CN100388144C - An intelligent two-wire electric valve positioner and its control method - Google Patents

Abstract

An intelligent two-wire electric valve positioner, including a control circuit unit, an I/P electrical conversion unit and a valve position detection feedback unit, the control circuit unit includes a power conversion circuit and a microprocessor control unit, and the I/P electrical conversion unit includes In the gas circuit control and amplification part, the valve position detection feedback unit includes a feedback potentiometer and a valve position feedback lever; the input signal and the valve position feedback signal enter the microprocessor control unit for comparison and operation, and output a control signal to the deviation between the two The I/P electrical conversion unit controls the output air pressure and the movement of the valve stem, and the stroke of the valve stem is fed back to the control circuit unit at the same time to form a closed-loop control. Among them, the power conversion circuit converts the 4~20mA input current signal into three groups of 6V, 3V and 24V Voltage. The invention takes the microprocessor as the control core, converts the electric control command into the precise control of the valve position by the pneumatic positioning increment, strengthens and expands the function of the positioner, and the whole machine is controlled by a single-chip microcomputer to realize full digitization and intelligence.

Description

An intelligent two-wire electric valve positioner and its control method

technical field

The invention relates to an electric regulating valve positioner, in particular to an intelligent electric regulating valve positioner system and a control method thereof.

Background technique

With the progress of industry, the positioner of electric control valve has developed from the original positioner based on pure pneumatic and mechanical force balance to the later electric/pneumatic valve positioner based on electromagnetic conversion, until today's intelligent valve positioner. type and positioners using fieldbus technology. Its general trend is electrification, intelligent operation and control, and it will be compatible with all-digital industrial control.

At present, the positioners used in my country are mainly mechanical positioners based on the principle of force balance, which use nozzle-baffle technology. This kind of positioner is easy to wear during use, and it is usually necessary to repeatedly adjust a series of spring screws during installation and adjustment. In order to achieve force balance, the operation process is cumbersome and complicated, the control is not flexible enough, and it cannot be easily matched with valves of different stroke forms, and the accuracy cannot be guaranteed.

Following the pneumatic valve positioner, an electric valve positioner has also appeared in this field, and its input adopts a direct current setting signal of 0-10mA or 4-20mA. The structure of this type of positioner is similar to the above-mentioned pneumatic valve positioner, the only difference is that the bellows is replaced by an electromagnet, and its output is an air pressure signal, which can realize the dual functions of a pneumatic valve positioner and an electrical converter. Since the input of the electric valve positioner is only a current signal, what is required in the actual circuit is a set of different voltages. For example, the MCU power supply requires a voltage of 3.3V, while the control of the piezoelectric ceramic valve requires a voltage of 24V or higher, so it must be After a certain conversion and processing. The task of the power conversion circuit in the electric valve positioner is to convert the input current into two sets of 3.3V and 24V power supplies for use by microcontrollers and other devices. In the prior art in this field, the implementation of the power conversion circuit is to first convert the input current into a lower voltage, then generate oscillation through the oscillator, and finally obtain the required voltage value through rectification, filtering and linear voltage stabilization. However, this The disadvantage of the solution is that the key part of the circuit (transformer) needs to be wound by itself. It is precisely because of the limitation of the process of winding transformers that it is difficult to guarantee the accuracy of such products, the consistency of operation results is poor, the work is unstable, and the power consumption is large, and the volume is also very large.

Contents of the invention

The present invention proposes an intelligent two-wire electric valve positioner and its control method just to solve the above-mentioned defects in the prior art, applies piezoelectric technology to the positioner, adopts a highly integrated power supply design scheme, and can Using a highly integrated microprocessor to realize the control of the intelligent two-wire electric valve positioner pneumatic linear stroke or quarter stroke actuator.

The invention provides an intelligent two-wire electric valve positioner, which includes a control circuit unit, an I/P electrical conversion unit and a valve position detection feedback unit, the control circuit unit includes a power conversion circuit and a microprocessor control unit, the The I/P electrical conversion unit includes a pneumatic circuit control and amplification part composed of two piezoelectric valve groups. The valve position detection feedback unit includes a feedback potentiometer and a valve position feedback lever; the input signal and the valve position feedback signal enter the The microprocessor control unit of the intelligent electric valve positioner control circuit is compared and calculated, and a control signal is output to the I/P electrical conversion unit according to the difference between the two, and the output air pressure of the I/P electrical conversion unit and the pneumatic control valve are controlled. The valve stem moves, and the stroke of the valve stem is fed back to the control circuit unit at the same time to form a closed-loop control. It is characterized in that the power conversion circuit is a power supply that converts the input current signal of 4-20mA into three sets of voltages of 6V, 3V and 24V conversion circuit.

The present invention also provides a control method for an intelligent two-wire electric valve positioner. In the control circuit unit, the microprocessor is used for data collection, button interruption and liquid crystal display operation, so as to realize the switching between various modes through the button, and execute the corresponding The action and control strategy, parameter display, is characterized in that, the method comprises the following steps:

1) Turn off the system watchdog clock generator, stop timing, and turn on the global interrupt;

2) port initialization;

3) Call the liquid crystal display subroutine to display the operation result;

4) Select the A/D channel, set the clock and timing time, and enable the A/D interrupt;

5) Set the button clock, set the timing time, and enable the button interrupt;

6) Enter the low power consumption mode of the present invention;

7) Judging whether it is the A/D interrupt timing time;

If the A/D interrupt timing has arrived, enter the A/D interrupt subroutine;

Execute the A/D interrupt subroutine;

Return from the interrupt, waiting for the next timing to be met;

Otherwise, judge whether the current time has reached the button interrupt timing;

If the button interrupt timing has arrived at this time, then enter the button interrupt subroutine;

Execute the key interrupt subroutine, return from the interrupt, and wait for the next timing to arrive.

Compared with the prior art, the speed regulation method of the asynchronous motor based on the motion electromotive force control proposed by the present invention, the intelligent electric valve positioner takes the microprocessor as the core, and adopts the principle of electric balance (digital balance) to replace the traditional force balance principle , by converting the electronic control command into pneumatic positioning increment to realize the precise control of the valve position, which strengthens and expands the function of the positioner. The whole machine is controlled by a single-chip microcomputer, which realizes full digitalization and intelligence, such as flow characteristic correction, automatic zero adjustment and range adjustment, alarm, fault self-diagnosis, on-site display, etc., can be realized by software functions. These features are unique to existing similar projects. What is not available has completely changed the traditional situation of relying on the processing of parts with different structures and on-site adjustments to adapt to on-site requirements.

