CN215599342U

CN215599342U - Low-power-consumption high-precision 4-20 mA signal detection device

Info

Publication number: CN215599342U
Application number: CN202121477134.4U
Authority: CN
Inventors: 荣宏伟; 李蕃; 马常松
Original assignee: Research Institute of Physical and Chemical Engineering of Nuclear Industry
Current assignee: Research Institute of Physical and Chemical Engineering of Nuclear Industry
Priority date: 2021-06-29
Filing date: 2021-06-29
Publication date: 2022-01-21
Anticipated expiration: 2031-06-29

Abstract

The utility model discloses a low-power-consumption high-precision 4-20 mA signal detection device, which comprises an N-path signal preprocessing unit, a main control unit, a display unit, a communication unit and a power management unit, wherein the N-path signal preprocessing unit is connected with the main control unit; the input end of each signal preprocessing unit is in communication connection with the current output end of one current signal sensor, the signal preprocessing units convert 4-20 mA current signals into 0-3V voltage signals, the voltage output ends of the signal preprocessing units are in communication connection with the main control unit, the main control unit converts the 0-3V voltage signals into current values, the current values are connected with the display unit to display the current values, and the main control unit is connected with the communication unit to send the current values to a user. The utility model has high detection precision and low energy consumption.

Description

Low-power-consumption high-precision 4-20 mA signal detection device

Technical Field

The utility model relates to the technical field of sensing detection, in particular to a low-power-consumption high-precision 4-20 mA signal detection device.

Background

The sensor is one of important components of an industrial monitoring system, is usually installed in a specific area, and converts physical signals such as pressure, flow, temperature and the like into standard current (4-20 mA) and voltage signals. Compared with a voltage signal, the current signal has the advantages of small attenuation loss, strong anti-interference capability, good stability and the like. Therefore, the 4-20 mA output type sensor is widely applied to industrial fields.

However, the special 4-20 mA signal detection device in the market has the defects of few types, low measurement precision, poor accuracy, large power consumption, few detection channels and the like. At present, a current acquisition card is generally adopted to convert a 4-20 mA current signal into an analog voltage signal, and then the signal processing and conversion are completed through a PLC analog input interface. This approach has the following disadvantages: (1) the PLC, the current acquisition card and the communication module are expensive and do not meet the economic requirement of industrial application. (2) Many current collection cards lack a calibration mechanism, and the measurement accuracy becomes worse as the use time becomes longer, the environmental temperature changes, the aging of components and parts and other factors affect.

SUMMERY OF THE UTILITY MODEL

The utility model aims to provide a signal detection device with low power consumption and high precision of 4-20 mA, aiming at the problems of high cost and low precision of the signal detection device in the prior art.

The technical scheme adopted for realizing the purpose of the utility model is as follows:

a low-power-consumption high-precision 4-20 mA signal detection device comprises an N-channel signal preprocessing unit, a main control unit, a display unit, a communication unit and a power management unit;

the input end of each signal preprocessing unit is connected with the current output end of a 4-20 mA output type sensor, the signal preprocessing units convert 4-20 mA current signals into 0-3V voltage signals, the voltage output ends of the signal preprocessing units are in communication connection with the main control unit, the main control unit converts the 0-3V voltage signals into current values and is connected with the display unit to display the current values, the main control unit is connected with the communication unit to send the current values to a user, and the power management unit is respectively electrically connected with the signal preprocessing units, the main control unit, the display unit and the communication unit to supply power.

In the above technical solution, the number of the signal preprocessing units is four.

In the technical scheme, the model of the chip selected by the signal preprocessing unit is LM324DT, the model of the chip selected by the main control unit is STM8L151, the display unit is an EINK ink screen, and the communication unit selects an RS-485 conversion chip JME 8871.

In the above technical solution, the power management unit is provided with a +5V power supply interface, and converts +5V into + 3.3V.

In the technical scheme, the +5V voltage is connected with the signal preprocessing unit, the display unit and the communication unit for power supply, and the +3.3V voltage is connected with the main control unit for power supply.

