Tag Archives: plc training

Application and characteristics of PLC in control system

What is the meaning of the programmable controller:

Acronym PLC programmable controller or PC, is evolved from the early relay logic control system, which constantly absorbing function of the microcomputer technology to growing gradually for complex control tasks.

Since 1836 relay came, people began to use it skillfully wire connected with the switching device, constitute use different logic control or sequential control. So far, the PLC Ladder programming language can also see the shadow of these wires. Until the late 1960s and early 1970s, the advent of programmable controllers, with the rapid development of microelectronics technology, computer technology and data communications technology, as well as the emergence of the microprocessor, PLC products towards small and ultra-small aspects of a leap , and finally to the early PLC from the initial logic control, sequential control, it has developed into a modern PLC logic, timing, counting, memory and arithmetic operations, data processing, communications and networking functions such as PID loop controller.

PLC viable reason is that it is more suitable for industrial field and the requirements of the market: high reliability and easy ability against various disturbances, programming installation, low price and long life. Than the microcontroller, its input and output closer to the field devices, without adding too many intermediate member or need more interfaces, which saves users time and money. PLC lower end (input) for the relay, transistor and thyristor control means and the upper end is generally user-oriented microcomputer. When people use it, you can not carry out specialized training in computers, programmable controllers can be operated and programmed. Used to perform a variety of different complexity industrial control tasks.
First, the main function of the programmable controller

PLC application is very broad, very rapid development of industrial automation equipment, factory automation (FA) and computer integrated manufacturing system (CIMS) in the important role. Today’s PLC function, far not only replace the traditional relay logic.
PLC system is generally constituted by the following basic functions: a variety of control functions. Data collection, storage and processing capabilities. Communications networking. Input / output interface conditioning. HMI function.

Programming, debugging features:
1, the control function logic control: PLC has the AND, OR, NOT, XOR logical operations and other functions, and triggers can replace relay switch control.
Time control: It provides users with a number of electronic timer, users can set their own: on-delay, off delay and timing pulses and other means.
Count Control: pulse control can add, subtract counting mode, you can connect encoder for position detection.
Sequence control: the first after the procedure is completed, it is transferred to the next process, so that a PLC can use as a multi-step controller.
Data collection, storage and processing math functions:
Basic arithmetic: add, subtract, multiply and divide.
Extended arithmetic: square roots, trigonometric functions and floating point arithmetic.
Compare: greater than, less than and equal to.
Data processing: Select, organize, normalize, move, and first in first out.
Analog data processing: PID, integral and filtering.
2, the input / output interface conditioning functions having A / D, D / A conversion, complete analogue control and regulation through the I / O modules. Median and accuracy can be selected according to user requirements.
3. Has the temperature measurement interface, direct connection to a variety of resistance or galvanic.
4, communications, networking have adopted most modern PLC communication, network technology, RS232 or RS485 interface for remote I / O control, more than one PLC to one another networking, communications, external devices and one or more between the programmable controller signal processing unit, program memory and data exchange, such as the transfer of the program, data file transfer, monitoring and diagnostics.

The communication interface or communication processor hardware interface standard or proprietary communication protocols and data transfer process is completed. Such as the Siemens S7-200 Profibus fieldbus port, the communication speed may reach 12Mbps.
When the system is constituted by a computer with multiple PLC constitute centralized management, decentralized control of distributed control network to complete large-scale complex control. Commonly referred to as SCADA systems, on-site and remote terminal PLC terminal can also be used for live machine. 5, man-machine interface function provides the operator to monitor machine / process work necessary information. Allows the operator and PC systems interacting with their applications, in order to make decisions and adjustments.

Means to achieve human-machine interface functions: from the grassroots operator screen text display, the stand-alone CRT display and keyboard operation and decentralized communication processor, a dedicated processor, a personal computer, industrial computers, and centralized operation and monitoring system. Use 6 different complexity, programming, debugging and other hand-held, portable and desktop programmer, and operator workstation screen, programming, debugging, monitoring, testing and records, and printing out the program files.

