J5 Automatic Control Flashcards
List some process variables
Motor speed Fluid pressure Liquid level Temperature Flow
Sensor
measures and senses the process variable to indicate its actual value and provide feedback to the controller
Actuator
alters the process variable
Set point
is the desired value of the process variable
Error (signal)
is the difference between the set-point signal and the feedback signal and is used by the actuator to control the process variable
Controlling device/controller
controls the actuator by comparing the feedback signal from the monitor with the set-point signal to generate an error signal
What two ways are control systems categorized?
open-loop control
closed-loop control
Describe open-loop control
one process variable is controlled by an operator
Describe closed-loop control
control of the process variable is automatic
Describe discontinuous control systems
full power is applied or removed to modify the process variable
Describe continuous control systems
power supplied to modify the process variable is controlled from very low power to full power
List the five elements of a closed-loop control system
Process variable set point Sensor Controller Actuator
Describe transducer
convert energy from one form to another
List the sensors of motion
Linear
Angular
Rotary
List four basic principles used to sense linear motion
Resistance change
Inductance change
Capacitive change
Transformer coupling change
Sensor of force
bonded wire strain gauge
List the sensors for fluid pressure
bourdon tube
bellows
diaphragm
List the sensors for temperature
Resistive
Thermistors
Thermocouple
List the sensors for light
Photoemission
Photoconduction
Photovoltaic
standard signal output is
4 mA to 20 mA DC
or 10 mA to 50 mA DC
What device is commonly used to express rotary motion as and electrical signal?
tachogenerator
How does a piezoelectric crystal work as a sensor?
as the crystal bends it gives off a measurable electrical signal
On what principle does a magnetic flow meter work?
electromagnetism
describe negative feedback
the desired condition where the error signal is the difference between the set point and the feedback signals
describe positive feedback
occurs because of a connection error. Is the sum of the set-point and the feedback signals
What two signals does the comparator use to determine error signals
set-point
feed-back signal
List three types of actuators (servomechanisms)
Electric
Hydraulic
Pneumatic
List two types of stepper motors
Variable reluctance
Permanent magnet
How can a stepper motor be reversed
Reverse the stepping switch sequence
What advantage can be gained by using half-step vs. full-step energization modes
increased step resolution by giving the motor more steps
