High-refresh-rate intelligent two-wire system transmitter and signal transmitting method

Abstract

The invention relates to a high-refresh-rate intelligent two-wire transmitter and a signal transmitting method. The technical problem that an existing two-wire transmitter is low in refresh rate is solved. The invention provides a high-refresh-rate intelligent two-wire system transmitter structure and a corresponding signal transmitting method, which are designed on the basis of a volt-second principle, so that the MCU of the intelligent transmitter intermittently works in a high dominant frequency interval, the calculation efficiency of a system is improved, and the refresh rate of the system is effectively improved on the premise of meeting the average power consumption of the system.

Description

Technical Field

[0001] The invention relates to a transmitter technology, and in particular to a high refresh rate intelligent two-wire transmitter and a signal transmission method. Background Art

[0002] Smart transmitters, with their integrated advanced sensor technology and digital processing technology, have the advantages of high precision, high reliability and easy integration, and therefore play an important role in the field of modern industrial automation and monitoring. However, as one of the commonly used smart transmitters, the two-wire smart transmitter has strict requirements on system power consumption and usually uses a low-frequency MCU as the main control unit, which limits the calculation speed of the system, resulting in a relatively low refresh rate of the transmitter (generally only about 10Hz), which is difficult to meet the test environment with high requirements for response speed.

[0003] Generally, the output range of a two-wire transmitter is 4-20mA (corresponding to 0-full scale). The fixed power consumption of a two-wire transmitter mainly includes 0.04mA of precision reference power supply, 0.8mA of Wheatstone bridge connected to the probe, 0.6mA of two-way differential amplifier, 0.8mA of display unit and 0.3mA of VI conversion circuit, totaling 2.54mA. In order to ensure the normal detection function of the system, the static current must not exceed 3.3mA.

[0004] Therefore, the MCU must work in low-frequency mode (0.7mA@4MHz). At this time, in this low-frequency mode, it usually takes tens of milliseconds to complete a series of operations such as data acquisition, calibration, and output, which greatly limits the improvement of the refresh rate. Summary of the invention

[0005] The purpose of the present invention is to solve the technical problem of low refresh rate of existing two-wire transmitters and to provide a high refresh rate intelligent two-wire transmitter and a signal transmission method.

[0006] In order to achieve the above purpose, the technical solution provided by the present invention is as follows:

[0007] A high refresh rate intelligent two-wire transmitter, used to output the signal of the Wheatstone bridge in the measuring sensor, its special features are:

[0008] It includes a first differential operational amplifier, a current sampling resistor, a second differential operational amplifier, an MCU, a power switch, an inductor, a capacitor and a transmitter power supply;

[0009] Definition: Take one of the nodes of the Wheatstone bridge as the starting point, and record the four nodes in the clockwise direction as 1#, 2#, 3# and 4#; record the two ends of the current sampling resistor as a and b respectively;

[0010] The 1# node of the Wheatstone bridge is connected to the in-phase input terminal of the first differential operational amplifier, and the 2# node is connected to the Wheatstone bridge driving power supply V ref The 3# node is connected to the inverting input terminal of the first differential operational amplifier, and the 4# node is connected to the a terminal of the current sampling resistor;

[0011] The a-end of the current sampling resistor is connected to the non-inverting input end of the second differential operational amplifier, and the b-end is connected to the inverting input end of the second differential operational amplifier; the a-end of the current sampling resistor is also connected to the b-end through an inductor and a capacitor in sequence, and the b-end is directly connected to the V-end of the transmitter power supply;

[0012] The output terminal of the first differential operational amplifier is connected to the ADC0 terminal of the MCU;

[0013] The output terminal of the second differential operational amplifier is connected to the ADC1 terminal of the MCU;

[0014] The PWM terminal of the MCU is connected to the control terminal of the power switch, and the detection result is output through the UART terminal;

[0015] The input end of the power switch is connected to the V+ end of the transmitter power supply, and the output end is connected between the inductor and the capacitor;

[0016] The MCU reads the differential voltage of the Wheatstone bridge through the first differential op amp, reads the loop current between the V- and V+ terminals of the transmitter power supply through the second differential op amp, and outputs the corrected and compensated loop current through the PWM terminal to meet the technical requirements of low power consumption.

