01 - Linear temperature sensors (LM35/TMP35)

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Datasheets (hojas de características):

The LM35, TMP35/36/37 are among the most popular temperature sensors. They are very easy to use. All of them are analog output temperature sensors that produce a linear output voltage in relation to the detected temperature.

They both feature a linear 10mV/°C output scaling and very low power consumption.

Package (encapsulado)

This family of sensors is tipically sold in TO-92 packaging, which is a THT package with three pins or leads (patillas, “pines”).

Components featuring TO-92 packages
Components featuring TO-92 packages

All electronic components require powering. Powering requires two pins:

The package has a notch (muesca) so you don’t place the component the other way around.

Attention!!! The image says bottom view. NOT top view.
Attention!!! The image says bottom view. NOT top view.

Pin number 2 provides the output signal, which is the temperature measure.

Exercise

Sign up to https://www.tinkercad.com/. Then click on “Create” > “Circuits”

Click on the name (which is randomized by default) to change it:

Time to place some components! Place a power supply and a TMP36:

Wire them together. Pay attention to the notch:

Now click on “Start Simulation”. The sensor is now on, but you will not see the measurement since the output is not wired to anything.

Stop the simulation. Now place a multimeter and wire it to the sensor: positive pin to Vout, negative pin to GND.

Now restart the simulation and you will see a measurement in the multimeter

This is the formula for the TMP36 (it has a 500 mV offset):

Vout=10 mV/ºCT (ºC)+500 mVV_{out}=10 \ mV/ºC · T\ (ºC) + 500\ mV

If you want to obtain the temperature from the measured voltage:

T (ºC)=Vout(mV)500 mV10 mV/ºCT\ (ºC) = \frac{V_{out} (mV) - 500\ mV}{10\ mV/ºC}

En electrónica los equipos suelen tener una entrada (input) y una salida (output), En este caso entra una temperatura y sale un voltaje. A la fórmula que relaciona entrada y salida se le llama función de transferencia (=transfer function).

Video explanation

Sources




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