04-06-2012, 12:34 PM
LM35 Precision Centigrade Temperature Sensors
[attachment=24116]
General Description
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).
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 expecially 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.
CAPACITIVE LOADS
Like most micropower circuits, the LM35 has a limited ability
to drive heavy capacitive loads. The LM35 by itself is able to
drive 50 pf without special precautions. If heavier loads are
anticipated, it is easy to isolate or decouple the load with a
resistor; see Figure 3. Or you can improve the tolerance of
capacitance with a series R-C damper from output to
ground;
[attachment=24116]
General Description
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).
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 expecially 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.
CAPACITIVE LOADS
Like most micropower circuits, the LM35 has a limited ability
to drive heavy capacitive loads. The LM35 by itself is able to
drive 50 pf without special precautions. If heavier loads are
anticipated, it is easy to isolate or decouple the load with a
resistor; see Figure 3. Or you can improve the tolerance of
capacitance with a series R-C damper from output to
ground;