Common Types of Sensors and Transducers Flashcards
What is a transducer?
Device the converts energy from one form to another
What is the difference between an analogue sensor and a digital sensor?
Analogue sensor’s output varies continuously and smoothly over its sensing range. Digital sensor’s output is in definite steps.
What are some common categories of sensors?
- Sensors of motion
- Sensors of force
- Sensors of fluids
- Sensors of light
- Sensors of temperature
What are four basic principles used to sense linear motion?
- Resistance change
- Inductance change
- Capacitance change
- Transformer coupling change
What device is commonly used to express rotary motion as an electrical signal?
Tachogenerators
What resistance parameters are changed when a strain gauge is subjected to a compression force?
Decrease in length and increase in cross-sectional area
What are three types of fluid pressure sensors?
- Bourdon tube
- Bellows
- Diaphragm
How does a piezoelectric crystal work as a sensor?
Can separate charges (create voltage) according to the amount of mechanical pressure applied. It is used to sense mechanical pressure changes.
On what principle does a magnetic flow meter work?
Principle of generation (electromagnetism)
What are the differences between an RTD and a thermistor?
RTD - made of metal wires or film and has a POSITIVE temperature coefficient of resistance
Thermistor - made of semiconductor material and has a NEGATIVE coefficient of resistance
What are three basic principles used in light sensors?
- Photoemission
- Photoconduction
- Photovoltaic
What is the function of a transmitter?
Accept sensor information and provide standard types of output signals for transmission over long distances
Controllers usually work with ________ and _______ forms of energy
electrical, pneumatic
Why does a linear motion potentiometer require periodic maintenance?
Slider of the potentiometer wipes mechanically on the resistance element, causing it to wear out over time
Why does a linear motion variable inductor last longer than a linear potentiometer?
Does not have contact wear
What are some unique features and characteristics of a linear variable differential transformer (LVDT)?
- can be made very small
- very sensitive to motion
- can be used with other circuit components to provide polarity sensitive DC voltage
- has two identical secondary windings and a single primary winding
How does a linear motion variable capacitor work?
Distance between fixed plate and movable plate varies according to linear position. As plate is moved closer to the fixed plate, its capacitance increases; when it is moved further away, its capacitance decreases.
How can you get a single voltage signal from a LVDT?
Connecting the two secondary windings in series opposition (differential) connection
What do fluid sensors supply information on?
- Fluid pressure
- Fluid flow
- Liquid level
What are some characteristics of a bourdon tube?
- slightly flattened tube of flexible steel arranged in a semicircle
- one end of tube is closed, other is open and fixed
- inexpensive, quite accurate, rugged, and reliable
How does a bourdon tube work?
As pressure in tube increases at the open end, the closed end tends to straighten. As pressure is reduced, the closed end moves back to its original position
What are some characteristics of a bellows?
- more sensitive than bourdon tubes
- used for low pressure applications
_____________ and ___________ are used to sense rates of fluid flow
orifice plates, manometers
What is a radiation pyrometer often used for?
Sensing very high temperatures of metals being melted in a furnace
What is the principle of photoemission?
Electrons are liberated from the material when light energy falls on it
What is the principle of photoconduction?
The resistance of the material is reduced with light
What is the principle of photovoltaic?
Voltage is generated in a cell due to light falling on it
A phototube works on what principle?
photoemission, where a cathode is coated with a light-sensitive substance that releases electrons when light shines on it
A light-dependant resistor (LDR) works on what principle?
Photoconduction
What are some characteristics of a photovoltaic cell?
Consists of a P-N junction with a large light-collecting surface area that generates emf according to the amount of light
What is usually an electrical output signal standard
4mA to 20mA direct current signal range, or 10mA to 50mA direct current signal range
