The main function of a sensor is to serve as a transducer, transforming a physical or chemical occurrence such as heat, into a quantifiable electrical signal, typically a variation in voltage, current, or frequency. The design of nearly all sensors relies on modifying basic electrical properties.
a). Resistive Principle
Figure 1: Resistance and Resistivity
Resistance refers to the opposition against the flow of electric current within a material or component, measured in ohms (Ω). It can be determined using two primary equations:
Ohm's Law,
R = V/I
where resistance is equal to voltage divided by current) for components that adhere to it, or
The Resistivity Formula, R = ρ(L/A), defines resistance as resistivity times length divided by cross-sectional area to calculate a material's inherent resistance.
Resistive sensors function based on the concept that the electrical resistance (R) of a substance varies in response to an external physical stimulus. Any physical condition that alters, the material's capacity to conduct electricity can thus be estimated by computing the resistance or any of the related variables.
Example 1
Calculate the resistance of a copper wire that is 10 meters long and has a cross-sectional area of 5 x 10^(-5) m^(2). Copper's resistivity is approximately 1.68 x 10^(-8) Ωm
Solution
R = [(1.68 x 10^(-8)) x 10] / [5 x 10^(-5)] = 3.36 x 10 x 10^(-3)Ω
Example 2
A circuit has a voltage of 12V and a current of 0.5 A flowing through it. What is the resistance?
Solution
R = V/I = (12V)/(0.5A) = 24Ω
b). Capacitive Principle
A capacitor resists the flow of alternating current, and this opposition is called capacitive reactance. As the frequency of the AC signal increases, the capacitive reactance decreases. Conversely, a lower frequency results in higher reactance. Capacitive sensors measure changes in capacitance (C) (Capacitance is determined by the distance between two conductive plates and the material (dielectric) placed between them.). Physical input, such as distance, or displacement, causes a change in the geometry or the nature of the dielectric. Since the electrical charge stored changes with capacitance, this results in a voltage change.
c). Inductive Principle
Inductance is the property of an electric conductor that causes an electromotive force to be generated by a change in the current flowing. Inductive sensors detect variations in inductance (L) found within a coil. As the physical input (such as position or displacement) alters the magnetic flux through the coil, the inductance of the coil changes. Devices like Linear Variable Differential Transformers (LVDTs) utilize this concept for precise position measurements.
2. Transduction Effects
A number of physical effects are employed for specialized sensor functions. These include:
a). Piezoelectric Effect
The piezoelectric effect refers to the phenomenon where specific materials produce an electric charge when they experience mechanical stress or pressure, which is referred to as the direct effect.
Some crystalline substances, such as quartz or particular ceramics, demonstrate the Piezoelectric Effect. When these materials undergo mechanical stress like force, pressure, or acceleration, they produce a direct and proportional electrical charge on their surface.
This has found application in accelerometers, vibration sensors, and pressure transducers.
b). Hall Effect
This is the generation of a voltage across an electrical conductor when a magnetic field is applied perpendicular to the direction of current flow.
The interaction generates a measurable voltage across the conductor, which is perpendicular to both the current and the magnetic field.
The generated voltage is directly related to the intensity of the magnetic field. This enables Hall Effect sensors to gauge magnetic field strength, ascertain the location of a magnet, and measure rotational speed without the need for physical contact.
3. Conclusion
In conclusion, the effectiveness of any measurement method is dependent on the foundational sensor principles. These principles are realized through effective transduction effects. The accurate transformation of a physical or chemical input into a measurable electrical output as an essential link. Comprehending phenomena like the Hall effect or the Seebeck effect enables engineers to design sensors for reliable and stable operation in various environments. Ultimately, all complexities are based on the understanding of these physical transduction mechanisms.
CLASS ACTIVITY - METHODS
Creating and Modifying a Gradebook
Activity 1: Creating a Student Gradebook
Task: Create a class named Student that takes two
pieces of information: the student's name and their score. These pieces of information are
attributes of the student object. The new student's
name is "Jane" with a
starting score of 82.
student1
= Student("Jane", 82)
Print the student's name and score to confirm that it worked.
print(f"{student1.name}'s
initial score is {student1.score}")
Activity 2: Adding a New score
Add a method to theStudent class to perform the modification. An instance method is a
function that belongs to an object and can change the object's data.
We create a
method and give it a nameadd_score. It will take a new score (an integer) and add to the existing. (Use self
to access the object's attributes). In this case add 10 marks to Jane
We
use the add_score
method to give Alex 10 extra points.
Confirm by printing the new mark.
student1.add_score(10)
# Print
the new score
print(f"{student1.name}'s
new score is {student1.score}")
Activity 3: Calculating the Average
Assuming a student has two scores. Add a new method to Student class
called get_average_score. Note that
the method does not take any more arguments.
Create a second student named "Mia"
with an initial score of 70. Use the
add_score method to give Mia 60 points.
Then, call the get_average_score method for Mia and print the returned average.
# Your
code here...
student2
= Student("Mia", 70)
student2.add_score(60)
#
Calculate and print the average
average =
student2.get_average_score()
print(f"{student2.name}'s
average score is {average}")
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