Circuit labthermistors (1)

Pat Arnott, ATMS 360 Atmospheric Instrumentation

thermistor based temperature control

• NAME ROLL NO• ankit dutta 31• tithi makar 08• koushik das 11• madhumanti saha 09• sourov saha 54


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.


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


thermistorthermal 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



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.


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.


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.


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


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.



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

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.


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.


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.

Circuit labthermistors (1)

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