latest results

Navodaya Vidyalaya Samiti, New Delhi

what is linear stepper motor and rotary stepper motor? any details or description for these?

A stepper motoris a motor that uses two or more electromagnetic pole assemblies with teeth on them such the teeth are are off set so you can get very precise movements base on which poles are energized.

There are two both linear and rotary steppers. Linear stepper motors are laid out in a linear configuration. Rotary steppers are similar to a conventional motor.

Which coupling is used for joing to shafts of different diameter.....?

There are a number of type of couplers which can be used to join shafts different diameters:

1.Spider Connectors - These connectors also allow for misalignment.

2. Straight connectors - With different hole diameters in each end.

Why is a "Cup Car" with a full tank of fuel faster than the same car with a half tank of fuel?

small adjustment can make a world of difference in performence pressure but with 2 identical car of same weight and same horsepower i would think that the power the power to weight ratio on the car with less fuel would be faster due to the pushing less weight

What is the process to measure the speed of aeroplane

The airspeed indicator is the only instrument connected to both the pitot tube and the static system. Air from the staticsystem fills the case of the airspeed indicator, providing a"base" pressure against an expandable diaphragm. Air forced into the pitot tube as theairplane moves fills the diaphragm, which expands as ram air pressure (and speed) increase. A needle connected to the diaphragm rotates as the diaphragm expands. The needle's position on the instrument face indicates airspeed

what is the difference between hydralic and pneumatic system

Pneumatic system is operated by compressed air while hydraulic system is operated with pressurised hydraulic oil
or any type viscous oil.
Hydraulic systems can usually produce higher control forces and work under extreme
operating conditions. This is the system that is primarily used on aircraft to move
control surfaces and engine controls.
You can often classify pneumatic systems because they have a pump (gas pump) and
hydraulic systems have a piston.
That is the difference. Also, pneumatic systems are louder because it is a gas under pressure.

1. By definition, hydraulics is used in controlling or harnessing power
with the use of pressurized fluids whereas pneumatics studies how pressurized
gases influences mechanical motion or movement.
2. Hydraulics uses an incompressible fluid medium like oil whereas pneumatics
uses a compressible gas like air.
3. Hydraulic applications demand greater pressures during operations that reach
thousands of pounds per square inch whereas pneumatic applications only
require 100 psi pressures more or less.
4. Most hydraulic applications generally use bigger components that pneumatic applications.
5. Hydraulic systems are generally more difficult to operate compared to pneumatic applications

What is the difference between Bolt and Screw?

The main difference was based on the load acting on it, and the size. For smaller loads, screws are enough but in case of greater-loads, bolts are to be used. In bolt we give centrifugal force or tangential force and screw we give axial force for driving.

Which is heavier 1kg of Iron or 1kg of Cotton? and why?

Both of them have same weight. The only difference is the volume of Iron is small compared to Cotton.

How to measure Temperature of a Bearing?

Normally the temperature range from 80 degree to 110 degree Celsius. So the following temperature measurement devices are used.

· Dial Type Bearing Temperature Detector

· Stator Winding Temperature Detector

· Resistance Bearing Temperature Detector (Bearing RTD)

· Specialized in Pin type RTD

What is the hottest part of refrigerant in the refrigeration System

Compressor. (Some types of refrigeration system will reach up to 311 deg Celsius.)

During the starting of a vehicle, the exhaust smoke appears white. Why?

There are a number of reasons why this happens. One of the main ones is water which has condensed in the cylinders and exhaust pipes is being turned into steam from the hot exhaust gasses

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because when carburreters work to mix fuels with air during injection
molding most part fuel mixers get compressed n remaining part of mixers that
is unburne gases get free by exhaust outlet nd its appears white

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When vehicle start, den more quanity of fuel is cnvrt in smoke as cmpared to d latr....whch is initialy white and colour change of smoke latr.

what is proximity senser

A proximity sensor is a sensor able to detect the presence of nearby objects without any physical contact.
A proximity sensor often emits an electromagnetic or electrostatic field, or a beam of electromagnetic radiation (infrared, for instance), and looks for changes in the field or return signal. The object being sensed is often referred to as the proximity sensor's target. Different proximity sensor targets demand different sensors. For example, a capacitive or photoelectric sensor might be suitable for a plastic target; an inductive proximity sensor requires a metal target.