The technical solution of the invention will be described in detail below in conjunction with the embodiments and with reference to the accompanying drawings.

Description of drawings

Fig. 1 is the functional module structural diagram of the intelligent two-wire electrical positioner of the present invention;

Fig. 2 is the main flowchart of the control method of the intelligent two-wire electric positioner of the present invention;

Fig. 3 is the flow chart of the A/D conversion interrupt program of the intelligent two-wire electric positioner control method of the present invention;

Fig. 4 is a flow chart of the keyboard interrupt processing program of the intelligent two-wire electrical positioner control method of the present invention.

Fig. 5 is the flow chart of the liquid crystal display processing program of the intelligent two-wire electric positioner control method of the present invention;

Fig. 6 is the power conversion circuit diagram in the intelligent electric-pneumatic valve positioner control circuit of the present invention;

Fig. 7 is the high-end current detection circuit diagram of the power conversion circuit in the intelligent two-wire electric positioner of the present invention;

Fig. 8 is the switched capacitor voltage inverter circuit of the power conversion circuit in the intelligent two-wire electrical positioner of the present invention;

Fig. 9 is the circuit diagram of the inductive switching mode DC-DC converter of the power conversion circuit in the intelligent two-wire electrical positioner of the present invention;

Fig. 10 is an overvoltage protection circuit diagram of the power conversion circuit in the intelligent two-wire electrical positioner of the present invention;

Fig. 11 is a hardware block diagram of the single-chip microcomputer control unit of the present invention;

12 is a block diagram of an interface application based on the I ² C bus used by the liquid crystal module of the present invention;

Fig. 13 is a control circuit diagram of the I/P electric appliance conversion unit of the intelligent two-wire electric positioner of the present invention.

Detailed ways

Normally, for a two-wire positioner, the input current signal range is 4-20mA, and this signal is used as a positioning signal, and at the same time provides the required energy for the positioner. The total current consumption of the system must be less than the minimum current requirement of the loop (that is, to ensure that the circuit can still work normally under the condition of a minimum current of 4mA). In order to leave a certain margin and to be compatible with the smart transmitter based on the HART protocol, the upper limit of the maximum consumption current of the entire circuit is designed to be 3.5mA. It is precisely because the two-wire system has strict requirements on power consumption, so the design and optimization of the control circuit is the key to the realization of the technical solution of the present invention, and the overall design of the present invention revolves around how to achieve low power consumption.

The intelligent two-wire electric valve positioner proposed by the present invention is composed of an intelligent electric-pneumatic valve positioner control circuit unit 101, an I/P electric (current/air pressure) conversion unit and a valve position detection feedback unit, and its system structure is as follows Figure 1 shows. The input signal from the regulator and the valve position feedback signal enter the microprocessor together for comparison and calculation, and output a control signal to the I/P conversion unit according to the deviation between the two to control the output air pressure of the I/P unit and the pneumatic control valve. The valve stem moves, and the stroke of the valve stem is fed back to the control unit at the same time, forming a closed-loop control.

Among them, the control circuit unit is a PCB printed circuit board assembly, mainly including:

1. The DC/DC power conversion circuit is used to convert the 4~20mA input current signal into three sets of voltages: 6V, 3V and 24V. Specifically, the three groups of voltages are: a. 6V power is generated by a linear power supply; b. 3V power is generated by a charge pump; c. 24V power is generated by an inductive switching mode DC-DC converter; A sampling circuit is also included.

2. Control unit

Adopt ultra-low power consumption single-chip application system, such as TI's MSP430 single-chip microcomputer, mainly including:

a. A/D conversion module; b. man-machine interface module; c. pulse drive module; d. system software design.

The above-mentioned control circuit unit is a PCB printed circuit board assembly, which has 4 connection terminals on the mounting frame to connect with the electrical conversion I/P unit under the printed board, and a screw terminal box to connect with the valve position feedback system; The valve position detection feedback unit cooperates with the valve stem of the regulating valve through a rigidly connected connecting rod without clearance.

The I/P electrical conversion unit is composed of two piezoelectric valve groups for air circuit control and amplification. The pneumatic valve group is installed inside the shell, and the pneumatic interface for the intake and output pressure is located on one side of the positioner, and is connected to the PCB printed circuit. boards are connected.

The valve position detection feedback unit includes a feedback potentiometer and a valve position feedback lever, which cooperates with the valve stem of the regulating valve through a rigidly connected connecting rod without clearance, thereby converting the stroke (displacement or rotation angle) of the regulating valve into the feedback potentiometer. Corner, which in turn can be converted into an electrical signal. The parameter setting adopts a potentiometer, and the potentiometer used for feedback is not a conventional potentiometer, but a special potentiometer equipped with ball bearings and durable resistor sheets. The resistor sheets are made of special wear-resistant conductive plastic material. Therefore, the potentiometer can be used in various occasions, and the continuous parts will not be damaged.

Control valves A and B are used to control compressed air in and out of the pneumatic regulating valve. Valve A is the intake valve, and valve B is the exhaust valve. Both valves have only two states: "open" and "closed". This control idea is actually to use a small valve to control the flow of compressed air, and then use compressed air to drive a large valve to control the flow of the controlled medium. It is a design scheme of hierarchical control.

Specifically, at any moment, only one of the valves A and B can be opened, and the other can be closed. If A is opened, because the compressed air pressure is greater than the internal pressure of the membrane head, the compressed air enters the regulating valve, and the valve stem moves downward; otherwise, when B is opened, the compressed air in the air chamber of the regulating valve is discharged into the atmosphere through B, and the valve The rod moves upward under the action of the spring. In the smart valve positioner, in order to interface with the control circuit, the opening and closing of valves A and B must be controlled by electricity. There are various types of valves A and B used in practice, such as solenoid valves and piezoelectric ceramic valves. What is used here is a piezoelectric ceramic control valve, the basic principle of which is based on the piezoelectric effect of piezoelectric materials. Use a small piece of specially made piezoelectric ceramic sheet, and apply 24-30V voltage on both sides of it. The piezoelectric ceramic sheet will bend, and the total deformation can reach tens of microns. Thereby, the air inlet or exhaust port can be blocked/released to achieve the purpose of controlling the air flow. Due to the high impedance of piezoelectric ceramics, the advantages of this control valve are extremely low power consumption, easy to implement two-wire instrumentation and explosion-proof. In addition, it is fast and lightweight, so it can still work reliably in environments with high vibrations.

