Due to the need to use the public network to achieve wireless meter reading, a DTU module based on 4G network was designed and developed to implement the application of the DTU module in the meter reading system. This article introduces the technical requirements of DTU module terminals , 4G modules and networking, DTU hardware circuit design, anti-interference/reliability design of PCB board, communication module software design, and discusses the DTU module AT command interaction function and the DTU module in Development and application in wireless meter reading.
1. Terminal technical requirements of DTU module
1) Power supply
In order to facilitate the installation of the electric energy meter and the interface level requirements, 5V power supply is used. It can be used for most electric energy meters and other industrial control equipment.
2) Interface parameters
As a wireless data terminal, it can support RS485/TTL/RS232 interface levels, and the baud rate can be adjusted from 1200-115200bps. In order to meet the needs of wireless meter reading, it can support
Maintain parity.
3) TCP/IP protocol
DTU has built-in TCP/IP protocol, which can automatically convert TCP/IP data to facilitate development.
4) Support point-to-point and point-to-multipoint data transmission
The DTU module can realize point-to-point and point-to-multipoint data transmission to the target server.
5) AT command test function
DTU provides AT setting commands of the hyper terminal, which can set GSM/4G parameters and functions.
6) Data transparent transmission function
The DTU module can realize real-time transparent transmission of data and can replace traditional cable communication.
7) Sleep function
In order to achieve low power consumption and low traffic operation, the module will automatically enter sleep mode when there is no data transmission, and only save the handshake keep-alive signal. Wait until there is a need for data transmission before waking it up.
2. DTU module solution
Chengdu Zongheng Intelligent Control Company recently launched a new 4G DTU module. The module uses CAT1 series modules, and the price is among the cheaper products on the market. Functionally, it supports one-to-one networking and one-to-many networking, which is suitable for the needs of this application solution. It also supports scheduled restart, scheduled triggering and other special functions.
3. Networking plan
The advantage of using domain name resolution (DNS) to obtain the IP address of the host computer for data communication with the host computer is that it is not necessary to have a fixed IP address, but to obtain the domain name provided by a domain name resolution service provider. DTU obtains the IP address of the host computer through domain name resolution, thereby transmitting data with the host computer. via DNS.
4. Communication module software design
The operation of the DTU module is performed by the GSM module for data collection through the connection to the directory server. After completing the connection, the GPRS terminal will actively connect to the directory server and continuously query the directory server for connection requests from the host computer. If there is a request, obtain the IP address and port number of the communication machine through the data packet sent from the directory server, and then initiate a connection to the upper computer. If the result is successful, the keep-alive program with the communication machine will be automatically started, and data transmission preparation will be started at the same time. Otherwise, reconnect after timeout. After the data transmission is completed, the connection is automatically disconnected and the keep-alive procedure is stopped.
5. Application of DTU module in wireless meter reading
According to the design principle, the DTU module cooperates with the host computer so that the hardware and software of the original 485 meter reading system remain unchanged. As a DTU module, the scalability and ease of use of the system must be taken into consideration, and interface forms such as RS232/RS485/TLL are provided when connecting to the electric energy meter, so that the DTU module can be connected to the electric energy meter terminal. There is no need to carry out secondary development of the electric energy meter, which facilitates the access of the equipment. The setting options of DTU include server IP, server disconnection, interface rate, setting delay, handshake keepalive with the server and other functions. It has built-in “DL/T645-2007 Multifunctional Electric Energy Meter Communication Protocol” and is connected to the host computer through the serial port, so the host computer software can communicate with the energy meter without modification. The function of the remote GPRS data transmission terminal is to wirelessly receive the protocol instructions of the electric energy meter sent by the host computer, transparently transmit the data through the original 485 and other interfaces, and transmit the data to the corresponding electric energy meter, and then the electric energy meter returns the corresponding response data. to the DTU module. The DTU module transmits the data to the communication machine through GPRS. The communication machine processes the received data through software.
RS485/RS232 to data center. The communication machine is connected to the directory server, and the directory server provides directory services and database services, allowing the communication machine to establish a connection with the DTU and maintain online communication. When reading meters, the communication machine obtains the DTU terminal information through the directory server, receives telegram instructions from the data center through the serial port, and then sends a connection request to the DTU through the directory server. After the DTU obtains the request, it establishes transparent transmission with the communication machine, so that the communication machine The command is sent to the corresponding DTU module and waits for the DTU data to be transmitted back to complete a meter reading.
The function of the remote GPRS data transmission terminal is to wirelessly receive the protocol instructions of the electric energy meter sent by the host computer, transparently transmit the data through the original 485 and other interfaces, and transmit the data to the corresponding electric energy meter, and then the electric energy meter returns the corresponding response data. To the DTU module, the DTU module transmits data to the communication machine through GPRS. The communication machine processes the received data through software and transmits it to the data center through RS485/RS232. The communication machine is connected to the directory server, and the directory server provides directory services and database services, allowing the communication machine to establish a connection with the DTU and maintain online communication. When reading meters, the communication machine obtains the DTU terminal information through the directory server, receives telegram instructions from the data center through the serial port, and then sends a connection request to the DTU through the directory server. After the DTU obtains the request, it establishes transparent transmission with the communication machine, so that the communication machine The command is sent to the corresponding DTU module and waits for the DTU data to be transmitted back to complete a meter reading.
The DTU module system has reasonable design, wide operating temperature range, convenient networking, and can facilitate network management. At the same time, the scalability and ease of use in the design of the electric energy meter are considered, and a variety of interfaces are configured, making the setting and use of the DTU module very simple. It has built-in “DL/T645-2007 Multifunctional Electric Energy Meter Communication Protocol” and can be connected to the host computer through the serial port for setting and data transmission, simplifying the software design. Although the DTU module has many advantages, due to the inherent problems of the current GPRS network, it will cause problems such as slow module response and inconsistent login time, which will affect the real-time performance of meter reading. However, it does not greatly affect the normal use of the meter reading system, so the DTU module meter reading system can be used as a supplement to the existing meter reading solution, or as a replacement for the existing meter reading system.