Lecture 2 - Sensors I Flashcards
What is a LinearVariable Differential Transformer used for?
It is a device which can read displacement using a push rod and outputting the displacement as a voltage.
How does a LinearVariable Differential Transformer (LVDT) work?
It is build of 3 coils. The middle coil (primary) has a AC source ran through it. Voltage is measured between the positive side of each of the outer coild (secondary 1 and 2). WITHOUT MODULATION the output is on wave form but phase shifted to the left if the rod is pushed to the right and vice versa
WITH MODULATION the output is postive if the rod is pushed to the right and vise versa
Formula:
V_out = V_s1 - V_s2
How does LinearVariable Differential Transformer (LVDT) modulation work?
It uses both a “Diode bridge” [I think] and a Low-pass filter. The Diode bridge uses diodes in a square to make the signal only positive or negative. The Low-pass filter is used to smoothen out the “waves”
(Skal måske undersøges nærmere)
What is a resolver and what is it used for?
A revolver is used to measure angle of rotation.
It is build of a rotor (rotates) and a stator (stationary). The stator has primary windings, cosine windings, and sine windings. The rotor also has windings which are placed inside the primary windings.
AC current is applied at the primary windings which is transferred to the rotor windings (like a transformer). Voltage is measured at the cosine and sine windings.
If the rotor winding is parallel to the cosine winding, maximum voltage is measured at the cosine winding and 0 is measured at the sine winding.
As the rotor rotates, this changes and an angle can be calculated from the voltage.
https://www.youtube.com/watch?v=7PKJ52b1Qvs
What is a Digital optical encoder? What is it used for?
It is a disk with a series of holes. Light is send out on one side and is recieved at the other. Line can only pass through the holes of the disk.
It is “a device that converts motion into a sequence of digital pulses”.
What types of Digital optical encoder have been discussed?
Grey,
Binary,
Incremental (has 3 different resolution: 1X, 2X, and 4X quadrature)
What are the 4 main types of proximity sensors and how do they work (described in one sentence)?
Inductive: Are used to detect metallic objects by the principle of electromagnetism and
induction.
Capacitive: Are used to detect
metallic and non-metallic objects by the principle of capacitance.
Ultrasonic: Are used to detect
metallic and non-metallic objects by sending an ultrasonic wave.
Optical: Are used to detect metallic and non-metallic objects by sending an optical wave.
How does a INDUCTIVE Proximity Sensors work? What are the advantages and disadvantages?
“Sensing metallic objects by induction effect”
A coil in the front of the sensor creates a magnetic field. As the magnetic field hits a metallic surface, it creates an eddy-current in said surface. This Eddy-current creates a magnetic field back which opposes the original magnetic field (This is based on Faraday’s law).
Advantages
* High accuracy
* High switching rate
* Can be used in harsh conditions
Disadvantages
* Short operating range
* Detect only metallic object
How does a CAPACITIVE Proximity Sensors work? What are the advantages and disadvantages?
“Sensing metallic/non-metallic objects by generating electric field”
There is two parallel plates inside the head of the sensor, one has + and the other -. There is air between the plates, which conducts electricity poorly. As electrons build up in the negative plate, electrons leave the positive plate to equal out. There is now build up capacitance. As an object with better conductivity than air gets closer to the sensor, it will help conduct the electricty, meaning the capacitance becomes lower. Meaning measuring this change, it can sensor objects.
Advantages:
* Low cost
* High speed
* Low power
Disadvantages:
* Less accuracy
* Sensitive to temperature and humidity
How does a ULTRASONIC Proximity Sensors work? What are the advantages and disadvantages?
The TRIGGER/Transmitter (OUTPUT) sends out an ultrasonic wave. The ECHO/Receiver (INPUT) switches to a one state until the ultrasonic wave is recieved again. The time the ECHO is one is recorded and can be caltulated to a distance using the speed of sound.
Advantages:
* Don’t get affected by
environment effects like
rain, dust, etc.
Disadvantages:
* Can not work under
vacuum or water
How does a OPTICAL Proximity Sensors work? What are the advantages and disadvantages?
“Sensing metallic/non-metallic objects by generating light wave”
A transmitter (OUTPUT) sends out a light wave. [I ASSUME:] The receiver (INPUT) records the time until the light is received by staying ON until signal is received, just as the US sensor. The distance is measured using the speed of light.
Advantages:
* High sensitivity
* Small and lightweight
* insensitive to electromagnetic
interference
* Wide dynamic range
Disadvantages:
* Could be costly
* Not precise for transparent
objects
* Not appropriate for objects
with rough surface
