Programmable Logic Controller (PLC)

A Programmable Logic Controller (PLC) is a device that is used to program for performing control functions. Automotive industry was innovated the first PLC in the late 1960s to replace relay logic controls .It has been become most important introduction for automation industry. Because of that reason, lot of industrial processes have been made using automation technology.

Relay logic controls was used in past time but it had lot of difficulties when taking desired performances .Because of that reason PLC was introduce to minimize the difficulties .There are lot of advantages when using PLC ,those advantages can be listed as following 

• Easy programming and installation,
• High control speed
• Hardware and software security
• Network compatibility
• Troubleshooting and testing convenience
• High reliability
• Can be used in a harsh environment conditions
• There are not any moving parts
• Easy wiring system 

Industrial and commercial environments are being widely used PLC in present time. PLC can be found in almost any manufacturing facility. There are several manufacturers of PLCs. Each brands have unique programing method, but basically all PLC‘s hardware structures and programming concepts are very similar .There are lot of different PLC brands, famous brands can be mentioned as following.

• Allen Bradley PLC
• GE Fanuc PLC
• Horner electric PLC
• Siemens PLC
• Array PLC
• Xinje PLC

Figure No 01 : PLC brands 

When considering PLC, every PLC consist of following component

• Central processing unit (CPU)
• Memory
• Inputs Output modules
• Power supply
• Programming Terminal

Connection between above mentioned components can be demonstrated using following figure

       Figure No 02 : Connection among PLC components

Central processing unit

PLC has a central processing unit like other computerized devices. It is the brain of the PLC It is controlled by operating system software The operating system program is a supervisory programs that are loaded and stored permanently in the PLC’s memory by PLC programmer .CPU does following operations

• Updating inputs outputs ,using inputs status it energizes or de-energizes it’s output
• Performing logic and arithmetic operations
• Communicating with memory ,Programmed data are stored in memory  .So CPU can read or change the content of memory locations
• Scanning application program
• Communicating with a programming terminal

Figure No 03 : Central processing unit 

Memory

Memory is the most important component that stores information, programs, and data in a PLC. There are two process that are being done using memory .The process of putting new information into a memory location is called writing. The process of retrieving information from a memory location is called reading.

There two common types of memory used in PLC, they are Read Only Memory (ROM) and Random Access Memory (RAM). A ROM location can be read, but it cannot be written. ROM is used to store programs and data that should not be altered. Because of that reason the PLC’s operating programs are stored in ROM.

A RAM location can be read or written. Therefore the information stored in a RAM location can changed. Ladder logic programs are stored in RAM, programing langue may be different with the PLC brands. When a new ladder logic program is loaded into a PLC’s memory, the old program that was stored in the same locations is over-written and essentially erased. The memory capacities of PLCs can vary. Memory capacities are often expressed in terms of kilo-bytes (K). One byte is a group of 8 bits. One bit is a memory location that may store one binary number that has the value of either 1 or 0. (Binary numbers are addressed in Module 2). 1K memory means that there are 1024 bytes of RAM. 16K memory means there are 16384 bytes of RAM.  

Input modules and output modules

A PLC is a control device. It takes information from inputs and makes decisions to energize or de-energize outputs. The decisions are made based on the statuses of inputs and outputs and the ladder logic program that is being executed. The input signal can be given to the PLC by using push buttons, limit switches, relay contacts, photo sensors, proximity switches, temperature sensors, and the like. These input devices can be AC (alternating current) or DC (direct current). The input voltages can be high or low. The input signals can be digital or analog. Differing inputs require different input modules. An input module provides an interface between input devices and a PLC’s CPU, which uses only a low DC voltage. The input module’s function is to convert the input signals to DC voltages that are acceptable to the CPU. Standard discrete input modules include 24 V AC, 48 V AC, 120 V AC, 220 V AC, 24 V DC, 48 V DC, 120 V DC, 220 V DC, and transistor-transistor logic (TTL) level.

The devices controlled by a PLC include relays, alarms, solenoids, fans, lights, and motor starters. These devices may require different levels of AC or DC voltages. Since the signals processed in a PLC are low DC voltages, it is the function of the output module to convert PLC control signals to the voltages required by the controlled circuits or devices. Standard discrete output modules include 24 V AC, 48 V AC, 120 V AC, 220 V AC, 24 V DC, 48 V DC, 120 V DC, 220 V DC, and TTL level.    

         Figure No 04 : Input modules and output modules

 Power supply

Standard commercial AC power lines are being used to power the PLC. But many PLC components are utilizing 5V or another low voltage of DC power. Those components are CPU and memory. The PLC power supply converts AC power into DC power to support those components of the PLC.