[0017] Furthermore, it also includes a display unit connected to the UART terminal of the MCU, and the MCU outputs the detection result of the Wheatstone bridge on the display unit through the UART terminal;

[0018] MCU is used to realize signal acquisition, data processing, data display, current compensation and program slicing.

[0019] Furthermore, the power switch is a field effect transistor, whose gate, source and drain serve as a control terminal, an input terminal and an output terminal respectively.

[0020] The present invention also provides a high refresh rate intelligent two-wire transmitter signal transmission method, which is special in that it includes the following steps:

[0021] S0, build the above-mentioned high refresh rate intelligent two-wire transmitter;

[0022] S1, load the high main frequency program into the MCU, and configure the MCU to two working modes: sleep mode and high main frequency mode; the MCU works in sleep mode by default;

[0023] Set the MCU's high-frequency loop current I h , Sleep loop current Il and carrier time T pwm ;

[0024] T pwm = T l + T h T l is the sleep working time, and T h is the high-frequency working time;

[0025] Collect the differential voltage signal through a Wheatstone bridge, and calculate the average loop current I that the transmitter needs to output according to the calibration coefficient o ;

[0026] Calculate the high-frequency working time T according to the volt-second balance principle of PWM h ;

[0027] S2, slice the high-main frequency program of the MCU into multiple segments as needed to form multiple sliced programs, and meet the condition: the running time of each sliced program does not exceed the high-frequency working time T h ;

[0028] According to the average loop current I calculated in step S1 o , calculate the zero-output time T of the high-frequency mode at zero output h0 ;

[0029] S3, the differential voltage signal of the Wheatstone bridge is sent to the ADC0 terminal of the MCU through the first differential amplifier; the divided voltage signal of the current sampling resistor is sent to the ADC1 terminal of the MCU through the second differential amplifier;

[0030] S4, the MCU calculates the average loop current I of the actual output according to the received differential voltage signal o , and judges:

[0031] When the average loop current I of the output o is less than the high-frequency loop current I h , the MCU alternately works in the sleep mode and the high-main frequency mode, and executes step S5;

[0032] When the average loop current I of the output o is greater than or equal to the high-frequency loop current I h , the MCU works in the high-main frequency mode and executes step S6;

[0033] S5, the sleep mode and the high-main frequency mode alternate

[0034] The MCU calculates the delay time T of the multiple sliced programs d , and delays the execution of the sliced programs through the delay module;

[0035] Based on the volt-second balance principle, the inductor and capacitor are used to filter the pulsed current in the output average loop current I o ;

[0036] The MCU adjusts the delay time T d according to the received voltage-dividing signal to complete the closed-loop control;

[0037] Until all programs are executed, the average loop current I o corresponds to the output physical quantity to be transmitted, and the signal detection and transmission are completed;

[0038] S6, high main frequency mode

[0039] The MCU directly runs the slice program;

[0040] The MCU generates a pulsed current I p through the control terminal of the driving power switch, and filters the output pulsed current I p through the inductor and capacitor, and compensates for the difference between the average loop current I p required to be output and the high-frequency loop current I o ; h The MCU adjusts the pulsed current I

[0041] according to the received voltage-dividing signal to complete the closed-loop control; p ;

[0042] Until all programs are executed, the average loop current I o corresponds to the output physical quantity to be transmitted, and the signal detection and transmission are completed.

[0043] Furthermore, in step S1, the operating current of the MCU loading the high main frequency program is 8 mA @ 48 MHz;

[0044] The high main frequency program includes signal acquisition, data processing, display data transmission, current compensation, and program slicing.

