CHE 352 Exam 1

electric signal

dashed line

flow of fluid

solid line

pneumatic signal

solid line with 2 dashes in it

communication signal (to DCS)

line with circles in it

FC or arrow down

fail closed

FO or arrow up

fail open

closed

filled in indicates a control valve is normally…

analysis

A (first letter)

flow rate

F (first letter)

current

I (first letter)

level

L (first letter)

pressure

P (first letter)

speed

S (first letter)

temperature

T (first letter)

alarm

A (second letter)

control

C (second letter)

element

E (second letter)

high

H (second letter)

indicate

I (second letter)

low

L (second letter)

record

R (second letter)

switch

S (second letter)

transmitter

T (second letter)

sensor —> transmitter —> controller —> actuator

feedback control scheme

sensor —> transmitter —> calculation block —> actuator (applied to two different variables (i.e. temperature and flow rate) of two different streams)

feedforward control scheme

feedback control scheme

feedforward control scheme

feedforward with trim control scheme

sensor —> transmitter —> proactive response block —> summing junction —> actuator (second stream to summing junction: sensor —> transmitter —> controller —> summing junction)

feedforward with trim control scheme

3-15 psig

pneumatic signal range

4-20 mA

electrical signal range

I/P transducer

converts signal from current to pressure (electrical to pneumatic)

spring and diaphragm, solenoid, motor

3 types of actuators

valve body

fluid ports, valve plug, valve stem

valve actuator

physically moves the resistor

spring and diaphragm control valve

pneumatic signal exerts pressure on diaphragm, pushes spring down and moves restrictor

solenoid control valve

current to coil generates magnetic field to move the restrictor downward

motor control valve

gear motor attached to valve stem receives a DC control signal from servo amp to move the restrictor to the desired position

I/P transducer explained

current is applied to electromagnet, as current changes, magnetism increases or decreases which affects the position of the beam in relationship to the nozzle to create changes in nozzle pressure

valve positioners explained

a pneumatic control signal is sent to a bellows to expand and act on a beam which pivots and moves a flapper in relation to a nozzle to create changes in nozzle pressure