What are the characteristics of RTU?

What are the characteristics of RTU?

RTU is the basic unit of SCADA system. RTU is an electronic device installed on a remote site, used to monitor and measure sensors and equipment installed on a remote site, and is responsible for monitoring and controlling on-site signals and industrial equipment. The RTU converts the measured state or signal into a data format that can be sent on the communication medium. It also converts the data sent from the central computer into commands to realize the functional control of the equipment.

RTU is a durable field intelligent processor, which supports the communication between the SCADA control center and field devices. It is an independent data acquisition and control unit. Its function is to remotely control and control field equipment, obtain equipment data, and transmit the data to the dispatch center of the SCADA system. It should have at least the following functions:

On-site signal and industrial equipment monitoring, control and alarm. For example: data acquisition and processing, on-site control, data transmission (network communication), on-site and remote alarms, etc.; some RTUs also have a series of metering functions for specific application areas, such as flow accumulation.

Because RTU is a dedicated device, there is no unified standard, especially in communication. Under normal circumstances, the RTU of one manufacturer cannot be mixed with the RTU of another manufacturer. The transformation and competition of the agreement has formed an industry. In the near future, the Expert Advisory Committee of the Chinese Society of Automation will release RTU general standards to the market. These standards generally include the following:

Communication standards DNPs and IEC870. RTU programming standard IEC1131-3

RTU building blocks

RTU's hardware mainly includes functional modules such as CPU, memory, and various input and output interfaces. These modules are integrated into the circuit board, and the functional modules of the RTU are connected through the circuit board wiring. The CPU is the central system of the RTU controller, responsible for processing various input signals, and after arithmetic processing, the output is completed. The memory is the RTU memory system, used to store various temporary or permanent data.

Among them, the switch input unit: collects various on-site switch signals. The on-site signal can be a relay contact switch (passive), a voltage signal, or a current signal. Due to the use of optical isolation devices, it can resist various interferences on site, and can work normally under strong electric field, strong magnetic field, dusty and humid environment.

Switch output unit: used to remotely control the start and stop, sound and light, and alarm of remote equipment.

Analog input unit: adopts analog switch and photoelectric isolation technology to collect various analog signals on site, which can be 4-20mA, 0-10mA standard analog signals; it can also be non-standard analog signals, such as AC 220V, etc., A/ D board adopts intelligent A/D conversion and software technology, which can resist 50Hz interference of power frequency, radio frequency interference, etc., and the accuracy of A/D conversion is up to 14 bits. The analog quantity circuit is isolated, which can be used for the simultaneous acquisition of different ground potential equipment.

Analog output unit: used for various automatic control systems in PID adjustment mode. Pulse input unit: the frequency of collecting pulse signals, with optical separation. The frequency range of the collected signal is 0-20MHz.

Digital input unit: Receive various serial data signals. It can be RS485 interface, RS232, RS422 interface, or asynchronous serial data under various baud rates such as V11 and V28. It can also collect 64K synchronized data.

Including various communication methods such as RS485 interface, RS232 interface, Ethernet interface, and HART instrument interface.

RTU application

Compared with the commonly used programmable controller PLC, RTU usually has excellent communication capabilities and larger storage capacity, is suitable for harsher temperature and humidity environments, and provides more computing functions. RTU products are widely used in SCADA systems in industries such as oil and gas, water conservancy, power dispatch, and municipal dispatch.