As shown in Figure 2, it is the main program flow of the intelligent two-wire electric valve positioner control method proposed by the present invention, mainly composed of data acquisition subroutine, key interruption subroutine, liquid crystal display subroutine and so on. Realize the control and result display of the locator system proposed by the present invention. In the main loop, switch between modes by pressing buttons, execute corresponding actions and control strategies, and display input parameters, valve opening and other parameters. This main program comprises the following steps: at first, close system watchdog clock generator, stop timing, and open global interruption, step 201; Initialize port, step 202; Call liquid crystal display subroutine, display operation result, step 203; Carry out A /D channel selection, clock, timing time setting, and open A/D interruption, step 204; Set key clock, set timing time, open key interruption, step 205; Enter low power consumption mode of the present invention, step 206; Judge current Whether to the A/D interrupt timing time, step 207; as the A/D interrupt timing has arrived, then enter the A/D interrupt subroutine, step 208; after executing the A/D interrupt subroutine, the interrupt returns, waiting to meet the next time Timing time; otherwise, the current A/D interrupt timing has not arrived, then continue to judge whether the current time has reached the button interruption timing, step 209; if the button interruption timing has arrived at this time, then enter the button interruption subroutine, step 210; Execute the button After the subroutine is interrupted, the interrupt returns and waits for the next timing to be met.

What can be realized in the above main program is: when the positioner is initialized, it can automatically determine the zero point, maximum stroke, action direction and positioning speed of the actuator according to the input parameters. When working, it can automatically modify the control parameters and compensate for errors such as valve aging and wear according to the mechanical performance changes of the valve or actuator. It realizes full digitalization and intelligence, such as flow characteristic correction, automatic zero adjustment and range adjustment, alarm, fault self-diagnosis, on-site display, etc., can be realized by software functions. These features are not available in existing similar projects, completely changing The traditional situation of relying on the processing of parts with different structures and on-site adjustments to adapt to on-site requirements has been eliminated.

As shown in Figure 3, it is the flow process of the A/D interrupt processing program 30 of the intelligent two-wire system electric valve positioner control method that the present invention proposes, and it is the subroutine that is called by the main program under conditional conditions, and this subroutine The program includes the following steps: first, sampling the input signal, step 301; judging whether the P6.4 sampling channel is currently used, step 302; if so, saving the A/D conversion result of the current sampling, step 303; judging that it has been completed 5 times Sampling, step 304; If so, then carry out digital filter processing, step 305; Carry out linearization process to digital filter output result, step 306; Output signal result setting bit AD1, step 307; If not, then further judge whether the current adopting is P6 .5 sampling channels, step 308; if 5 samplings are not satisfied, then return to step 301, and continue to complete signal sampling;

If the current sampling channel is not P6.4, then continue to judge whether the current sampling channel is P6.5, step 308; if yes, then save the A/D conversion result of the current sampling result, step 309; judge whether to complete 5 samplings, step 308 310; if yes, perform digital filtering, step 311; and linearization processing, step 312; and set the output signal result as AD2; similarly, if the number of sampling times does not meet 5 times, return to step 301 and continue to complete sampling.

As shown in Figure 4, it is the button interrupt processing program of the intelligent two-wire system electric valve positioner control method proposed by the present invention, which is also a subroutine called by the main program flow when the conditions are met, and it includes the following Step: enter the button interrupt processing program 40, judge whether to receive the button press operation at present; Step 401; Obtain the key value of the button currently pressed by the button recognition function, step 402; Judge whether the mode button is pressed, step 403 If not, then return to the beginning of the subroutine, and wait for the reception of the new button action again; if so, then further judge whether the time that the current button is pressed exceeds 5 seconds, step 404; if so, then be set to configuration mode, step 405 ; According to the user's continuous operation time of the key, select different working modes: configuration mode, manual mode and automatic mode; step 405 to step 409. The function of the keys depends on the selectable operating mode:

1. Automatic mode, the initialized (and configured) positioner automatically changes according to the set value and continuously makes the deviation of the system tend to the minimum value as much as possible. At this time, the +1 key and -1 key do not work;

2. Manual mode Press the working mode key to switch the positioner from automatic mode to manual mode. Step adjustment is achieved by pressing the +1 key or -1 key. In order to achieve a rapid increase, press the +1 key first, and then press the -1 key; similarly, to achieve a rapid decline, first press the -1 key, and then press the +1 key. Once the +1/-1 key is released, the actuator stops at its current position. The internal setpoint is adjusted to the current manipulated variable. Since the control in the manual mode is closed-loop, the current valve position can still be maintained even in the event of an air source leakage accident of the positioner;

3. The working mode button for configuration mode can be converted from automatic mode or manual mode to configuration mode. For this purpose, the mode conversion button must be pressed for at least 5 seconds until the conversion is completed.

Among them, the configuration parameters mainly include: the type of execution structure (angular stroke or linear stroke), feedback angle (30° and 90°), stroke value, automatic initialization, manual initialization, input current range, positive and negative effects, valve confinement function .

In the configuration mode, the parameter value of the positioner can be changed, and the next parameter can be selected by using the mode key. If the -1 key is pressed while pressing the mode key (<5s), the parameters can be selected in reverse order. Use the +1 button or -1 button to change the parameter value.

As shown in Figure 5, it is the liquid crystal display subroutine flow process of the present invention, which is called by the main program, and it includes the following steps: write the initialization command definition mode, step 501; define the internal RC oscillation mode, step 502; start the oscillator, step 503; turn on the display, step 504; continuously write data timing, step 505; display the valve position program, step 506; display the configuration mode program, step 507.

The present invention adopts the liquid crystal module LCM046, which has a small size, low power consumption, and powerful functions. Therefore, when the system is designed, the built-in liquid crystal drive module of the MSP430 microcontroller is not used, but the connection method based on the I ² C bus is adopted. ,

The implementation scheme of the intelligent two-wire electric valve positioner system of the present invention will be further specifically described below through specific embodiments.

(1) Positioner control circuit unit

Currently commonly used DC-DC converters mainly include linear regulators, inductive switch mode DC-DC converters and capacitor charge pump DC-DC converters. Among the three power converters, the linear regulator is simple, has no ripple and electromagnetic interference (EMI), but has low efficiency and the output voltage can only be lower than the input voltage; the switching power supply has high efficiency and is the most flexible, and can provide boost, Buck and reverse polarity output are ideal for voltages higher than V _out /V _in . The key to ensuring low ripple, EMI and noise lies in circuit design; charge pumps can also provide boost, buck, reverse polarity The output has high efficiency, simple external circuit, low EMI and low ripple, but its output current is limited.

