CN115980436A

CN115980436A - Direct current quantity acquisition system based on linear algorithm

Info

Publication number: CN115980436A
Application number: CN202211563185.8A
Authority: CN
Inventors: 颜霞; 陈磊; 王刚; 孟良; 陈品富; 米东文; 杨东晓
Original assignee: Shandong Taikai Electric Automation Co ltd
Current assignee: Shandong Taikai Electric Automation Co ltd
Priority date: 2022-12-05
Filing date: 2022-12-05
Publication date: 2023-04-18

Abstract

The invention relates to a direct current quantity acquisition system based on a linear algorithm, which comprises a signal isolation circuit, a voltage stabilizing circuit, an amplifying circuit, an AD conversion circuit, a single chip microcomputer and a liquid crystal display screen, wherein a current signal is converted into a voltage signal after sequentially passing through the signal isolation circuit and the amplifying circuit, and the voltage value after isolation is obtained through an operational amplifier and an optical coupler; to an AD conversion circuit; the AD conversion circuit is connected with the single chip microcomputer through an SPI bus; the single chip microcomputer is in communication connection with the liquid crystal display screen and converts the AD sampling data read by the SPI bus into actually input direct current quantity; the direct current signals are collected by 4-20mA, and AD sampling values are in linear proportion relation, so that input signals corresponding to the sampling points are obtained. The visual calibration interface of this patent sees AD's value, and each passageway acquisition precision homoenergetic reaches more than 0.2 level. The problem of inconsistent conversion of each channel caused by errors of a sampling circuit is solved, and high-precision sampling accuracy is kept in a full-range.

Description

Direct current quantity acquisition system based on linear algorithm

Technical Field

The invention relates to a direct current acquisition system, in particular to a direct current acquisition system of a relay protection and measurement and control device.

Background

4-20mA is a standard current signal commonly used in industrial control industry, and is mainly used on industrial sensors, and the current signal has strong anti-interference capability, is not easily interfered by external factors and can be remotely transmitted, so that the current signal is more frequently applied on the sensors. After the sensor is connected with the measurement and control device, the accuracy of 4-20mA direct current acquisition directly influences the analysis of a sensor signal, a sampling circuit generally adopts non-high-precision operational amplifiers and resistors for saving cost, and the consistency of sampling values of all paths is poor.

The prior art has the following problems:

1. the 4-20mA direct current signal is converted into a voltage signal through a resistor, and then enters the operational amplifier through photoelectric isolation after being stabilized through the operational amplifier circuit. In the transmission process, errors are accumulated for many times, and due to engineering cost factors, the circuit selects a resistor with the precision of 1% and does not meet the requirement of 0.2% error, so that the output difference of each loop is large when the input quantity is the same.

2. The traditional calibration method is to multiply each loop by a coefficient for calibration, but the calibration method has poor effect on 4-20mA acquisition, and the calculated value is smaller when small signals appear and larger when large signals appear after calibration.

3. If the subsection coefficient calibration is adopted, a plurality of calibration coefficients need to be set, and the standard sources of different subsections are applied for respective calibration.

Disclosure of Invention

In order to solve the technical problem, the invention provides a direct current quantity acquisition system based on a linear algorithm, which adopts the technical scheme that:

comprises a signal isolation circuit, a voltage stabilizing circuit, an amplifying circuit, an AD conversion circuit, a singlechip and a liquid crystal display screen, and is characterized in that,

the voltage stabilizing circuit converts a 5V system power supply into 2.5V reference voltage and is connected with the singlechip through the AD conversion circuit;

the current signal is converted into a voltage signal after sequentially passing through the signal isolation circuit and the amplifying circuit, and the voltage value after isolation is obtained through the operational amplifier and the optical coupler; to an AD conversion circuit;

the AD conversion circuit is connected with the single chip microcomputer through an SPI bus;

the singlechip is in communication connection with the liquid crystal display screen, caches the data received from the AD conversion circuit, performs algorithm processing, and converts the data received by the AD conversion circuit into actual input direct current;

the liquid crystal display screen is provided with a calibration interface and a telemetering information interface, and the sampling data received from the AD conversion circuit is displayed in real time on the calibration interface; and displaying the actual input value of the direct current quantity on a telemetry information interface.

Furthermore, the AD conversion circuit adopts a 12-bit AD7327 analog-to-digital conversion chip and supports 8 paths of signal acquisition.

Furthermore, the signal isolation circuit, the voltage stabilizing circuit and the amplifying circuit are used for stabilizing and isolating the direct current signal.

Further, the AD conversion circuit is used for analog-to-digital signal conversion.

Furthermore, the value range of the AD sampling value is 0-20 mA; the AD sampling value is in linear proportional relation in the collection range of 4-20 mA.

