Design of intelligent monitoring node for the hott

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Design of intelligent monitoring node of anti-corrosion power supply

Abstract: This paper introduces a design method and related hardware circuit of intelligent monitoring node of anti-corrosion power supply, which is used to realize the unmanned monitoring and detection of field anti-corrosion power supply. The system hardware structure, signal conditioning circuit and the interface circuit between chip and microprocessor are studied, and the design idea of monitoring software is expounded. The test shows that the system has simple structure, low cost and reliable performance, and can meet the needs of industrial sites

key words: corrosion prevention power supply monitoring node single chip microcomputer

the phenomenon of metal corrosion can be seen everywhere. The direct and indirect losses caused by corrosion to metal materials are huge, resulting in catastrophic damage accidents and serious environmental pollution. The research shows that the loss caused by corrosion generally accounts for 3% - 4% of the gross national product, of which about 15% can be avoided by the existing anti-corrosion technology, and the development of cathodic protection technology is inseparable from the progress of anti-corrosion technology

anti corrosion power supply is the most critical equipment in cathodic protection technology. Since most of the corrosive metal components are distributed in the field or underground, and have a wide range of distribution, such as oil pipelines, transmission lines, offshore platforms, etc., it is inevitable to develop a new type of corrosion-resistant power supply with high reliability and intelligence, and it is required to collect field data remotely through industry, calculate and analyze, and realize remote control, so as to improve the reliability of field equipment and realize unmanned management

1 the anti-corrosion power supply system flows back to the oil tank structure through the oil return valve body through the pressure oil pipe

cathodic protection technology is simply to measure the potential of the protected metal components (i.e. pipe ground potential), and adjust the compensation protection current according to its size change, so as to protect the metal components. Figure 1 is the schematic diagram of remote monitoring anti-corrosion power supply system

Figure 1 Schematic diagram of remote monitoring anti-corrosion power supply

obviously, the anti-corrosion power supply is the core equipment in the cathodic protection system, and its monitoring system should be able to detect and control its potential, current, voltage and other operating parameters, realize network monitoring, and meet the requirements of real-time and rapid response

2 hardware design of monitoring node

the system hardware is composed of two circuit boards. One is an analog board, which is mainly used to filter, amplify, sample and hold the measurement signal from the anti-corrosion power supply, and automatically select the amplification factor; One is a digital board, which mainly completes the analog-to-digital conversion of sampling signals, calculation (eliminating noise and restoring signals), parameter setting and data transmission [1]. The overall block diagram of the monitoring system is shown in Figure 2

Figure 2 overall block diagram of monitoring nodes

the monitoring system directly measures the electrical signals of the anti-corrosion power supply site, including voltage signals and current signals. The on-site environment of anti-corrosion power supply is poor, and many interference signals are mixed in the signals to be measured. The pre conditioning circuit includes differential mode amplification circuit and active filter circuit, which are used to suppress common mode interference signal and high-frequency interference signal in the field signal. The system communicates with the upper computer through 485 bus and uses the agreed protocol to exchange data

2.1 analog circuit design

the analog circuit block diagram is shown in Figure 3, in which vin1, vin2, iin1, iin2 are signals collected from the anti-corrosion power supply site with the advantages of stable operation, high reliability, simple protection, wide application range and so on. Because the signal to be measured is relatively weak and the on-site environment is relatively bad, many interference signals are superimposed in the signal to be measured. In order to extract useful signals from the noise, the conditioning circuit combining differential mode conditioning circuit and active filter circuit is used to interfere with the input signal, and then the range of the signal is estimated through the voltage grading circuit and provided to the single chip microcomputer. The single chip microcomputer calculates the appropriate amplification factor according to the given signal, then controls the amplification factor of the programmable amplifier ad526, amplifies the conditioned signal to the effective range, and inputs it to the AD574 on the digital board for analog-to-digital conversion [2]