In the above technical solution, in the signal preprocessing unit, R1 is respectively connected to positive and negative pins of the current input terminal; r3 is respectively connected with GND and 5 pins of LM324 DT; r4 is respectively connected with the current negative input end and the pin 6 of LM324 DT; r5 is respectively connected with

pins

6 and 7 of LM324 DT; r6 is respectively connected with

pins

3 and 7 of LM324 DT; r14 is respectively connected with GND and 3 pins of LM324 DT; r7 is respectively connected with

pins

1 and 2 of LM324 DT; r8 is respectively connected with pin 2 of LM324DT and pin 13 and pin 14 of LM324 DT; r9 is respectively connected with

pins

1 and 10 of LM324 DT; r10 is respectively connected with 12 pins of +5V and LM324 DT; r11 is respectively connected with 12 pins of LM324DT and GND; r12 is respectively connected with GND and the 9 pins of LM324 DT; r13 is respectively connected with

pins

8 and 9 of LM324 DT; 4 pins of LM324DT are connected with + 5V; the 11 pins are connected with GND; the 8 pins are 0-3V voltage output pins connected with an AD conversion interface of the main control unit.

In the above technical solution,

pins

6, 16, 23, and 24 of the STM8L151 are a/D sampling interfaces, and are respectively connected to voltage output pins of the four signal preprocessing units;

pins

27 and 28 of the STM8L151 are UART interfaces and are respectively connected with a transmitting and receiving end of RS-485; the 21 pin of the STM8L151 is a GPIO interface used for connecting a direction control interface of RS-485; 17, 18, 19, 20 of STM8L151 are SPI interfaces, insert the display element.

In the above technical solution, the communication unit is used for detecting data interaction between the device and a user. The connection relationship is as follows: the communication unit is an RS-485 conversion chip JME8871, and a pin 1 of the JME8871 is connected with a pin 28 of the STM8L 151;

pins

2 and 3 of JME8871 are connected with pin 21 of STM8L 151; pin 4 of JME8871 is connected with pin 27 of STM8L 151;

pins

5 and 8 of JME8871 are connected with GND and +5V respectively;

pins

6 and 7 of JME8871 are respectively a transmitting interface and a receiving interface of RS-485.

In the above technical solution, the display unit is used for displaying the four current values in real time.

Pins

1, 2, 3 and 4 of an EINK ink screen are connected with

pins

20, 19, 18 and 17 of an STM8L151 respectively;

pins

5 and 6 of the EINK ink screen are respectively connected with +5V and GND.

In the above technical solution, the power management unit is a power conversion chip ASM117-3.3, and the connection relationship is as follows: a pin 3 of the ASM117 is a +5V input end, a pin 1 of the ASM117 is connected with GND, and a pin 2 is a +3.3V output end; c1 is respectively connected with +5V and GND; c2 is respectively connected with +3.3V and GND.

On the other hand, the detection method of the low-power-consumption high-precision 4-20 mA signal detection device comprises the following steps:

step 1, according to the signal preprocessing unit, the following steps are known:

CH＝(I_in*R₁-V_O)*K/V_ref*2¹²

wherein CH is an AD sampling value; i is_inIs the output current value, I, of a 4-20 mA output type sensor_in∈(4mA,20mA)；R₁Is a high precision resistor, R₁＝100Ω；V_oFor outputting a voltage value, V, to the voltage follower circuit_O0.4V; k is the amplification factor of the operational amplification circuit, and K is 1.8; v_refSampling reference voltage, V, for AD_ref＝3V。

Therefore, the sensor outputs a current value

I_in＝(CH*V_ref/K/2¹²+V_O)/R₁

Step 2, calibration:

(1) recording current value standard array buf1[9] ═ 4, 6, 8, 10, 12, 14, 16, 18, 20} in the range of 4-20 mA at intervals of 2 mA;

(2) calibrating the device by using a FLUKE 754 process signal calibrator (the precision of the calibrator is 0.001mA), recording the actual measurement current value of the device at intervals of 2mA, and establishing an actual measurement array buf2[9]]＝{I₀，I₁，I₂，......，I₇，I₈}，I_nReserving 3-bit decimal numbers for actually measured current values;

(3) buf1[9] in (2)]Middle group element and (3) buf2[9]]Making difference between the measured array elements, and recording error value Buf3[9]]＝{error₀，error₁，error₂，......，error₇，error₈}；

(4) With Buf2[9]]The element in (B) is the abscissa, Buf3[9]]The element in the formula (I) is a vertical coordinate, the least square method is used for fitting for one time, and a fitting equation of error k is obtained₁*I+k₀Wherein I is the measured current value, error is the deviation value, k₀、k₁A coefficient constant;

step 3, step 1 obtaining I_inAnd (4) adding the calibration value error obtained in the step (2) to obtain a final detection value.