Further, according to the constant slope K of the direct current signal, the horizontal axis represents an AD sampling value and is expressed by ADbuf; the vertical axis represents the input current, denoted by Idc; the relationship between the input current Idc1 and the sampled value Buf at any point is as follows:

the input current Idc1 at any point can be obtained as:

the invention has the beneficial effects that: the invention relates to a direct current quantity acquisition system based on a linear algorithm, wherein a direct current signal is acquired by adopting 4-20mA, and AD sampling values are in a linear proportional relation, so that input signals corresponding to the sampling points are obtained. The visual calibration interface of this patent sees AD's value, and each passageway acquisition precision homoenergetic reaches more than 0.2 level. The problem of inconsistent channels is solved, and high-precision sampling accuracy is kept in the full-range.

Drawings

FIG. 1 is a block diagram of the present invention;

FIG. 2 is a reference voltage source;

FIG. 3 is a signal isolation circuit;

fig. 4 an AD conversion circuit;

FIG. 5 is a minimum system circuit of a single chip microcomputer;

FIG. 6 is a DC acquisition parameter calibration interface;

FIG. 7 illustrates a DC calibration range lowest point interface;

FIG. 8 illustrates a DC calibration range peak setting interface;

FIG. 9 shows the actual sampled values when 4mA, 12mA and 20mA are applied, respectively;

FIG. 10 is a functional implementation;

fig. 11 is a linear proportional graph of the AD sampling value and the input signal according to the present invention.

Detailed Description

As shown in the figure, the invention is a direct current acquisition system based on a linear algorithm. As shown in fig. 1, the device includes a hardware isolation, voltage stabilization, amplification circuit for anti-electromagnetic interference processing of a dc signal; the AD conversion circuit is used for converting analog-to-digital signals; the single chip microcomputer is used for sampling calculation, algorithm processing, real-time communication and the like and is a core processor of the device; the liquid crystal display is used for man-machine interaction functions such as data calibration, real-time display and the like.

And the voltage stabilizing circuit converts a 5V system power supply into a high-precision 2.5V reference voltage and provides a 2.5V reference voltage for the high-precision 2.5V reference voltage.

And the signal isolation circuit firstly converts the current signal into a voltage signal and then obtains an isolated voltage value through the conversion of the operational amplifier and the optical coupler.

A12-bit AD7327 analog-to-digital conversion chip is adopted to support 8 paths of signal acquisition and is transmitted to a singlechip through an SPI bus to read data.

And the single chip microcomputer caches the data read by the SPI bus, performs algorithm processing, and converts the AD sampling value into the actual input direct current quantity. And communicating with the liquid crystal screen, receiving and storing the input calibration value, and determining a sampling conversion equation.

And (4) displaying the AD channel data in real time on a calibration interface by using a liquid crystal display with high resolution of 320-240, setting a calibration point, and displaying the actual input value of the direct current on a telemetering information interface.

The invention can realize high-precision signal acquisition of a low-cost hardware circuit, the hardware circuit only needs to ensure linear transformation without adopting expensive high-precision resistors and operational amplifiers, and the high-precision direct current acquisition of 0.2 percent can be realized by setting a calibration equation through software. The invention creates a direct current calibration mode, determines a straight line according to two points, adopts a visual calibration technology, inputs two endpoint sampling values, obtains a sampling equation according to known parameters, obtains a direct current actual value in a full-range and greatly reduces the hardware cost.

As shown in fig. 11, according to the circuit principle analysis and the actual addition test, although the output of each loop has an error, the AD sampling value is in linear proportion in the 4-20mA acquisition range. Therefore, according to the principle that one straight line is determined by two points, a sampling straight line can be drawn, and therefore the input signal corresponding to each sampling point is obtained.

The circuit can realize acquisition in a range of 0-20mA, the calibration lower limit of the calibration equation is selected to be 3.9mA, and the lower limit of the calibration equation is considered to be 0mA below 3.9 mA. If the calibration lower limit is selected to be 4mA,4mA or less and is considered to be 0, the AD sampling fluctuates in a small range, when the input is 4mA, the measured value fluctuates between 0mA and 4mA, and the normal input or the broken line cannot be distinguished, so the calibration lower limit selected by the patent is 3.9mA, and the calibration upper limit is selected to be 20mA.

This patent is uploaded AD chip real-time sampling value to liquid crystal display's direct current volume and is gathered calibration interface, and the testing personnel of being convenient for set up the calibration value. The tester only needs to apply a 3.9mA reference source, the real-time sampling value displayed at the moment is recorded as Buf _ L and stored, the real-time sampling value displayed at the moment is recorded as Buf _ H and stored after applying a 20mA reference source, and the software can generate a calculation formula and automatically calibrate.

According to the fact that the slope K of the straight line is unchanged, the relation between the input current Idc1 and the sampling value Buf at any point is as follows:

the input current Idc1 at any point can be obtained as:

the functional implementation is shown in fig. 10.

The invention has simple debugging and setting and lower requirement on circuit precision, is popularized and applied to a plurality of products and solves the problem of direct current quantity sampling precision which is puzzled for a long time.

