The document discusses a student project to develop a temperature control system using a thermistor. The thermistor is a negative temperature coefficient sensor whose resistance decreases with increasing temperature. The project involves taking resistance measurements of the thermistor at different water bath temperatures in order to characterize its temperature-resistance relationship. An operational amplifier circuit will be used to actuate a relay and switch on a lamp if the temperature rises above a certain threshold, indicating the temperature control system is working automatically. The goal is to obtain hands-on knowledge of temperature control using a thermistor and demonstrate its applications in engineering fields.

1. Pat Arnott, ATMS 360 Atmospheric
thermistor based temperature control
• NAME ROLL NO
• ankit dutta 31
• tithi makar 08
• koushik das 11
• madhumanti saha 09
• sourov saha 54

2. Pat Arnott, ATMS 360 Atmospheric
acknowledgement
 The main objective of this project is to obtain first-hand
knowledge on how temperature can be controlled by using a
thermistor and how it can be applied to the main work field and
also to prove its main impact in the field of Engineering and
Technology.
 It is my heartiest gratitude to respected MRS S.Maity, our faculty
and guide through-out this project work for her professional
guidance, advice, motivation, endurance and encouragements
during her supervision period. The present work would have
never been possible without her vital supports and valuable
assistance.
 Needless to mention that she has rendered her whole -hearted
support and help to make this project a success.
 It is only because of her and our all-out effort that we could draw
up to this extent in such a field of excellence in the present days
of Science and Technology.

3. Pat Arnott, ATMS 360 Atmospheric
thermistor
thermal resistor
A thermistor is a type of resistor used to measure
temperature changes, relying on the change in its resistance
with changing temperature. Thermistor is a combination of
the words thermal and resistor. The Thermistor was
invented by Samuel Ruben in 1930, and has U.S. Patent
#2,021,491.
Leads, coated Glass encased Surface mount

4. Pat Arnott, ATMS 360 Atmospheric
thermistor
thermal resistor
Assume a simple linear relationship between
resistance and temperature for the following
discussion:
ΔR = k ΔT
where
ΔR = change in resistance
ΔT = change in temperature
k = first-order temperature coefficient of
resistance

5. Pat Arnott, ATMS 360 Atmospheric
thermistor
thermal resistor
Thermistors can be classified into two types depending
on the sign of k.
If k is positive, the resistance increases with increasing
temperature, and the device is called a positive temperature
coefficient (PTC) thermistor, Posistor.
If k is negative, the resistance decreases with increasing
temperature, and the device is called a negative
temperature coefficient (NTC) thermistor.

6. Pat Arnott, ATMS 360 Atmospheric
aim of the project
 The project is designed to develop a
temperature control system using thermistor.
 The thermistor is a negative temperature
coefficient temperature sensor. So increase in
temperature will decrease its resistance.
 Thus at higher temperature conditions , the
thermistor will be capable of conducting more
amount of current through it.
However, due to the non-linear resistance
versus temperature characteristics of the
thermistor, care should be taken to make it as
linear as possible.
 A lamp or an optical source is connected to
the overall circuitry which is mainly used as an
indicator.

7. Pat Arnott, ATMS 360 Atmospheric
STEPS UNDERTAKEN /
PLANNING REQUIRED
STEP 2:
Increase in
temperature
decreases its
resistance. The
minimum and
maximum
resistance
values are
noted down.
:
STEP 3:
No conclusion is
found as no
graph can be
drawn from it.
STEP 5:
The
tempersture of
water after a
specific time
period is noted
down .
STEP 6:
At this
temperature
values, the
corresponding
thermistor
resistance values
are measured.
Now its possible
to draw a graph.
STEP 1:
Heat is supplied to
the thermistor using
soldering iron.
STEP 4:
A water bath is
completely filled with
water and is heated
by dipping an
immersion heater
into it.

8. Pat Arnott, ATMS 360 Atmospheric
thermistor
thermal resistor

9. Pat Arnott, ATMS 360 Atmospheric
components
Resistors
R1,R2 8.2k
R4 1K Thermistor
R5 470 ohm
R6 22k
R7 820 ohm
R3 All 100 ohm
Diodes
D1 Zener Diode 5.1 v ,400 mW
D2,D5,D6 1N4001
D3,D4 15 V 1w
Other Parts
IC1 op amp 741
T1 BC 147
X1 18V
C1,C2 capacitor 470micro 50V
R1 Relay 12V, 250 ohm
S1 1 Pole ,10 way switch
Immersion Heater 50W
Thermometer

10. Pat Arnott, ATMS 360 Atmospheric
ADVANTAGES OF USING
THERMISTOR
Sensitivity: Large change in resistance with temperature, typically -5% per K.
Accuracy: Thermistors offer both high absolute accuracy and interchangeability.
Small size: Thermistors have very small sizes and this makes for a very rapid
response to temperature changes.
Ruggedness: Most thermistors are rugged and can handle mechanical and thermal
shock and vibration better than other types of temperature sensors.
Remote measurement: Thermistors can be used to sense the temperature of
remote locations via long cables
Low cost: Thermistors cost less than most of the other types of temperature sensors.
Interchangeability: Thermistors can be manufactured with very close tolerances.

11. Pat Arnott, ATMS 360 Atmospheric
thermistor
thermal resistor
Example Applications:
• Temperature measurement.
• Time delay (self heating from large current ‘opens’ the
thermistor so it can be used as a slow switch).
Heating = i2
R where R is the resistance and i is the
current.
• Surge suppression when a circuit is first energized.
Current needs to flow through the thermistor for awhile
to heat it so that it ‘opens’, and acts again as a switch.

12. Pat Arnott, ATMS 360 Atmospheric
12
Example Applications
• Thermometry!
• PTC thermistors can be used as current-limiting devices
for circuit protection, as fuses.
• Current through the device causes a small amount of
resistive heating.

13. Pat Arnott, ATMS 360 Atmospheric
APPLICATION OF THERMISTOR
Household Electronics: Refrigerators and deep-freezers,
washing machines, electric cookers
Automotive Electronics: Motor management, airbags
Heating and Air-conditioning: Heating cost distributors,
room temperature monitoring.
Industrial electronics: Temperature stabilization of laser
diodes and photo elements.
Computer and consumer electronics: HDDs, printer
and PC main boards.
Telecommunications: TCXO.

14. Pat Arnott, ATMS 360 Atmospheric
PROPOSED WORK
Whenever temperature increases beyond a certain value, a
lamp (indicating a cooler) is switched on to bring the
temperature to normal value. As switching ON of load is
done automatically so this system doesn’t require
anyone to monitor the temperature in person. Negative
co-efficient thermistor is used along with an operational
amplifier to actuate the relay in the event of temperature
going out of range. Characteristics are highly nonlinear
and need correction for applications that require a linear
response. A change in temperature will alter the input
parameters to the op-amp. The op-amp delivers an
output to energize the relay and switch ON/OFF the
lamp.