The maximum distance that this sensor can detect is defined "nominal range". Some sensors have adjustments of the nominal range or means to report a graduated detection distance.

what is the different between contactor or relay

Relays are used where it is necessary to control a circuit by a low-power signal (with complete electrical isolation between control and controlled circuits), or where several circuits must be controlled by one signal. A contactor is an electrically controlled switch used for switching a power circuit, similar to a relay except with higher current ratings. A contactor is controlled by a circuit which has a much lower power level than the switched circuit.

what are the differences of normal A.C induction motor and servo motor

an induction motor has high inertia and servo motor has low inertia ‎& servo motor works according sensor & induction motor have not sensor

Differentiate between service factor and factor of safety.

Service factor is the allowable over load factor for motors or other similar devices. Safety Factor is the ratio between the rated load or force and the theoretical structural rated load or force.

At maximum load base on Service the Unit will not fail. At the theoretical load of safety factor the unit will fail.

Quiz

What are the improvements which can be done in an automobile to avoid the tendency of accidents??
You can take any automobile for example CAR, TRUCK, BUS, MOTORCYCLE etc. Give innovative ideas which are practical and can be implemented to an automobile.?

Ans:-automation facility shud b provided in automobiles take 4 eg. the latest fully automated car launched by GOOGLE which has radar employed on its roof with the help of which it detects the vehicles on roads & perform its action accordingly bcoz of radar it can perform actions such applying E BRAKES. d most interesting feature wich i lyk abut dis vehicle is dat the passenger has jst to feed d location : to & fro location in digital screen & with d help of radar it tracks d location from the satellite & thus moves 2wrds its destination.

What is boolean algebra?

Boolean algebra is used to describe the output of electronic circuits that use only 0 or 1, i.e. binary. Such as And gates, Nand gates, Or gates and Nor gates. For example, an And gate might have two inputs, either one a 0 or 1. If both are 0 then the output is 0. If either is 1 and the other 0 then the output is 0. Only if both inputs are 1 is the out put a 1. Hence the name And gate, if the inputs are 1 and 1 then the output is 1. Wikipedia has an extensive article on Boolean algebra but it is a bit difficult to understand if you don't already have an idea of what Boolean is.

Why the torque of elec. motor is low at high RPM where the cause of the speed is the production of torque?

Remember work or energy in rotary motion applications is a function of rotary speed and torque. If the input energy to the motor is a constant (Watts) then the torque must go down as the rotary speed goes up.

http://www.youtube.com/watch?v=3ZZ1wYDB8nQ&feature=player_embedded

why is the flat belt pulley crowned or tapered at slight angle toward the two sides of the pulley.is there a design calculation for the tapered angle

A pulley is crowned to ensure that the belt remains centered on the pulley.

The total height of the crown is a function of the elasticity of the belt, the diameter of the pulley and the speed of the belt. There are calculations and rules of thumb for determining the correct crown height.

what are the parts of electric arc welding machine?

There are several types of arc welding machines.
1. The machine that we find in most shops. This is a somewhat stationary machine that has 1 Main cable that receives energy from the source (Usually 3 phase 220 or 440 Volts AC), the starter or switch, the transformer, the rectifiers, the controls of tension (Voltage) and current (Amps-or-Amperage), the two secondary wires: one is to ground the machine to the building + structure + part that you are to weld, the other is to put your electrode and produce the welding. Some other Arc welders are known as "wire welders" these use a reel of wire that will be the metal you provide in the welding, and instead of the solid flux that you have in the electrodes, you will use a gas that helps the welding to happen, the metal to melt and deposit. Wire welders have a metal reinforced hose that travels along with the secondary cable to the tip of the gun. The wire is pushed by an electric motor that is triggered at the gun, this wire travels through through the hose, which also allows the gas to flow as well.
Other type of welder which is usually portable, may work with a generator normally operated by a gasoline engine. These do not require rectifiers since the generator is providing already Direct Current (DC). Same thing, the secondary may use electrodes to weld or a wire gun. These wire welders are more common nowadays. Only specialized welding like non ferrous metals are still popular in form of electrodes.