Referring to fig. 2,5V the system power supply is converted to a high precision 2.5V reference voltage via U16, which is connected to pin 5 of "analog to digital conversion chip" U12 to provide a voltage reference for it.

Referring to fig. 3, this part is the signal isolation circuit: 4-20mA current signal I1+ flows through R1 to GGND, according to ohm's law U = IR, a voltage signal V1 is generated at both ends of R1, and this voltage signal flows through resistor R7 to pin 2 of the negative input terminal of operational amplifier U21A, since the positive input terminal of the operational amplifier is connected to signal ground (without considering feedback of U24 first), pin 1 of operational amplifier U21A outputs 0V voltage, according to the circuit connection, 5V will drive 1,2 pin of linear optocoupler U24 through current limiting resistor R10, at this time, the light emitting diode in U24 emits light, the light is received by the photocell of 3,4 pin, the generated current is negatively fed back to pin 2,3 of operational amplifier input terminal U21A, since the current direction is 4 positive 3 negative, and the current flowing through V1 through R7 is cancelled, the operational amplifier U21A is in a balanced state of negative feedback, the current flowing through R7 is V1/R7, therefore 4325 of U24 flows through pin 357, the current is converted into a 3536V 24/V19, and the voltage signal V1/V19 is converted into the same voltage signal V26, therefore, the voltage signal V1/V is also converted into the voltage signal V3527 and the voltage of the photoelectric conversion circuit is generated by the circuit connected to the circuit.

Referring to fig. 4, V1 inputs channel 1 (pin 7 of U12) of the 12-bit adc, and the single chip U1 sends an AD conversion start command to U12 through the SPI bus, and after a proper delay (after the U12 completes AD conversion), the single chip U1 reads the conversion result of U12 through the SPI bus.

Referring to fig. 5, this is the minimum system circuit of the single chip microcomputer, and U1 is an ARM single chip microcomputer of a cortex tm-M3 core, which has a very high cost performance.

Referring to fig. 6, taking channel 1 as an example, a direct current input signal source is connected to the first 4-20mA input positive and negative terminals of the device, a 3.9mA direct current signal is applied, a direct current acquisition parameter calibration interface is opened, fig. 6, the lowest point of the direct current calibration range is selected, and data of the AD channel at this time is input, fig. 7, and stored.

Referring to fig. 8, a 20mA direct current signal is applied, a direct current acquisition parameter calibration interface is opened, the highest point of the direct current calibration range is selected, and data of the AD channel at this time is input and stored.

Referring to fig. 9, the calibration is completed, and the accuracy after the calibration is verified by inputting a direct current signal in the range of 4-20 mA.

FIG. 9 shows the actual sampling values when the standard signals of 4mA, 12mA and 20mA are applied.

The direct current quantity 1-4 of the invention is 4-20mA collection, and it can be seen from figures 7 and 8 that the calibration values of the lowest point and the highest point of each channel are different, which is caused by the error on the hardware circuit, but the collection precision of each channel can reach more than 0.2 grade after the calibration by the calibration mode of the invention. The problem of the inconsistent passageway has been solved very much to the calibration mode of this patent, and keeps the sampling accuracy degree of high accuracy in the full scale range.

The above-described embodiments are merely illustrative of several embodiments of the present invention, which are described in more detail and detail, but are not to be construed as limiting the scope of the present invention. It should be noted that, for those skilled in the art, other various changes and modifications can be made according to the above-described technical solutions and concepts, and all such changes and modifications should fall within the protection scope of the present invention.

Claims

1. The direct current acquisition system based on the linear algorithm comprises a signal isolation circuit, a voltage stabilizing circuit, an amplifying circuit, an AD conversion circuit, a singlechip and a liquid crystal display screen, and is characterized in that,

2. The linear algorithm-based direct current acquisition system according to claim 1, wherein the AD conversion circuit adopts a 12-bit AD7327 analog-to-digital conversion chip and supports 8-way signal acquisition.

3. The linear algorithm based dc acquisition system according to claim 1, wherein the signal isolation circuit, the voltage regulator circuit and the amplification circuit are used for voltage regulation and isolation processing of the dc signal.

4. The linear algorithm-based direct current amount acquisition system according to claim 1, wherein the AD conversion circuit is configured to convert an analog-to-digital signal.

5. The linear algorithm-based direct current acquisition system according to claim 1, wherein the value range of the AD sample value is 0 to 20mA; the AD sampling value is in linear proportional relation in the collection range of 4-20 mA.

6. The linear algorithm-based direct current quantity acquisition system according to claim 1, wherein according to the fact that the slope K of the direct current signal is constant, the horizontal axis represents an AD sample value, which is expressed by ADbuf; the vertical axis represents the input current, denoted by Idc; the relationship between the input current Idc1 and the sampled value Buf at any point is as follows:

the input current Idc1 at any point can be obtained as:

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