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What is the definition of "PLC"?

What is PLC ?

Programmable Logic Controller (PLC) focuses on automating different electro-mechanical processes taking place in various industries. With a well-programmed microprocessor, It has specially designed and implemented controllers which are immune to extremely high and low temperatures, humidity, dust, etc.
Just like any usual program, the coding is programmed on a computer. From here it is transferred to the PLC using a cable. After downloading the programs, these are loaded and stored in the PLC. In order to make sure the programs do not vanish at the time of power cut or switch off, it uses non-volatile memory storage.
It is programmed using a programming language called Ladder Logic. It is already known that it is an industrial computer. In order to program it, a programming language had to be designed in such a way, that the electricians and electrical engineer in an industry could easily understand and feel comfortable enough to code in it.
A Programmable Logic Controller consists of various input and output terminals. Using the input terminals, it interprets the logical states from switches and sensors. There are two logical states also known as high(or 1) and low(or 0). The output from the output terminals is used as a signal for various devices, providing them on/off controls. The electrical engineers understand the ladder logic diagrams and so it was the inspiration behind the programming language used to program its.
The most commons areas of use are in a washing machine, elevators and also traffic signals.

Definition:-

Programmable Logic Controller, more popularly known as PLC is a digital computer without a mouse or a keyboard or a monitor.
Or
A Programmable Logic Controller, or PLC, is a ruggedized computer used for industrial automation. These controllers can automate a specific process, machine function, or even an entire production line

Understanding PLC:-

Programmable Logic Controller is a small computer which automatically controls various processes and components in an industrial system. For the sake of comparison, let’s take a process that is manual as an example thinks of PLC as a brain controlling a finger on a trigger of an applicator. The brain sends a signal to the finger directing it to pull the finger when something is dispensed and when the brain wants to stop it sends another signal. Like most of the brains, it can multitask and it’s lightning fast Just like that, it can control much input and output signal like direct a paint line to change colors so all the widgets being painted go from one color to other.

Working:-

It communicates to the CPU status of the field devices as well as acts as a tool to control. The programming device is actually a computer loaded with programming software which will allow a user to create and make changes in the PLC software. The memory provides storage media for the PLC program as well as for other data.

How does a PLC work?

The PLC receives information from connected sensors or input devices, processes the data, and triggers outputs based on pre-programmed parameters.
Depending on the inputs and outputs, a PLC can monitor and record run-time data such as machine productivity or operating temperature, automatically start and stop processes, generate alarms if a machine malfunctions, and more. Programmable Logic Controllers are a flexible and robust control solution, adaptable to almost any application.

There are a few key features that set PLCs apart from industrial PCs, microcontrollers, and other industrial control solutions:
• I/O – The PLC’s CPU stores and processes program data, but input and output modules connect the PLC to the rest of the machine; these I/O modules are what provide information to the CPU and trigger specific results. I/O can be either analog or digital; input devices might include sensors, switches, and meters, while outputs might include relays, lights, valves, and drives. Users can mix and match a PLC’s I/O in order to get the right configuration for their application.

• Communications – In addition to input and output devices, a PLC might also need to connect with other kinds of systems; for example, users might want to export application data recorded by the PLC to a supervisory control and data acquisition (SCADA) system, which monitors multiple connected devices. PLCs offer a range of ports and communication protocols to ensure that the PLC can communicate with these other systems.

• HMI – In order to interact with the PLC in real time, users need an HMI, or Human Machine Interface. These operator interfaces can be simple displays, with a text-readout and keypad, or large touchscreen panels more similar to consumer electronics, but either way, they enable users to review and input information to the PLC in real time.

Advantages:-

Easily programmable
Well shielded to outlast harsh situations
Input and output interface available where thousands of input and output can be controlled through a single PLC
Highly reliable
Easy to maintain

Required skills:-

PLC professionals are experts in concepts, electrical designs. They are also knowledgeable about fabrication and circuit board layout.
Also, they entail meeting with global standards in providing solutions to companies. This ensures making tasks easier by correct relaying of messages and the required team coordination.

Why should we use PLC?

The most common use of it is in washing machines, controlling traffic signals, elevators, etc. Also, we cannot neglect the use of PLCs in industries to monitor and control building systems and production processes.

Why do we need PLC and What can you do with PLC?