Since the power supply module needs to convert the input current into multiple sets of power supplies, the characteristics of the three are integrated, and the power supply design scheme combining the three methods is adopted to generate power supply voltages of different amplitudes. The present invention proposes a novel two-wire system power supply, and its power conversion circuit diagram is shown in FIG. 6 . In this power conversion circuit, it includes polarity protection and front-end anti-interference part of the power supply, 6V power supply generated by linear power supply, high-side current detection circuit, 3V power supply generated by switched capacitor voltage inverter, inductive switch mode DC-DC converter Realize 24V power supply, 2.5V voltage reference; overvoltage protection unit.

1. Polarity protection and power front-end anti-interference part;

Box 1: JP1 is the input terminal, 3 is the positive terminal of 4 ~ 20mA, and the output of terminals 1 and 2 is short-circuited to the output terminal of the current loop. 3 is connected with U0 (Schottky diode) for polarity protection. U0 is connected to inductor L11, JP1 terminal 1 is connected to inductor L12, and then they are respectively connected to U1. U1 is a common mode choke coil. This connection method is to eliminate common mode interference and high frequency crosstalk at the front end of the power supply. R1 and C1 are connected in series with U1 to prevent resonance in a certain frequency band. The circuit input is a 4-20mA current loop, and its polarity will be wrongly connected due to operation errors or accidents, which will damage the switching regulated power supply. The purpose of polarity protection is that the power supply will only work when connected with the correct polarity. It can be realized by using a unidirectional conduction device, and a low-dropout Schottky diode is used here as the polarity protection of the circuit.

2. Generate a 6V power supply with a linear power supply

The sampling resistor Rsense is connected to the rear section of block 1, and the other end is connected to U2. U2 is a 6V Zener diode, one end of which is connected to the sampling resistor Rsense, and the other end is connected to the ground plane. Ceramic capacitors, C2, C3 and U2 are connected in parallel, in order to eliminate low frequency and high frequency interference.

The positive terminal of U2 is the 6V power supply terminal of the power supply circuit. It can be seen from square 2 that the circuit is simple and reliable.

Since the power supply circuit is connected in series in the 4-20mA current loop, it is ideal to use a parallel voltage regulator circuit. Zener diodes, buried Zener diodes, and bandgap voltage references can all be designed as two-terminal parallel circuits or three-terminal series circuits. Zener diodes are reverse biased diodes that require a series current limiting resistor. In the case where high precision and low power consumption are required, Zener diodes are usually not suitable, but Zener diodes are often used in voltage clamping circuits, and their clamping voltage range is very wide, from 2V to 200V, and the power can be from Watts to several watts, and its ability to sink current is very strong, and the price is cheap. Therefore, using the characteristics of Zener diodes that can effectively clamp voltage and absorb current, generate 6V power supply and absorb excess current at the same time. At the same time, a low-dropout Schottky diode is used as the polarity protection of the circuit (when the current is tens of mA, the forward voltage drop is <0.3V).

3. Design of sampling circuit

The valve positioner requires the single-chip microcomputer to receive the current signal (4-20mA) from the regulator to control the valve opening. For this reason, a sampling resistor is connected in series at the front end of the power circuit, and the two ends of the sampling resistor are amplified by a differential amplifier and sent to the micro-processing to sample. In order to reduce the impact of temperature drift on the measurement accuracy of the system, the current detection resistor is made of constantan wire with good thermal stability and small drift.

Based on the requirements of power consumption, a single-supply operational amplifier needs to be selected, which will reduce the signal range. Therefore, the position selection of the sampling resistor is particularly important. According to the different positions of the sampling resistors, the author designs two different sampling methods. Sampling method 1: High-end current detection

The input common-mode range of the high-side current-sense amplifier is independent of the operating voltage, which ensures that the current-sense loop remains active even at low operating voltages. Its circuit connection is shown in Figure 7. This circuit is taken from the partial enlarged view of block 3 in FIG. 6 . Among them, U3 is a high-end current detection amplifier, terminal 1 is a power supply terminal, which is directly connected to the 6V terminal of block 2, and C4 is a bypass capacitor, which is connected to terminal 1 and terminal 3 respectively. Terminals 8 and 6 are respectively connected to both ends of the sampling resistor Rsense. Terminal 4 is the output voltage terminal, and R2 and C5 form a filter circuit connected to terminal 4, and then the filtered voltage value is sent to AD1 of the microprocessor.

The present invention selects max4372 of Maxim Company, which is a high-side current detection amplifier with a buffer output. max4372 has the following features: wide power supply voltage range: 2.7V ~ 28V; circuit structure allows 0V to 28V input; independent power supply voltage; when the input common-mode voltage is close to the ground voltage, the ground detection input maintains good linearity and prevents The output phase is reversed. In addition, the current consumption of the amplifier is only 30μA, and the accuracy of the full scale is 0.18%, and the output impedance is 1.5Ω. Voltage output for gain setting is omitted.

Maxim's high-side current-sense amplifiers use a resistor connected between the positive terminal of the power supply and the power inlet of the circuit under test to sense current. The high-side current sense avoids the introduction of external resistance to the ground plane, improves the overall performance of the circuit and simplifies the layout.

4. Use switched capacitor voltage inverter to generate 3V power supply

Charge pump, also known as switched capacitor voltage converter, the loss of the charge pump mainly comes from the ESR of the capacitor and the on-resistance (RDSON) of the internal switching transistor, both of which can be made very low. The biggest advantage of using a charge pump is to eliminate the magnetic field interference caused by the inductor or transformer. The input noise of the pump can be eliminated by the filter capacitor, and the circuit design is simple and effective, only external ceramic capacitors are needed.

When designing, we use the idea of "voltage is a relative quantity" and the phase inversion characteristics of switched capacitors to cleverly design a stable 3V power supply. The circuit connection relationship is shown in Figure 8. That is, it corresponds to the local amplification circuit of block 4 in FIG. 6 . Ground the output terminal 1, the ground terminal 4 is the output terminal, and the input terminal 2 is the 6V voltage terminal. In this way, the output of the ground terminal is actually 0.5 times that of the input terminal, that is, the 3V power supply.

Because max1720 has the characteristics of high efficiency and high output current, the power consumption of this part of the circuit is extremely low, and because the switching power supply step-down conversion can increase the output current, the load capacity of the power supply is greatly enhanced.

We chose Maxim's switched capacitor voltage inverter max1720, which is packaged in SOT23-6, which can invert or double the input voltage within the range of 1.5V to 5.5V, and the voltage conversion efficiency is 99.9%. Quiescent current of 50μA (lower when using the shutdown pin), the output current can reach 25mA.

