Survey

* Your assessment is very important for improving the work of artificial intelligence, which forms the content of this project

Document related concepts

Control system wikipedia, lookup

Electrical ballast wikipedia, lookup

Rectifier wikipedia, lookup

Thermal runaway wikipedia, lookup

Current source wikipedia, lookup

Potentiometer wikipedia, lookup

Surge protector wikipedia, lookup

Alternating current wikipedia, lookup

Multimeter wikipedia, lookup

Stray voltage wikipedia, lookup

Power MOSFET wikipedia, lookup

Voltage regulator wikipedia, lookup

Buck converter wikipedia, lookup

Ohm's law wikipedia, lookup

Switched-mode power supply wikipedia, lookup

Mains electricity wikipedia, lookup

Schmitt trigger wikipedia, lookup

Voltage optimisation wikipedia, lookup

Lumped element model wikipedia, lookup

Current mirror wikipedia, lookup

Opto-isolator wikipedia, lookup

Resistive opto-isolator wikipedia, lookup

Transcript
```Instructions
• To run the slideshow:
– Click: view – full screen mode, or press Ctrl +L.
– Left click advances one slide, right click returns to
previous slide.
– To exit the slideshow press the Esc key.
Thermistor System – Potential Dividers
KS5
Potential Dividers
• Draw a simple potential divider circuit.
• Explain without calculation what a potential
divider is used for.
Potential Dividers
R1
Vin
R2
Vout
• A potential divider is a useful circuit which
allows the user to control the output voltage
from 0V up to a maximum, determined by R1
and the input voltage.
Example
• Using the potential divider equation or otherwise, determine
the output voltage of the following circuit when:
a) R2 has a value of 50Ω
b) R2 has a value of 10Ω
200 Ω
12V
R2
Vout
Solution
• Using the potential divider equation:
𝑉𝑜𝑢𝑡
𝑅2
=
× 𝑉𝑖𝑛
𝑅1 + 𝑅2
a) 𝑉𝑜𝑢𝑡
50
=
× 12 = 2.4𝑉
250
b) 𝑉𝑜𝑢𝑡
10
=
× 12 = 0.6𝑉
210
Output voltage
• It should be clear form the solutions to the
previous example that decreasing the
resistance of R2 leads to a decrease in the
output voltage.
• Connecting a variable resistor in place of R2
would allow the output voltage to be varied
between 0V and a maximum, determined by
R1 and the input voltage.
Sensors
• Connecting any component whose resistance
varies in response to a stimulus in the place of
R2 allows us to build a circuit where the
output voltage varies in response to an
external event.
• Such components are called sensors.
Thermistors
• A thermistor is a circuit component whose
resistance changes with temperature.
• What do you think is going to happen to the
resistance of the thermistor as the
temperature increases?
Investigating thermistors
• For this investigation a
thermistor is mounted inside a
sealed glass tube.
• Resistance measurements can
be taken directly using a
multimeter or through current
and voltage measurement and
calculation.
Taking measurements
• You should measure the resistance of the thermistor for a
range of temperatures.
• Bring a beaker of water to the boil and take readings as the
water cools down.
• Readings should be taken at roughly 5oC intervals. (monitor
the temperature of the water using a thermometer)
• To reduce risk of damage it is advisable that the thermistor
system be supported by a clamp.
Sample Data
16000
• From the data opposite you
should be able to see that
resistance decreases as the
temperature increases.
14000
Resistance Ω
12000
10000
• We say that the thermistor
has a Negative Temperature
Coefficient
8000
6000
4000
• It is an NTC Thermistor
2000
0
0
20
40
60
Temperature oC
80
100
Add the title ‘Resistance against temperature for an
120
Thermistors
• Suggest what you think the relationship
between resistance and temperature would
be for a PTC Thermistor (Positive temperature
coefficient)
Thermistors
• Suggest what you think the relationship
between resistance and temperature would
be for a PTC Thermistor (Positive temperature
coefficient thermistor)
• For a PTC thermistor, as temperature
increases, the resistance of the thermistor
increases.
Using Thermistors
• Look at the potential divider below.
• The thermistor is an NTC type.
• State what will happen to the output voltage as the