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What are the five advantages that PLC's have over a relay logic solution?
Wiki User
∙ 12y ago
Reduces the Hardware wiring
The System can be made compact
Contact Failure rate is very less
Speed of opeartion is very high
Easy for Trouble shooting
Reduces the Maintainance cost
Easier way of Making logics
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∙ 12y ago
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Why would relays be used in place of PLCs?
na tum jano na hum
What is the function of RS 485 connection?
The symmetrical pin layout of the RJ11 sockets on the Unitronics PLCs allows an easy way of interconnecting the PLCs with both RS232 and RS485 communications. For RS232a crossover cable is used where pin 1 is connected with pin 6 at the other connector, pin 2 with pin 5, etc. This interconnects the transmit and receive signals of both PLCs, and also the handshaking signals DTR and DSR. If handshaking is not necessary, an ordinary 4 wire telephone cable could be used, provided that the pins are cross-connected as shown in the picture below. Otherwise a full 6 wire cable must be used. Two wire telephone cables will not function because in that case the ground signal levels on both sides will be floating. Unitronics RJ11 RS232 crossover cableRJ11 plug 1RJ11 plug 2Function16DTRDSR25Signal ground34TxDRxD43RxDTxD52Signal ground61DSRDTRRS485 is in its design a different interface from RS232. The RS485 interface allows the creation of multipoint networks. The normal way to implement this is with a two wire system with differential signal levels. These signals are commonly called A and B in RS485 systems. The A signals of all devices should be connected with each other and the same goes for the B signals. Therefore for RS485 communications no crossover cable is used. To prevent noise to interfere with the communications, often twisted pair cable is used. The diagram below shows a basic RS485 cable for use with the RJ11 socket on Unitronics PLCs. You can easily connect more devices by splitting the cable at one connector and adding another cable to it.Unitronics RJ11 RS485 cableRJ11 plug 1RJ11 plug 2Function11A (+)A (+)
What is the advantages of digital analog converter?
The advantage of Digital to analog convertersA digital to analog converter has drawbacks, but it has advantages of allowing signals to be controlled and processed to the best of speed and precision with the use of a micro processor. One can generate a perfect sine or triangular wave with a microprocessor and convert it into a real analog wave. One can process audio with a CPU or DSP and convert it back to audio. Once you have audio inside a processor the sky is the limit to what you can do with it and with custom firmware.Then the use is also obvious for precision digital instrumentation such as reading a load cell, thermo-couple or any sensor, converting it into an industry standard 4-20mA , 0-20mA or 0-5V or 0-10V output for PLCs or other instruments to interface with.Digital to analog converters may offer an economical and compact way to have precision signals. For a 24bit resolution, an 16.7million divisions of it's full scale deflection can be expected and perform thousands of conversions per second.The drawbacks are that they don't always produce perfectly smooth outputs, which may be subjected to some quantisation noise and the use of external filters may be required in some cases.Very nice technologies are available these days that allow SPI, I2C serial interfacing with high speed, high resolution and compact SMD chipsets at economical prices.The thing to note is that a digital to analog converter is rather useless without a micro processor to control and feed it with data and commonly they are build into DSP (digital signal processors) already.
Basics of programmable logic controllers?
PLCs were invented in the 60/70's for the automotive manufacturing industry. Since this time, they have developed into one of the most versatile tools used for industrial automation. A working knowledge of PLCs and other microprocessor based control systems are critical to technical personnel who are staying current with technology in industry. Programmable Logic Controllersor PLC are the hub of many manufacturing processes. These microprocessor based units are used in processes as simple as boxing machines or bagging equipment to controlling and tracking sophisticated manufacturing processes. They are in virtually all new manufacturing, processing and packing equipment in one form or another. Because of their popularity in industry, it becomes increasingly more important to learn skills related to these devices. Click on the buttons to learn more about industrial automation and this invaluable tool. The microprocessor or processor module is the brain of a PLC system. It consists of the microprocessor, memoryintegrated circuits, and circuits necessary to store and retrieve information from memory. It also includes communications ports to other peripherals, other PLC's or programming terminals. Today's processors vary widely in their capabilities to control real world devices. Some control as few as 6 inputs and outputs (I/O) and others 40,000 or more. One processor can control more than one process or manufacturing line. Processors are often linked together in order to provided continuity throughout the process. The number of inputs and outputs PLCs can control are limited by the overall capacity of the PLC system hardware and memory capabilities. The job of the processor is to monitor status or state of input devices, scan and solve the logic of a user program, and control on or off state of output devices.RAM or Random Access Memory is a volatile memory that would lose it's information if power were removed..This is why some processor units incorporate a battery back up. The type of RAM normally used is CMOS orComplementary Metal Oxide Semiconductor. CMOS RAM is used for storage of the user's program (ladder logic diagrams) and storage memory.ROM or Read Only Memory is a non-volatile type of memory. This means you don't need an external power source to keep information. In this type of memory, information can be read, but not changed. For this reason the manufacture sometimes calls this firmware. It is placed there for the internal use and operation of processor units EEPROM or Electrically Erasable Programmable Read Only Memory is usually an add-on memory module that is used to back up the main program in CMOS RAM of the processor. In many cases, the processor can be programmed to load the EEPOM's program to RAM