When the voltage increases & when the temperature also rises. We can see this operation by using a diode.The temperature sensor series are precision integrated-circuit temperature sensors, whose output voltage is linearly proportional to the Celsius temperature. The LM35 is operating at -55˚ to +120˚C.
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.
The two resistors are calibrated in the factory to produce a highly accurate temperature sensor.
The integrated circuit has many transistors in it — two in the middle, some in each amplifier, some in the constant current source, and some in the curvature compensation circuit. All of that is fit into the tiny package with three leads.
USE OF SENSOR:
This sensor used to measure a temperature of a room or any. So, we can make any application that required a temperature.
- Linear + 10.0 mV/oC scale factor
- 0.5oC accuracy (at +25oC)
- Rated for full −55o to +150oC 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, 0.08oC in still air
- Nonlinearity only ±1⁄4oC typical
- Low impedance output, 0.1 Ω for 1 mA load
- Calibrated directly in o Celsius (Centigrade)
- LM35 Temperature Sensor
- Jumper Wire
Connection with Arduino:
The LM35 IC has 3 pins-2 for the power supply and one for the analog output.It is a low voltage IC which uses approximately +5VDC of power.The output pin provides an analog voltage output that is linearly proportional to the Celsius (centigrade) temperature. Pin 2 gives an output of 1 millivolt per 0.1°C (10mV per degree).So to get the degree value in Celsius, all that must be done is to take the voltage output and divide it by 10-this give out the value degrees in Celsius.
The circuit connections are made as follows:
- Pin no. 1 of the LM35 goes into +5V of the Arduino
- 2nd pin of the LM35 goes into analog pin A0 of the Arduino
- 3rd pin of the LM35 goes into the ground (GND) of the Arduino