Unit 17 Assignment 4, Transducers and Measuring Devices
Applied Science Level 3 2nd year physics unit 17, assignment 14 on Transducers and Measuring Devices. Includes experiments and hand drawn graphs, and referneces.
Task 1:
Type of transducer: Active or Passive:
LDR- photocell resistor Passive
Speaker- Sound Transducer Passive
NTC Thermistor-Thermal Passive
sensitive resistor
Thermocouple – Active
Temperature Transducer
Piezoelectric Transducer Active
Strain gauge -Force sensor Passive
resistor
Photoelectric cells Active
LDR- photocell resistor:
The resistor is commonly used to detect the light levels, specifically its presence and lack of
light. So, when there is light or there isn’t the resistor will detect it. This is useful for many
applications such as streetlights, the way this works is that the lights can automatically turn
on and off depending on the amount of light shining on it. So, in the dark/ night the
streetlights will turn on and, in the light/ daytime the lights will turn off. This is because
when there is no light shining on the LDR and it is dark then the resistance is at its highest
and causes the current to be at its lowest so there is less current flowing allowing the
transistor to turn on and the transistor will cause the current to flow from the collector to
the emitter. This will cause a potential difference across the light and the current causing
the light to turn on or off. The LDR is positioned high so any sudden light changes will not
differ with it for example car headlights. Another application it is useful in is alarm clocks or
burglar alarm so, when light falls on the LDR the resistance decreases which will activate an
alarm to be heard by the user.
Speaker- Sound Transducer:
A sound transducer requires A input and output device as well as a controller. For example,
a speaker is an example of an output device and a microphone is an example of an output
device. Within both processes there are many energy transformations. In a speaker
electrical energy that comes from the audio signal is converted into mechanical energy
which is the vibration caused by the diaphragm and the cone of the speaker. This is then
transformed into kinetic energy and is outputted into the surrounding which will cause a
sound to wave an create sound. Whereas in a microphone it is the opposite sound wave is
converted into electrical energy. So, if there is any sound detected the microphone will
automatically produce sound waves, the sound waves will cause vibration to the diaphragm
because of the sound waves hitting it and so the vibrations produced are then converted to
an electric current which makes it an audio signal. The conversion between the sound and
electrical signal is so that it can be recorded or amplified.
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, Saba Khan
Applied Science
Level 3 Group 2
NTC Thermistor-Thermal sensitive resistor:
This is a thermally sensitive resistor; its resistance decreases with increasing temperature.
An application of this would be a fire alarm because they are made to detect temperature
changes that are high than the temperature threshold causing an alarm. They can also
detect fires due to their semiconducting materials. The alarm can be activated easily just by
the presence of too much heat. PTC thermistors can be used as alternatives for fuses. So,
the current flowing through the device can cause little production however the larger the
current the more heat is released by the device. This will cause an increase in resistance,
and so slowly the current will decrease and protect the device.
Thermocouple – Temperature Transducer:
These are the most popular types of temperature sensors, they are used as hospital
thermometers, and in diagnostic testing for vehicle engines. Some gas appliances such as
boilers, water, heaters and ovens use them as safety features; if the pilot light is out, the
thermocouple stops the gas valve from operating. They are also used as an acid in milk
pasteurization, and as food thermometers. In industry they are valuable as probes and
sensors. These measure the temperature for exhaust gases, so they help reduce pollutions.
Based on the metal wire of the transducer they can measure temperature up to -200°C and
2500°C. Exhaust gases are basically hot reasons why these are used are because of the
metal wires that can handle high temperatures and low temperatures. So, they can be used
as flame sensors in safety devices for gas-powered appliances. Another application of this is
that it can be used within digital thermometers, depending on the electrical signals there
will be a display of numerical temperature. They are most used for displaying temperature
because they are known for their accuracy and reliability due to the low rate of errors.
Piezoelectric Transducers:
It is a transducer that convert the electrical charges produced by some forms of solid
materials into energy. It can be used as a seismograph, this where the vibrations are
measured in. Within rockets, the piezoelectric crystal is placed under a strain because the
kinetic energy from the vibration produces a small current due to the photoelectric effect.
Another use of this is ultrasound imaging the piezoelectric effect converts the mechanical or
kinetic energy formed by the deformation of the crystal into electrical energy which causes
the transducer will receive the sound waves and form an image. They can also be used to
measure the distance of an object based on reflection of sound. Different types of probes
are used to check the womb for foetus.
Strain gauge -Force sensor resistor:
These transducers are present with anything that requires force the main use of these are
instruments. For example on a drum when force is applied the electrons are delocalized so
they move from a valence band to another band such as the conductance band this is
commonly known as the Band theory it causes the electricity to flow meaning the current
which means that the resistance reduces. These transducers can also be used within cars
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