Figure 3 analog circuit block diagram

2.1.1 signal conditioning design

through the analysis of the field signal through the test, it is found that the interference signal mainly comes from the coupling interference of the power line, the transient voltage interference of the power supply and the external electromagnetic radiation interference. Therefore, this part of the circuit has two functions: one is to design a filter circuit according to the frequency characteristics of the interference signal to effectively filter the interference signal; The second is to properly amplify the input signal to complete the impedance conversion

2.1.2 design of automatic gain adjustment circuit

the conditioned signals are selected and processed one by one through multiple analog switches. After the signal passes through the analog switch, one way enters the measuring range of the grading circuit, and the other way enters the amplification unit to amplify to the appropriate working range

ad526 is a special five stage variable gain operational amplifier. The gain stages are g = 1, 2, 4, 8, 16, and there are three gain control input pins. In the design, two ad526 are connected in series to form an amplification unit with 1 ~ 256 gain. The variable gain amplification circuit is shown in Figure 4

Figure 4 automatic gain circuit

this circuit consists of eight voltage comparators. The single chip microcomputer reads its output signal, sets the appropriate amplification factor according to the obtained grading signal, controls the operation of the amplification unit, realizes automatic gain adjustment, and ensures that each signal can be amplified to the best working range of a/d, meeting the design requirements of high precision and wide range

2.2 digital circuit design

the digital circuit block diagram is shown in Figure 5. Single chip microcomputer 80C51 is the core of this system, which increases the data storage capacity of the system by expanding ROM. A/d is the data acquisition module, d/a is the standard current control signal output module, MAX485 is the module communicating with the upper computer, and Vin is the output signal of the analog part [3]

Figure 5 digital circuit block diagram

2.2.1 communication interface design

the system communicates with the upper computer through 485 communication interface to exchange data. RS-485 adopts a pair of balanced differential signal lines and adopts half duplex communication mode. RS-485 is very convenient for multi station connection. Its standard allows up to 32 drives and 32 receivers to be connected in parallel, which is enough to meet the requirements of a multi-point corrosion protection system for medium-sized components. The two ends of the bus are connected with matching resistors, which improves the anti-interference ability. The maximum transmission rate of RS-485 is 10mbit/s, and the maximum cable length is 1200m. Considering the harsh working environment on site, TVs tube is used to realize the lightning protection function, protect the system from instantaneous high voltage damage, and improve the reliability of operation

2.2.2 standard control current output design

the upper computer processes the received data and uses a certain control algorithm to obtain the required feedback control signal. As the anti-corrosion power supply is a simulator circuit, it cannot directly receive the digital control signal, so it must be converted into analog signal by single chip microcomputer to control the power supply

The AD421 used in the system is a monolithic high-performance digital to analog converter. It is powered by current loop, 16 bit digital signal is input in serial mode, and 5 ~ 20mA current is output, which can realize remote intelligent industrial control. The digital input signal ensures the accuracy and effectiveness of the signal through photoelectric isolation, and the output is a standard current signal, which has strong anti-interference ability and can directly drive the relevant simulator

3 software design of monitoring node

in order to improve the efficiency of programming, MCS-51 single chip microcomputer high-level language C51, which is widely used at present, is used as a software development tool [4]

the whole program of the monitoring system is mainly composed of the main program, three interrupt processing programs, and two calculation programs. The main functions completed are: initialization after system reset, control sampling, a/d conversion, signal processing according to the sampling value, selection of amplification factor (range), control of communication interface to transmit data, etc. The main program flow chart is shown in Figure 6 [5]

Figure 6 main program flow chart

this design uses general components and modules, which are divided into powder, spherical, sheet, column, needle and fiber filler design methods and variable gain circuits according to their shapes. While meeting the requirements of high precision and wide range, it simplifies the system structure, greatly improves the reliability of the system, and saves costs. This design has practical significance for realizing remote intensive management in the anti-corrosion industry


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