[0045] Furthermore, in step S1, the calculation formula for the high-frequency working time T h is:

[0046]

[0047] Furthermore, in step S2, the calculation formula for the zero-output time T h0 is:

[0048]

[0049] Furthermore, in step S5, the calculation formula for the delay time T d is:

[0050] T d =T h -T h0

[0051] Among them, high-frequency working time

[0052] Furthermore, in step S6, the average loop current I o The pulse current I p is a square wave current.

[0053] Further, in step S1, the carrier of the MCU is a 10kHz pulse width modulation wave;

[0054] High frequency program operating current I h =8mA;

[0055] High frequency working time T h =10μs;

[0056] Sleep loop current I l =2.6mA;

[0057] Sleep working time T l =90μs;

[0058] Carrier time T PWM =100μs;

[0059] In step S2, the high main frequency program is segmented and sliced into sections for signal acquisition, data processing, data display, and current compensation.

[0060] The beneficial effects of the present invention compared with the prior art are as follows:

[0061] A high refresh rate intelligent two-wire transmitter and a signal transmission method provided by the present invention are designed based on the volt-second principle, so that the MCU of the intelligent transmitter works intermittently in a high main frequency range, thereby improving the computing efficiency of the system and effectively improving the system refresh rate while meeting the average power consumption of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0062] Figure 1 It is a structural schematic diagram of an embodiment of a high refresh rate intelligent two-wire transmitter of the present invention;

[0063] Figure 2 It is a filtering schematic diagram of step S5 in the signal transmission method according to an embodiment of the present invention. DETAILED DESCRIPTION

[0064] The specific technical solutions in the embodiments of the present invention will be further described below in conjunction with the accompanying drawings.

[0065] Figure 1The circuit schematic diagram of a high-refresh-rate intelligent two-wire transmitter provided by an embodiment of the present invention is used to output the signal of the Wheatstone bridge 1 in the measurement sensor. Its structure includes a first differential operational amplifier 2, a current sampling resistor 3, a second differential operational amplifier 4, an MCU 5, a power switch 6, an inductor 7, a capacitor 8, a display unit 9, and a transmitter power supply.

[0066] Definition: Taking one of the nodes of the Wheatstone bridge 1 as the starting point, the four nodes are respectively denoted as 1#, 2#, 3#, and 4# in the clockwise direction; the two ends of the current sampling resistor 3 are respectively denoted as a and b; the 1# node of the Wheatstone bridge 1 is connected to the non-inverting input terminal of the first differential operational amplifier 2, the 2# node is connected to the Wheatstone bridge drive power supply V ref terminal, the 3# node is connected to the inverting input terminal of the first differential operational amplifier 2, and the 4# node is connected to the a terminal of the current sampling resistor 3.

[0067] The a terminal of the current sampling resistor 3 is connected to the non-inverting input terminal of the second differential operational amplifier 4, and the b terminal is connected to the inverting input terminal of the second differential operational amplifier 4; the a terminal of the current sampling resistor 3 is also sequentially connected to the b terminal through the inductor 7 and the capacitor 8, and the b terminal is directly connected to the V- terminal of the transmitter power supply.

[0068] The output terminal of the first differential operational amplifier 2 is connected to the ADC0 terminal of the MCU 5; the output terminal of the second differential operational amplifier 4 is connected to the ADC1 terminal of the MCU 5; the PWM terminal of the MCU 5 is connected to the control terminal of the power switch 6. The display unit 9 is connected to the UART terminal of the MCU 5, and the MCU 5 outputs the detection result of the physical quantity (such as voltage, current, pressure, temperature, etc.) detected by the Wheatstone bridge 1 on the display unit 9 through the UART terminal.

[0069] The input terminal of the power switch 6 is connected to the V+ terminal of the transmitter power supply, and the output terminal is connected between the inductor 7 and the capacitor 8, jointly forming a BUCK circuit for supplementing current to meet the transmitter output current requirement.

[0070] The MCU 5 reads the differential voltage of the Wheatstone bridge 1 through the first differential operational amplifier 2, reads the loop current between the V- terminal and the V+ terminal of the transmitter power supply through the second differential operational amplifier 4, and outputs the corrected and compensated loop current through the PWM terminal to meet the technical requirements of low power consumption.