Compared with the prior art, the utility model has the beneficial effects that:

1. through the signal detection device, a user can finish the calibration of the detection device through the communication interface, and the signal detection device has the advantages of low design cost, high precision and the like.

2. By combining the 4-20 mA signal detection and transmission circuit and the calibration method aiming at the detection circuit, the accuracy of signal detection is improved.

3. According to the utility model, the low-power acquisition and transmission of the 4-channel 4-20 mA signal are realized by selecting the low-power main control chip, the communication chip, the display screen, the signal processing chip and other devices, and the detected 4-20 mA current signal can be displayed through the display screen.

Drawings

FIG. 1 is a schematic diagram of current signal conversion;

FIG. 2 is a block diagram of the apparatus;

FIG. 3 is a schematic diagram of the signal preprocessing unit 2;

FIG. 4 is a schematic diagram of the main control unit 4;

FIG. 5 is a schematic diagram of the communication unit 5;

FIG. 6 is a schematic view of the display unit 3;

FIG. 7 is a schematic diagram of the power management unit 6;

FIG. 8 is a data processing flow diagram;

FIG. 9 is a block diagram of a data calibration algorithm.

Detailed Description

The utility model is described in further detail below with reference to the figures and specific examples. It should be understood that the specific embodiments described herein are merely illustrative of the utility model and are not intended to limit the utility model.

Example 1

A low-power-consumption high-precision 4-20 mA signal detection device comprises an N-channel signal preprocessing unit 2, a main control unit 4, a display unit 3, a communication unit 5 and a power management unit 6; the input end of each signal preprocessing unit 2 is connected with the current output end of a 4-20 mA output type sensor 1, and the main control unit can only identify 0-3V voltage signals and cannot identify 4-20 mA signals. The function of the signal preprocessing unit is to convert 4-20 mA signals into 0-2.88V voltage for the main control unit to further identify, the voltage output end of the signal preprocessing unit 2 is in communication connection with the main control unit 4 (when N is 4, the detection device converts 4-20 mA current signals into 0-3V voltage signals through 4 signal preprocessing units), the main control unit 4 converts 0-3V voltage signals into current values to be connected with the display unit 3 for displaying the current values, the main control unit 4 is connected with the communication unit 5 for sending the current values to the user, and the power management unit 6 is respectively in electrical connection with the signal preprocessing unit 2, the main control unit 4, the display unit 3 and the communication unit 5 for supplying power. The main control unit 4 is responsible for converting the voltage of 0-3V into a digital signal and calculating the current value, the current value is transmitted to the display unit 3 through the SPI interface to complete numerical value display on one hand, and is transmitted to a user through the communication unit 5 on the other hand for further calculation of the current value. In the detection device, a main control unit adopts +3.3V power supply, and a signal preprocessing unit, a display unit and a communication unit adopt +5V power supply. The power management unit has the function of converting the +5V voltage of the battery into the +3.3V voltage, +3.3V is used for the power supply of the main control unit, and +5V is used for the power supply of the signal preprocessing unit, the display unit and the communication unit.

Example 2

Preferably, the number of the signal preprocessing units 2 is four, the signal preprocessing units are implemented by a chip LM324DT, the model of the chip selected by the main control unit 4 is STM8L151, the STM8L151 is an ultra-low power consumption 8-bit MCU, and the number of the chips is only 5.4uA in a low power consumption operation mode; the display unit 3 is an EINK ink screen, the EINK ink screen is selected as the display unit, the refreshing power consumption is 50mW, and the sleep current is less than 0.01 mu A; the communication unit 5 selects an RS-485 conversion chip JME 8871. JME8871 is a low-power chip, supports 2.5-5.5V power supply, and has a typical current value of 1.7 muA in a receiving mode and a typical current value of 70 muA in a sending mode. In addition, the detection device of the utility model has the advantages that under the condition that a signal of 4-20 mA is not received, the running current is less than or equal to 50mA, and the running power consumption is less than or equal to 0.6W. All units of the utility model are low-power consumption chips, and in the prior art, for example, the power consumption of a TD-4017+ type current acquisition card of Shanghai Peng Hei electronic technology Limited company consumes 2W.

