“With the continuous development of computer technology and communication technology, the Internet and embedded intelligent instruments have been widely used. Its appearance provides powerful technical support for distributed control system to realize real-time and reliable data communication between nodes. It is a serial communication network that effectively supports distributed control or real-time control. This paper analyzes the design of the intelligent anti-theft electricity system based on LPC2132.
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With the continuous development of computer technology and communication technology, the Internet and embedded intelligent instruments have been widely used. Its appearance provides powerful technical support for distributed control system to realize real-time and reliable data communication between nodes. It is a serial communication network that effectively supports distributed control or real-time control. This paper analyzes the design of the intelligent anti-theft electricity system based on LPC2132.
1 Hardware overall design scheme
According to the above functional planning of the device, the device design can be divided into two parts. The intelligent monitoring system consists of two parts: the upper computer and the lower computer, wherein the upper computer is realized by the PC. The lower computer includes a main control single-chip microcomputer composed of MSP430F149, a 4×4 man-machine interface keyboard, a relay control circuit and an audio-optical alarm circuit.
1.1 Sensor selection
1.1.1 Selection of energy metering chips
The electricity collection part mainly realizes the electricity collection and storage through the electric energy metering chip AD7755. A day can be divided into 48 time periods, that is, one time period every half an hour. The single-chip microcomputer sends the number of pulses collected within half an hour and the high power value collected within half an hour to the database server, and then the database The server realizes real-time data update and publishes it in the form of dynamic web pages. The electric energy sampling circuit is the key circuit of electric energy measurement, as shown in Figure 1.
Figure 1 Electric energy sampling circuit
1.1.2 Selection of oil temperature sensor
Using platinum resistance as the sensor for transformer oil temperature measurement, its temperature measurement circuit is shown in Figure 2. The oil temperature sensor is used to measure the oil temperature of the transformer. When the oil temperature is higher than the set value, it will alarm and cut off the transformer switch.
Figure 2 Temperature measurement circuit
Its parameters are as follows:
①Measuring range: -200℃～+850℃; ②Allowable deviation value △℃: Grade A ±(0.15+0.002│t│), Grade B ±(0.30＋0.005│t│); ③ Small insertion depth : The minimum insertion depth of the thermal resistance is ≥200 mm; ④The let-through current is ≤5 mA.
1.1.3 Selection of oil level sensor
Use UZF2 (side-mounted) remote transmission type column-turning control level gauge. The magnetic flipping column level gauge is a device specially developed for liquid level measurement, which is developed and developed according to the principle of magnetism, Archimedes (the law of buoyancy) and other principles ingeniously combined with the characteristics of mechanical transmission. On the basis of the level gauge, a magnetic control switch is added, and the magnetic control switch signal can be used to control or alarm the liquid level while monitoring the liquid level; Send the sensor, monitor the liquid level on-site and transmit the change of the liquid level to the control room through the transmission sensor, cable and instrument to realize remote monitoring and control.
1.1.4 Selection of anti-stealing signals
After the whole system is powered on, the main control system starts self-checking, and after initialization, if it does not receive the command sent by the remote management center through GPRS, the monitoring and control main system reads the current and monitoring data of the meter sequentially, and measures the transformer oil temperature and oil temperature. The measurement and monitoring data sent by the measurement and control subsystem are regularly received, and data processing and output control are carried out. At the same time, the measurement and control subsystem sequentially measures the current and the oil temperature in the high-voltage magnetic sleeve. And monitor the status and oil level of the positioning electromagnet in the high-voltage magnetic sleeve. When the monitoring and control main system receives the command sent by the remote management center through GPRS, it will judge the command to determine whether it is the closing or disconnecting command of the internal load switch of the transformer, or the positioning or releasing command of the positioning electromagnet in the magnetic sleeve and the internal measurement box door. Positioning electromagnet position or release command. The main measurement and control system sends the corresponding command content to the measurement and control subsystem and outputs the control to complete each function. In addition, the main measurement and control system forms two curves on the LCD and stores the measured current value and the current value read from the meter in real time. The control circuit mainly realizes the control of the positioning electromagnet in the measuring box, and the positioning electromagnet mainly realizes the locking control of the measuring box door. When the direction is energized, the positioning bolt of the electromagnet is released, and the door of the metering box can be opened. Figure 3 is the circuit diagram of the output control electromagnet.
When both PTC3 and PTF6 are at high level, the positive direction of the electromagnet coil is energized, and the door of the metering box is locked and cannot be opened. When it needs to be opened, make PTF7 and PTC0 both high level, the electromagnet is released, and the door of the metering box can be opened.
Figure 3 Circuit of output control electromagnet
1.2 MCU selection
The design adopts the LPC2132 chip of PHILIPS Company based on ARM architecture as the data acquisition terminal. The LP C2132 microcontroller is based on a 32-bit ARM7TDMI-SCPU that supports real-time emulation and embedded trace, with 64 kB of high-speed Flash memory.
A 128-bit wide memory interface and unique acceleration structures enable 32-bit code to run at high clock rates. The remote data acquisition system is connected to the Ethernet through the network interface module, and the remote computer sends the task request or the acquisition system actively transmits the data to the remote monitoring computer to realize the interconnection between the equipment and the Internet.
1.3 Selection of network interface chip
The design adopts the 28-pin independent Ethernet controller ENC28J60 introduced by Microchip Technology; the EIA/568A wiring standard of RJ45 connector network cable is adopted, and the transmission medium uses eight-core twisted pair cable, and RJ45 is used as the interface.
The design of the network interface circuit is based on the functions, timing and logic levels of LPC2132 and ENC28J60. The network interface circuit is shown in Figure 4.
1.4 Serial bus interface
LP C2132 has two UART serial interface modules, which can be easily connected with serial devices. In the design, UART0 is used as the RS232 interface, and UARTI is used as the RS485 interface. RS232 is mainly used for system debugging, and can also be connected with equipment using RS232 communication. RS485 is used as the input and output channel of the gateway.
Figure 4 Network interface circuit
1.4.1 RS-232 conversion circuit
The design uses the SP3232E chip. It can convert the input level to standard TTL level (give), or convert the input TTL level to negative logic level (give to PC). Its working circuit is shown in Figure 5.
Figure 5 SP3232E circuit
1.4.2 RS485 interface circuit
The design adopts the low-voltage RS485 interface chip SP3481 of Sipex Company, which only needs a +3.3 V power supply to generate the 1.5 V voltage difference required by the differential output. SP348lE works in half-duplex mode, the chip includes a driver and a receiver, and there are 8 external pins.
The R/D signal output by LPC2132 directly controls the transmitter/receiver enable of SP3481 chip: R/D signal is “1”, the transmitter of SP3481 chip is valid, the receiver is disabled, at this time LPC2132 can send to RS485 bus Data byte; if the R/D signal is “0”, the transmitter of the SP3481 chip is disabled, the receiver is valid, and the LPC2132 can receive data bytes from the RS-485 bus at this time. As shown in Figure 6. In this circuit, only one of the “receiver” and “transmitter” in the SP3481 chip can be in a working state at any time.
2 Conclusion
With the wide application, intelligent anti-stealing control technology will definitely become a development trend. This paper proposes to use gateways and new sensors to test transformer parameters. The debugging results show that the system has high reliability and is easy to use. The anti-power theft intelligent control system established by the above method has the characteristics of simple wiring, stable system controller and high reliability of data transmission, and has achieved good results in practical use. It has certain promotion significance.
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