Sensors Actuators Control Flashcards
What do sensors do?
Provide feedback about process.
What do actuators do?
Produce useful work through mechanisms.
What do controllers do?
Control process based on input from sensors.
What are some position sensors?
Potentiometers
Linear variable differential transformers
Encoders
What is a potentiometer?
- It’s a variable resistance transducer.
- Measures absolute rotary or linear displacement.
- Consists of a sliding contact and a winding.
What is the equation for the output of a potentiometer?
Vo = k(Vr)x
where
Vo = output
Vr = known voltage applied across winding
x = displacement of contact point
k = sensitivity
List 5 characteristics of potentiometers.
- discrete resolution
- low cost
- low accuracy
- simple
- reliable
What is a linear variable differential transformer?
Consists of:
- one primary coil
- two secondary coils (with opposing voltages)
- a ferromagnetic core
output voltage = Vo = kx
where
k = sensitivity
x = distance moved
What are 5 characteristics of a linear variable differential transformer?
- high resolution
- limited range
- bandwidth is about 1/10 of excitation (which is in range of 50 Hx to 25 kHz)
- discrete sampling is possible over time with a DAS
- static measurements are taken with a voltmeter.
What is the most used position sensor for electric motors?
Encoder
Describe an encoder.
Can be rotary or linear.
Measure absolute or incremental position.
Consists of:
- transparent patterned disk
- light source
- photodetectors
If an engineer wants to know the velocity of a part in a system, what methods are there that they can follow?
1) use a moving coil transducer
(E = pi* B * Dc * L * N * (dy/dt))
- E is induced voltage
- B is magnetic field strength
- D is coil diameter
- N is number of turns in coil
- L is coil length
or
2) differentiate displacement
or
3) integrate acceleration
