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SENSORS

  . SENSORS

3.3.1 TEMPERATURE SENSOR (LM35):

Precision Centigrade Te!erat"re Sensor:

In this project, in order to monitor the temperature continuously

and compare this with the set temperature preprogrammed in the

microcontroller, initially this temperature value has to be read and fed

to the microcontroller. his temperature value has to be sensed. hus a

sensor has to be used and the sensor used in this project is !"#$. Itconverts temperature value into electrical signals.

!"#$ series sensors are precision integrated%circuit temperature

sensors whose output voltage is linearly proportional to the &elsius

temperature. he !"#$ re'uires no e(ternal calibration since it is

internally calibrated. . he !"#$ does not re'uire any e(ternal

calibration or trimming to provide typical accuracies of )*+-& at room

temperature and )#+-& over a full $$ to /*$0-& temperature range.

 he !"#$1s low output impedance, linear output, and precise

inherent calibration ma2e interfacing to readout or control circuitry

especially easy. It can be used with single power supplies, or with plus

and minus supplies. 3s it draws only 40 53 from its supply, it has very

low self%heating, less than 0.*-& in still air.

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#eat"res:

*. &alibrated directly in - &elsius 6&entigrade7

8. !inear / *0.0 m9:-& scale factor

#. 0.$-& accuracy guaranteed 6at /8$-&7

. Rated for full $$- to /*$0-& range

$. Suitable for remote applications

4. !ow cost due to wafer%level trimming

;. Operates from to #0 volts

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microcontroller, a bu@@er indication is provided in the circuit to alert

the people in the industry to stop the process immediately. hus the

temperature sensor !"#$ has to read the temperature continuously

and the microcontroller has to compare this temperature value withthe set temperature preprogrammed in it. >hen this temperature

e(ceeds the set value, the microcontroller sends an indication to the

bu@@er which gives a loud noise.

THERMISTER:

The thermister is, as the name implies, a temperature sensitive resistor, that is it’s

terminal resistance is related to its body temperature. It is a not a junction device and is

constructed of a germanium, silicon or a mixture of cobalt, nickel, strontium or manganese. The

compound employed determines whether the device is a positive or negative co- efficient.

ymbol of thermister !

• Thermister are normally having the negative temperature co-efficient.

• "hen ever the temp increases resistance value decreases and vice versa

• In particular that at room temperature #$%degree centigrade& the resistance of the

thermister is approximately ' k ohms. "here as at (%% degree centigrade the resistance

decreases to (%% ohms.

• The temperature span of )% degree centigrade. Therefore results in a '% ! ( change in

resistance

• The change in resistance in typically * + to '+ per degree change in temperature.

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4. SENSORS

&.1. 'R SENSOR'N#RA RE L'*+T EM'TT'N* 'OE

IR TRANSMITTER :

#ig &.5.1 'R T,

  S3!4800 is a high eAciency infrared emitting diode in Ba3l3s on Ba3s

technology, molded in clear, bluegrey tinted plastic pac2ages. In comparison with

the standard Ba3s on Ba3s technology these emitters achieve more than *00 Cradiant power improvement at a similar wavelength. he forward voltages at low

current and at high pulse current roughly correspond to the low values of the

standard technology. herefore these emitters are ideally suitable as high

performance replacements of standard emitters.

#eat"res:

• xtra high radiant power and radiant intensity

• igh reliability

• ow forward voltage

• uitable for high pulse current operation

• tandard T-(/ # ' mm& package∅

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• 0ngle of half intensity 1 2 3 (45

• 6eak wavelength 7p 2 89% nm

• :ood spectral matching to i photo detectors

4.2 IR RECEIVER :

The 6;T;

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Application Circuit:

  Fig 4.2 Application circuit o RF T! " R!.

 0s shown in fig '.G.$, the circuit of the T;6(4 is designed in that way that unexpected output

 pulses due to noise or disturbance signals are avoided. 0 band pass filter, an integrator stage and

an automatic gain control are used to suppress such disturbances. The distinguishing mark 

 between data signal and disturbance signal are carrier freFuency, burst length and duty cycle. The

data signal should fulfill the following condition!

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• Darrier freFuency should be close to center freFuency of the band pass #e.g. *) k?&.

• Hurst length should be (% cycles=burst or longer.

• 0fter each burst which is between (% cycles and 4% cycles a gap time of at least (9 cycles is

necessary.

• or each burst which is longer than (.)ms a corresponding gap time is necessary at some

time in the data stream. This gap time should have at least same length as the burst.

• Jp to (9%% short bursts per second can be received continuously. 

"hen a disturbance signal is applied to the T;6(4. It can still receive the data signal. owever 

the sensitivity is reduced to that level that no unexpected pulses will occur.