if RAM is lost or corrupted.Input ModuleThere are many types of input modules to choose from. The type of input module used is dependent upon what real world input to the PLC is desired. Some examples of inputs are limit switches, electric eyes, and pushbuttons. DC inputs, such as thumbwheel switches, can be used to enter integer values to be manipulated by the PLC. DC input cards are used for this application. Since most industrial power systems are inherently noisy, electrical isolation is provided between the input and the processor. Electromagnetic interference (EMI) and Radio Frequency Interference (RFI) can cause severe problems in most solid state control systems. The component used most often to provide electrical isolation within I/O cards is called an optical isolator or optocoupler. The wiring of an input is not complex. The object is to get a voltage at a particular point on the card. Typically there are 8 to 32 input points on any one input module. Each point will be assigned a unique address by the processor. Analog input modules are special input cards that use analog to digital conversion (A to D) to sense variables such as temperature, speed, pressure, and position. The external device normally is connected to a controller (transducer) producing an electrical signal the analog input card can interpret. This signal is usually 4 to 20 Ma or a 0 to 10 volt signal.Output ModuleOutput modules can be for used for ac or dc devices such as solenoids, relays, contractors, pilot lamps, and LED readouts. Output cards usually have from 6 to 32 output points on a single module. The output device within the card provides theconnection from the user power supply to the load. Usually silicon controlled rectifiers (SCR), triac, or dry contact relays are use for this purpose. Individual outputs are rated most often at 2 to 3 amperes. Output cards, like input cards have electricalisolation between the load being connected and the PLC. Analog output cards are a special type of output modules that use digital to analog conversion (D to A). The analog output module can take a value stored in a 12 bit file and convert it to an analog signal. Normally this signal is 0 -10 volts dc or 4 to 20 Ma. This analog signal is often used in equipment such as motor operated valves and pneumatic position control devices PLC programs are made up of a combination of the above "gates" together with inputs, outputs, timers, counters, internal memory bits, analog inputs, analog outputs, mathematical calculations, comparators etc. We will now look closer at some of these and the operation of the PLC. INPUTS These are the physical connections from the real world to the PLC. They can be limit switches, push buttons, and sensors, anything that can "switch" a signal on or off. The voltage of these devices are usually, but not always, 24 Volt DC. Manufacturers make inputs that can accept a wide range of voltages both ac and dc. It should be remembered that an input will be ON, "status 1", when the voltage is present at the input connection and OFF, "status 0", when the voltage is no longer present at the input connection. OUTPUTS These are the connections from the PLC to the real world. They are used to switch solenoids, lamps, contactors etc on and off. Again they are usually 24 Volt DC, either relay or transistor, but can also be 115/220 Volt ACINTERNAL MEMORY BITS (RELAYS)These so called relays only exist in the PLCs memory, they are used to remember certain "states" or functions that have been performed. They react exactly like ordinary relays and can be on, off or latching. Manufacturers of PLCs also pre-program certain internal relays with special functions such as, always on; always off; on whilst the PLC is powering up; on for the first scan of the program; on if there is an error. For details of other pre-programmed relays you will have to check the manual for the PLC you are going to use. THE PLC Now that we have a basic understanding of the workings of a PLC and some of the numbering systems used we can look at the operation of PLCs.A PLC operates by continually scanning the program and acting upon the instructions, one at a time, to switch on or off the various outputs. In order to do this the PLC first "looks" at all the inputs and remembers their states ( i.e.. "1" or "0" / on or off) this information is then stored in memory. The PLC then scans the program instructions and decides if an output should be on or off BUT, and this is important to remember, the physical output is NOT turned on immediately. When the PLC has finished scanning the programmed instructions it will, finally, turn on the required outputs. This is called updating the process output image.At this point the PLC then checks its own operating system and if everything is ok it then goes and checks the states of the inputs and starts all over again.This is program scanning and the delay is called the program scan time.From the above statement it should be seen that there is a delay from when an input is turned on; the program scanned and then a physical output being turned on or off. As the delay is only mS it is not usually a problem unless you are using the PLC in a high speed process. However it should be remembered that in a PLC with many thousand I/O an input could turn on and then off before the PLC has finished scanning the programmed instructions.This could result in an output coming on for one or two scans when in fact it should be off. COMMUNICATIONSThere are several methods to communicate between a PLC and a programmer or even between two PLCs.Communications between a PLC and a programmer (PC or Hand held) are provided by the makers and you only have to plug in a cable from your PC to the programming port on the PLC. This communication can be RS232; RS485 or TTY.Communications between two PLCs can be carried out by dedicated links supplied/programmed by the makers (RS232 etc) or via outputs from one PLC to the inputs on another PLC.This direct link method of communication can be as simple as, if an output on the first PLC is on then the corresponding input on the second PLC will be on and then this input is used within the program on the second PLC.If a word of input/outputs (16 bits) are used then numerical data can be transferred from one PLC to the other (refer back to the section on numbering systems).There are many other methods of communication between PLCs and also from PLC to PC. Please refer to the manuals supplied with the PLC that you are using for full details on communications
What are the differences between plc solution and relay ladder logic solution?
