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Part 1
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Part 6
What is furnace draft control?
Balanced draft boilers are generally used negative furnace pressure. When both
forced draft and induced draft are used together, at some point in the system
the pressure will be same as that of atmosphere. Therefore the furnace pressure
must be negative to prevent hot gas leakage. Excessive vacuum in the furnace
however produces heat losses through air infiltration. The most desirable
condition is that the one have a very slight negative pressure of the top of
furnace.
What is intrinsically safe system?
Intrinsic safety is a technique for designing electrical equipment for safe use
in locations made hazardous by the presence of flammable gas or vapours in the
air. Intrinsically safe circuit is one in which any spark or thermal effect
produce either normally or under specified fault conditions is incapable of
causing ignition of a specified gas or vapour in air mixture at the most
ignited concentration.
What is zener diode? What is voltage regulator?
The breakdown region of a p-n diode can be made very sharp and almost vertical
diodes with almost vertical breakdown region are known a s zener diodes. A
zener diode operating in the breakdown region is equivalent to a battery.
Because of this current through zener diode can change but the voltage remains
constant. It is this constant voltage that has made the zener diode an
important device in voltage regulation.
Voltage regulator: The output remains constant despite changes in the input
voltage due to zener effect.
What is force balance principle? State some of its’ advantages.
Force balance principle: A controller which generates an output signal by
opposing torque. The input force is applied on the input bellows which moves
the beam. This crackles nozzle back pressure. The nozzle back pressure is
sensed by the balancing bellows which brings the beam to balance. The baffle
movement is very less about 0.002 for full scale output.
Advantages:
a. Moving parts are fewer.
b. Baffle movement is negligible
c. Frictional losses are less
What is motion balance principle?
A controller which generates an output signal by motion of its parts. The
increase in the baffle is to move towards the nozzle. The nozzle back pressure
will increase. This increase in the back pressure acting on the balancing
bellows, will expand the bellows. The nozzle is moved upward due to this. The
nozzle will move until motion almost equals the input baffle motion.
How will you test a transistor with a multimeter?
1. Emitter +ve of meter and base -ve output =Low resistance
2. Emitter -ve of meter and base +ve output =High resistance
3. Collector +ve and base -ve output =Low
4. Collector -ve and base +ve output =Low
Emitter: Collector = High resistance
PNP: Opposite Results
Explain ratio control system.
A ratio control system is characterized by the fact that variations in the
secondary variable don’t reflect back on the primary variable. A ratio control
system is the system where secondary flow is hold in some proportion to a
primary uncontrollable flow.
If we assume that the output of a primary transmitter is A. and the output of
the secondary transmitter is B, and that the multiplication factor of the ratio
relay is K, then for equilibrium conditions which means set valve is equal to
measured valve, we find the following relation:
KA-B=0 or B/A = K where ‘K’ is the ratio setting off the relay.
What is solenoid valve? Where it is used?
A solenoid is electrically operated valve. It consists of solenoid coil in which
magnetic plunger moves. This plunger is connected to the plug and tends to open
or close the valve. There are two types of solenoid valves:
1. Normally Open
2. Normally closed
Use: It is used for safety purpose in different electric work
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Part 6
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