Sensor - The LM35
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The LM35 is an integrated circuit sensor that can be used to measure temperature
with an electrical output proportional to the temperature (in
LM35 - An Integrated Circuit Temperature Sensor
Why Use LM35s To Measure
You can measure temperature
more accurately than a using a thermistor.
The sensor circuitry is
sealed and not subject to oxidation, etc.
The LM35 generates a higher
output voltage than thermocouples and may not require that the output voltage
What Does An LM35 Look
LM35 comes in many different packages, including the following.
What Does an LM35 Do?
How does it work?
It has an output voltage
that is proportional to the Celsius temperature.
The scale factor is .01V/oC
The LM35 does not require
any external calibration or trimming and maintains an accuracy of
+/-0.4 oC at room temperature and +/- 0.8 oC
over a range of 0 oC to +100 oC.
Another important characteristic
of the LM35DZ is that it draws only 60 micro amps from its supply and possesses
a low self-heating capability. The sensor self-heating causes less than
0.1 oC temperature rise in still air.
TO-92 plastic transistor-like
T0-46 metal can transistor-like
8-lead surface mount SO-8
small outline package
TO-202 package. (Shown
in the picture above)
Do You Use An LM35? (Electrical Connections)
Here is a commonly used
circuit. For connections refer to the picture above.
In this circuit, parameter
values commonly used are:
Vc = 4 to 30v
5v or 12 v are typical
Actually, it can range
from 80 KW
to 600 KW
, but most just use 80 KW.
Here is a photo of the
LM 35 wired on a circuit board.
The white wire in the
photo goes to the power supply.
Both the resistor and
the black wire go to ground.
The output voltage is
measured from the middle pin to ground.l
What Can You Expect When
You Use An LM35?
You will need to use a
voltmeter to sense Vout.
The output voltage is
converted to temperature by a simple conversion factor.
The sensor has a sensitivity
of 10mV / oC.
Use a conversion factor
that is the reciprocal, that is 100 oC/V.
The general equation used
to convert output voltage to temperature is:
Temperature ( oC)
= Vout * (100 oC/V)
So if Vout
is 1V , then, Temperature = 100 oC
The output voltage varies
linearly with temperature.
What If You Want More
Data On The LM35?
here to get the National Semiconductor data sheet for the LM35.
using an LM35, you obtain an output voltage of 0.173 v. What is the
temperature (in oC)?
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