[0071] Among them, the MCU 5 is used to implement signal acquisition, data processing, data display, current compensation, and program slicing. The power switch 6 is a field effect transistor in this embodiment, and its gate, source, and drain are respectively used as the control terminal, input terminal, and output terminal. In this embodiment, the MCU 5 can specifically adopt a low-power single-chip microcomputer based on the ARM Cortex-M0+ architecture, such as HC32L196 of Xiaohua Semiconductor.

[0072] The signal transmission method of this embodiment includes the following steps:

[0073] S0, build the above-mentioned high refresh rate intelligent two-wire transmitter.

[0074] S1, load the high main frequency program into MCU5, and configure MCU5 to two working modes: sleep mode and high main frequency mode; MCU5 works in sleep mode by default;

[0075] The operating current of the high-frequency program is 8mA@48MHz; the high-frequency program includes signal acquisition, data processing, display data transmission, current compensation and program slicing.

[0076] Set the high-frequency loop current I of MCU5 h , Sleep loop current I l and carrier time T pwm , T pwm =T l +T h , T l is the sleep working time, T h High frequency working time.

[0077] The differential voltage signal is collected through the Wheatstone bridge 1, and the average loop current I that the transmitter needs to output is calculated according to the calibration coefficient. o , this feedforward is used to improve the response speed.

[0078] According to the volt-second balance principle of PWM, calculate the high-frequency working time T h :

[0079]

[0080] Specifically:

[0081] The carrier of MCU5 is 10kHz pulse width modulation wave; the running current of high frequency program I h =8mA; Sleep loop current I l =2.6mA; high frequency working time T h =10μs; Sleep working time T l =90μs; carrier time T PWM =100μs. At this time, the average loop current I o =3.14mA, which meets the technical requirement that the static current is less than 3.3mA.

[0082] S2, the high main frequency program of MCU5 is divided into sections according to the needs (signal acquisition, data processing, data display, current compensation), forming a multi-section slicing program, and the conditions are met: the running time of each slicing program does not exceed the high frequency working time T h ;

[0083] Based on the average loop current I calculated in step S1 o , calculate the zero-output time T of the high-frequency mode at zero output h0 ;

[0084] The zero-output time T h0 The calculation formula is as follows:

[0085]

[0086] S3. The differential voltage signal of the Wheatstone bridge 1 is sent to the ADC0 terminal of the MCU5 through the first differential operational amplifier 2; the voltage-dividing signal of the current sampling resistor 3 is sent to the ADC1 terminal of the MCU5 through the second differential operational amplifier 4;

[0087] S4. The MCU5 calculates the actually output average loop current I o ,

[0088] and judges:

[0089] When the output average loop current I o is less than the high-frequency loop current I h (that is, controlled between 4 and 8 mA), the MCU5 alternately operates in the sleep mode and the high main frequency mode, and executes step S5;

[0090] When the output average loop current I o is greater than or equal to the high-frequency loop current I h (that is, it needs to exceed 8 mA), the MCU5 operates at full speed in the high main frequency mode and executes step S6;

[0091] S5. Alternate between the sleep mode and the high main frequency mode

[0092] The MCU5 calculates the delay time T of the multi-segment slicing program d , and delays the slicing program through the delay module to lengthen the working time of the slicing program to ensure an output of 4 - 8 mA, and the missing current is compensated by the power switch 6;

[0093] The delay time T d The calculation formula is as follows:

[0094] T d = T h - T h0

[0095] Among them, the high-frequency working time

[0096] Refer to Figure 2 , based on the volt-second balance principle, through the inductor 7 and the capacitor 8 for the output average loop current Io Filter the pulsed current in

[0097] Based on the received voltage-dividing signal, MCU5 adjusts the delay time T d to complete closed-loop control for correcting the drift of the loop current.