LED & LCD & CRT

A liquid crystal display (LCD) is a flat panel display, electronic visual display, video display that uses the light modulating properties of liquid crystals (LCs). LCs do not emit light directly.

A light-emitting diode (LED) is a semiconductor light source.[1] LEDs are used as indicator lamps in many devices and are increasingly used for other lighting

The cathode ray tube (CRT) is a vacuum tube containing an electron gun (a source of electrons) and a fluorescent screen, with internal or external means to accelerate and deflect the electron beam, used to create images in the form of light emitted from the fluorescent screen.

agar refrigrator ka door open chod diya jaye to ghar k temprture main ka change hoga or kyu?

firstly very low cool effect will come but after some time compressor will heatup $ tempreture increase than the heat of compressor ll increase the volume of oil inside the compressor it can be cerculate with refrgrent or chowk the caplary coil regular pressor ll increase $ compressor ll become faulty than after ur room tempreture will come back to it's original state

ball valve or butterfly valve main kya difference hai?

ball valve need rotery motion while butterfly valve need angular motion to operate

chemical oxygen demand (COD) test

A solution of 1.485 g 1,10-phenanthroline monohydrate is added to a solution of 695 mg FeSO₄·7H₂O in water, and the resulting red solution is diluted to 100 mL.

Calculations

The following formula is used to calculate COD:

where b is the volume of FAS used in the blank sample, s is the volume of FAS in the original sample, and n is the normality of FAS. If milliliters are used consistently for volume measurements, the result of the COD calculation is given in mg/L.

The COD can also be estimated from the concentration of oxidizable compound in the sample, based on its stoichiometric reaction with oxygen to yield CO₂ (assume all C goes to CO₂), H₂O (assume all H goes to H₂O), and NH₃ (assume all N goes to NH₃), using the following formula:

COD = (C/FW)(RMO)(32)

Where C = Concentration of oxidizable compound in the sample,

FW = Formula weight of the oxidizable compound in the sample,

RMO = Ratio of the # of moles of oxygen to # of moles of oxidizable compound in their reaction to CO₂, water, and ammonia

For example, if a sample has 500 wppm of phenol:

C₆H₅OH + 7O₂ → 6CO₂ + 3H₂O

COD = (500/94)(7)(32) = 1191 wppm

Basic types of Valves

• Ball valve, for on/off control without pressure drop, and ideal for quick shut-off since a 90º turn offers complete shut-off angle, compared to multiple turns required on most manual valves.
• Butterfly valve, for flow regulation in large pipe diameters.
• Ceramic Disc valve, used mainly in high duty cycle applications or on abrasive fluids. Ceramic disc can also provide Class IV seat leakage
• Check valve or non-return valve, allows the fluid to pass in one direction only.

3 Hastelloy check valves

• Choke valve, a valve that raises or lowers a solid cylinder which is placed around or inside another cylinder which has holes or slots. Used for high pressure drops found in oil and gas wellheads.
• Diaphragm valve, which controls flow by a movement of a diaphragm. Upstream pressure, downstream pressure, or an external source (e.g., pneumatic, hydraulic, etc.) can be used to change the position of the diaphragm.
• Gate valve, mainly for on/off control, with low pressure drop.

Stainless steel gate valve

• Globe valve, good for regulating flow.
• Knife valve, similar to a gate valve, but usually more compact. Often used for slurries or powders on/off control.
• Needle valve for accurate flow control.
• Pinch valve, for slurry flow regulation.
• Piston valve, for regulating fluids that carry solids in suspension.
• Plug valve, slim valve for on/off control but with some pressure drop.
• Poppet valve
• Spool valve, for hydraulic control
• Thermal expansion valve, used in refrigeration and air conditioning systems.
• Pressure Relief Valves
• Sampling valves

The 8 Ps (used in service industry)

• Product=Service
• Price
• Place
• Promotion/Entertainment
• People(key person)
• Process
• Physical Evidence
• Productivity & Quality

The 8 Ms (used in manufacturing)

• Machine (technology)
• Method (process)
• Material (Includes Raw Material, Consumables and Information.)
• Man Power (physical work)/Mind Power (brain work): Kaizens, Suggestions
• Measurement (Inspection)
• Milieu/Mother Nature (Environment)
• Management/Money Power
• Maintenance

Quiz

P T C relay kise kehte hain aur woh kahan use hota hai ?

positive tempreture coefficent used in tv for degojing coil

oldham coupling ka kya work h????