Second, the main features of the programmable controller
1, high reliability PLC’s MTBF is generally 40000 ~ 50000h above, Siemens, ABB, Panasonic and other micro PLC of up to 100,000 h or more, and have a sound self-diagnostic function to determine the fault quickly and easy to maintain. 2, the modular combination of flexible programmable controller series products, the module structure commonly used to accomplish different tasks combinations. I / O from 8 to 8192 points, there are a variety of models, a variety of function modules can be flexibly combined, structure is also diverse. 3, powerful PLC application of microelectronics and micro-computer, simply type have logic, timing, counting sequence control. The basic types plus analog I / O, the basic arithmetic operations, communications and so on. In addition to the basic types of complex types of functions, but also has a scalable computing power, multi-level terminal mechanism, intelligent I / O, PID regulation, process monitoring, network communications, remote I / O, multiple processors and high-speed data processing capability . 4, convenient programming PLC control suitable for industrial ladder, function block diagram, instruction list and sequential function chart (SFC) programming, without much knowledge of computer programming. The new programming workstation with a comprehensive software toolkit, and on any PC-compatible programming. 5, to adapt to the technical conditions of the industrial environment PLC can work under the general high temperature, vibration, shock and dust and other harsh environment, can work reliably under strong electromagnetic interference environment. This is the market value of existence PLC products. 6, installation and maintenance is simple compared with the computer system, PLC installation does not require special rooms and rigorous screening. When you use as long as connectivity to various devices is correct, the system can work with operating and fault indication means on each module, easy to find fault, most of the modules can be hot plug, the module can be replaced, so that users can in the shortest isolated time fault, and exclude, to maximize compression downtime, rapid recovery of production. Then repair fault module, which is particularly suitable for large-scale production situations.
Some PLC housing is made of an alloy that can operate under poor working conditions, with the simple structure, with a heat sink above, at high temperatures, unlike the housing plastic deformation, as also anti-radio frequency (RF high frequency) electromagnetic interference, fire and so on. 7, fast with microprocessor applications, so that the speed of the PLC faster, make it more in line with the processing speed of complex control tasks, the difference between it and the microcomputer is not very obvious. 8, the low weight of the total price of the PLC, volume, power, and hardware prices have been reduced, although the proportion of total software price has increased, but the manufacturers to compete also a corresponding reduction in prices. In addition, the use of PLC can also greatly shorten the design, programming and commissioning period, bringing the total price is further reduced.
PLC systems and industrial computer bus and DCS system of mutual penetration, mutual learn, compete and development. Promoting the progress of industry.
PLC fieldbus products face development, innovation will once again meet the higher needs of the industrial and civilian control. Third, communications and networking PLC communication between the PLC, including PLC, the communication between PLC and host computer and PLC and other intelligent devices. PLC system can be a general purpose computer or via the communication processing unit, a communication adapter connected directly to form a network to achieve the exchange of information and may constitute centralized management, decentralized control of distributed control system to meet factory automation (FA) systems development needs of each PLC or remote I / O module according to the functions of each place at the production site decentralized control, then using a distributed network system connected to form a network of centralized management.
Siemens company SIMATICNET example, in the Totally Integrated Automation (TIA) system concept proposed in its core content which includes integration and integrated communication configuration and programming of integrated data management. Communication networks are important, the key components of this system to provide inter-network components and improve the industrial communication.

SIMATICNET contains three main levels:
International standard AS-I network sensors and actuators communication scan time 5ms, the transmission medium is twisted pair, unshielded line length of 300m, a maximum of 31 slaves.
PROFIBUS industrial field bus, the international standard for the workshop and field level, the maximum transmission rate of 12m / s, the transmission medium is shielded two-wire cable (up to 9.6km) or cable (up to 90km), can connect up to 127 from station.
International standard industrial Ethernet networking for regional and unit, the network size of up to 1024 stations 1.5km (electrical network) or 200km (optical network).

In this network system, it is particularly worth mentioning is the PROFIBUS fieldbus, PROFIBUS field bus is one of the most successful, have been widely used. It is not dependent on the manufacturer, open field bus, a wide range of automation devices can exchange information through the same interface. A large number of manufacturers to provide high-quality products PROFIBUS, the user can freely choose the most suitable product. PROFIBUS has become the national standard DIN19245 German and European standards prEN50170, and in the world has the largest number of users. Four, PLC and industrial control computer (IPC) to compare and distributed control systems (DCS) 1, the origin of their computer technology to meet the rapid development of large amounts of data processing equipment required. Hardware structure, high degree of standardization of the bus, compatibility, rich software resources, especially the support of real-time operating system, so the requirements of fast, real-time control and computation model complex workload industrial objects advantage.

Distributed system development from the industrial automation instrumentation control systems to industrial control computer as the center of the distribution system, so its processing in the analog loop adjustment has certain advantages, mainly used in the initial stage continuous process control, focusing loop control functions.
PLC is evolved by the relay logic system, mainly used in discrete manufacturing, process control, instead of the initial main relay control system, switch the order of emphasis on control.

With the development of microelectronics technology, large scale integrated circuit technology, computer technology and communication technology, etc., PLC happened leap in technology and functionality. On the basis of the initial logic operation, an increase of numerical computation, loop adjustment and other functions, and adds analog PID control function modules; computing speed, CPU capacity to catch up with industrial control computer; enhance communications capabilities developed more species and local bus network (LAN), and thus can also be configured as a distributed system. Especially personal computer can also be absorbed into the PLC system.

