TEMPERATURE SENSOR(LM35)
Features
Ø n Calibrated
directly in ˚ Celsius (Centigrade)
Ø n Linear + 10.0 mV/˚C scale factor
Ø n 0.5˚C accuracy guarantee able (at +25˚C)
Ø n Rated for full −55˚ to +150˚C range
Ø n Suitable for remote applications
Ø n Low cost due to wafer-level
trimming
Ø n Operates from 4 to 30 volts
Ø n Less than 60 µA current drain
Ø n Low self-heating, 0.08˚C in still air
Ø n Nonlinearity only ±1⁄4˚C typical
Ø n Low impedance
output, 0.1 for 1 mA load
The LM35 series are precision integrated-circuit temperature sensors, whose output voltage is linearly proportional to the Celsius (Centigrade)
temperature. The
LM35 thus
has an
advantage over
linear temperature
sensors calibrated
in Kelvin, as the
user is
not required
to subtract
a large
constant voltage from its output to obtain convenient
Centigrade scaling. The
LM35 does
not require
any external calibration or trimming to provide typical accuracies of ±1⁄4˚C
|
at room temperature
and ±3⁄4˚C over
a full
−55 to
+150˚C temperature range. Low cost
is assured
by trimming
and
calibration at the wafer level. The LM35’s low output impedance, linear output, and
precise inherent calibration make interfacing to readout or control circuitry especially easy. It can be
used with
single power
supplies, or
with plus
and minus
supplies. As it draws only 60 µA from its supply, it has very low self-heating, less than 0.1˚C in still air.
The
LM35 is rated to operate over a −55˚ to +150˚C temperature range,
while the LM35C is rated for a −40˚ to +110˚C range (−10˚
with improved accuracy).
The LM35 series is available
packaged in hermetic
TO-46 transistor
packages, while
the LM35C, LM35CA, and
LM35D are
also available
in the
plastic TO-92 transistor package. The LM35D is also avail-
able in an 8-lead surface mount small outline package and a plastic TO-220 package.
Basic Centigrade Temperature Sensor (+2˚C to +150˚C)
Applications:
•
The LM35 can be applied
easily in the same way as other integrated circuit temperature sensors.
It can
be glued
or cemented to a
surface and
its temperature
will be
within about 0.01˚C of the surface temperature.
•
This presumes
that the ambient
air temperature is almost the
same as the surface temperature; if the air temperature were much higher or lower
than
the surface temperature,
the actual
temperature of the LM35 die would be at an intermediate temperature between the surface temperature and the air temperature. This is especially true for the TO-92 plastic
package, where the copper leads are the principal
thermal path to carry heat into the device, so its temperature might be
closer to the air temperature
than to
the surface
temperature.
•
To minimize
this problem,
be sure
that the
wiring to
the LM35,
as it leaves the device, is held at the same temperature as the surface of interest. The easiest way to do this is to
cover up
these wires
with a
bead of
epoxy which
will insure
that the leads and wires are all at the same temperature as the surface, and that the LM35 die’s temperature will not be affected by the air temperature.
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