In electric power and industrial automation control systems, circuit breakers, motor start and stop, solenoid valve opening and closing, etc., there are many actuators that need to be remotely controlled. In the past system design, multiple PLCs or The field instruments of communication and digital output function form a remote automatic control system, but the high cost and cumbersome system structure bring trouble to the automation design and application.
This article introduces an ARTU-J16 with 16 remote control contact output. The device is connected to the host computer via RS485 bus. It is used as a remote relay output module for receiving computer commands, performing remote control or automatic control of the system. Road, the device has 1600 sets of operational event records, with GPS timing function, can ensure that the SOE event record is not lost within one month after the external power supply is powered off. Compared with the previous control mode, this design provides a simplified control network structure. A low cost, high reliability alternative.
1 circuit design principle
The ARTU-J16 remote control unit hardware mainly consists of main CPU chip, DIP switch setting input, real-time clock, dual RS485 communication, SOE event record storage, watchdog control, relay control and output, and power supply module. see picture 1).
Figure 1 circuit structure
1.1 Master CPU
The ARTU-J16 16-channel remote control unit is designed by ATMEL's ATmega128, which realizes dual RS485 communication, data processing, event record access, display and 16-way relay normally open contact output state control. ATmega128 is an 8-bit RISC high-speed low-power MCU introduced by ATMEL. The system performance can reach 16MIPS at 16M clock frequency, with 128k FlashROM, 4k EEPROM, 4k system SRAM; expandable 64k external memory; Road UART communication port. At the same time, the chip has JTAG online programming port, which is convenient for users to debug and reduce development cost. 53 programmable I/O ports can hook enough peripheral devices.
1.2 DIP switch setting input
The DIP switch provides the user with a simplified man-machine interface for setting the address, baud rate, data format and other setting functions in RS485 communication. The 10-bit data port of the DIP switch (SW1) is connected to the 10k resistor pull-up. To Vcc, the circuit uses a 74HC244 (IC5) data buffer to transfer the state of the DIP switch to the 8-bit data bus, and the remaining two data lines are directly connected to the I/O port of the CPU (see Figure 2).
Figure 2 DIP switch setting input
1.3 real time clock
The real-time clock chip RX-8025A (IC4) provides a time-recording point for system SOE events. The chip has a 400kHz serial bus interface and a 32.768 kHz crystal oscillator with wide-temperature, high-stability real-time data.
1.4 Communication method
The communication method adopts the dual RS485 mode. The debugging and setting and the communication part of the host computer are physically divided into two paths without mutual interference, which effectively prevents possible misoperations (see Figure 3).
Figure 3 Dual RS485 communication circuit
1.5 SOE event record storage
The SOE event record memory uses a 32k low-power SRAM (IC3) IC61C256AH and a backup power supply to form a data storage unit that is not lost during power-off, using the data latch 74HC373 (IC2) and the PC port of the CPU to form a 15-bit data address for IC3. Data storage operations (see Figure 4).
Figure 4 event record storage circuit
1.6 Watchdog Control
The power-saving automatic save part uses the MAX691CWE (IC8) as the power management. When the system has auxiliary power supply, the IC3 is guaranteed to be powered by the main power supply Vcc. When the main power supply is powered off, it automatically switches to the backup battery power supply mode. At the same time, this chip also has a watchdog function. In the extreme case of system crash, the CPU is reset in time to quickly restore the system to a controlled state (see Figure 5).
Figure 5 watchdog circuit
1.7 Relay Control and Output
The relay control output uses a 74HC273 (IC14) to latch the 8-way relay output state that needs to be output, and then drives the corresponding relay via ULN2803 (IC15) (K1 is only one of 16 channels), and diode D1 can bypass relay K1 to disconnect. The reverse current generated by the moment, and the varistor VZ1 connected to the K1 output contact can absorb the back electromotive force generated by the inductive load after the shutdown, effectively extending the life of the output relay contact (see Figure 6). ).
Figure 6 Relay Control and Output
1.8 Power section
The power module adopts PI's switching power supply chip, the input range is AC/DC 80-270V, and the power supply has 3 outputs, which provide power to some circuits such as CPU, relay drive and communication.
2 software design
The software design flow is shown in Figure 7.
3 Product structure characteristics and technical indicators
The ARTU-J16 is mounted on a DIN 35mm rail. The front end with communication indication and signal operation channel indicates 2 groups of indicators, the communication has two RS485 interfaces, one for general parameter setting and debugging, and the other for communication with the host computer. The top of the product is equipped with a DIP switch window, which can be used to set the product communication address and baud rate through the DIP switch. The product complies with JB/T10388-2002 "General technical conditions for intelligent measurement and control node products with bus communication function", GB/T7261-2000 "Basic Test Methods for Relays and Devices" and GB/T13729-2002 "Remote Terminal Equipment" standards.
4 Application case
Taking a case of a power distribution system as an example, one ARTU-J16 controls eight low-voltage feeders, and the CM1 circuit breaker is equipped with a motor operating mechanism. The primary scheme is shown in Figure 8(a), and the control method is shown in Figure 8(b). The start-stop button manually controls the closing and opening of each circuit breaker. The remote control unit centrally controls the working state of the 8-way circuit breaker through the communication interface to realize the working mode of the local and remote control of the circuit breaker.
Figure 8 (a) Figure 8 (b).
5 Conclusion
The ARTU-J16 remote control unit was tested at the National Relay Protection and Automation Equipment Quality Supervision and Inspection Center in December 2007 and meets the relevant standards. The product has been applied in an oilfield power supply and supply company, a taxation building in Suzhou, a mine in Inner Mongolia, and other engineering power distribution monitoring systems, which has reduced investment costs and produced good social and economic benefits.
Guangdong Ojun Technology Co., Ltd. , https://www.ojunconnector.com