Oldham Coupling
Oldham couplings are ideal for many motion control applications. Comprised of aluminum hubs with drive tenons that mate to a torque transmitting plastic disc, their design allows for easy sliding to accommodate misalignment with a very light bearing load. Oldham couplings also have the advantages of electrical isolation, low inertia and a balanced design for higher rpm applications. While the couplings accommodate a small amount of angular and axial misalignment, they are especially useful in applications with parallel misalignment.

Oldham couplings are offered in seven sizes of set screw or clamp style hubs with bore from 1/8" (3mm) to 1-1/8 " (25mm). The hubs are anodized for improved lubricity and increased life. The replaceable center discs are available in two materials to suit different applications. Nylon discs are compliant to dampen vibrations and reduce noise. Acetal discs are designed for precision applications requiring zero backlash and high torque capacity. Since the discs are replaceable, they may be used as a torque limiter.

solinoid valve kya hai ?

A solenoid valve is an electromechanical valve for use with liquid or gas. The valve is controlled by an electric current through a solenoid: 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.

Charpy impact test

The Charpy impact test, also known as the Charpy v-notch test, is a standardized highstrain-rate test which determines the amount of energy absorbed by a material during fracturehis absorbed energy is a measure of a given material's toughness and acts as a tool to study temperature-dependent brittle-ductile transition. It is widely applied in industry, since it is easy to prepare and conduct and results can be obtained quickly and cheaply. But a major disadvantage is that all results are only comparative.

what is the right hindi name of laser

vikeran k uddipit utserjan dwara prakash ka praverdhan

what is the use of ruby laser ????

due to low efficiency very less uses of this mostly using in cutting of dimond or militry

syncronus moter?

A synchronous electric motor is an AC motor distinguished by a rotor spinning with coils passing magnets at the same rate as the power supply frequency and resulting rotating magnetic field which drives it.

Another way of saying this is that it does not rely on slip under usual operating conditions and as a result, produces torque at synchronous speed. Synchronous motors can be contrasted with aninduction motor, which must slip in order to produce torque. They operate synchronously with line frequency. As with squirrel-cage induction motors, speed is determined by the number of pairs of poles and the line frequency.

quiz time?

Q:1in 12 hour how much time 1 digri angle made by analog watch's needle between hour or minute?

Ans":-23 time

Q2:-what is name of that liquid which is used in lcd panel

Ans:-nemetic liquid

lcd means liquid cerstal disply

Q-9:-how much frame required to make a picture flicker free

ans:-70 FRAME per sec

Q-4:-what is dolby spec tech?

ans:-new tech design by dolby its give 15.1 directionly surround sound

A photo of a 35 mm film print featuring all four audio formats (or "quad track")- from left to right: SDDS (blue area to the left of the sprocket holes), Dolby Digital (grey area between the sprocket holes labelled with the Dolby "Double-D" logo in the middle), analog optical sound (the two white lines to the right of the sprocket holes), and the DTStime code (the dashed line to the far right.)

Q-5which gas is used in tubelight

ans:-actully neon or argon hoti hai per with some mixture of mercury most probebly xenon is using in current mkt status

gear which iz made of cast iron can take heavy load????

C.I. Gears can take heavy load but can not bear impact or jurk, one of the C.I. gears are, these are having self lubricating property.

