What is the difference between the data acquisition module and the PLC?

The data acquisition module is based on the communication module of the remote data acquisition module platform, and integrates the communication chip and the memory chip on a circuit board, so that it has the functions of transmitting short messages, voice calls, data transmissions, etc. through the remote data acquisition module platform. . The remote data acquisition module can realize the main communication function of the ordinary remote data acquisition module shou machine, and can also be said to be a "lite version" shou machine. The computer, single-chip microcomputer and ARM can be connected to the remote data acquisition module through the RS232 serial port, and realize various voice and data communication functions through the AT command control module.

Compared with GSM, remote data acquisition module technology is a more advanced mobile communication technology, except for remote data acquisition module radiation; in terms of data transmission, remote data acquisition module 2000 1X is also significantly different from GPRS in technology. The rate of 1X is almost 3-4 times the speed of GPRS.

application

Therefore, the main application area of ​​the industrial module for data transmission, the remote data acquisition module has a significant advantage over the GPRS module. However, the application of remote data acquisition modules in the industrial field lags far behind the application of GPRS modules. The main reason is that the coverage and construction of the remote data acquisition module network is not as good as the GSM network, and the other is because the cost of the remote data acquisition module is much higher than that of the GSM module at least 2-4 times, which makes the production cost much higher.

In the early days of China, remote data acquisition modules were mainly provided by Korean and European companies, such as AnyData and Wavecom. In the past two years, domestic Huawei and Zhongxing launched their own high-quality remote data acquisition module modules, which made the overall price drop. Currently, common models include Huawei's EM200, Anydata's DTGS-800, and Wavecom's Q2358/2438. These modules all have the data transmission function of the remote data acquisition module 1X, and also have a built-in TCP/IP communication protocol stack. Since China Telecom's operation of the remote data acquisition module platform has driven the rapid growth of the business, the entire remote data acquisition module market has also developed rapidly.

At present, the remote data acquisition module is mainly used in the field of mobile data transmission, including vehicle navigation monitoring, smart meter reading, remote data acquisition and other fields, especially in the field of multimedia transmission with high bandwidth requirements. The remote data acquisition module has obvious bandwidth advantage. .

PLC (Programmable Logic Controller)

Programmable Logic Controller is a digital computing operation electronic system specially designed for application in industrial environments. It uses a programmable memory that stores instructions for performing operations such as logic operations, sequence control, timing, counting, and arithmetic operations, and controls various types of mechanical equipment or production through digital or analog input and output. process.

basic structure

The programmable logic controller is essentially a computer dedicated to industrial control. Its hardware structure is basically the same as that of a microcomputer. The basic structure is as follows:

1, the power supply

The power supply is used to convert the AC power into the DC power required inside the PLC. At present, most PLCs use a switching regulator power supply.

2, central processing unit (CPU)

The central processing unit is the control center of the PLC and the core component of the PLC. Its performance determines the performance of the PLC.

The central processing unit is composed of a controller, an arithmetic unit and a register. These circuits are concentrated on one chip and connected to the input/output interface circuit of the memory through an address bus and a control bus. The role of the central processor is to process and run user programs, perform logical and mathematical operations, and control the entire system to coordinate.

3, memory

Memory is a semiconductor circuit with memory function that stores system programs, user programs, logic variables, and other information. The system program is a program that controls the PLC to implement various functions, is written by the PLC manufacturer, and is solidified into a read-only memory (ROM), which the user cannot access.

4, the input unit

The input unit is an input interface between the PLC and the controlled device. It is a bridge for the signal to enter the PLC. Its function is to receive the signal from the main component and the detection component. The input types are DC input, AC input, AC and DC input.

5, the output unit

The output unit is also a connection component between the PLC and the controlled device. Its function is to transmit the output signal of the PLC to the controlled device, that is, convert the weak electric signal sent by the central processor into a level signal to drive the execution of the controlled device. element. The types of outputs are relay output, transistor output, and gate output.

In addition to the above parts, PLC has a variety of external devices depending on the model. Its function is to help programming, monitor and network communication. Commonly used external devices are programmers, printers, cassette tape recorders, computers, and the like.

Features

(1) High reliability. Since most PLCs use a single-chip microcomputer, the integration is high, and the corresponding protection circuit and self-diagnosis function improve the reliability of the system.

(2) Programming is easy. PLC programming mostly uses relay control ladder diagrams and command statements, the number of which is much less than that of microcomputer instructions. In addition to medium and high-end PLCs, there are only about 16 small PLCs in general. Due to the simplicity of the ladder image, it is easy to grasp, easy to use, and even requires no computer expertise to program.

(3) Flexible configuration. Since the PLC adopts a modular structure, the user can flexibly change the function and scale of the control system simply by combining, so that it can be applied to any control system.

(4) The input/output function modules are complete. One of the biggest advantages of PLC is that for different field signals (such as DC or AC, switching, digital or analog, voltage or current, etc.), there are corresponding templates for industrial devices (such as buttons and switches). , sensor current transmitter, motor starter or control valve, etc.) are directly connected and connected to the CPU board through the bus.

(5) Easy to install. Compared with computer systems, PLC installation requires neither a dedicated machine room nor strict shielding measures. When you use it, you only need to connect the detection device to the I/O interface terminal of the actuator and PLC correctly, and it can work normally.

(6) The running speed is fast. Since the control of the PLC is controlled by the program, regardless of its reliability or operating speed, the relay logic control cannot be compared. In recent years, the use of microprocessors, especially with the large number of single-chip microcomputers, has greatly enhanced the capabilities of PLCs, and the difference between PLCs and microcomputer control systems has become smaller and smaller, especially for high-end PLCs.

Application overview

(1) Open-loop control of switching quantity

The open-loop control of the switch is the most basic control function of the PLC. The PLC's command system has powerful logic computing capabilities, making it easy to implement various logic control methods such as timing, counting, and sequencing (stepping). Most PLCs are used to replace the traditional relay contactor control system.

(2) Analog closed-loop control

For the analog closed-loop control system, in addition to the switching input and output, there must be analog input and output points, so that the sampling input and the regulated output can realize the continuous adjustment of parameters such as temperature, flow, pressure, displacement and speed. With control. The current PLC not only has this function for large and medium-sized machines, but also some small-sized machines.

(3) Intelligent control of digital quantity

When the control system has a rotary encoder and a pulse servo device (such as a stepping motor), the PLC can realize the function of receiving and outputting high-speed pulses to realize digital control. The advanced PLC also specially developed a digital control module to realize the curve. The interpolation function has recently introduced a new type of motion unit module, and also provides a programming language for digital control technology, making PLC digital control easier.

(4) Data collection and monitoring

Since PLC is mainly used for on-site control, it is very necessary to collect field data. On this basis, the PLC can be connected with the host computer or touch screen, and the current value of these data can be observed, and statistical analysis can be performed in time. The PLC has a data recording unit that can be inserted into the unit using a memory card of a general personal computer to store the collected data. Another feature of PLC is the self-test signal. With this feature, the PLC control system can realize white diagnostic monitoring, reduce system failure and improve system reliability.