Automatic Control of Hydraulic System Using Plc Essay Example

parameters. We are designing a ladder diagram to control all the parameters automatically. In this paper, we are describing about the hydraulic drive system in which PLC is used to control its working. An introduction of PLC is provided and also the ladder diagram overview. We will be discussing about the advantages of PLC and also the power saving estimation in the industries by using PLC. The machine which we have taken under consideration for implementation is BOW CORRECTION MACHINE. Also, the chiller unit is described as it plays a major role for the power saving purpose.

HYDRAULIC DRIVE SYSTEM 

A hydraulic drive system is a drive or transmission system that uses pressurized hydraulic fluid to drive hydraulic machinery. The term hydrostatic refers to the transfer of energy from flow and pressure, not from the kinetic energy of the flow. Principle of a hydraulic drive Pascal's law is the basis of hydraulic drive systems. As the pressure in the system is the same, the force that the fluid gives to the surroundings is therefore equal to pressure  rea. In such a way, a small piston feels a small force and a large piston feels a large force.

For an understanding of how a hydraulic system works, we must know the basic principles, or laws, of hydraulics, that is, of confined liquids under pressure. This will be made easier, however, if we first examine the somewhat simpler laws governing the behavior of liquids when unconfined, that is, in open containers. Liquids in open containers. Density and specific gravity. The first characteristic of an unconfined liquid which interests us is its density.

The

density of a fluid is the weight of a unit volume of it. The unit of volume normally used in this text is the cubic foot; the unit of weight normally used is the pound. The standard of density, to which the densities of all other liquids are referred, is that of pure water at zero degrees centigrade (32 degrees Fahrenheit), and at sea-level atmospheric pressure. Force and pressure. A liquid has no shape of its own. It acquires the shape of its container up to the level to which it fills the container. However, we know that liquids have weight.

This weight exerts a force upon all sides of the container, and this force can be measured. Therefore, for unconfined liquids, that is, liquids in open containers, the pressure in pounds per square inch exerted by the liquid on the bottom of the container is equal to the weight of the liquid on each square inch of the bottom of the container. It must be emphasized that the weight of the liquid is here thought of as a forceexerted on the bottom of the container. Expressed as a formula, we have: Pressure = Force per unit area

It is understood that the word pressure, when not otherwise qualified, means pressure in pounds per square inch. This is called the total force and is obtained by the formula: Total Force = Pressure X Area The pressure exerted by a liquid on the bottom of a container is independent of the shape of the container, and depends only on the height and density of the liquid.  Liquids in enclosed systems.  Liquids are practically incompressible.

The following

two basic principles will help to explain the behavior of liquids when enclosed: Liquids are practically incompressible. The applied pressure is transmitted equally in all directions at once. Increase of force with area. The ratio between the force applied to the smaller piston and the force applied to the larger piston is the same as the ratio between the area of the smaller pistonand the area of the larger piston.

Expressed as a proportion, then, we have: Force on larger piston/Force on smaller piston = Area of larger piston/Area of smaller piston This means that the mechanical advantage obtainable by such an arrangement is equal to the ratio between the areas of the two pistons.

Since the area of the larger cylinder is 10 times as great as that of the smaller cylinder, pushing the smaller piston downward a distance of 1 inch will move the larger piston upward only 1/10 of an inch. The ratio between the displacement of liquid in the smaller cylinder and the displacement of liquid in the larger cylinder is once again equal to the ratio between their areas. so that the amount of work (force X distance) done by the larger piston is exactly the same as the amount done by the smaller piston. c. Multiple units.

It is not necessary to confine our system to a single line from the source of hydraulic power. Hydraulic power may be transmitted in many directions to do multiple jobs. PUMP - In practice we usually need some device which will deliver, over a period of time, a definite volume of fluid at the required pressure, and which will

continue to deliver it as long as we desire it to do so. Such a device is called a pump. Basic principles of pumps. A hydraulic pump is a mechanical device which forcibly moves, or displaces, fluids.

Various pumping principles are employed in the different types of hydraulic pumps, but one fundamental principle applies to all: a volume of fluid entering the intake opening, or port, is moved by mechanical action and forced out the discharge port. Hydraulic fluids. Almost any free-flowing liquid is suitable as a hydraulic fluid, as long as it will not chemically injure the hydraulic equipment. For example, an acid, although free-flowing, would obviously be unsuitable because it would corrode the metallic parts of the system. a. Basic units of a hydraulic system.