PLC ladder programming rules

Although the ladder and relay circuit is similar in structure, elements, symbols and logic control functions and other aspects of phase, but they have many differences, the ladder program has its own rules.

1) Each logical line is always to the left from the bus, and then the contact is connected, the final termination of the coil or the right bus (right bus can not draw). Note: The bus between the left and the coil must be contacts between the coil and the right bus but you can not have any contact.

2) The ladder can contact any series or in parallel, but only in parallel to the relay coil and not in series.

3) the use of contacts unlimited number of times.

4) In general, the same coil can appear only once in the ladder. If in the program, the same coil is used twice or more times, known as “dual-coil output.” For the “dual-coil output”, some PLC treats it as a syntax error, and definitely not; some will be in front of the PLC output as invalid, only the last valid output; and some PLC, containing a jump or step ladder instruction allowed dual coil output.

5) For non-programmable ladder must be equivalent transformation into programmable ladder.
6) when there are several series circuit in parallel, the circuit with many serial contacts should be on the top, as shown in Figure 5-2a. There are several in parallel circuit in series, the circuit should be parallel contacts on the left, as shown in Figure 5-2b. Such a program compiled concise, less statements.


In addition, the input of the relay contacts in the design of the ladder according to the best state of all the input device is normally open to design more appropriate, less error-prone. Is recommended as an input device open with a constant contact with the PLC input terminal, the signal can only be used if some normally closed input, press input device is normally open to design, and then the ladder corresponding input relay contacts point negated (normally open into a normally closed, normally open normally closed change).

Turning hydraulic control system

Turning hydraulic control system

OYES PLC applied using a small wave soldering machine design

I. Overview
Usually large wave soldering machines, production lines, but some customers such as laboratories, schools, small factories need a small lead-free wave soldering machine. Certain electronic equipment factory developed this product, using the Austrian letter OYES series PLC and touch screen. The device requires three temperature control, a total of three PID, the Austrian letter OYES series PLC to achieve 8-channel PID, to meet the equipment requirements. Matched on the touch screen with a high price.
II. Process Description
Dual-wave soldering machine is first necessary to solder temperature, preheat temperature, preheat temperature compensation temperature value added to a total of three temperature settings. When the condition is satisfied, the machine can be produced. The PCB board placed on the track, press the start button, the transmission motor running, start the pump, spray flux, PCB board flux coating is completed, the delay pump stops. When the PCB board to the left after the preheat zone, the transport motor is stopped, parked in the PCB board preheat zone, preheat countdown, after the time to transfer the motor starts, the right to run the PCB, tin pump motor start HAL, PCB board after preheat temperature compensation zone into the HAL area, after HAL zone, tin pump stops when the PCB to the right, the motor stops transmission, cold start the motor. Such a complete cycle is over.
III. Hardware Configuration
Input: detection switch, the operating switch.
Switch detection are: the right point switch, left switch point.
Switch operation are: start switch, emergency stop switch.
Output point: heating solid state relay three regions, the transmission motors, two motors tin pump, exhaust motors, pump motors, motor cooling, the power to protect themselves point.
Analog inputs: three zones of temperature detection.
Motor transport and tin pump motor speed is required, using a frequency converter, the speed required communication settings.
Hardware Configuration:
Model Number Function
FBS-32MA 1 master controller, AC 220V input, relay output
FBS-16EYT 1 8x24V, transistor output module
FBS-6TC 1 4-channel thermocouple input module
Panelvisa PV057TST 1 Touchscreen HMI
IV. Programming
Including programming PLC program and touch screen program includes four major functions: Device parameters, manual debugging, production screen, alarm queries.
The following are some of the features: each movement device can be done manually debug screen is very useful when you start debugging and maintenance of equipment.
Device parameters can be set from the touch screen, including temperature, time, PID coefficients.
Alarm query, you can quickly find the cause of the malfunction.
Production data display screen is used in the production, buttons are placed in this picture, and user-friendly in this screen monitors three temperature zones, process instructions and operating in these images.
Transmission speed motor and pump motor tin set is set to the touch screen PLC, and then passed by the PLC via PORT1 each motor drive. Function uses the PLC MODBUS master station, very convenient.

Delay ON / OFF circuit

Delay ON / OFF circuit

Flashing circuit

Flashing circuit

Three-phase asynchronous motor reversing control circuit

Three-phase asynchronous motor reversing control circuit

sample PLC circuit diagram

PLC circuit diagram

PLC control inverter circuit diagram

PLC control inverter circuit diagram

PLC conduction delay timer instruction (TON)

When the limit switch 1 is set, the indicator 2 ON 180ms (timer clocked). When the accumulated value of the timer 1 (.ACC) reaches 180, 2 lights off, the indicator 3 is turned on, and remains on until the TON instruction is disabled. If you disconnect the timer is timing the limit switch 1, then turn off light 2.

Ladder Diagram