What is the definition of PLC, programmable logic controller

Programmable logic controller, said the English Programmable Controller, called PC. However, due to the personal computer PC is easy and (Personal Computer) confused, so people are still accustomed to using ethernet module plc programmable controller as an abbreviation. Electronic digital computing device operating system, it is a microprocessor core, specifically designed for applications in the industrial field, for it uses programmable memory for storage in its internal implementation of logical, sequential control, timer / counting and arithmetic operations such as operating instructions, and digital or analog input through output interface, control of all types of machinery or production processes. analog output plc is the product of computer technology with traditional relay contactor control technology, which overcomes the wiring relay contactor control system complex mechanical contact, low reliability, high power, versatility and flexibility shortcomings of the poor, full advantage of the microprocessor, and take care of operation and maintenance personnel to the site electrical skills and habits, especially PLC programming does not require specialized knowledge of computer programming languages, but with a set of relay ladder based simple instruction form, so that the image of the user programming, intuitive and easy to learn; debugging and troubleshooting is also very convenient. After the user to purchase the desired analog input plc, just follow the prompts manual, do a small amount of wiring and easy user programming work, it can flexibly and easily be applied to production practice PLC.

Medium programmable control system

Medium controller may provide the functionality and flexibility you need, do not have that kind of overhead systems, it is the perfect solution for medium-sized application projects. Select rack-based, modular package design standards and safety certification from the controller. Typical applications include complex machine plc digital input module, batch processing and building automation.

Micro & Nano programmable control system

Our micro and nano-plc industrial controller can provide an economical solution to meet the basic needs of a simple mechanical control, including relay replacement, and simple control timing and logic. The controller uses a compact package, integrated I / O and communication, and easy to use, ideal for conveyor automation, security systems and building and parking lot lighting applications projects.

Large programmable control system

Our large-scale control system can be adapted to the needs of the most demanding application projects. They provide a modular architecture and a variety of I / O and networking options. These powerful control solutions for all areas, including processing, security and sports, including providing world-class capabilities. Our large-scale programmable automation controller (PAC) and programmable logic controllers (digital input plc) designed for distributed control applications or host project design, with excellent reliability and performance.

PLC current loop transmission

Application of the current plc temperature control module loop is started in the early 1900s teletype, the earliest use of the 0-60mA loops and later changed to 0-20mA loop, PLC system is the first to use the 4-20mA loop.
4-20mA current loop has many advantages. Need to be carefully calculated in the traditional discrete component designs, and compared with the current integrated 4-20mAIC, circuit take up a lot of space.
Any current values ​​measured are representative of certain information. Practical applications, 4-20mA current loop in 0mA to 24mA current range. But 0mA to 4mA and 20mA to 24mA current range for diagnostics and system calibration. Due to lower than 4mA and above 20mA are used for diagnostics, it is believed readings between 0mA and 4mA could indicate a broken wire in the system. Similarly, between 20mA and 24mA between readings can indicate a potential short circuit occurred in the system.
Plus 4-20mA communications Highway Addressable Remote Sensor, which is backward compatible with 4-20mA instrumentation. In HART system uses microprocessor-based intelligent integration of field devices enables two-way communication. The HART protocol capable of carrying additional digital information on the same line 4-20mA analog current signal for process control.
PLC functions can be divided into several functional groups. Many plc IO module vendors will integrate these functions as separate modules, each module with features vary with the specific application. Many modules have multiple functions, it can interface with a variety of sensors. However, for specific applications will design special modules or expansion modules, such as in most cases: resistance temperature detector (RTD), sensor, or thermocouple sensor. In general, all modules have the same core functions: analog input, analog output, distributed control (eg fieldbus), interface, digital input and output (I / O), CPU and power supply.

Basic PLC operation

Plc logic controllers can be simple and to what extent? We have a common household space heater.
Heater member sealed in a container, ease of system communications. This concept can be extended to a remote control home thermostat heater, communication distance of a few meters, usually voltage control.
Now, we are in this small, simple process control system to be expanded on the basis of which the control and configure a plant need?
Long-distance transmission line impedance, EMI and RFI voltage control scheme makes implementation very difficult, in this case, the current loop is a simple and effective solution. Kirchhoff's law by the current loop current loop at any point is equal to all other points in the current, which can offset the impact of the transmission line impedance. Because the loop impedance and bandwidth (a few hundred ohms and "100Hz), EMI and RFI spurious pickup issues are minimized. digital output plc system is useful for properly controlling such a factory production system.

PLC basic instruction Overview

FX series plc temperature control module basic logic instructions 20 or 27, stepping instruction 2, features more than 100 instructions (different series vary).
FX2N plc intelligent controller a total of 27 basic logic instructions, which contains 20 basic logic instructions some sub-series PLC Programmable Logic Controller.
Instruction fetch and output instruction (LD / LDI / LDP / LDF / OUT)
(1) LD (instruction fetch) a normally open contact and left instruction bus connection, a normally open contact each logical row starting with this directive.
(2) LDI (negated instruction) a normally closed contact and left the bus connection instruction, a normally closed contact each logical row starting with this directive.
(3) LDP (transition instruction fetch) normally open contact with the left leading edge detection instruction bus connected only at the rising edge of the specified bit device is turned on when a scan cycle (from the OFF → ON).
(4) LDF (falling instruction fetch) normally closed contacts of falling edge detection instruction and left the bus connection.
(5) OUT (output command) coil for driving instruction, also known as output instruction.

Analog output module expansion

Here take a 12 bit analog output as an example, the design will use 12 bit D/A conversion chip MAX531 to realize the number of conversion. We then output the operational amplifier at MAX531, micro smart plc ,adjust the analog output to 0 ~ 5V, and output the hardware circuit of the output part as shown in Figure 3. Here, MAX531 is the 12 serial D/A, with a high conversion speed, MAX531 has internal reference voltage, both 10# pin (REFOUT) is 2.048V, so the full range of D/A conversion is 2.048V. And the output signal is a standard 0 ~ 5V, plc input output modules ,therefore, to a level of operational amplifier to max531 output 0 ~ 2.048v signals into 0 ~ 5V signal.