Preferably, the power management unit 6 is provided with a +5V power supply interface and a +3.3V power supply interface, the +5V voltage is connected with the signal preprocessing unit 2, the display unit 3 and the communication unit 5 for power supply, and the +3.3V voltage is connected with the main control unit 4 for power supply. This device both accessible two sections +5V dry battery power supply, also can supply power through +5V power to convert into +3.3V voltage through AMS 1117-3.3. In the detection device, a main control unit adopts +3.3V power supply, and a signal preprocessing unit, a display unit and a communication unit adopt +5V power supply. The power management unit has the function of converting +5V voltage into +3.3V voltage, +3.3V is used for the power supply of the main control unit, and +5V is used for the power supply of the signal preprocessing unit, the display unit and the communication unit.

Preferably, in the signal preprocessing unit 2, R1 is respectively connected to positive and negative pins of the current input terminal; r3 is respectively connected with GND and 5 pins of LM324 DT; r4 is respectively connected with the current negative input end and the pin 6 of LM324 DT; r5 is respectively connected with

pins

6 and 7 of LM324 DT; r6 is respectively connected with

pins

8 and 9 of LM324 DT; 4 pins of LM324DT are connected with + 5V; the 11 pins are connected with GND; the 8 pins are 0-3V voltage output pins connected with the AD conversion interface of the main control unit 4.

In this embodiment, R1 ═ 100 Ω 0.1%, R2 ═ 10k, R3 ═ 10k, R4 ═ 10k, R5 ═ 10k, R6 ═ 10k, R14 ═ 10k, R7 ═ 10k, and R8 ═ 10 k; r9 ═ 10 k; r10 ═ 6 k; r11 ═ 4k, R12 ═ 10k, and R13 ═ 8 k.

The signal preprocessing unit 2 is built by adopting a low-power consumption four-channel operational amplifier LM324DT chip. As shown in fig. 1, channel a of LM324DT is a subtraction circuit; the channel B is a current conversion circuit, and the channel C is an amplifying circuit; the D channel is a follower circuit. In the current conversion circuit, R1 is a high-precision resistor of 100 Ω, that is:

V_o1＝R₁*i＝100Ω*(4～20mV) (1)

thus, V_o1∈{0.4V,2V}

The voltage follower circuit adopts the voltage division principle to output a voltage V_o2Adjustable, typical value V_o2＝0.4V。

Will V_o1、V_o2The circuit is connected with a subtraction circuit, the subtraction circuit is an amplifying circuit which combines reverse input and same-direction input, and the circuit can meet the phenomena of virtual short and virtual disconnection under ideal conditions.

From the virtual break, a node equation can be obtained:

(V_O1-V_P)/R₂＝(V_P-0)/R₃ (2)

(V_O2-V_n)/R₆＝(V_n-V_o3)/R₇ (3)

from the virtual shortness, the node equation can be derived:

V_p＝V_n (4)

the formula (1), (2) and (3) can be used for obtaining:

resistor R selected by the utility model₂＝R₃＝R₆＝R₇The following can be obtained:

V_O3＝V_O1-V_O2i.e. V_O3∈{0V,1.6V}

The amplifying circuit is used for converting V_O3And (4) amplifying. The phenomena of virtual shortness and virtual breaking are satisfied under ideal conditions.

From the virtual break, a node equation can be obtained:

from the virtual shortness, the node equation can be derived:

V_O3＝V_P1＝V_n1 (7)

the following formulas (6) and (7) can be obtained:

resistor R selected by the utility model₁₀＝8k，R₉＝10k，V_out＝1.8*V_O3I.e. V_o3Is larger than {0,2.88V }, so the signal preprocessing unit 2 converts the 4-20 mA signal into a voltage of 0-2.88V.