Programming Terminal

A PLC requires a programming terminal and programming software for operation. The programming terminal is used for programming the PLC and monitoring the PLC’s operation. It may also download a ladder logic program (the sending of a program from the programming terminal to the PLC) or upload a ladder logic program (the sending of a program from the PLC to the programming terminal). 

Programming device

Generally personal computers are used to program the PLC. Working software allows users to modify, store, troubleshoot the program. Personal computers communicate with PLC using processor via a serial or parallel data communications link

Hand-held unit are often used for modifying, troubleshooting or transferring programs to multiple machines on the factory floor.

Conveyors

A conveyor is very important piece of mechanical system that moves material between locations. Conveyors are especially useful in applications involving the transportation of heavy or bulky materials. Conveyor systems allow quick and efficient transportation for a wide variety of materials, which make them very popular in the material handling and packaging industries. So it is very important thing to understand about conveyors designing and operating process. Conveyors are generally powered by electric motors, hydraulic motors, or by gravity. When selecting a conveyor the following factors must be carefully defined 

• Type of material transported. Is it bulk material, or unit goods.
• Physical characteristic of transported goods.
• Flow rate, tons per hour or number of units per hour.
• Load carrying capacity of structure.
• Distance traveled (Conveyor length).
• Direction of travel.(head to tail or tail to head)
• Conveyor height from floor.
• Level change. (Horizontal, Upward or downward path ).
• Support type (Floor stand, ceiling suspended, wall mounted, etc).
• Environment and operating conditions (Food grade, moisture, water splash etc.).

Detailed description about widely used conveyor types can be mentioned as following

Gravity roller conveyor

A gravity conveyor moves the load without utilizing motor power sources, usually down an incline or through a person pushing the load along a flat conveyor. Gravity conveyors transport products or work in process from one work area to another. Low cost, low maintenance are the advantages of this type of conveyors.

Power roller conveyor

Power roller conveyor is same as gravity roller conveyor, main difference is there is a motor or other equipment to power the system. Without a powered conveyor, materials handling can be difficult, time consuming and costly. Power roller conveyors can have significant advantages, depending on the type of materials that need to be transported.

Roller Bed Conveyor

Roller Bed Belt Conveyors are utilized for the transportation of hard to convey items such as small parts or items with inconsistent shapes or sizes Roller bed conveyors have a much higher load weight capacity than slider bed conveyors by reducing the friction caused by the belt against the bed surface.

Bucket Conveyor

This type of conveyors are very important , because they are designed to gently transport a wide variety of products, both horizontally and vertically, without transfer points. Capable of handling most dry, granular, free flowing products, these machines also work well with many non-free flowing products.

Screw conveyor

A screw conveyor or auger conveyor is a mechanism that uses a rotating helical screw blade, called a "flighting", usually within a tube, to move liquid or granular materials. They are used in many bulk handling industries. Screw conveyors in modern industry are often used horizontally or at a slight incline as an efficient way to move semi-solid materials, including food waste, wood chips, aggregates, cereal grains, animal feed, boiler ash, meat and bone meal, municipal solid waste, and many others. The first type of screw conveyor was the Archimedes' screw, used since ancient times to pump irrigation water.

Pneumatic Conveyor

pneumatic conveying systems move bulk materials that are suspended in an air stream that is introduced by a positive pressure blower upstream of material intake points, or by a vacuum pump that removes air from the system downstream of material discharge points. Material is separated from the conveying air at the use point, then discharged on a batch basis via butterfly or slide gate valves, or continuously via rotary airlock valves.

Flexible conveyor

The flexible conveyor is based on a conveyor beam in aluminum or stainless steel, with low friction slide rails guiding a plastic multi-flexing chain. Products to be conveyed travel directly on the conveyor, or on pallets/carriers. These conveyors can be worked around obstacles and keep production lines flowing. They are made at varying levels and can work in multiple environments. They are used in food packaging, case packing, and pharmaceutical industries but also in retail stores such as Wal-Mart and Kmart.

Vibrating conveyor

A Vibrating Conveyor is a machine with a solid conveying surface which is turned up on the side to form a trough. They are used extensively in food grade applications where sanitation, wash-down, and low maintenance are essential. Vibrating conveyors are also suitable for harsh, very hot, dirty, or corrosive environments. They can be used to convey newly cast metal parts which may reach upwards of 1,500 °F (820 °C). Due to the fixed nature of the conveying pans vibrating conveyors can also perform tasks such as sorting, screening, classifying and orienting parts. Vibrating conveyors have been built to convey material at angles exceeding 45° from horizontal using special pan shapes. Flat pans will convey most materials at a 5° Incline from horizontal line.