5. Inductive switch mode DC-DC converter realizes 24V power supply

Because 24V power supply needs to be provided in this design, and the switching power supply is an ideal choice for a voltage higher than V _out /V _io , so the inductive switching mode DC-DC converter is selected to realize the 24V power supply.

The working principle of the inductive DC-DC converter is to store energy first, and then release the energy in a controlled manner to obtain the required output voltage. Usually at least one external inductor, capacitor and Schottky diode are needed. Here, max1605 is selected. The working voltage of this chip is +2.4V to +5.5V, which can raise the battery voltage as low as 0.8V to 28V, and its working current is only It is 18μA, and the conversion efficiency is 88%. It is beneficial to reduce the ripple of the output voltage and the size of external components in small current applications. The circuit connection is shown in Figure 9. That is, the local amplification circuit of block 5 in FIG. 6 . Terminals 1 and 2 of U5 are shorted and connected to a 3V power supply. C7 is a bypass capacitor, one end is connected to the power supply, and the other end is grounded. Terminal 5 and terminal 3 are shorted and connected to the ground plane. One end of the inductance L3 is connected to 6V passing through the protection circuit, and the other end is connected to the 4-terminal and D1. Terminal 6 is the feedback input, and its threshold is 1.25V.

An inductive boost converter cannot be replaced by a low-dropout linear regulator (LDO). Although a regulated charge pump can boost the voltage, the efficiency is low and the output current is small. The disadvantage of a boost converter is higher output ripple and switching noise. It is necessary to choose a good control scheme to eliminate oscillation and reduce the efficiency loss caused by switching FETs. To this end, the following solutions are adopted:

(1) Selection of energy storage inductance: Inductance is a key device that affects the performance of DC-DC converters. The main parameters considered are inductance, saturation current and DC resistance. We choose a power inductor with low DC resistance and high saturation current, which is generally a coil wound on a ferrite core. When the current flowing through the inductor is large, coupled with the saturation of the magnetic core, the actual inductance value will decrease, so an inductor with a large saturation current (greater than the actual peak current flowing through the inductor) should be selected. Generally speaking, 20 % mild saturation (20% drop in inductance) is acceptable.

The inductance value can generally be selected between 10μH and 300μH. Too small inductance will make the inductor current discontinuous, resulting in reduced current output capability and increased output ripple, and may increase the inductor current to a large value before the current-limiting comparator turns off the power switch, resulting in DC - Damage to the DC converter; excessive inductance will cause poor transient response and increase the volume of the DC-DC converter. The selection of inductance should be based on the actual input and output conditions and the requirements for output ripple and transient response.

The input/output conditions in this design are:

Input voltage _Vfn = 3V;

Output voltage V _out = 26V;

Output current I _out = 20mA;

Maximum operating frequency F _max = 500kHz;

The peak value of the inductor current ripple at the rated output current ΔI = 0.5A.

The calculation steps of inductor peak current are as follows:

① Calculate the duty cycle: D = (V _out -V _in )/V _out = 88.5%;

② Calculate the average inductor current: I _Lavb = I _out / (1-D) = 0.173A;

③ Calculate the inductor peak current: I _LP = I _Lavb + ΔI/2 = 0.423A;

④ Calculate the inductance value: L≈V _in *D/(ΔI*F _max )＝10.6μH.

Then you can choose an inductor with a saturation current not lower than 0.173A and an inductance value of about 11μH.

(2) Selection of freewheeling diode D

In order to improve the conversion efficiency, the device should choose a Schottky diode with a lower forward voltage drop. Its main parameters are the maximum reverse voltage _VR and the maximum forward current I _D , here we choose Motorola's MBRS0530.

(3) Selection of wave capacitor

The equivalent series resistance ESR of the filter capacitor is the main factor causing the output ripple, and it will also affect the conversion efficiency. Ceramic capacitors and tantalum electrolytic capacitors have low ESR, and aluminum electrolytic capacitors with low ESR can also be used, but standard aluminum electrolytic capacitors should be avoided as much as possible. The capacity is generally 10μF to 100μF. For heavier loads, a larger capacitor should be selected . Larger capacitance filter capacitor is beneficial to improve output ripple and transient response. Here, a small ceramic capacitor is selected. The ceramic capacitor can obtain low input and output noise, work reliably under high temperature conditions, and occupy a small area at the same time.

(4) Eliminate DC-DC noise

A common approach to eliminating DC-DC noise is suppression techniques, specifically filtering and shielding. Another cost-effective solution is to lock the operating frequency (noise source) of the DC-DC converter to the clock frequency. The ripple and radiation of this frequency will not affect the system performance, and at the same time, the noise spectrum can be moved to improve the system performance. and cost savings (no shielding required).

6 2.5V voltage reference

Terminal 1 of U6 is the power terminal, which is connected to the 6V power supply and terminal 5, and terminals 2 and 4 are ground terminals, which are directly connected. 1. Connect capacitor C10 between terminals 2 and C11 between terminals 3 and 2. C10 and C11 are tantalum capacitors with a capacitance of 1 to 10uf. Terminal 3 is an output terminal with an output reference voltage of 2.5V.

7. Overvoltage protection

When the Zener diode breaks down or fails to stabilize the voltage normally, the switching regulator will not work normally, and even damage the internal components. Therefore, it is necessary to use the input overvoltage protection circuit to automatically turn off the buck-boost circuit of the switching power supply. The circuit connection is shown in FIG. 10 , which is a partial enlarged circuit diagram corresponding to block 7 in FIG. 6 .

U7 is a charge pump op amp, used as a comparator. Terminal 2 of U7 (the negative terminal of the operational amplifier) is connected to the 2.5 reference, and terminal 3 (the positive terminal of the operational amplifier) is connected to the divided voltage value of the 6V power supply. output low level, and the field effect transistor U8 is not turned on, then each power supply circuit remains in working state. When the Zener diode cannot stabilize the voltage normally, the voltage at terminal 3 is higher than that at terminal 2, and terminal 6 outputs a high level, and the field effect transistor U8 is turned on, then the voltage at the other terminal of R8 is clamped at zero potential, and the switching power supply is automatically turned off. Step-up and step-down circuits.

8. PCB design of switching power supply

The wiring method of the printed circuit board and the layout of the components often affect the performance of the circuit, so when designing the printed circuit board, it is necessary to carefully consider the wiring method and the placement of the components. Otherwise, the efficiency, maximum output current, output ripple and other characteristics of the printed circuit board will be affected. The two main causes of these effects are the connections of the ground (GND, VSS) and power lines (VCC, VDD). If the design of the ground wire and the power line is reasonable, the circuit will work normally and obtain better performance indicators, otherwise problems such as interference and performance indicators will occur.

