Pinagem do sensor de temperatura LM35, guia de interface, construção de circuito e princípios de funcionamento

LM35 Temperature Sensor Pinout, Interface Guide, Circuit Construction and Working Principles

LM35 is a temperature sensor that emits an analog signal proportional to the instantaneous temperature. The output voltage can be easily interpreted to obtain a temperature reading in Celsius. The advantage of the lm35 over the thermistor is that it does not require any external calibration. The coating also protects against self-heating. The low cost (approximately $0.95) and greater accuracy make it popular among hobbyists, DIY circuit makers, and students. Many low-cost products take advantage of low cost, higher precision and use LM35 in their products. There are approximately more than 15 years until its first launch, but the sensor still survives and is used in any product.

LM35 Temperature Sensor Features

  • Calibrated directly in Celsius (Centigrade)
  • Linear scaling factor + 10 mV/°C
  • Guaranteed accuracy of 0.5°C (at 25°C)
  • Rated for full range of −55°C to 150°C
  • Suitable for remote applications
  • Operates from 4V to 30V
  • Drain current less than 60 µA
  • Low self-heating, 0.08°C in still air
  • Nonlinearity only ±¼°C Typical
  • Low impedance output, 0.1 Ω for 1 mA load

LM35 pinout

Lm35 pinout

LM35 pinout
The LM35 can measure from -55 degrees centigrade to 150 degrees centigrade. The level of accuracy is very high if operated at ideal temperature and humidity levels. Converting the output voltage to degrees centigrade is also easy and straightforward.

The input voltage for LM35 can be from +4 volts to 30 volts. It consumes about 60 microamps of current. Lm35 has many family members, some names are LM35C, LM35CA, LM35D, LM135, LM135A, LM235, LM335. All members of the LM35 family work on the same principles, but temperature measurement capabilities vary and are also available in various packages ( SOIC, PARA-220, PARA-92, PARA ).

LM35 working principle (understanding LM35 linear scaling factor)

Scale factor Lm35 Scale factor LM35

To understand the working principle of the LM35 temperature sensor, we have to understand the linear scale factor. In the characteristics of the LM35 it is given as +10 millivolts per degree centigrade . This means that with an increase in the output of 10 thousand volts through the sensor pin, the temperature value increases by one. For example, if the sensor is emitting 100 thousand volts at the vout pin, the temperature in degrees centigrade will be 10 degrees centigrade. The same goes for the negative temperature reading. If the sensor is producing -100 millivolts, the temperature will be -10 degrees Celsius.

LM35 Temperature Sensor Circuit Configuration

Photograph

The LM35 can be used in two circuit configurations. Both produce different results. In the first setting, you can only measure positive temperature from 2 degrees Celsius to 150 degrees Celsius. In this first configuration, we simply power the lm35 and connect the output directly to the analog-to-digital converters. In the second configuration, we can utilize the full capabilities of the sensor and measure the entire temperature range from -55 degrees centigrade to 150 degrees centigrade. This setup is a bit complex but produces high results. We have to connect an external resistor in this case to increase the negative voltage level. The external resistor value can be calculated from the formula given below the configuration circuit. The second configuration circuit can be done in several ways. To see more about second configuration circuits, visit the Texas Instruments LM35 datasheet. The Texas Instruments datasheet lists the circuit with clear component values.

Although the first configuration did not need a resistor on the output side, I recommend connecting an 80 k to 100 k resistor between the vout and gnd pin. When I performed several experiments, I noticed that the readings fluctuate for some time and the check pin fluctuates. Therefore, a resistor between vout and gnd tightens the vout pin and prevents the pin from floating.

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