Process Control Exam 2

proportional (correction that is directly proportional to the current error)

P

adjusts proportionally to the error (applies a corrective output that is directly proportional to the current error)

proportional controller

integral (adjusting based on integral of error over time)

I

adjusts based on the integral of error over time and adjusts directly proportional to the error (P provides immediate correction proportionally, I accumulates the error over time)

proportional integral controller

derivative (adds a derviative term on the error to see the rate of change of the error)

D

reacts to past, future, and present errors (proportional reacts to the current error directly proportionally, integral reacts to the past errors by accumulating error over time, derivative reacts to future errors by measuring the rate of change of the error)

proportional integral derivative controller

simple, easy to tune

pros of a P controller

offset from setpoint

cons of a P controller

no offset

pros of a PI controller

harder to tune, reset windup

cons of a PI controller

no offset, potential for faster, more accurate control

pros of a PID controller

reset windup, derivative kick on setpoint change, hardest to tune within 3 parameters, amplify noisy signals

cons of a PID controller

controller gain (multiplies the current error and proportional action directly)

Kc

integral time (time per repeat, accumulates past errors to reduce offset)

Ti

derivative time (predicts future error based on current rate of change)

Td

speeds up response time, reduces offset, increases overshoot and oscillation

increasing Kc

slows down response time, increases steady state error, improves stability

decreasing Kc

slows down offset elimination, reduces overshoot and oscillation

increasing Ti

eliminates steady state error faster, increases overshoot and oscillation, risks reset windup

decreasing Ti

reduces overshoot and oscillation, improves settling time, increases noise sensitivity

increasing Td

reduces damping action, protects actuators from noise

decreasing Td

used for open/close only, named after its gate-like disk, linearly actuated (vertical circular plate moves up and down to open it and close it)

gate valves

named after its globe-like body, used to start/stop/regulate flow, linearly actuated (horizontal circular plate moves up and down to regulate flow)

globe valve

named for its ball-like disk, ball rotates 90 degrees to open and close the valve, used only to open and close

ball valve

allows flow in only one direction, named after its circular disk which swings up and down on a hinge, disk remains seated (closed) if pressure on the inlet side is not greater than the outlet side and the weight of the disk, used for start/stop only

swing check valve

indicate when a product is present at a certain point (capacitance, optical, conductivity, vibrating (tuning fork), float switch)

point level measurement sensors

indictae the continuous levels of a product as it rises and falls (ultrasonic, radar (microwave))

continuous level measurment sensors

pressure (inches of water) is equal to the density of the liquid multiplied by the height of the surface of the liquid in inches

differential pressure level measurement

shear force, microwave, optical

consistency sensors

as consistency increases, shear force increases, moves sensor in some way

shear force consistency sensor

propogation velocity of microwaves is affected by the material in the suspension

microwave consistency sensor

light waves reflect or transmit through the fiber slurry, increasing consistency reflects more light and allows less light transmission

optical consistency sensor

two holes before and after orifice plate, connected to differential pressure sensor by two tubes with two separate pressure chambers, tiniest pressure difference in flowing fluid can be precisely measured

differential flow measuring principle

sensr is placed in line and measures an induced voltage generated by the fluid as it flows through the pipe, transmitter takes the measured voltage, converts it into a flow measurement, and transmits it to a control system

magnetic flow meter