Here are a few issues to keep in mind when designing:

a. Use the planar pattern to ground and connect the power line to ensure low noise on the ground line and avoid splitting the ground plane by many long jumpers;

b. Place the components one by one according to the signal current direction in the circuit diagram to ensure the shortest connection between them to reduce noise. At the same time, place the components in the same direction to facilitate reflow soldering;

c. Since stray capacitance will be generated between the wiring, too long wiring will generate impedance, so paying attention to the stray capacitance between the lines and shortening the wiring length in the design will help eliminate noise and reduce the generation of radiation;

d. According to the layout of the circuit schematic diagram, the input current line and the output current line should be distinguished;

e. If coils and transformers are used in the circuit, they must be connected with care;

f. There must be a gap of more than 0.5mm between components or between component pads and pads to avoid bridging.

In a boost converter, there are a few more things to keep in mind:

a. Place the output capacitor as close as possible to the IC to minimize the current loop;

b. Use the plane wiring method to connect the ground wire on the back of the PCB board, and the ground wire on the back of the board is connected to the ground wire on the front of the board through a via hole;

c. Ensure that the feedback resistor and the feedback pin are as short as possible and the wiring area at the feedback pin is as small as possible;

d. Capacitors are used in parallel to reduce the parallel equivalent series resistance (ESR) of the filter capacitor, and also enable each capacitor to shunt a part of the ripple current.

In order to further reduce the power consumption of the system, first of all, it is necessary to shorten the working time as much as possible and extend the power-down time; secondly, cooperate with the external circuit to reduce the power consumption of the system, that is, some settings must be made before entering the power-down mode:

a Turn off the power supply of unused peripheral devices, etc.;

b. Handle the port: For the I/O port used as a quasi-bidirectional port, if the port line has an external pull-up resistor, it should be set high before entering the power-down mode, and the internal pull-down transistor should be turned off; if the port line is not connected to the external pull-up resistor pull-up resistor (using internal pull-up), it should be set low before entering the power-down mode to close the internal pull-up transistor; the port line configured with open-drain output should be set high before entering the power-down mode, of course, these operations should first ensure that the port external functions;

c. Turn off some unused functions, such as power-down detection analog comparator, etc. The watchdog function is special and can only be configured during programming. Once used in the program, it cannot be turned off. It is not necessary to enable the watchdog function when programming.

Among them, the positioning part and the execution part form a feedback loop, and the input unit receives the 4-20mA current signal from the controller. The control valve position feedback signal is compared with the given signal value in the microprocessor as the controlled variable, and the deviation sends pulses of different lengths through the output port of the main control board to generate the output pressure applied to the control I/P conversion unit, thereby Complete the action of driving the regulating valve.

(2) Single-chip microcomputer control system

The control unit selects MSP430F149 ultra-low power MCU with FLASH, its FLASH memory up to 60KB, RAM up to 2KB; 12-bit A/D converter with internal reference source, sample hold and automatic scanning features; flexible clock source Allows the device to achieve the lowest power consumption; a digitally controlled oscillator (DCO) enables the device to wake up quickly from low-power modes, active in less than 6μs. Its hardware block diagram is shown in Figure 11. The realization of the low power consumption of the MSP430 single-chip microcomputer system of this system is to work intermittently or even make the system in idle or power-down mode in most cases. In a single-chip microcomputer system that works intermittently, the static power consumption of peripheral devices is the preferred indicator. MSP430 series single-chip microcomputer integrates a large number of CPU peripheral modules in the chip and each module of the system is completely independent operation, timer (Timer), input/output port (I/O Port), A/D conversion, watchdog (Watchdog) ), liquid crystal display (LCD), etc. can all run independently under the state of main CPU sleep. When the main CPU is required to work, any module can wake up the CPU through an interrupt, so that the system can run with the lowest power consumption. This function can greatly reduce the power consumption of the peripheral system of the microcontroller. MSP430F149 has a 60KB Flash memory, which can write system configuration parameters, thereby reducing the current consumption caused by the external EEPROM.

1. LCD display module

Because LCD has low power consumption and can achieve better man-machine dialogue effect, it is selected as the display device. The LCD and the buttons provide a human-computer interaction interface. The display is used to display various status information of the valve positioner, and the buttons are used to input configuration data and manual operation.

The liquid crystal display module adopts the 4-digit 8-segment liquid crystal display module LCM046, which contains a watchdog (WDT) clock generator, a buzzer driving circuit with 2 frequencies, and a built-in display RAM, which can display strokes in any field, 3-4 line strings Line interface, can interface with any single-chip microcomputer, IC, low power consumption, display status 40μA (typical value), power saving mode <1μA, working voltage 2.4 ~ 5.2V, adjustable viewing angle contrast, clear display, stable and reliable, using programming Simple, it is the best general-purpose display module for instrumentation, handheld portable instruments, etc.

The liquid crystal module LCM046 has a small size, low power consumption, and powerful functions. Therefore, when designing the system hardware, the built-in LCD driver module of the MSP430 microcontroller is not used, but the connection method based on the I ² C bus is used. The interface application block diagram is as follows As shown in Figure 12, I/O ports can be greatly saved, which is convenient for the expansion of the microprocessor in the future. Because there is a pull-up resistor inside LCM046, in order to ensure low power consumption, /CS, /RD, /WR, and DATA must be connected to high level or suspended after each data transmission. Here the MCU and LCM046 have the same operating voltage and can be connected directly. /RD, /IRQ, BZ can not be used, just use the three-wire interface: /CS, /WR and DATA.

2. I/P control circuit

Because the piezoelectric ceramic needs to be driven by a voltage above 24V, and the pulse amplitude output by the microprocessor can only reach its power supply amplitude, which is not enough to drive the piezoelectric ceramic valve. Therefore, an additional I/P control circuit is required to convert a small-amplitude pulse (3V) into a large-amplitude (above 24V) pulse.

Since the insulated gate field effect transistor uses the electric field effect on the surface of the semiconductor to change the conductive channel to control the current by the amount of induced charge, its gate is in a non-conductive (insulated) state, so it not only has the small size and low weight of the general semiconductor triode , low power consumption, long life, etc., and also has the advantages of very high input impedance (up to 10 ¹⁵ Ω), low noise, good thermal stability, strong radiation resistance and simple manufacturing process, thus greatly expanding its application application range.