It is needed to automate machines in the industry so that human efforts can be reduced thus minimizing the human errors that might occur in the process. Consider a situation where a human handling a system missed to switched the motor on. Imagine the delay it might cause in the operation to begin. The simple solution to solve this is by automating the motor using PLC. So the basic and most important use of it is in the automation of machines.

Who is the right Audience for learning PLC Technologies?

The one-step solution to learning is various available courses online. It is also the best economical and easy way, however, the challenge in learning PLC online is you might learn the names and functioning of software and hardware parts of PLC, the ladder logic diagrams creation or configuring the various modules but just the theoretical knowledge is not enough. In order to be successful, one needs to have a hands-on experience. The one with an interest and background in logic diagrams and controls can start with the PLC programming tool. An elaborate program for an application is not at all an easy task to create. You need a lot of practice and hands-on to do so. In order to excel in this, one can begin from a small machine building company to gain insight and full-fledged skills and experience of the job.

Scope and How this Technology will help you in Career Growth?

As we all know that every industry is moving on to automating its processes and tools, the demand for the programmer is rapidly increasing. Industrial sectors in India like food and beverages, manufacturing industry, oil and gas industry, transport, process industries, etc are also stepping into Industrial Automation. As a matter of fact, technologies like AI, IOT are merging with OT or operational technologies which includes PLC, SCADA, DCS. Renowned companies like SIEMENS, Mitsubishi, Fanuc, Honeywell, etc provide their product and services all over the world. One can find many opportunities in IT and OT sectors as developer, testers, an analyst for it and so we can say that there awaits a bright successful future in automation for the same.

Conclusion

These applications are specifically highly customized systems. It is cheaper when compared to the price of a specific custom-built controller. Generally, it requires less maintenance and is more robust, henceforth making the things they control work better, despite the environment.

V Curve of a Synchronous Motor:-

V curve is a plot of the stator current versus field current for different constant loads. The Graph plotted between the armature current Ia and field current If at no load the curve is obtained known as V Curve. Since the shape of these curves is similar to the letter “V”, thus they are called V curve of synchronous motor.

The power factor of the synchronous motor can be controlled by varying the field current If. As we know that the armature current Ia changes with the change in the field current If. Let us assume that the motor is running at NO load. If the field current is increased from this small value, the armature current Ia decreases until the armature current becomes minimum. At this minimum point, the motor is operating at unity power factor. The motor operates at lagging power factor until it reaches up to this point of operation.

If now, the field current is increased further, the armature current increases and the motor start operating as a leading power factor. The graph drawn between armature current and field current is known as V curve. If this procedure is repeated for various increased loads, a family of curves is obtained.

The V curves of a synchronous motor are shown below.

The point at which the unity power factor occurs is at the point where the armature current is minimum. The curve connecting the lowest points of all the V curves for various power levels is called the Unity Power Factor Compounding Curve. The compounding curves for 0.8 power factor lagging and 0.8 power factor leading are shown in the figure above by a red dotted line.

The loci of constant power factor points on the V curves are called Compounding Curves. It shows the manner in which the field current should be varied in order to maintain constant power factor under changing load. Points on the right and left of the unity power factor corresponds to the over excitation and leading current and under excitation and lagging current respectively.

The V curves are useful in adjusting the field current. Increasing the field current If beyond the level for minimum armature current results in leading power factor. Similarly decreasing the field current below the minimum armature current result results in lagging power factor. It is seen that the field current for unity power factor at full load is more than the field current for unity power factor at no load.

The figure below shows the graph between power factor and field current at the different loads.

It is clear from the above figure that, if the synchronous motor at full load is operating at unity power factor, then removal of the shaft load causes the motor to operate at a leading power factor.

Synchronous Motors: Applications, Starting Methods & Working Principle:-

Electrical motors are an Electro-mechanical device that converts electrical energy to mechanical energy. Based on the type of input we have classified it into single phase and 3 phase motors.

The most common type of 3 phase motors are synchronous motors and induction motors. When three-phase electric conductors are placed in certain geometrical positions (i.e. in a certain angle from one another) – an electrical field is generated. The rotating magnetic field rotates at a certain speed known as the synchronous speed.

If an electromagnet is present in this rotating magnetic field, the electromagnet is magnetically locked with this rotating magnetic field and rotates with the same speed of rotating field.

This is where the term synchronous motor comes from, as the speed of the rotor of the motor is the same as the rotating magnetic field.

It is a fixed speed motor because it has only one speed, which is synchronous speed. This speed is synchronized with the supply frequency. The synchronous speed is given by:

What is Capacitor? What is Capacitance???

