Question { Reliance, 57675 }

what is DCS?

Answer

Distributed Control System :-
it consists of
redundant Servers, routers, Application highways,
Automation highways, Automation processors, Optical
switching modules for communications, Communication
processors, I/O modules, Profibus/ethernet/modbus
communications.

For example:-
I can tell u about first redundant servers only:-

They are called application servers with hard disks, UPS
of redundant type.
we have different containers inside the servers for
archiving informations, trend displays, communication
containers, run time containers(our PLC or automation
processors), continuous function chart containers, plant
display container, alarm container, license container, and
some more.

PLC :-

it consists of
Redundant automation processors, HMI ,
profibus/ethernet/etc communication, display module or
laptop computer.

Hope u got some information from the above explanation.
i didnt mention completely.
anyone interested can bug me on mail.

Question { HTA Instrumentation, 14518 }

what is the difference between 3,4 wire RTD sensor?

Answer

the difference between is that,the third wire for 3 wire
RTD is used for lead compensation.

Question { IBM, 9320 }

how the 2.5bar pressure able to control the 40bar steam

Answer

the 2.5 bar is used to control the valve by giving it to
the diaphragm to actuate it.so the process pressure 40bar
is controlled.

Question { TATA, 6732 }

how pressure reduce through pressure control valve? suppose
we have to reduce 20 kg pressure to 10 kg pressure , then
what we do ? open the valve or close the valve , initially
it is 20 % is upon ( for ur knowledge ).

Answer

My dear,
In control valve we ll compare the setpoint(operator interference value) and the actual pressure on the line.this deviation is given to the control valve.When the error is positive(means pressure is high),the C/V starts closing and when the error is negative(means pressure is low),the C/V opens and maintains the pressure.
One more thing,why u need to fix the low limit of control valve to open 20%.Depending on the deviation the controller controls the process pressure.
Finally,the controller tuning is must for this control.play with the gain and integral time and deadband to make steady process..

Question { 6970 }

can a control valve works without positioner?why need
tunning of c/v?

Answer

my dear,
when there is no positioner it is not called as control valve.i think u dont know about it.we will give 4 to 20 milliamps to the positioner accordin to tht the valve throttles b/w 0 to 100%.Tuning is different concept which i can give u details to go through it.senthilrmohan@gmail.com

Question { Reliance, 12126 }

how can we measure the level measurement with the help of
pressure gauge?

Answer

Height(level)=Pressure / sp.gravity.

So,if u fix the pressure gauge at the bottom tapping of the tank.the pressure reading is divided with the sp.gravity of the liquid in the tank.

you can cross check by measuring the level and multiplying it with sp.gravity

Question { Honeywell, 4159 }

Why even multiple power supplu r used in instrumentation
system?

Answer

Redundancy concepts.
For server we have two power supplies.one is master and other standy.
Same for Automation processors,OSM also.
For I/O cabinets also

the main thing the system should not get disturbed itself and the process.

Question { 15542 }

What is the difference between Error and Offset.

Answer

I can give you simple example:-

Consider a temperature controller(on/off valve),
setpoint - 100deg
Offset - (-4)
dead band - 2
ERROR - SETPOINT - ACTUAL VALUE

If temperature raises from 90deg>>>>94>>at >96degrees the
valve closes.this is becoz we have an OFFSET of (-4
degrees)(setpoint - offset value)
So,now the valve is closed.temperature drops down from
96degrees<<95<< at 94degrees the valve starts open.this is
becoz we have a DEADBAND of 2degrees.

Error(contrl valve):-
setpoint - 100degree and actual value - 90degrees.
temp range - ( 0 to 200)for error scaling(becoz
controller works from 0 to 100%)
error scaling = 100/200 - 0.2 which is multiplying
factor for error to the controller
Finally,
ERROR = [ SETPOINT - ACTUAL VALUE ] X ERROR SCALING.
[ 100 - 90 ] X 0.2
[ 10 ] X 0.2
2.

hope you guys understand.