The circuit of the I/P conversion unit is controlled by the switching action of an N-channel enhanced insulated gate field effect transistor (MOSFET). The so-called enhanced type means that when U _GS =0, there is no conductive channel between the drain and source, even if a voltage is applied between the drain and source (in a certain range), there is no drain current, and its control circuit is shown in Figure 13. In this control circuit, the timers A0, A1, B0, and B1 of the MSP430 single-chip microcomputer are used to generate output modes with different amplitudes to control the four terminals of piezoelectric ceramics. Take one of the units as an example, when P1.0 outputs a high level, the Q1 tube is turned on, and the gate voltage of Q2 is 0V, then the Q2 tube is turned off, and the piezoelectric ceramic 1 terminal outputs 0V at this time; when P1.0 outputs Low level, the Q1 tube is cut off, the Q2 tube is turned on, and the piezoelectric ceramic terminal 1 outputs 24V. By controlling the output waveform of the timer A0, the different states of the piezoelectric valve, such as continuous opening, intermittent opening or constant valve position, can be controlled. The principles of the other three units are the same and will not be repeated here.

3. System software design

One of the software design tasks of the low-power system is to cooperate with the hardware circuit to further reduce the power consumption of the system. The system software adopts a modular design, which not only has a clear program structure, but also facilitates further expansion. The system software consists of main program, timer interrupt service program, keyboard interrupt service program, data acquisition and processing subroutine, liquid crystal display subroutine, power-down protection subroutine and other modules.

After the main program is initialized, enter the dormant state, and turn off the peripheral power supply. Each function program is regularly scheduled by the timer, wakes up the CPU, performs analog conversion and other processing. After the processing is completed, it enters the dormant state. The interrupt service routine is the core of the system software design. In order to reduce power consumption, the main subroutine modules are completed in the interrupt service routine.

(1) Main program

MSP430 single-chip microcomputer has a very convenient development environment, and can use C or C++ language, which greatly improves the efficiency of development and debugging work; at the same time, the generated documents are also easy to understand and easy to transplant. For the FLASH type single-chip microcomputer, there is a very convenient development and debugging environment, because the device has a JTAG debugging interface on the chip, and there is also an electrically erasable FLASH memory, so you can download the program to the FLASH, and then use the software in the device. The operation of the control program is read by the JTAG interface for the designer to debug and develop. This way only needs a PC and a JTAG debugger instead of emulator and programmer.

The MSP430 microcontroller has 1 active mode and 5 low power consumption modes, and its working mode is set by the control bit. In various working modes, the active states of the three clocks generated by the clock system and the power consumption of the system are different.

Using the low power consumption mode of the MSP430 single-chip microcomputer, after the microcontroller is powered on and reset, the system first performs initialization operations, such as interrupt settings, port allocation, etc., and then enters a sleep state. Turn off all peripheral power. Each function program is regularly scheduled by the timer, wakes up the CPU, performs analog conversion and other processing. After the processing is completed, it enters the sleep state.

See Figure 2, the main program is mainly composed of data acquisition subroutine, key interrupt subroutine, liquid crystal display subroutine and so on. In the main loop, switch between modes by pressing buttons, execute corresponding actions and control strategies, and display input parameters, valve opening and other parameters.

In order to further reduce the power consumption of the system, first of all, it is necessary to shorten the working time as much as possible and extend the power-down time; secondly, cooperate with the external circuit to reduce the power consumption of the system, that is, some settings must be made before entering the power-down mode:

a Turn off the power supply of unused peripheral devices, etc.;

b. Handle the port: For the I/O port used as a quasi-bidirectional port, if the port line has an external pull-up resistor, it should be set high before entering the power-down mode, and the internal pull-down transistor should be turned off; if the port line is not connected to the external pull-up resistor pull-up resistor (using internal pull-up), it should be set low before entering the power-down mode to close the internal pull-up transistor; the port line configured with open-drain output should be set high before entering the power-down mode, of course, these operations should first ensure that the port external functions;

c. Turn off some unused functions, such as power-down detection analog comparator, etc. The watchdog function is special and can only be configured during programming. Once used in the program, it cannot be turned off. It is not necessary to enable the watchdog function when programming.

(2) Data acquisition interrupt service program

This module mainly completes the processing and closed-loop control of ADC sampling data, converts the setting signal and feedback signal of the valve position into digital quantities, and calculates the error. At the moment of power failure, it automatically protects useful information and system running status, and automatically restores the working status before power failure when the power comes in, ensuring the continuity of processing. The flow chart is shown in Figure 3.

The main operations are completed in the timer, which can make the microcontroller work intermittently to fully reduce power consumption; when not working, make it in low power consumption mode 3. The analog-to-digital conversion part is completed in timer A1; the piezoelectric drive module uses timers A0 and B0 to work in comparison mode to generate the required signals to meet the system's requirements for low power consumption.

In the control of the valve position, the system adopts a five-contact switch control algorithm. The so-called five-contact switch refers to dividing the error range into five areas: positive large, positive middle, dead zone, negative middle, and negative large, and performs different actions in different areas to reduce the error: when the error is in the positive large or negative large area, control The device outputs a continuous signal to the piezoelectric control valve, continuously intakes or exhausts, so that the stroke changes rapidly; in the positive center or negative center area, outputs a pulse signal of a certain width, intermittently intakes or exhausts, and the stroke changes slowly; In the zone, no signal is output, and the stroke does not change.

In order to reduce the interference to the sampling value and improve the reliability of the system, the method of digital filtering is often adopted. Median value filtering is to arrange several sampling values in a certain order, such as from small to large, and then take the middle value as the current sampling value. This method is suitable for the process of variable changes relatively slowly, eliminating the interference caused by accidental factors; and the arithmetic mean value filter is to add and sum several consecutive sampling values, divide by the number of sampling times n, and the result is used as the sampling value of this time. This method is suitable for sampling signals with periodic pulse changes. This system adopts the composite digital filter which combines the arithmetic mean value filter and the median value filter, which can eliminate both periodic pulse interference and random pulse interference.

(3) Button interrupt service program

The program flow is shown in Fig. 4. The key setting unit shares three keys (+1 key, -1 key and working mode key) to be used together to complete the setting of the working mode, manual control of the valve position, setting of control parameters, etc. Similarly, in order to reduce power consumption, this design uses an interrupt method to process the key response and switch between modes. The function of any configured key depends on the selectable working mode:

①Auto mode

Automatic mode is the commonly used mode, the initialized (and configured) positioner automatically changes according to the set value and continuously makes the deviation of the system tend to the minimum value as much as possible. At this time, the +1 key and -1 key do not work.