Its an alloy of Fe.
In which-
carbon- 2 to 4.5%
silicon- 1 to 3%
sulphur- upto 0.15%
phosphorus- upto 1%
manganese- 0.5 to 1%.and it is manufactured by remelting pig iron with limestnoe,coke etc. in cupola furnace.
Offfffff....

knoweledge

WORLD'S LARGEST VACUUM COLUMN MADE IN INDIA BY L&T

This column having 3 section
First section : 11000 mm inside diameter (SA 516 Gr. 70 cs material)
Middle section : 14200 mm inside diameter (SA 516 Gr. 70 cs material + SS410S clad material)
Bottom section : 9000 mm inside diameter (SA 516 Gr. 70 cs material + SS410S clad material)

wts diff. b/w cycloidal n involute gear?????????? any one can describe???

1. Cycloidal gear mst cmnly used in mechanical clock & watch but involute gear is popular in car, robotics etc.
2. Inv. gear produce lesser noise than cycl. gear.
3. Manufacturing is easy of inv. gear.
4. Cycl. Teeth r stronger than inv.

difference between valve and servo valve

A servo valve is a valve which is operated by an electrical actuator called a servo. There are lots of ways to operate a valve they include

1. Manually
2. Servos
3. Pilot operators
4. Hydraulic operators ,,,

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You can classify these two on the basis of Control system. Servo valve is closed loop control valve which is electricaly controlled & Mechanically operated, while a simple valve is Mechanical only.

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car ka engine kase start hota hai?

जब कार का इग्नीशन स्विच ऑन करते हैं तो कार्बुरेटर द्वारा इंजिन के इग्नीशन चैम्बर में भेजे गये फ्यूल मिक्सचर को पिस्टन द्वारा कम्प्रेस्ड कर उसका टेम्परेचर लगभग 600-700 डिग्री सेन्टिग्रेड कर दिया जाता है , तब इस HOT MIXTURE में SPARK PLUG द्वारा CURRENT SPARK करने पर MIXTURE BLAST के साथ जलता है और GASES का प्रेशर पिस्टन को पावर देता है जिससे CONNECTING ROD के द्वारा CRANK SHAFT और उस पर लगा FLY WHEEL घूमता है । ये POWER FLY WHEEL में STORE हो जाती है जो अगली बार फिर से PISTON घुमाने के काम आती है । ऐसे इंजिन START होता है।

A. P. J. Abdul Kalam

A. P. J. Abdul Kalam, is an Aerospace engineer, professor, and chancellor of the Indian Institute of Space Science and Technology (IIST), who served as the 11th President of India from 2002 to 2007.^[1] During his term as President, he was popularly known as the People's President.^[2][3]He was awarded the Bharat Ratna, India's highest civilian honor in 1997.Before his term as India's president, he worked as an aeronautical engineer with DRDO andISRO. He is popularly known as the Missile Man of India for his work on development of ballistic missile and space rocket technology.^[4] Kalam played a pivotal organizational, technical and political role in India's Pokhran-II nuclear test in 1998, the first since the original nuclear test by India in 1974.^[5]

He is currently the chancellor of Indian Institute of Space Science and Technology, a professor at Anna University (Chennai), a visiting professor at Indian Institute of Management Ahmedabad,Indian Institute of Management Indore, and an adjunct/visiting faculty at many other academic and research institutions across India.

In May 2011, Dr. Kalam launched his mission for the youth of the nation called the What Can I Give Movement.^[6] Dr. Kalam better known as a scientist, also has special interest in the field of arts like writing Tamil poems, and also playing the music instrument Veena

Sun and planet gear

The sun and planet gear converted the vertical motion of a beam, driven by a steam engine, into circular motion using a 'planet', a cogwheel fixed at the end of the pumping rod (connected to the beam) of the engine. With the motion of the beam, this revolved around, and turned, the 'sun', a larger rotating cog which turned the drive shaft, thus generating rotary motion. An interesting feature of this arrangement, when compared to that of a simple crank, is that when both sun and planet have the same number of teeth, the drive shaft completes two revolutions for each stroke of the beam instead of one. Note the planet-gear is fixed to the pumping rod and thus does not rotate around its own axis.The axis of the planet gear is connected to the axle of the sun gear, and therefore the flywheel, by a linkage that freely rotates around the axis of the sun gear and keeps the planet-gear engaged with the sun-gear.