Preferably, pins 6, 16, 23, and 24 of the STM8L151 are a/D sampling interfaces, and are respectively connected to voltage output pins of the four signal preprocessing units 2; pins 27 and 28 of the STM8L151 are UART interfaces and are respectively connected with

pins

1 and 4 of JME 8871; the 21 pin of the STM8L151 is a GPIO interface and is used for connecting 2 and 3 pins of JME 8871; 17, 18, 19, 20 of STM8L151 are SPI interfaces, insert display element 3. The STM8L151 has a plurality of power management modes including a 5.4 μ a low power consumption operation mode, a 3.3 μ a low power consumption standby mode, a 1 μ a active stop mode, and a 350nA stop mode, can wake up from the stop mode within 4 μ s, and supports the frequent use of the lowest power consumption mode. In addition, the STM8L151 supports UART and SPI communication and analog signal acquisition functions, and a 12-bit 4-channel sampling mode with the sampling frequency of 1MHz can be configured through software.

Preferably, the communication unit 5 is used for detecting data interaction between the device and the user. The connection relationship is as follows: the communication unit 5 is an RS-485 conversion chip JME8871, and a pin 1 of the JME8871 is connected with a pin 28 of the STM8L 151;

pins

5 and 8 of JME8871 are connected with GND and +5V respectively; pins 6 and 7 of JME8871 are the sending and receiving interfaces for communication, respectively. JME8871 is a low-power-consumption RS-485 communication interface chip, supports a wide working voltage of 2.5-5.5V, has a typical receiving mode current value of 1.7 muA and a typical sending mode current value of 70 muA, has an A/B end ESD withstand voltage of +/-15V, has no self-excitation phenomenon, and has a highest communication rate of 64 Kbps.

Preferably, the display unit 3 is used for displaying the four-way current value in real time.

Pins

1, 2, 3 and 4 of an EINK ink screen are connected with

pins

20, 19, 18 and 17 of an STM8L151 respectively; pins 5 and 6 of the EINK ink screen are respectively connected with +5V and GND. EINK adopts the technology of microcapsule electrophoresis display to carry out image display, and its basic principle is that the charged nanoparticles suspended in liquid receive the electric field effect and produce the migration, need not be shaded, leans on reflected environment light to show the pattern, has advantages such as low-power consumption, low cost, and EINK outside adopts 3.3/5V power supply, through SPI interface and external communication, refreshes power consumption 50mW, and quiescent current is less than 0.01 mu A.

Preferably, the power management unit 6 is responsible for converting +5V to + 3.3V. The power management unit 6 is a power conversion chip ASM117-3.3, and the connection relation is as follows: a pin 3 of the ASM117 is a +5V input end, a pin 1 of the ASM117-3.3 is connected with GND, and a pin 2 is a +3.3V output end; c1 is respectively connected with +5V and GND; c2 is respectively connected with +3.3V and GND. In this example, C1 ═ 10 μ f and C2 ═ 1 μ f. AMS1117-3.3 is a forward low-voltage drop voltage stabilizer, an overheat protection circuit and a current limiting circuit are integrated inside, the output error is less than 1.5 percent, and the forward low-voltage drop voltage stabilizer is the best choice for battery power supply and portable equipment.

Example 2

The calibration method of the low-power-consumption high-precision signal detection device according to embodiment 1 includes two parts, namely current conversion and data calibration.

The software of the 4-20 mA signal detection device comprises a data processing module and a data calibration module (which are both completed by programming in the main control unit). The data processing module is mainly used for completing AD acquisition, processing and conversion; the data calibration module is used for calibrating the detection device to improve the accuracy of measurement, and the specific process comprises the following steps:

s1: and starting.

S2: initializing a system clock: and starting external clocks such as SPI, UART, GPIO and the like.

S3: UART initialization: and completing parameter configuration of UART baud rate, stop bit, parity bit and the like.

S4: initialization of SPI: and completing the configuration of the clock line, the control bit, the writing pin and the reading pin.

S5: AD conversion unit initialization: and completing the parameter configuration of the A/D conversion rate, the sampling frequency and the like.