• A reservoir, or supply tank, containing oil which is supplied to the system as needed and into which the oil from the return line flows.
• A pump, which supplies the necessary working pressure.
• A hydraulic cylinder, or actuating cylinder, which uses the hydraulic energy developed in the pump to move the door.
• A cut-out valve, by means of which the pressure in the actuating cylinder may be maintained or released as desired.
• A check valve, placed in the return line to permit fluid to move in only one direction.
• "Hydraulic lines," such as piping or hose, to connect the units to each other.

The supply tank must have a capacity large enough to keep the entire system filled with oil and furnish additional oil to make good the inevitable losses from leakage. The tank is

vented to the atmosphere; thus atmospheric pressure (14. 7 pounds per square inch) forces the oil into the inlet, or suction, side of the pump. The tank is generally placed at a higher level than the other units in the system, so that gravity assists in feeding oil into other units. The pump is the hand-operated, reciprocating piston type.

SOLENOID VALVE 

A solenoid valve is an electromechanically operated valve. The valve is controlled by an electric current through asolenoid: in the case of a two-port valve the flow is switched on or off; in the case of a three-port valve, the outflow is switched between the two outlet ports. Multiple solenoid valves can be placed together on a manifold.

Solenoid valves are the most frequently used control elements in fluidics. Their tasks are to shut off, release, dose, distribute or mix fluids. They are found in many application areas. Solenoids offer fast and safe switching, high reliability, long service life, good medium compatibility of the materials used, low control power and compact design.

There are many valve design variations. Ordinary valve can have many ports and fluid paths. A 2-way valve, for example, has 2 ports; if the valve is closed, then the two ports are connected and fluid may flow between the ports; if the valve is open, then ports are isolated. If the valve is open when the solenoid is not energized, then the valve is termed normally open (N. O. ). Similarly, if the valve is closed when the solenoid is not energized, then the valve is termednormally closed. There are also 3-way and more complicated designs.

A 3-way valve has

3 ports; it connects one port to either of the two other ports (typically a supply port and an exhaust port). Solenoid valve are also characterized by how they operate. A small solenoid can generate a limited force. If that force is sufficient to open and close the valve, then a direct acting solenoid valve is possible. An approximate relationship between the required solenoid force Fs, the fluid pressure P, and the orifice areaA for a direct acting solenoid value is: Where d is the orifice diameter.

A typical solenoid force might be 15 N (3.  lbf). An application might be a low pressure (e. g. , 10 pounds per square inch (69 kPa)) gas with a small orifice diameter in (9. 5 mm) for an orifice area of 0. 11 sq in  and approximate force of 1. 1 lbf (4. 9 N)). When high pressures and large orifices are encountered, then high forces are required. To generate those forces, an internally piloted solenoid valve design may be possible. [1] In such a design, the line pressure is used to generate the high valve forces; a small solenoid controls how the line pressure is used.

Internally piloted valves are used in dishwashers and irrigation systems where the fluid is water, the pressure might be 80 pounds per square inch (550 kPa) and the orifice diameter might be 3 4 in (19 mm). In some solenoid valves the solenoid acts directly on the main valve. Others use a small, complete solenoid valve, known as a pilot, to actuate a larger valve. While the second type is actually a solenoid valve combined with a pneumatically actuated valve, they are sold and packaged

as a single unit referred to as a solenoid valve.

Piloted valves require much less power to control, but they are noticeably slower. Piloted solenoids usually need full power at all times to open and stay open, where a direct acting solenoid may only need full power for a short period of time to open it, and only low power to hold it. A direct acting solenoid valve typically operates in 5 to 10 milliseconds. The operation time of a piloted valve depends on its size; typical values are 15 to 150 milliseconds. Solenoid valves are used in fluid power pneumatic and hydraulic systems, to control cylinders, fluid power motors or larger industrial valves.

Domestic washing machines and dishwashers use solenoid valves to control water entry into the machine. Solenoid valves are used in dentist chairs to control air and water flow. In the paintball industry, solenoid valves are usually referred to simply as "solenoids. " They are commonly used to control a larger valve used to control the propellant (usually compressed air or CO2). In addition to this, these valves are now been used in household water purifiers (RO systems).

