The basic component of any PLC is shown in figure....
It consist
1)input interface
2)processor
3)output interface
4)power supply
5)communication interfaces
6)programming devices
1)input interface:
Input interface is also called as input module. Input module connect the different kind of field devices to the plc..Types of input module depends on the kind of input device..
To interface the analog device to PLC we have to use analog input module. Analog input module has in built ADC. To interface digital device we have to use discrete module. that accept the signal and send to PLC for further internal operations.
types of input module:
1)discrete input module
2)analog input module
3)network input module
1) discrete input module:
A “discrete” data point is one with only two states on and off. Process switches, pushbutton switches, limit switches, and proximity switches are all examples of discrete sensing devices. In order for a PLC to be aware of a discrete sensor’s state, it must receive a signal from the sensor through a discrete input channel. Inside the discrete input module is (typically) a light-emitting diode (LED) which will be energized when the corresponding sensing device turns on. Light from this LED shines on a photo-sensitive device such as a phototransistor inside the module, which in turn activates a bit (a single element of digital data) inside the PLC’s memory. This opto-coupled arrangement makes each input channel of a PLC rather rugged, capable of isolating the sensitive computer circuitry of the PLC from transient voltage “spikes” and other electrical phenomena capable of causing damage..
one important concept of interfacing input devices to plc is way in which the devices are connected.
i.e. either sinking or sourcing..while buying a input devices and input module we have to decide whether the module is sourcing type or sinking type..
In the sinking type input module the input module will sink the current from the input device...
while in sourcing type input module the current will be sources by the module to the input device..means the current first come to the plc module from the power supply and then go to the device and then ground....
we can see from belows figure...
Here if we have sourcing type input module then the device which connect must be sinking type and vice versa..we can see from belows figure...
typical images of input module will look like as below..........
All type of input device we will see later.....
2)analog input interface:
The heart of all PLC i.e CPU is basically digital in nature...That means CPU understand only binary numbers..While in real environment there may condition that we have to interface the analog devices to the PLC... so we need such device that convert the analog input to equivalent digital form..this purpose is served by analog input module... the analog input module has built in ADC(i.e Analog to Digital Converter)... when input module receive analog signal from field device then this signal will convert in to digital form through ADC ....so PLC will understand this digital data which is analog outside plc....
typically the analog module are available in different range of current and voltage...
that are basically...
the optical isolation in analog input module in plc is as below.....
typical analog input module look like below.......
3)network input module:
network input module we will see later....when we discussed about DCS..........
2) processor:
the block diagram of the plc CPU is as below......
CPU is the brain of PLC system...CPU will get condition of all input devices..calculate the program..In that program CPU use condition of all input devices..execute the program and update the output devices status...this is how PLC scan cycle works...the working of PLC cpu parts are same as any controller or processor cpu......
all component of PLC cpu we will discussed when we learn about PLC software.......
3)output interface:
PLC output unit may be of three types
1)relay type
2)transistor type
3)triac type
before connecting an output device to the PLC we have to check the specification of output device.This specification should match with PLC output module...that is check the maximum current carried by output device should same in output module....
1) relay type output module:
Triac is bi-directional diode...triac type output module is use to switch only AC supply..
4)power supply:
The power supply provides power to memory system, processor and I/O Modules.
6)programming devices:
there are three way in which we program a PLC
1) some PLC are there the have on body key to load a program in to the PLC memory....like below.....this is siemens PLC....and of relay type module....
1)input interface:
Input interface is also called as input module. Input module connect the different kind of field devices to the plc..Types of input module depends on the kind of input device..
