicating excellent fitting performance.

(3)

A control program for adjustment and the flow measurement is designed based on the adjustment characteristics of the valve body. The test shows that the flow adjustment effect is excellent, with a maximum adjustment time t_s of 78 s, an overshoot Δh of less than 5%, a steady-state error e_ss of less than 6%, and a better adjustment effect with increased pressure. The measured flow and the actual flow are also well matched, with an error of less than 3%.

(4)

Compared to other relevant devices on the market, the device is simple in construction, less costly, and the regulation meets production needs. Subsequent research will be based on the application of this valve body in specific irrigation scenarios.