Lecture 22 flapper nozzle & ip converter

flapper nozzle & ip converter

1. ICE401: PROCESS INSTRUMENTATION
AND CONTROL
Class 22: Flapper Nozzle & I/P Converter
Dr. S. Meenatchisundaram
Email: [email protected]
Control System Components (ICE 3015)
Dr. S.Meenatchisundaram, MIT, Manipal, Aug – Nov 2017

2. Nozzle / Flapper System:
•Signal conversion from pressure to mechanical motion and vi ce
versacanbeprovidedbyanozzle/flappersystem(sometimescalled
anozzle/bafflesystem).
•AdiagramofthisdeviceisshowninFigure.
Control System Components (ICE 3015)
Dr.
S.Meenatchisundaram, MIT, Manipal, Aug
–
Nov 2017

3. Nozzle / Flapper System:
•A regulated supply of pressure, usually over 20 psig, provid es a
sourceofairthroughtherestriction.
•The nozzle is open at the end where the gap exists between the
nozzleandflapper,andairescapesinthisregion.
•Iftheflapper movesdown and closesoffthenozzleopening sothat
noairleaks,thesignalpressurewillrisetothesupplypres sure.
•Astheflappermovesaway,thesignalpressurewilldropbecauseof
theleakinggas.
•Finally, when the flapper is far away, the pressure will stab ilize at
somevaluedeterminedbythemaximumleakthroughthenozzle.
•Figure shows the relationship between signal pressure and g ap
distance.
Control System Components (ICE 3015)
Dr.
S.Meenatchisundaram, MIT, Manipal, Aug
–
Nov 2017

4. Nozzle / Flapper System:
•Note the great sensitivity in the central
region.
•A nozzle/flapper is designed to operate
in the central region, where the slope of
thelineisgreatest.
•In this region, the response will be such
that a very small motion of the flapper
can change the pressure by an order of
magnitude.
•This system is used in pneumatic
controllerdesign.
Control System Components (ICE 3015)
Dr.
S.Meenatchisundaram, MIT, Manipal, Aug
–
Nov 2017

5. Current-to-Pressure Converters:
•The I/P converter gives us a linear way of translating the 4- t o 20-
mAcurrentintoa3-to15-psigsignal.
•There are many designs for these converters, but the basic pr inciple
almostalwaysinvolvestheuseofanozzle/flappersystem.
•Figureillustratesasimplewaytoconstructsuchaconverter.
Control System Components (ICE 3015)
Dr.
S.Meenatchisundaram, MIT, Manipal, Aug
–
Nov 2017

6. References:
• Process Control Instrumentation Technology, by Curtis D.
Johnson, Eighth Edition, Pearson Education Limited.
Process Instrumentation and Control (ICE 401)
Dr. S.Meenatchisundaram, MIT, Manipal, Aug
–
Nov 2015