[0098] Until all programs are executed, make the average loop current I o correspond to the output physical quantity to be transmitted, and complete signal detection and transmission;

[0099] S6, high main frequency mode

[0100] MCU5 directly runs the slicing program;

[0101] MCU5 generates a square-wave pulsed current I by driving the control terminal of the power switch 6 p , and filters the output pulsed current I through the inductor 7 and the capacitor 8 p Filter the pulsed current I p Compensate for the difference between the average loop current I to be output o and the high-frequency loop current I h (BUCK circuit);

[0102] Based on the received voltage-dividing signal as feedback, MCU5 adjusts the pulsed current I p to control the duty cycle in the BUCK circuit and complete closed-loop control;

[0103] Until all programs are executed, make the average loop current I o correspond to the output physical quantity to be transmitted, and complete signal detection and transmission.

[0104] The above content is only one embodiment of the present invention, and it is not a limitation on the protection scope of the present invention. Any equivalent transformation made by using the specification and drawings of the present invention, or directly or indirectly applied in other related technical fields, is included in the patent protection scope of the present invention.

Claims

1. A high refresh rate intelligent two-wire transmitter for outputting the signal of the Wheatstone bridge (1) in a measurement sensor, characterized in that: It includes a first differential operational amplifier (2), a current sampling resistor (3), a second differential operational amplifier (4), an MCU (5), a power switch (6), an inductor (7), a capacitor (8), and a transmitter power supply; Definition: Taking one of the nodes of the Wheatstone bridge (1) as the starting point, the four nodes are respectively denoted as 1#, 2#, 3#, and 4# in the clockwise direction; the two ends of the current sampling resistor (3) are respectively denoted as a and b; The 1# node of the Wheatstone bridge (1) is connected to the non-inverting input terminal of the first differential operational amplifier (2), the 2# node is connected to the Wheatstone bridge drive power supply V ref terminal, the 3# node is connected to the inverting input terminal of the first differential operational amplifier (2), and the 4# node is connected to the a end of the current sampling resistor (3); The a end of the current sampling resistor (3) is connected to the non-inverting input terminal of the second differential operational amplifier (4), and the b end is connected to the inverting input terminal of the second differential operational amplifier (4); the a end of the current sampling resistor (3) is also sequentially connected to the b end through an inductor (7) and a capacitor (8), and the b end is directly connected to the V- terminal of the transmitter power supply; The output terminal of the first differential operational amplifier (2) is connected to the ADC0 terminal of the MCU (5); The output terminal of the second differential operational amplifier (4) is connected to the ADC1 terminal of the MCU (5); The PWM terminal of the MCU (5) is connected to the control terminal of the power switch (6), and the detection result is output through the UART terminal; The input terminal of the power switch (6) is connected to the V+ terminal of the transmitter power supply, and the output terminal is connected between the inductor (7) and the capacitor (8); The MCU (5) reads the differential voltage of the Wheatstone bridge (1) through the first differential operational amplifier (2), reads the loop current between the V- terminal and the V+ terminal of the transmitter power supply through the second differential operational amplifier (4), and outputs the corrected and compensated loop current through the PWM terminal to meet the technical requirements of low power consumption.

2. The high refresh rate intelligent two-wire transmitter according to claim 1, characterized in that: It further includes a display unit (9) connected to the UART terminal of the MCU (5), and the MCU (5) outputs the detection result of the Wheatstone bridge (1) on the display unit (9) through the UART terminal; The MCU (5) is used to implement signal acquisition, data processing, data display, current compensation, and program slicing.

3. The high refresh rate intelligent two-wire transmitter according to claim 1, characterized in that: The power switch (6) is a field effect transistor, and its gate, source, and drain are respectively used as the control terminal, input terminal, and output terminal.