Besides controlling the flow of air and fluids, solenoids are used in pharmacology experiments, especially for patch-clamp, which can control the application of agonist or antagonist. Many variations are possible on the basic, one-way, one-solenoid valve described above:

• one- or two-solenoid valves;
• direct current or alternating current powered;
• different number of ways and positions;

INTRODUCTION TO PLC

A Programmable Logic Controller, or PLC, is more or less a small computer with a built-in operating

system (OS). This OS is highly specialized to handle incoming events in real time, i. . at the time of their occurrence. The PLC has input lines where sensors are connected to notify upon events (e. g. temperature above/below a certain level, liquid level reached, etc. ), and output lines to signal any reaction to the incoming events (e. g. start an engine, open/close a valve, etc. ). The system is user programmable. It uses a language called "Relay Ladder" or RLL (Relay Ladder Logic). The name of this language implies that the control logic of the earlier days, which was built from relays, is being simulated.

The PLC is primarily used to control machinery. A program is written for the PLC which turns on and off outputs based on input conditions and the internal program. In this aspect, a PLC is similar to a computer. However, a PLC is designed to be programmed once, and run repeatedly as needed. In fact, a crafty programmer could use a PLC to control not only simple devices such as a garage door opener, but their whole house, including switching lights on and off at certain times, monitoring a custom built security system, etc.

Most commonly, a PLC is found inside of a machine in an industrial environment. A PLC can run an automatic machine for years with little human intervention. They are designed to withstand most harsh environments. When the first electronic machine controls were designed, they used relays to control the machine logic (i. e. press "Start" to start the machine and press "Stop" to stop the machine). A basic machine might need a

wall covered in relays to control all of its functions. There are a few limitations to this type of control.  Relays fail. *The delay when the relay turns on/off. There is an entire wall of relays to design/wire/troubleshoot. A PLC overcomes these limitations, it is a machine controlled operation. PLCs are becoming more and more intelligent.

In recent years PLCs have been integrated into electrical communications networks - i. e. , all the PLCs in an industrial environment have been plugged into a network which is usually hierarchically organized. The PLCs are then supervised by a control center. There exist many proprietary types of networks. One type which is widely known is SCADA (Supervisory Control and Data Acquisition).

The PLC is a purpose-built machine control computer designed to read digital and analog inputs from various sensors, execute a user defined logic program, and write the resulting digital and analog output values to various output elements like hydraulic and pneumatic actuators, indication lamps, solenoid coils, etc. Scan cycle Exact details vary between manufacturers, but most PLCs follow a 'scan-cycle' format. Overhead Overhead includes testing I/O module integrity, verifying the user program logic hasn't changed, that the computer itself hasn't locked up (via a watchdog timer), and any necessary communications.

Communications may include traffic over the PLC programmer port, remote I/O racks, and other external devices such as HMIs (Human Machine Interfaces). Input scan A 'snapshot' of the digital and analog values present at the input cards is saved to an input memory table. Logic execution The user program is scanned element by element, then rung by rung until the end of the program,

and resulting values written to an output memory table. Output scan Values from the resulting output memory table are written to the output modules. Once the output scan is complete the process repeats itself until the PLC is powered down.

LADDER LOGIC DIAGRAM

What is a Ladder Diagram? A Ladder Diagram is one of the simplest methods used to program a PLC. It is a graphical programming language evolved from electrical relay circuits. Each program statement is represented with a line, called the rung, that has all relevant inputs to the left and the output to the right. The output device of a rung is energized if electric power can conceptually flow from the left side of the rung to the right side.

Input devices are assumed to block the flow of power if they are not activated. During the execution of a ladder diagram, the PLC reads the states of all inputs, then determines the states of all outputs starting from the rung at the top side, going down to the last rung, and finally updates the state of the output devices. * Naming Convention During the development of a PLC program, we must use specific names to identify the inputs, outputs, memory flags, timers and counters. PLC manufactures use a variety of approaches in naming the inputs, outputs and other resources.

A typical naming convention is to identify inputs with the letter “I” and outputs with the letter “O”, followed be a 1-digit number that identifies the slot number and a 2-digit number that identifies the position of the input or output in the slot. For example: I1:00 refers

to the first input of slot 1 O2:00 refers to the first output of slot 2. Some manufactures number the inputs or outputs starting from 00, while others use the number 01 to identify the first input or output. It is also common to use numbers like 400 e. t. c.