S6: reading an AD sampling value: and the main control unit reads the AD sampling value of the signal preprocessing unit.

S7: and judging whether the sampling value is correct or not. If S8 is performed correctly, otherwise, return to S6.

S8: calculating the current value: according to the sampling principle, the current value is calculated.

S9: current value calibration: and finishing current value calibration according to a data calibration algorithm.

Fig. 7 is a flowchart of a data calibration algorithm, which includes the following specific steps:

s10: creating a theoretical array BUF1[9 ]: and recording a standard array buf1[9] ═ 4, 6, 8, 10, 12, 14, 16, 18, 20} at an interval of 2mA in a range of 4-20 mA.

S11: creating measured array BUF2[9]: calibrating the device by using a FLUKE 754 process signal calibrator (the precision of the calibrator is 0.001mA), recording the actual measurement current value of the device at intervals of 2mA, and establishing an actual measurement array buf2[9]]＝{I₀，I₁，I₂，......，I₇，I₈}，I_nFor actually measuring the current value, 3 decimal places are reserved.

S12：BUF1[9]、BUF2[9]Correspondingly making difference to obtain array BUF3[9]]: mixing buf1[8 ]]Middle group element and buf2[8 ]]Making difference between the measured array elements, and recording error value Buf3[9]]＝{error₀，error₁，error₂，......，error₇，error₈}。

S13, building a fitting curve by using BUF2[9] and BUF3[9] to obtain a fitting equation: and taking elements in Buf2[9] as abscissa and elements in Buf3[9] as ordinate, performing first fitting by using a least square method, and obtaining a fitting equation error which is k 1I + k0(I is measured current value, error is deviation value, and coefficients of k0 and k1 are constant).

S14: and substituting the fitting equation into a current calculation formula to finish calibration: in S9I_inWhen calculating the value, the measured resistance value (current value before calibration) I should be_inAnd adding a calibration value error on the basis to obtain a final detection value.

Example 3

As the current collection card in the market becomes longer and more accurate, the current collection card will be degraded slowly, and the user will usually change to a new current collection card or return to the factory to recalibrate the current collection card. The software calibration method matched with the detection device provided by the utility model can finish calibration only by modifying the fitting equation without replacing or returning to a factory. In addition, the current acquisition card in the market has the problem of high energy consumption, for example, the power consumption of the current acquisition card of TD-4017+ type of Shanghai Peng Hei electronic technology Limited is 2W; power consumption of a current acquisition card of ZH-4023A-14D2, a Chunzhen science and technology Limited company, is 1 w.

The detection device of the utility model has low power consumption and high precision, and the result data detected by the detection device of the utility model is shown in the following table:

in statistics, the mean generally represents the mean level of the group of data and the standard deviation represents the degree of dispersion of the group of data. The mean value of the detection deviation values of the device is 0.007mA, the standard deviation is 0.003, the mean value of the power consumption is 0.18w, the standard deviation is 0, the maximum detection deviation of the current is not more than |0.01mA |, and the power consumption is about 0.18 w.

Spatially relative terms, such as "upper," "lower," "left," "right," and the like, may be used in the embodiments for ease of description to describe one element or feature's relationship to another element or feature as illustrated in the figures. It will be understood that the spatial terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as "below" other elements or features would then be oriented "above" the other elements or features. Thus, the exemplary term "lower" can encompass both an upper and a lower orientation. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly.

Moreover, relational terms such as "first" and "second," and the like, may be used solely to distinguish one element from another element having the same name, without necessarily requiring or implying any actual such relationship or order between such elements.

The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, several modifications can be made without departing from the principle of the present invention, and these modifications should also be construed as the protection scope of the present invention.

Claims

1. A low-power-consumption high-precision 4-20 mA signal detection device is characterized by comprising an N-path signal preprocessing unit, a main control unit, a display unit, a communication unit and a power management unit;

the input end of each signal preprocessing unit is connected with the current output end of a 4-20 mA output type sensor, the signal preprocessing units convert 4-20 mA current signals into 0-3V voltage signals, the 0-3V voltage output ends of the signal preprocessing units are connected with the main control unit, the main control unit converts the 0-3V voltage signals into current values, the current values are connected with the display unit to display the current values, the main control unit is connected with the communication unit to send the current values to a user, and the power management unit is electrically connected with the signal preprocessing units, the main control unit, the display unit and the communication unit to supply power.