All the symbols in the relay logic represent actual components and contacts present in the system, but the inputs\outputinstructionin PLC ladder logic represent only data values stored in the PLC memory.
List seven distinct advantages that plcs offer over the conventional relay control system?
ambut...
Aims of plcs?
PLCs (programmable logic controllers) automate electromechanical processes in factories (particularly automobile factories) and amusement rides.
Four tasks in addition to relay switching that PLCs are capable of performing?
I. Timing II. Counting III. Calculating IV. Comparing
What does plc in electrical terms mean?
Programmable Logic Controllers PLCs are kind of Digital Computers (small scale) which run on a predefined logic. These are commonly used in industries for production lines which could take multiple inputs & could handle multiple outputs. Further, 'Ladder Logic' is used to program these items.
PLC Training is a Great Way to Develop a New Career?
Due to many changes in the economy, many people have been forced to consider new career options. One possibility you should consider is PLC training. PLC stands for programmable logic controller. The PLC is a kind of computer first designed during the 1960’s and 70’s to replace incredibly complicated electrical systems in automobiles that at one time had to use a few hundred thousand different relays. Out of this effort to find a simpler way for automobile electronic systems to operate came the PLC. PLCs, unlike the kind of computers we are most used to, were designed with electrical technicians in mind as opposed to regular computer programmers. Due to this design influence many PLCs implement a computer language referred to as “ladder logic.” Ladder logic programming language is similar to the schematic design of circuits. The logic was that ladder logic would be easily understood by technicians and engineers without much new training. Many PLCs today still implement ladder logic. However, new programming languages are now used in a number of PLCs. These include BASIC programming as well as “state logic.” State logic is a kind of programming language specifically designed for use in PLCs that implements state transition diagrams that use a series of “tasks,” “states,” and “statements” to tell electronic systems what to do. State logic is considered one of the most advanced programming languages that exist. Due to the use of these complex programming languages and the use of multiple inputs and outputs, PLCs are implemented as a way to control the very intricate timed electrical processes of the many different components in a machine. Uses of PLCs across different industries are wide and varied. They are of course used in the assembly of automobiles for which they were designed. A PLC has probably told the traffic light you have stopped at to change from red to green. You may have even encountered one that told the roller coaster car you were riding in to slow down. Due to the many uses of PLCs and the specified knowledge it takes to work on one, PLC training is a great option for developing a brand new career.
Where can one find information on programmable logic controllers?
One can easily find information on programmable logic controllers by searching on the internet, however, the some quick info can be found right here.Programmable logic controllers (PLCs), are digital computers that are made to perform logical computations to ensure smooth operations of mechanical devices.
What would you a rack mounting PLC for?
A rack mounted PLC refers to specific types of programmable logic controllers. Rack mounted PLCs can be used in any machine or application that has a control panel.
What applications would you use a rack mounting plc?
A rack mounted PLC refers to specific types of programmable logic controllers. Rack mounted PLCs can be used in any machine or application that has a control panel.
What applications would use a rack mounted plc?
A rack mounted PLC refers to specific types of programmable logic controllers. Rack mounted PLCs can be used in any machine or application that has a control panel.
What are the advantages of Program Logic Control?
A Programable Logic Controller is simply a small computer used to control some system such as garden watering systems. They are everywhere. The computer in microwave ovens, television sets, fridges etc are all PLCs. Generally the term is used to describe a computer that doesn't normally interact with a human but just controls something like those things listed above. There are many many more PLCs around the place than computers that humans comminicate with.
Where are all the tokens on wimpy boardwalk?
plcs
