Sensors Flashcards
What is the range of a sensor?
The range is the maximum and minimum values that can be read by the sensor
What is the span of a sensor?
The span is the difference between the values of the range
What is the sensitivity of a sensor?
This is how much the output varies depending on the input
What is the linearity of a sensor?
This is how close the approximate values of the sensor are to the real values of the environment
What is the definition of accurate?
Accurate readings are when the measurements are in close agreement to the real readings
What is the definition of precise?
This is when the measurements are in close agreement with each other, but they may not be close to the true values still
What is the resolution of a sensor?
This is the smallest input variation that can be detected on the output signal
What is the time response of a sensor?
This is the time needed by the sensor to output a variation of the input signal
What is the bandwidth of a sensor?
This is the frequency domain where the sensor can measure an input
What is a limit switch?
These are mechanical switches that have the same principles as light switches
What is a bimetallic strip used for and how does it work?
These are used to detect temperature changes as they are two different metals that expand differently due to temperature changes, causing the strip to bend and open or close the switch
What do we use a pressure switch to measure?
We can measure gas pressure and fluid pressure
What does a phototransistor detect?
Light intensity
What does a tilt switch detect?
It detects the orientation of objects and sees if the object has been tilted
How is a flow switch triggered?
There needs to be a flow of gas or fluid passing to trigger the switch
How does a level switch work?
A floating element will mechanically trigger the switch at a calibrated level
What are some of the main considerations for the selection and connection of switches?
- Range
- Threshold
- Breaking Capacity
- NO/NC
- Response Time
What is the breaking capacity?
It is how much current can be stopped by the switch, however, this isn’t a large consideration when using a PLC
Why do we need to consider if a switch is normally open or normally closed?
Because if there is a fault in the system, this will determine how that sensor will act if there is a fault within
Why is response time a consideration for sensors?
Because mechanical actions may take a while to switch
How does a through beam optical sensor work?
This is similar to a light gate, where a transmitter and receiver have a connection between them, which is then broken as something passes through, letting the sensor know something is in the way
How does a Retro-reflective optical sensor work?
The transmitter and receiver are combined within one system, and a reflector is on the other side, so the system reads the beam that is reflected back. The sensor will stop detecting the light as it won’t be reflected back
How does a diffuse optical sensor work?
The transmitter and receiver are a combined system, and then when the object passes infront of the light, it’s reflected back, and will then be detected by the receiver
What are inductive sensors used to detect?
Metallic objects
What do capacitve sensors detect?
Many types of materials, including liquids
What is another name for Magnetic Proximity Sensors?
“Reed” Switches
How do Magnetic Proximity Sensors work?
They can be mechanically opened or closed when a magnetic field is applied close by
What is the formula to relate the distance between a sensor and the target and the time of flight?
d = (ct)/2 * cos(x)
d = Distance
c = Speed of light
t = Time of flight
x = Angle of reflection
What are the two types of encoders?
- Absolute Encoders / Return a unique digital word that corresponds to a particular position of the encoder
- Incremental Encoders / Return impulses everytime the encoder changes position
What are the two languages used for absolute encoders, and which is more common?
Binary (Uncommon)
Gray (Common)
How many tracks are generally on an incremental encoder?
2 Tracks
What is the minimum amount of satellietes required to use a GPS system?
3, but we use more incase some of the potential satellietes are blocked
What is the typical accuracy of a GPS system?
Accuracy is typically 5m vertically and 3m horizontally
What is the average range of an Electromagnetic Tracker?
Small Range ~ 0.5m
How does an electromagnetic tracker work?
We have a coil inside the transmitter that we can charge to then make it emit magnetic flux. The flux intensity is then measured by the receiver, to then determine the distance and orientation of the transmitter
How does a doppler effect sensor work?
We can use these to measure the speed of a moving object or fluid. We send a wave of a known frequency to collide with the moving object, and then measure the speed of the object comparing the relative difference
How does a strain gauge work?
A strain gauge is a sensor made of a conductive element whose resistance varies depending with the applied force. As a force is applied, there is a strain, which leads to a variation of the gauge material dimensions, which allows us to equate the strain with the varying resistance
How does a load cell work?
We have an element that can deform in a precise way, and then we can measure the deformation to see the load
How does a fiber optic force sensor work?
Small sections of the sensor act as reflectors, so white light will reflect different colours before and after a force is applied
How does a Piezoelectric force sensor work?
As a force is applied to the sensor, there will be a charge generated, which will allow us to then measure the voltage and equate it to the force applied
What types of forces can be measured with a Piezoelectric force sensor?
Dynamic Forces
Static Forces can’t be measured as charge is lost when measuring
How does a thermocouple work?
It equates the temperature and voltage
