Process Controls

Control variable

the process variable being sensed and maintained at a desired condition (set point)

Manipulated variable

the process variable that we change to influence the CV

Actuator

the physical device that changes the MV

Sensor

the physical device that measures the CV

Disturbance

a non-steady state and unpredictable mass or energy flow that influences the CV

5 major subsystems

controllers, actuators, processes, sensors, and communication networks

cascade control

a series of feedback control loops that reject disturbances

secondary loop should be

3x faster than the primary loop

accuracy

measured value - true value

precision

gives the same value every time (reliable)

Systematic error

average reading - true value

transducer

a device that converts one form of energy to another

transmitter

a device converting an electrical signal into a standardized signal that can be transmitted over long distances without interference

pneumatic signal

pressure changes in a gas or fluid (analog)

analog electronic signals

continuous function of time

digital signals

discrete function of time

analog vs digital

analog is continuous and digital is discrete

A/D converter converts analog signals to

digital signals

D/A converter converts digital signals to

analog