②Manual mode

Press the working mode key to switch the positioner from automatic mode to manual mode. Step adjustment is achieved by pressing the +1 key or -1 key. In order to achieve a rapid increase, press the +1 key first, and then press the -1 key; similarly, to achieve a rapid decline, first press the -1 key, and then press the +1 key. Once the +1/-1 key is released, the actuator stops at its current position. The internal set value is adjusted to the current manipulated variable. Since the control in the manual mode is closed-loop, the current valve position can still be maintained even in the event of an air source leakage accident of the positioner.

③Configuration mode

The working mode key can be used to switch from automatic mode or manual mode to configuration mode. To do this, the mode switching key must be pressed for at least 5 seconds until the conversion is completed.

The configuration parameters mainly include:

a. The type of execution structure (rotary stroke or linear stroke)

b. Feedback angle (30° and 90°)

c. Travel value

d. Automatic initialization

e. Manual initialization

f. Input current range

g. Positive and negative effects

h. Valve confinement function

In the configuration mode, the parameter value of the positioner can be changed, and the next parameter can be selected by using the mode key. If the -1 key is pressed while pressing the mode key (<5s), the parameters can be selected in reverse order. Use the +1 button or -1 button to change the parameter value.

(4) LCD display program

The liquid crystal module LCM046 has a small size, low power consumption, and powerful functions. Therefore, the system design does not use the built-in LCD driver module of the MSP430 microcontroller, but uses the connection method based on the I ² C bus. The flow chart is shown in the figure 5.

Claims (9)

1. An intelligent two-wire electric valve positioner includes a control circuit unit, an I/P electrical conversion unit and a valve position detection feedback unit, and the control circuit unit includes a power conversion circuit and a microprocessor control unit, and the I The /P electrical conversion unit includes an air circuit control and amplification part composed of two piezoelectric valve groups. The valve position detection feedback unit includes a feedback potentiometer and a valve position feedback lever; the input signal and the valve position feedback signal enter the The microprocessor control unit of the control circuit of the intelligent electric valve positioner performs a comparison operation, outputs a control signal to the I/P electrical conversion unit according to the difference between the two, and controls the output air pressure of the I/P electrical conversion unit and the valve of the pneumatic control valve. The stem moves, and the stroke of the valve stem is fed back to the control circuit unit at the same time to form a closed-loop control. It is characterized in that the power conversion circuit is a power conversion that converts the input current signal of 4~20mA into three sets of voltages of 6V, 3V and 24V circuit. 2. The intelligent two-wire electric valve positioner as claimed in claim 1, wherein the power conversion circuit of the control circuit unit includes a polarity protection and power front-end anti-interference unit, and a linear power supply to generate a 6V power supply circuit unit , Sampling circuit unit, high-side current detection circuit unit, switched capacitor voltage inverter to generate 3V power supply unit, inductive switch mode DC-DC converter to realize 24V power supply unit, 2.5V voltage reference and overvoltage protection unit. 3. The intelligent two-wire electric valve positioner as claimed in claim 2, characterized in that, in the 6V power supply circuit unit produced by the linear power supply, one end of the sampling resistor is connected to the polarity protection and the front-end anti-interference unit of the power supply. The output end is connected, and the other end is connected to the positive end of a Zener diode that provides a 6V power supply. The other end of the Zener diode is grounded, and two capacitors connected in parallel with the Zener diode are respectively arranged in the circuit unit. 4. The intelligent two-wire electric valve positioner as claimed in claim 2, characterized in that, in the sampling circuit unit, a sampling resistor is connected in series at the front end of the power supply circuit, and the two ends of the sampling resistor are amplified by a differential amplifier to send The sampling resistor is a resistor made of constantan wire. 5. The intelligent two-wire electric valve positioner as claimed in claim 2, wherein the high-side current detection circuit unit adopts a high-side current detection amplifier with a buffer output. 6 . The intelligent two-wire electric valve positioner as claimed in claim 2 , wherein the switched capacitor voltage inverter is a max1720 switched capacitor voltage inverter capable of generating 3V power. 7. The intelligent two-wire electric valve positioner as claimed in claim 2, wherein the overvoltage protection unit uses a charge pump operational amplifier as a comparator, and its negative terminal is connected to a 2.5V reference, and its positive terminal is connected to a 6V power supply The voltage division value, the output terminal of the operational amplifier outputs a low level, and the field effect tube is not turned on, then each power supply circuit remains in the working state; when the Zener diode cannot stabilize the voltage normally, the positive terminal voltage of the operational amplifier is higher than the negative terminal, The output end outputs a high level, and the field effect transistor is turned on, then the voltage at the other end of the parallel resistor is clamped at zero potential, and the step-up and step-down circuits of the switching power supply are automatically turned off. 8. An intelligent two-wire system electric valve positioner control method as claimed in claim 1, utilizes the microprocessor in the control circuit unit to operate through data collection, button interruption and liquid crystal display, and realizes the operation between each mode by the button. Switching, performing corresponding actions and control strategies, and displaying parameters, is characterized in that the method includes the following steps: Turn off the system watchdog clock generator, stop timing, and turn on the global interrupt; port initialization; Call the liquid crystal display subroutine to display the operation result; Select the A/D channel, set the clock and timing time, and enable the A/D interrupt; Set the button clock, set the timing time, and enable the button interrupt; Enter the low power consumption mode of the present invention, that is, enter the dormant state after initialization, turn off each peripheral power supply, and each function program is regularly scheduled by the timer, wake up the CPU, perform analog conversion and other processing, and then enter the dormant state after processing , to reduce power consumption; Determine whether the current A/D interrupt timing time is reached; If the A/D interrupt timing has arrived, enter the A/D interrupt subroutine; Execute the A/D interrupt subroutine; Return from the interrupt, waiting for the next timing to be met; Otherwise, judge whether the current time has reached the button interrupt timing; If the button interrupt timing has arrived at this time, then enter the button interrupt subroutine; Execute the key interrupt subroutine, return from the interrupt, and wait for the next timing to arrive. 9. The intelligent two-wire system electric valve positioner control method as claimed in claim 8, wherein said A/D interrupt processing subroutine further comprises the following steps: Sampling the input signal; Determine whether the current sampling channel is P6.4; If so, save the A/D conversion result of the current sampling; Determine whether 5 samples have been completed; If so, perform digital filter processing; Linearize the output result of digital filtering; The output signal result is set to AD1; If not, further judge whether the currently used P6.5 sampling channel is used; If the 5 sampling times are not met, continue to complete the signal sampling; If the current sampling channel is not P6.4, continue to judge whether the current sampling channel is P6.5; If yes, then save the A/D conversion result of the current sampling result; Determine whether to complete 5 samples; If so, perform digital filtering; and linearization; And set the result of this output signal as AD2; If the number of sampling times does not meet 5 times, continue to complete the sampling.

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