Figure No 01 : Conveyor types 

Conveyor systems are being used widespread across a range of industries due to the numerous benefits they provide. Some of the benefits can be mentioned as following

• Conveyors are able to safely transport materials from one level to another, which when done by human labor would be strenuous and expensive.
• They can be installed almost anywhere, and are much safer than using a forklift or other machine to move materials.
• They can move loads of all shapes, sizes and weights. Also, many have advanced safety features that help prevent accidents.
• There are a variety of options available for running conveying systems, including the hydraulic, mechanical and fully automated systems, which are equipped to fit individual needs.

Conveyor systems are commonly used in many industries, including the automotive, agricultural, computer, electronic, food processing ,aerospace, pharmaceutical, chemical, bottling and canning, print finishing and packaging. Although a wide variety of materials can be conveyed, some of the most common include food items such as beans and nuts, bottles and cans, automotive components, scrap metal, pills and powders, wood and furniture and grain and animal feed. Many factors are important in the accurate selection of a conveyor system. It is important to know how the conveyor system will be used beforehand. Some individual areas that are helpful to consider are the required conveyor operations, such as transportation, accumulation and sorting, the material sizes, weights and shapes and where the loading and pickup points need to be.

When considering above mentioned all the facts, it can be mentioned that conveyors are very important piece of mechanical equipment which makes lot of benefits for production floor.

Diesel Engine Exhaust Gas Properties

Engine exhaust gas properties are very important matter to be considered. Because it becomes one of the main reason for environmental pollution, green house effect, air pollution etc. Both petrol and diesel engine have two methods to measure their exhaust gas properties. Opacity of the exhaust gas is checked in diesel engines

Opacity is the measure of impenetrability to electromagnetic or other kinds of radiation, especially visible light. In radioactive transfer, it describes the absorption and scattering of radiation in a medium, such as a plasma, dielectric, shielding material, glass, etc. An opaque object is neither transparent (allowing all light to pass through) nor translucent (allowing some light to pass through). When light strikes an interface between two substances, in general some may be reflected, some absorbed, some scattered, and the rest transmitted (also see refraction). Reflection can be diffuse, for example light reflecting off a white wall, or specular, for example light reflecting off a mirror. An opaque substance transmits no light, and therefore reflects, scatters, or absorbs all of it. Both mirrors and carbon black are opaque. Opacity depends on the frequency of the light being considered. For instance, some kinds of glass, while transparent in the visual range, are largely opaque to ultraviolet light. More extreme frequency-dependence is visible in the absorption lines of cold gases. Smoke and smoke opacity meters are instruments measuring the optical properties of diesel exhaust. These instruments have been designed to quantify the visible black smoke.

Emission utilizing such physical phenomena as the extinction of a light beam by scattering and absorption. In general, smoke and opacity meters are much simpler (some of them very simple) and less costly in comparison to most other instruments used for PM measurement. They are often used to evaluate smoke emissions in locations outside the laboratory, such as in maintenance shops or in the field. In fact, the smoke opacity measurement is the only relatively low-cost and widely available method to measure a PM-related emission parameter in the field. For this reason, opacity limits are used in most inspection and maintenance (I&M) or periodic technical inspection (PTI) programs for diesel engines. Smoke opacity limits may be also included as auxiliary limits in new engine emission standards.

Diesel soot is by nature oily thus quickly clogging the filters and sample piping of a "normal" petrol exhaust gas analyzer. Those maintenance items are fairly expensive to be changed after every single test. That's why the smoke metering method for diesel engines has been implemented by all governments. A modern Smoke meter is a almost no-maintenance device.

Absorption factor (K factor ) is a more important factor to be considered when considering the opacity of an engine. This factor is also known as “Light Extinction Coefficient” and “Light Absorption Coefficient. K factor  is expressed on a per meter basis . The smoke density is a function of the number of smoke particles per unit gas volume, the size distribution of the smoke particles, and the light absorption and scattering properties of the particles. In the absence of blue or white smoke, the size distribution and the light absorption, scattering properties are similar for all diesel exhaust gas samples and the smoke density is primarily a function of the smoke particle density. Large K factor values indicate that air pollution is high, so there are standards for each type of vehicle  to minimize the environmental effect.

                                           

    Figure no 01 : How to use the instruments 

Figure no 02 : How to calculate the Opacity of the engine 

Wind Energy Extraction

Wind is a large scale flow of gases, so it consists of the bulk movement of air which carries large amount of energy.  Energy has become very important matter with scarcity of nonrenewable energy sources. Fossil fuel will be over in near future, so world must have alternative energy sources to fulfill energy demand of fossil fuel. Wind becomes significant as a renewable energy source for extracting energy. Wind energy is extracted by using wind turbines to produce electrical power, windmills for mechanical power, wind pumps for water pumping or drainage, or sails to propel ships. In here important thing is power generation.There are large wind farms to generate electricity. A wind turbine is a device that converts kinetic energy from the wind into electrical power. A wind turbine used for charging batteries may be referred to as a wind charger .Generally two types of wind turbines are being used in wind farm, they are horizontal axis wind turbine and vertical axis wind turbine. 