Sun and planet gear

The sun and planet gear converted the vertical motion of a beam, driven by a steam engine, into circular motion using a 'planet', a cogwheel fixed at the end of the pumping rod (connected to the beam) of the engine. With the motion of the beam, this revolved around, and turned, the 'sun', a larger rotating cog which turned the drive shaft, thus generating rotary motion. An interesting feature of this arrangement, when compared to that of a simple crank, is that when both sun and planet have the same number of teeth, the drive shaft completes two revolutions for each stroke of the beam instead of one. Note the planet-gear is fixed to the pumping rod and thus does not rotate around its own axis.The axis of the planet gear is connected to the axle of the sun gear, and therefore the flywheel, by a linkage that freely rotates around the axis of the sun gear and keeps the planet-gear engaged with the sun-gear.

What are the loads considered when designing the Nut and Bolts

Shear Loads & crushing loads

The Design of crane parameters are:

1. Maximum Load
2. Span of the crane
3. Height from Floor to Gantry Rail Level
4. Class of work of the crane
5. Headroom
6. End clearance
7. Operating Speeds Under Loaded Condition

Maximum Load:

The maximum load in tons is the customer’s requirement and must be specified clearly. Design of almost all the components of the crane are influenced by this parameter. In some cases it is necessary to arrange for a second hoisting machinery called the auxiliary hoist, to lift a much lighter load. If the load at which the crane is operated in general is considerably less than the maximum load, an auxiliary hoist may be used. Cranes used for power plant maintenance is an example of such cases where auxiliary hoist may be fitted. For an entirely different reason auxiliary hoist may be fitted with cranes used for foundries, steel casting shop handling ladles containing molten metal. In these industries the main hoist of the crane is used for hoisting the ladle containing the molten metal, while the auxiliary hoist is used to lift the ladle very slowly to pour the liquid in the mould.

An auxiliary hoist machinery consists of a completely separate hoist mechanism built on a second crab which may run either above or below the crab of the main hoist. The auxiliary hoist is generally of much less capacity than the main hoist.

Span of the Crane:

The distance between the centre to centre of the gantry rails over which the wheels of the bridge run. The section of the gantry rails should also be specified for the design of the wheels of the bridge.

Check EOT Crane Parts

Height from Floor to Gantry Rail Level:

To arrange for the correct height of lift this parameter should be specified. If the crane is required to lift out of pits or from below the floor level, particulars should be specified.

Class of Work of the crane:

For the purpose of design of their frames, every crane and hoist is classified with respect to the frequency of application, variation of magnitude of the load and the effect of impact.

Cranes are divided into four classes.

Light duty cranes come under class I type.

Heaviest duty crane are class 4 type.

Light duty and Heavy duty cranes are discerned by the working period, effective load and dynamic effect. It should be remembered that this classification is applicable to the entire crane and the structure.

The working period is short if the crane is operated for less than 500 hours per year. The effective load is high if the crane is used to lift loads greater than two third of its safe working load on more than one thousand occasions per year.

The dynamic effect may be considered low if the speed of travelling of both crab and bridge or hoist are each less than 100 m per minute. If the speed of operation is higher than this the dynamic effect is high.

Headroom:

The clear height available from the gantry rail level to the lowest overhead obstruction is called the head room. This should be specified by the customer. The height of the hoisting machinery over the crab should not foul with the structural obstruction.

End Clearance:

The distance from the centre of gantry rail horizontally to the nearest obstruction on either side is called the end clearance.

Operating speeds under Loaded Condition:

The operating speeds in m/min for the main hoist, auxiliary hoist, cross traverse and long travel should usually be specified by the customer. When there are no special requirements, the speeds will follow the usual standard practice for the size of crane under consideration.

Apart from the above mentioned important parameters the customer should also specify the following particulars:

• Electrical details like the type (AC or DC),
• Voltage,
• Number of phase,
• Frequency,
• Electrical control,

Whether the control is to be in operator’s cabin for hand operation, or whether from floor by means of pendant.