4. A high refresh rate intelligent two-wire transmitter signal transmission method, characterized in that: It includes the following steps: S0, build the high refresh rate intelligent two-wire transmitter according to any one of claims 1-3; S1, load a high-frequency program into the MCU (5), and configure the MCU (5) into two working modes: sleep mode and high-frequency mode; the MCU (5) defaults to work in sleep mode; Set the high-frequency loop current I of the MCU (5) h , the sleep loop current I l and the carrier time T pwm ; T pwm = T l + T h , T l is the sleep working time, and T h is the high-frequency working time; Collect the differential voltage signal through the Wheatstone bridge (1), and calculate the average loop current I that the transmitter needs to output according to the calibration coefficient o ; Calculate the high-frequency working time T according to the volt-second balance principle of PWM h ; S2, segment and slice the high-frequency main program of the MCU (5) as required to form multiple sliced programs, and meet the condition that the running time of each sliced program does not exceed the high-frequency working time T h ; According to the average loop current I calculated in step S1 o , calculate the zero-output time T of the high-frequency mode at zero output h0 ; S3, the differential voltage signal of the Wheatstone bridge (1) is sent to the ADC0 terminal of the MCU (5) through the first differential operational amplifier (2); the voltage division signal of the current sampling resistor (3) is sent to the ADC1 terminal of the MCU (5) through the second differential operational amplifier (4); S4, the MCU (5) calculates the average loop current I actually output according to the received differential voltage signal o , and makes a judgment: When the average loop current I of the output o is less than the high-frequency loop current I h , the MCU (5) alternately operates in the sleep mode and the high main frequency mode, and executes step S5; When the average loop current I of the output o is greater than or equal to the high-frequency loop current I h the MCU (5) operates in the high main frequency mode and executes step S6; S5, alternate between sleep mode and high-frequency mode The MCU (5) calculates the delay time T of multiple segments of the slicing program d and delays the operation of the slicing program through the delay module; Based on the volt-second balance principle, the inductor (7) and capacitor (8) are used to filter the pulsed current in the average loop current I o ; The MCU (5) adjusts the delay time T according to the received voltage division signal to complete the closed-loop control; d ​ Until all programs are executed, the average loop current I o corresponds to the output physical quantity to be transmitted, and signal detection and transmission are completed; S6, high-frequency mode The MCU (5) directly runs the sliced program; The MCU (5) generates a pulsed current I by driving the control terminal of the power switch (6). p The pulsed current I is filtered through the inductor (7) and the capacitor (8). p The pulsed current I compensates for the difference between the average loop current I p to be output and the high-frequency loop current I o by compensating for the difference between the average loop current I h to be output and the high-frequency loop current I The MCU (5) adjusts the pulsed current I according to the received voltage division signal p to complete the closed-loop control; Until all programs are executed, the average loop current I o corresponds to the output physical quantity to be transmitted, and signal detection and transmission are completed.

5. The high refresh rate intelligent two-wire transmitter signal transmission method according to claim 4, characterized in that: In step S1, the operating current of the MCU (5) loading the high-frequency program is 8 mA @ 48 MHz; The high main frequency program includes signal acquisition, data processing, display data transmission, current compensation and program slicing.

6. The high refresh rate intelligent two-wire transmitter signal transmission method according to claim 5, characterized in that: In step S1, the high-frequency working time T h is calculated by the formula:

7. The high refresh rate intelligent two-wire transmitter signal transmission method according to claim 6, characterized in that: In step S2, the zero output time T h0 is calculated by the following formula:

8. The high refresh rate intelligent two-wire transmitter signal transmission method according to claim 7, characterized in that: In step S5, the delay time T d is calculated by the following formula: T d = T h - T h0 Among them, the high-frequency working time 9. The high refresh rate intelligent two-wire transmitter signal transmission method according to claim 8, characterized in that: In step S6, the average loop current I o of the pulse current I p is a square wave current.

10. The high refresh rate intelligent two-wire transmitter signal transmission method according to claim 9, characterized in that: In step S1, the carrier wave of the MCU (5) is a 10kHz pulse width modulation wave; The operating current I of the high-frequency program h = 8 mA; The high-frequency working time T h = 10 μs; The sleep loop current I l = 2.6 mA; The sleep working time T l = 90 μs; The carrier time T PWM = 100 μs; In step S2, the high main frequency program is segmented and sliced according to signal acquisition, data processing, data display, and current compensation.

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