LM35 Tempreture sensor

Description:

LM35 is commonly used temperature sensor that can be used to measure temperature with an electrical o/p comparative to the temperature (in °C). It can measure temperature more correctly compare with a thermistor. This sensor generates a high output voltage than thermocouples. The LM35 has an output voltage that is proportional to the Celsius temperature. The scale factor is .01V/°C.The LM35 does not need any exterior calibration and maintains. An exactness of +/-0.4°C at room temperature and +/-0.8°C over a range of 0°C to +100°C.

Working Principle:

There are two transistors in the center of the drawing. One has ten times the emitter area of the other. This means it has one tenth of the current density, since the same current is going through both transistors. This causes a voltage across the resistor R1 that is proportional to the absolute temperature, and is almost linear across the range. The “almost” part is taken care of by a special circuit that straightens out the slightly curved graph of voltage versus temperature. The amplifier at the top ensures that the voltage at the base of the left transistor (Q1) is proportional to absolute temperature (PTAT) by comparing the output of the two transistors.The amplifier at the right converts absolute temperature (measured in Kelvin) into either Fahrenheit or Celsius, depending on the part (LM34 or LM35).The little circle with the “i” in it is a constant current source circuit.

 

Types of temperature Sensor:

LM19  (http://www.ti.com/lit/ds/symlink/lm19.pdf)

LM20 (http://www.ti.com/lit/ds/symlink/lm20.pdf)

LM26 (http://www.ti.com/lit/ds/symlink/lm26.pdf)

LM27 (http://www.ti.com/lit/ds/symlink/lm27.pdf)

LM34 (http://www.ti.com/product/lm34)

LM35 (http://www.ti.com/lit/ds/symlink/lm35.pdf)

LM45 (http://www.ti.com/lit/ds/symlink/lm45.pdf)

LM50 (http://www.ti.com/lit/ds/symlink/lm50.pdf)

LM57 (http://www.ti.com/lit/ds/symlink/lm57.pdf)

 

Features:

  • Calibrated directly in ̊ Celsius (Centigrade)
  • Linear + 10.0 mV/ ̊C scale factor
  • 5 ̊C accuracy guaranteeable (at +25 ̊C)
  • Rated for full −55 ̊ to +150 ̊C range
  • Suitable for remote applications
  • Low cost due to wafer-level trimming
  • Operates from 4 to 30 volts
  • Less than 60 μA current drain
  • Low self-heating, 0.08 ̊C in still air
  • Nonlinearity only±1⁄4 ̊C typical
  • Low impedance output, 0.1Ω for 1 mA load

 

Specifications:

 

Link to Datasheet:

http://www.ti.com/lit/ds/symlink/lm35.pdf

Applications:

  • Measuring temperature of a particular environment
  • Checking Battery Temperature

 

Advantages:

  • Remote temperature range between -55 to +150 °C
  • Low self-heating, at 0:08 oC
  • Operating at a voltage of 4 to 30 V
  • The circuit is not complicated
  • Does not require signal conditioning

 Limitations:

  • Require source voltage to operate.
  • It is not suitable for measuring temperature in the liquid.

Schamatic:

Connection with arduino:

1)Vcc: input voltage is +5v for typical application.

2)Vout: connect to analog pin of arduino.(A0 to A5 any)

3)GND: connect to ground terminal of the circuit.

 

Arduino code:

float temp;
int tempPin = 0;

void setup()

{

Serial.begin(9600);

}

void loop()

{

temp = analogRead(tempPin);

temp = temp * 0.48828125;

Serial.print(“TEMPRATURE = “);

Serial.print(temp);

Serial.print(“*C”);

Serial.println();

delay(1000);

}

Reference:

http://www.instructables.com/id/Arduino-Temperature-Sensor-Interfacing-LM35-THE-EA/

https://wiki.eprolabs.com/index.php?title=Temperature_Sensor_LM35

 

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