What is Capacitor? What is Capacitance?

There are three fundamental electronic components that form the foundation of a circuit – resistors, inductors, and capacitors. A capacitor in an electrical circuit behaves as a charge storage device. It holds the electric charge when we apply a voltage across it, and it gives up the stored charge to the circuit as when required. The most basic construction of a capacitor consists of two parallel conductors (usually metallic plates) separated by a dielectric material.

When we connect a voltage source across the capacitor, the conductor (capacitor plate) attached to the positive terminal of the source becomes positively charged, and the conductor (capacitor plate) connected to the negative terminal of the source becomes negatively charged. Because of the presence of dielectric in between the conductors, ideally, no charge can migrate from one plate to other.
parallel plate capacitor
So, there will be a difference in charging level between these two conductors (plates). Therefore an electric potential difference appears across the plates. The charge accumulation in the capacitor plates is not instantaneous rather it is gradually changing. The voltage appears across the capacitor exponentially rises until it becomes equal to that of the connected voltage source.

Capacitance:-

Now we understand that the charge accumulation in the conductors (plates) causes the voltage or potential difference across the capacitor. The quantity of charge accumulated in the capacitor for developing a particular voltage across the capacitor is referred to as the charge holding capacity of the capacitor. We measure this charge accumulation capability of a capacitor in a unit called capacitance. The capacitance is the charge gets stored in a capacitor for developing 1 volt potential difference across it. Hence, there is a direct relationship between the charge and voltage of a capacitor. The charge accumulated in the capacitor is directly proportional to the voltage developed across the capacitor.

Where Q is the charge and V is the voltage.

Here C is the constant of proportionality, and this is capacitance,

The capacitance depends upon three physical factors, and these are the active area of the capacitor conductor (plates), the distance between the conductors (plates) and permittivity of the dielectric medium.

Here, ε is permittivity of the dielectric medium, A is the active area of the plate and d is the perpendicular distance between the plates .

Capacitance of plates capacitor:-

The capacitance (C) of the plates capacitor is equal to the permittivity (ε) times the plate area (A) divided by the gap or distance between the plates (d):

$C=\varepsilon \times \frac{A}{d}$

C is the capacitance of the capacitor, in farad (F).

ε is the permittivity of the capacitor's dialectic material, in farad per meter (F/m).

A is the area of the capacitor's plate in square meters (m²).

d is the distance between the capacitor's plates, in meters (m).

DC Motor or Direct Current Motor:-

What is DC Motor ?

The electric motor operated by dc is called dc motor. This is a device that converts DC electrical energy into a mechanical energy

Principle of DC Motor

When a current carrying conductor is placed in a magnetic field, it experiences a torque and has a tendency to move. In other words, when a magnetic field and an electric field interact, a mechanical force is produced. The DC motor or direct current motor works on that principal. This is known as motoring action.

The direction of rotation of a this motor is given by Fleming’s left hand rule, which states that if the index finger, middle finger, and thumb of your left hand are extended mutually perpendicular to each other and if the index finger represents the direction of magnetic field, middle finger indicates the direction of current, then the thumb represents the direction in which force is experienced by the shaft of the DC motor.

Structurally and construction wise a direct current motor is exactly similar to a DC generator, but electrically it is just the opposite. Here we unlike a generator we supply electrical energy to the input port and derive mechanical energy from the output port.Here in a DC motor, the supply voltage E and current I is given to the electrical port or the input port and we derive the mechanical output i.e. torque T and speed ω from the mechanical port or output port.

the parameter K relates the input and output port variables of the direct current motor.

So from the picture above, we can well understand that motor is just the opposite phenomena of a DC generator, and we can derive both motoring and generating operation from the same machine by simply reversing the ports.

Advantages of DC Motor:

Provide excellent speed control for acceleration and deceleration
Easy to understand design

Simple, cheap drive design

Types of DC Motors

Direct motors are named according to the connection o the field winding with the armature. There are 3 types:

Detailed Description of a DC Motor:-

To understand the DC motor in details lets consider the diagram below,

dc motor
The circle in the center represents the direct current motor. On the circle, we draw the brushes. On the brushes, we connect the external terminals, through which we give the supply voltage. On the mechanical terminal, we have a shaft coming out from the center of the armature, and the shaft couples to the mechanical load. On the supply terminals, we represent the armature resistance Ra in series.