To interface the analog device to PLC we have to use analog input module. Analog input module has in built ADC. To interface digital device we have to use discrete module. that accept the signal and send to PLC for further internal operations.
types of input module:
1)discrete input module
2)analog input module
3)network input module
1) discrete input module:
A “discrete” data point is one with only two states on and off. Process switches, pushbutton switches, limit switches, and proximity switches are all examples of discrete sensing devices. In order for a PLC to be aware of a discrete sensor’s state, it must receive a signal from the sensor through a discrete input channel. Inside the discrete input module is (typically) a light-emitting diode (LED) which will be energized when the corresponding sensing device turns on. Light from this LED shines on a photo-sensitive device such as a phototransistor inside the module, which in turn activates a bit (a single element of digital data) inside the PLC’s memory. This opto-coupled arrangement makes each input channel of a PLC rather rugged, capable of isolating the sensitive computer circuitry of the PLC from transient voltage “spikes” and other electrical phenomena capable of causing damage..
one important concept of interfacing input devices to plc is way in which the devices are connected.
i.e. either sinking or sourcing..while buying a input devices and input module we have to decide whether the module is sourcing type or sinking type..
In the sinking type input module the input module will sink the current from the input device...
while in sourcing type input module the current will be sources by the module to the input device..means the current first come to the plc module from the power supply and then go to the device and then ground....
we can see from belows figure...
Here if we have sourcing type input module then the device which connect must be sinking type and vice versa..we can see from belows figure...
typical images of input module will look like as below..........
All type of input device we will see later.....
2)analog input interface:
The heart of all PLC i.e CPU is basically digital in nature...That means CPU understand only binary numbers..While in real environment there may condition that we have to interface the analog devices to the PLC... so we need such device that convert the analog input to equivalent digital form..this purpose is served by analog input module... the analog input module has built in ADC(i.e Analog to Digital Converter)... when input module receive analog signal from field device then this signal will convert in to digital form through ADC ....so PLC will understand this digital data which is analog outside plc....
typically the analog module are available in different range of current and voltage...
that are basically...
- voltage(0-10volt or 0-5 volt)
- current(0-20mA or 4-20mA)
- thermocouple type( millivolt range)
- RTD type(millivolt range)
- strain gauges(millivolts range)
the optical isolation in analog input module in plc is as below.....
typical analog input module look like below.......
3)network input module:
network input module we will see later....when we discussed about DCS..........
2) processor:
the block diagram of the plc CPU is as below......
CPU is the brain of PLC system...CPU will get condition of all input devices..calculate the program..In that program CPU use condition of all input devices..execute the program and update the output devices status...this is how PLC scan cycle works...the working of PLC cpu parts are same as any controller or processor cpu......
all component of PLC cpu we will discussed when we learn about PLC software.......
3)output interface:
PLC output unit may be of three types
1)relay type
2)transistor type
3)triac type
before connecting an output device to the PLC we have to check the specification of output device.This specification should match with PLC output module...that is check the maximum current carried by output device should same in output module....
1) relay type output module:
as shown in figure...there is simple circuit of relay output module...here the relay is provide inside of output terminal so when it get signal from cpu it will make contact and complete the circuit..and output device will operate...
this type of relay output module is use for both AC and DC device...
2)transistor type output module:this type of relay output module is use for both AC and DC device...
The transistor type output module us to switch only DC supply..when the LED get signal from cpu it will give light to the base of photo transistor..and this is how it switch the DC device....we can see that from the figure...
3) triac type output module:
4)power supply:
The power supply provides power to memory system, processor and I/O Modules.
- It converts the higher level AC line Voltage to various operational DC values.
- for electronic circuitry.
- It filters and regulates the DC voltages to ensure proper computer operations.
for basic about plc you can refer the video........
5)communication interfaces:
the term communication interface is generally used in DCS(i.e distributed control system)..where the PLC are connected in network...
for that u have to refer below link....
6)programming devices:
there are three way in which we program a PLC
1) some PLC are there the have on body key to load a program in to the PLC memory....like below.....this is siemens PLC....and of relay type module....
2) there are PLC with hand-held programming devices...we can make the program in hand-held programming device and load that in to PLC memory.....this is allen bradley PLC programmer....
3) u can make the program in to your computer and connect PLC to the computer...this way u can load a program in to the PLC memory......here the siemens PLC is connect to the computer....
win cc is software that use to load a program in to the siemens PLC
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