Programmable Logic Controller (PLC) |
PLC TRAINING : Introduction :
The Programmable Logic Controller was developed in 1968 by the Engineers of General
Motors for replacing the complex relay logic control. |
Working Principle :
PLC is a microprocessor based solid state device.PLC works on the principle of Logic Gates. The input device may be pushbutton or limit s/w, relay contacts or timers etc. which send signal to the control elements and the o/p device may be motors, solenoid, relay coil, etc.
Inputs is given in the input image memory, CPU process it according to logic written in the memory and update the o/p in o/p image memory. PLCs control the components in the DCS and SCADA systems but they are primary components in smaller control configurations.
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S No |
TOPIC |
RLC |
PLC |
1. |
Programme |
Made by Hardware |
Made by Software |
2. |
CPU Element
(Contactors,Timers and Counters) |
Physically used in RLC |
Replaced by Software |
3. |
Ladder Diagram Elements-
- Input
- Output
- Rung
|
Digital
Digital
Known as step |
Digital, high speed & Analog
Digital, high speed & Analog
Known as rung |
4. |
Digital Programme |
Is known as electrical control ckt. Diagram & made by steps. |
Is known as Ladder diagram & made by Rungs. |
5. |
Programme Scan |
RLC Scane the programme parallel |
PLC Scan the Programme sequencely in steps from top rung to bottom rung & scanning will be continue If PLC is in run mode & will be stop if PLC is in stop mode. One scan time is generally 10 to 20 ms. |
6. |
Use |
Digital Application |
Digital High Speed & Analog Application. |
7. |
Maintenance
- a – MTTR
b – MTBF
- Maintenance Time
- Running Cost
- Capital Cost
|
More
Less
More
More
Medians |
Less (if software is available)
More
Less
Less
More for small applications Less for big panels |
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The new control system developed with following:
1) Simple programming.
2) Program change (editing) without system intervation (no internal rewiring) in a software.
SCADA
Supervisory Control And Data Acquisition refers to a centralized system and this system is composed of various subsystems like Remote Telemetry Units, Human Machine Interface, Programmable Logic Controller or PLC and Communications.
SCADA system is composed of 3 main elements.
PLC Training in Delhi NCR (Programming Languages & Logic Gates) :
The switching unit at input and output operate according to certain logic. The inputs can have only two values viz. 0 or 1, the basic elements may be electrical s/w, and transistors, relays, which have two states viz. 0 or 1. The languages for logic design are through the use of Boolean algebra. The basic logic function are ‘AND’, ‘OR’ and ‘NOT’.
PLC Programming Languages:
1) LADDER
2) FBD
3) STL
1) LADDER:
It is a language which represents the graphical view of electrical circuit. It is the combination of more than one ‘RUNGS’.
RUNGS:
When a coil is connected with series or parallel combination of digital inputs (NO/NC Contacts) elements is known as one ‘RUNG’. Combination of rungs known as Ladder diagram.
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Programming Logic Control (PLC training in delhi NCR) system consist of
- • Inputs, Outputs
- • CPU
- • Power Supply
- • Memory for program & data storage
- • Power Supply
- • Operator Interface
- • Programming Device
KITC (Krishna Automation - Plc training in delhi ncr) is established to prepare young students/ aspirants for modern industrial need by their experience and knowledge. So that they can be productive from day one.
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SCADA (PLC Training in Delhi, Delhi NCR)
Supervisory Control And Data Acquisition or SCADA is a system used to monitor and control a plant form a central location. This is not frequently used because of the control override possibility. SCADA itself changes the control set points quite frequently. It is widely used in water treatment plants and lately it has been used chlorination and pumping stations.
- SCADA system is composed of 3 main elements.
- RTU (Remote Telemetry Unit)
- HMI (Human Machine Interface)
- Communications
RTU (Remote Telemetry Unit):
The function of an RTU is to collect the onsite information and this information is sent to a central location with the help of the communication element. If system wants to send information back to the RTU then this communication element take it back too.
HMI (Human Machine Interface): The function of the HMI element is to display the information received in an easy to understand graphical way and also archive all the data received. It is usually a high end computer system capable of displaying high quality graphics and running advanced and complex software.
Communication happens through various means. It will happen via data cable within a plant or through a fiber optic. The communication may happen via radio between different regions. |
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PLC Operations:
- Input Relays -
These are connected to the outside world. They physically exist and receive signals from switches, sensors, etc. Typically they are not relays but rather they are transistors.
-
Internal Utility Relays -
These do not receive signals from the outside world nor do they physically exist. They are simulated relays and are what enables a PLC to eliminate external relays.There are also some special relays that are dedicated to performing only one task.
-
Counters -
These do not physically exist. They are simulated counters and they can be programmed to count pulses. Typically these counters can count up, down or both up and down. Since they are simulated they are limited in their counting speed.
Some manufacturers also include high speed counters that are hardware based.
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Timers -
These also do not physically exist. They come in many varieties and increments.
The most common type is an on-delay type. Others include off-delay and both retentive and non-retentive types. Increments vary from 1ms through 1s.
-
Output Relays -
These are connected to the outside world. They physically exist and send on/off signals to solenoids, lights, etc.They can be transistors, relays, or triacs depending upon the model chosen.
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Data Storage -
Typically there are registers assigned to simply store data. Usually used as temporary storage for math or data manipulation. They can also typically be used to store data when power is removed from the PLC
Communication:
Serial communication is when data is transmitted one bit at a time. A data word has to be separated into its constituent bits for transmission and then reassembled into the word when received. Serial communication is used for transmitting data over long distances. Might be used for the connection between a computer and a PLC.
Serial standards
RS-232 communications is the most popular method of plc to external device communications. RS 232 is a communication interface included under SCADA applications. Other standards such as RS422 and RS423 are similar to RS232 although they permit higher transmission rates and longer cable distances.
There are 2 types of RS-232 devices:
1) DTE – Data Terminal Equipment and a common example is a computer.
2) DCE – Data Communications Equipment and a common example is a modem.
PROFIBUS: PROFIBUS or Process Field Bus was introduced in 1989 and it is sometimes confused with PROFINET. It links plant automation modules with the process control. PROFIBUS uses a multi drop single cable to connect the devices. This method is cost effective especially for larger sites when compared to old methods. Its installation cost is low and it is easy to find faults as well because it is a single cable.
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