Now, let the input voltage E, is applied across the brushes. Electric current which flows through the rotor armature via brushes, in presence of the magnetic field, produces a torque Tg. Due to this torque Tg the dc motor armature rotates. As the armature conductors are carrying currents and the armature rotates inside the stator magnetic field, it also produces an emf Eb in the manner very similar to that of a generator. The generated Emf Eb is directed opposite to the supplied voltage and is known as the back Emf, as it counters the forward voltage.
The back emf like in case of a generator is represented by

Where, P = no of poles
φ = flux per pole
Z= No. of conductors
A = No. of parallel paths
and N is the speed of the DC Motor.
So, from the above equation, we can see Eb is proportional to speed ‘N.’ That is whenever a direct current motor rotates; it results in the generation of back Emf. Now let’s represent the rotor speed by ω in rad/sec. So Eb is proportional to ω.
So, when the application of load reduces the speed of the motor, Eb decreases. Thus the voltage difference between supply voltage and back emf increases that means E − Eb increases. Due to this increased voltage difference, the armature current will increase and therefore torque and hence speed increases. Thus a DC Motor is capable of maintaining the same speed under variable load.

Now armature current Ia is represented by

Now at starting,speed ω = 0 so at starting Eb = 0.

Now since the armature winding electrical resistance Ra is small, this motor has a very high starting current in the absence of back Emf. As a result we need to use a starter for starting a DC Motor.
Now as the motor continues to rotate, the back emf starts being generated and gradually the current decreases as the motor picks up speed.

Types of Induction ( AC ) Motors:-

Types of Induction Motors

The types of induction motors can be classified depending on whether they are a single phase or three phase induction motor.

Single Phase Induction Motor

The types of single phase induction motors include:

Split Phase Induction Motor
Capacitor Start Induction Motor
Capacitor Start and Capacitor Run Induction Motor
Shaded Pole Induction Motor

Three Phase Induction Motor
The types of three phase induction motors include:
Squirrel Cage Induction Motor
Slip Ring Induction Motor
We have already mentioned above that the single-phase induction motor is not a self-starting motor, and that the three-phase induction motor is self-starting.When the motor starts running automatically without any external force applied to the machine, then the motor is referred to as ‘self-starting’. For example, we see that when we put on the switch the fan starts to rotate automatically, so it is a self-starting machine. Point to be noted that fan used in home appliances is a single phase induction motor which is inherently not self-starting. How? Does a question arise as to how it works? We will discuss it now.

So what is a self-starting motor?

Why is Three Phase Induction Motor Self Starting?

In a three phase system, there are three single phase lines with a 120° phase difference. So the rotating magnetic field has the same phase difference which will make the rotor to move. If we consider three phases a, b, and c when phase a gets magnetized, the rotor will move towards the phase a winding a, in the next moment phase b will get magnetized and it will attract the rotor and then phase c. So the rotor will continue to rotate.

Why Single Phase Induction Motor is not Self Starting?

It has only one phase still it makes the rotor to rotate, so it is quite interesting. Before that, we need to know why a single phase induction motor is not a self-starting motor and how we overcome the problem. We know that the AC supply is a sinusoidal wave and it produces a pulsating magnetic field in the uniformly distributed stator winding.

Since we can assume the pulsating magnetic field as two oppositely rotating magnetic fields, there will be no resultant torque produced at the starting, and hence the motor does not run. After giving the supply, if the rotor is made to rotate in either direction by an external force, then the motor will start to run. We can solve this problem by making the stator winding into two winding – one is the main winding, and another is auxiliary winding.

We connect one capacitor in series with the auxiliary winding. The capacitor will make a phase difference when current flows through both coils. When there is a phase difference, the rotor will generate a starting torque, and it will start to rotate. Practically we can see that the fan does not rotate when the capacitor gets disconnected from the motor, but if we rotate with the hand, it will start rotating. That is why we use a capacitor in the single-phase induction motor.

Due to the various advantages of an induction motor, there is a wide range of applications of an induction motor. One of their biggest advantages is their high efficiency – which can go as high as 97%. The main disadvantage of an induction motor is that the speed of the motor varies with the applied load. The direction of rotation of induction motor can easily be changed by changing the phase sequence of three-phase supply, i.e., if RYB is in a forward direction, the RBY will make the motor to rotate in reverse direction. This is in the case of three phase motor, but in a single phase motor, the direction can be reversed by reversing the capacitor terminals in the winding.