2. The low-power-consumption high-precision 4-20 mA signal detection device according to claim 1, wherein the number of the signal preprocessing units is four.

3. The low-power-consumption high-precision 4-20 mA signal detection device according to claim 2, wherein the model of a chip selected by the signal preprocessing unit is LM324DT, the model of a chip selected by the main control unit is STM8L151, the display unit is an EINK ink screen, and the communication unit is an RS-485 conversion chip JME 8871.

4. The signal detection device with low power consumption and high precision of 4-20 mA according to claim 1, wherein the power management unit is provided with a +5V power supply interface and converts +5V into + 3.3V.

5. The signal detection device with low power consumption and high precision of 4-20 mA as claimed in claim 4, wherein +5V voltage is connected with the signal preprocessing unit, the display unit and the communication unit for power supply, and +3.3V voltage is connected with the main control unit for power supply.

6. The low-power-consumption high-precision 4-20 mA signal detection device according to claim 2, wherein in the signal preprocessing unit, R1 is respectively connected with positive and negative pins of the current input end; r3 is respectively connected with GND and 5 pins of LM324 DT; r4 is respectively connected with the current negative input end and the pin 6 of LM324 DT; r5 is respectively connected with pins 6 and 7 of LM324 DT; r6 is respectively connected with pins 3 and 7 of LM324 DT; r14 is respectively connected with GND and 3 pins of LM324 DT; r7 is respectively connected with pins 1 and 2 of LM324 DT; r8 is respectively connected with pin 2 of LM324DT and pin 13 and pin 14 of LM324 DT; r9 is respectively connected with pins 1 and 10 of LM324 DT; r10 is respectively connected with 12 pins of +5V and LM324 DT; r11 is respectively connected with 12 pins of LM324DT and GND; r12 is respectively connected with GND and the 9 pins of LM324 DT; r13 is respectively connected with pins 8 and 9 of LM324 DT; 4 pins of LM324DT are connected with + 5V; the 11 pins are connected with GND; the 8 pins are 0-3V voltage output pins connected with an AD conversion interface of the main control unit.

7. The signal detection device of claim 6, wherein pins 16, 23 and 24 of the STM8L151 are A/D sampling interfaces and are respectively connected with voltage output pins of four signal preprocessing units; pins 27 and 28 of the STM8L151 are UART interfaces and are respectively connected with a transmitting and receiving end of RS-485; the 21 pin of the STM8L151 is a GPIO interface used for connecting a direction control interface of RS-485; 17, 18, 19, 20 of STM8L1051 are SPI interfaces and are connected to the display unit.

8. The signal detection device with low power consumption and high precision of 4-20 mA according to claim 7, wherein the communication unit is used for detecting data interaction between the device and a user. The connection relationship is as follows: the communication unit is an RS-485 conversion chip JME8871, and a pin 1 of the JME8871 is connected with a pin 28 of the STM8L 151; pins 2 and 3 of JME8871 are connected with pin 21 of STM8L 151; pin 4 of JME8871 is connected with pin 27 of STM8L 151; pins 5 and 8 of JME8871 are connected with GND and +5V respectively; pins 6 and 7 of JME8871 are respectively a transmitting interface and a receiving interface of RS-485.

9. The low-power-consumption high-precision 4-20 mA signal detection device according to claim 8, wherein the display unit is used for real-time display of four current values, pins 1, 2, 3 and 4 of an EINK ink screen are respectively connected with pins 20, 19, 18 and 17 of an STM8L 151; pins 5 and 6 of the EINK ink screen are respectively connected with +5V and GND.

10. The signal detection device with low power consumption and high precision of 4-20 mA according to claim 9, wherein the power management unit is a power conversion chip ASM117-3.3, and the connection relationship is as follows: a pin 3 of the ASM117 is a +5V input end, a pin 1 of the ASM117 is connected with GND, and a pin 2 is a +3.3V output end; c1 is respectively connected with +5V and GND; c2 is respectively connected with +3.3V and GND.