jadhav amit


{ City } pune
< Country > india
* Profession * design instrumentation
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Question { Reliance, 14145 }

Describe how to calibrate various types of instruments and
transmitters using ISA industrial consensus standard
techniques.


Answer

Calibration of instruments are carried out under master equipment,they are calibrated under the "National Instrumentation Laboratory".
I can not tell u about the detail because it is under rule But i will explain it with example:

To calibrate a temperature Gauge-
The master equipment use is "Fluidless temperature Calibrate".
it work With out fuel so it is called Fluidless Temperature Calibrator the only thing u have to do is Put the End nod into the master equipment and initially set the temp. to 0degree cent. and step up to 30degree cent. with this see the reading proportionally in the Gauge no need to calibrate if it give +-0.2 reading. if it give deviation of +-5 then adjust the span and zero to set point result we been seen these is the method of calibration of temperature gauge.
Other example of master equipment are microprocessor based pressure calibrator,Macloid gauge etc.

Is This Answer Correct ?    0 Yes 3 No

Question { Jindal, 19667 }

Convert a pressure, level, flow, or temperature process
variable value into the appropriate pneumatic or electrical
value given different types of instruments.


Answer

You can use pressure switch for pressure indication,
for level u can use DPT
for flow u can use mass flow meter/turbine flow meter/magnetic flow meter/ultrasonic flow meter
and for temperature u can use RTD/Thermocouple.
keep in mind 1 note that every transmitter output is 4-20mAh these is read by every controller and switch output is in form of 1 or 0, means 1 high to its set point and 0 below setpoint.

Is This Answer Correct ?    2 Yes 1 No


Question { 2109 }

What is the purpose of a process loop? What is the
controllers responsibily?


Answer

The above question answer is explained by an example-
suppose we have to control the temperature of the water from "Heat Exchanger", for these we required a following instruments-
Temperature Transmitter=The transmitter sense the temperature of the boiler and convert these signal to standard signal 4-20 mAh.
Temperature Indicator and controller= The indicator use in the process has a facility of setting a SP(set point) for the desire process, these indicator with its inbuilt technology find out weather to increase the flow of steam or decrease the flow of steam. these condition depend on the logic E(error)=SP(set point)-PV(process variable).

suppose the output water has to maintain the temperature 200 degree cent. these is the SP to the controller.The controller will receive the signal from the temperature transmitter which is process variable(PV) and compare it with the SP i.e. let x be the PV(process value) then,
E=SP-PV
E=200-x
let x=150
then E=200-150
E=50
the value indicate that the inlet flow of the water should be OFF so that the outlet water temperature will reach to SP.

Note- Positive value OFF the inlet flow.
Negative value ON the inlet flow.

Temperature converter(I to P converter)= The signal send by the controller logically is converted into pneumatic by I to P converter with standard signal 3-15psi.
i.e. 3psi =4mAh &
15psi=20mAh respectively.

Valve= The valve can be air to open or air to close depend on the site selection and safety aspect.

*The controller responsibility is to maintain the process in SP and take the proper decision.
*Beside these was short or easy process so we can control it manually but when there is a large process parameter or it is not possible for a human to pay attention or also in hazardous area then at these place the controller play a vital roll in industries.

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