Process Control Flashcards
Give two examples of process variables
Speed
Position
Fluid pressure
Liquid level
Liquid flow
Temperature
What is open loop?
Not automatic
No feedback
Requires operator
What is closed loop?
Automatic
Feedback
No operator required
What is a transducer?
Converts energy from one form to another
What are three common uses of sensors? (What do they detect?)
Motion
Force
Temperature
Light
Position
Fluid pressure/flow
List four types of linear motion sensors
Potentiometer
Variable inductor
Variable capacitor
Variable differential transformer
What is a bonded wire strain gauge used to sense?
Force
What device is used to send an electrical signal from a motor in order to interpret its speed?
Tach generator (most common)
Incremental encoder
List three type of fluid pressure sensors
Bourdon tube
Bellows
Diaphram
Which device consists of two dissimilar metals that when heated produce a small voltage?
Thermocouple
Which feedback sensor would produce a small voltage when subjected to vibration?
Piezo electric crystal
Which two signals does a comparator use to determine an error signal?
Set point
Feedback
What is the function of an actuator?
Converts electrical energy to;
Motion
Heat
Light
What does a solenoid do?
Provides linear motion
What are three types of stepper motors?
Permanent magnet
Variable reluctance
Hybrid
How can a stepper motor be reversed?
Reverse order of switching
In regards to a stepper motor, what is a full step?
90°
In regards to a stepper motor, what is a half step?
45°
What are the three necessary parts of an optical encoder?
Light
Rotating disc
Light sensor
What device could be used to minimize overshoot in regards to a baseboard heater?
Heat anticipator
What is a sensor?
Measures and senses the process variable and provides feedback to the controller
What type of sensor is this?
Linear motion potentiometer. Works with both AC and DC
What type of sensor is this?
Linear motion variable inductor. Works with AC only
How many degrees of travel can an angular motion potentiometer measure?
Up to 300°
How many degrees of travel can an angular motion variable inductor measure?
More than 300°
What is an actuator?
A device that converts an input signal into mechanical motion
What is a stepper motor?
- Incremental, brushless DC motor
- Moves in discrete steps
- Each time its pulsed it will rotate by a certain angle
What is a variable reluctance stepper motor?
- The rotor will align itself with the energized salient pole
- Will not hold position when de-energized
What is the process variable?
A variable that needs to be controlled
What is the set point?
The desired value of the process variable