Vertical axis wind turbine. 

Horizontal axis wind turbine 

Vertical-axis wind turbines (VAWTs) are the type of wind turbine where the main rotor shaft is set vertically and the main components have been  installed  at the base of the turbine. This arrangement allows the generator and gearbox to be located close to the ground, facilitating service and repair. VAWTs do not need to be pointed into the wind, which removes the need for wind-sensing and orientation mechanisms

Horizontal-axis wind turbines (HAWT) have the main rotor shaft and electrical generator at the top of a tower, and must be pointed into the wind. Small turbines are pointed by a simple wind vane, while large turbines generally use a wind sensor coupled with a servo motor. Most have a gearbox, which turns the slow rotation of the blades into a quicker rotation that is more suitable to drive an electrical generator.

Horizontal axis wind turbines are widely used than vertical axis wind turbine. Lift force is used to rotate horizontal axis wind turbines and drag force is used to rotate vertical axis wind turbines. There are some advantages and also disadvantages for both types of turbines.

Advantages and disadvantages of vertical axis wind turbine 

Advantages

• They can produce electricity in any wind direction
• Strong supporting tower in not needed because generator, gearbox and other components are placed on the ground
• Low production cost as compared to horizontal axis wind turbine
• As there is no need of pointing turbine in wind direction to be efficient so yaw drive and pitch mechanism is not needed
• Easy installation as compared to other wind turbine
• Easy to transport from one place to other
• Less maintenance cost
• They can be installed in urban area
• Low risk for human and birds because blades moves at relatively low speed
• They are particularly suitable for areas with extreme weather conditions, like in the mountains where they can supply electricity to mountain huts.

Disadvantages

• As only one blade of wind turbine work at a time so efficiency is very low
• They need an initial push to start, this action use few of its own produce electricity
• When compared to horizontal axis wind turbine they are very less efficient with respect to  them.  this is because they have an additional drag when their blades rotates.
• They have relative high vibration because the air flow near the ground creates turbulent flow
• Because of vibration bearing wear increase which result in the increase of maintenance cost
• They create noise pollution

Advantages and disadvantages of horizontal axis wind turbine

Advantages

• Variable blade pitch, which gives the turbine blades the optimum angle of attack. Allowing the angle of attack to be remotely adjusted gives greater control, so the turbine collects the maximum amount of wind energy for the time of day and season.
• The tall tower base allows access to stronger wind in sites with wind shear. In some wind shear sites, every ten meters up, the wind speed can increase by 20% and the power output by 34%.
• High efficiency, since the blades always moves perpendicularly to the wind, receiving power through the whole rotation. In contrast, all vertical axis wind turbines, and most proposed airborne wind turbine designs, involve various types of reciprocating actions, requiring airfoil surfaces to backtrack against the wind for part of the cycle. Backtracking against the wind leads to inherently lower efficiency.

Disadvantages

• Taller masts and blades are more difficult to transport and install. Transportation and installation can now cost 20% of equipment costs.
• Stronger tower construction is required to support the heavy blades, gearbox, and generator.
• Reflections from tall Horizontal Axis Wind Turbine (HAWT)s may affect side lobes of radar installations creating signal clutter, although filtering can suppress it.
• Mast height can make them obtrusively visible across large areas, disrupting the appearance of the landscape and sometimes creating local opposition.
• Downwind variants suffer from fatigue and structural failure caused by turbulence when a blade passes through the tower’s wind shadow (for this reason, the majority of HAWTs use an upwind design, with the rotor facing the wind in front of the tower).
• They require an additional yaw control mechanism to turn the blades toward the wind.

Wind turbines are operated on a simple principle. Same process is used to generate electricity from both turbine types. For horizontal axis turbine, the energy in the wind turns two or three propeller-like blades around a rotor. The rotor is connected to the main shaft, which spins a generator to create electricity. Wind turbines are mounted on a tower to capture the most energy. At 100 feet (30 meters) or more above ground, they can take advantage of faster and less turbulent wind. Wind turbines can be used to produce electricity for a single home or building, or they can be connected to an electricity grid (shown here) for more widespread electricity distribution. The process can be demonstrated as following manner. 

Process involved with conversion of kinetic energy of wind into electricity

When considering power demand wind energy is very important and reliable renewable energy source for world. Usage of this sources minimize air pollution , green house effect, environmental pollution etc .