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PDF LM235AH Datasheet ( Hoja de datos )

Número de pieza LM235AH
Descripción Precision Temperature Sensors
Fabricantes National Semiconductor 
Logotipo National Semiconductor Logotipo

Total 14 Páginas
		
LM235AH Hoja de datos, Descripción, Manual
May 1999
LM135/LM235/LM335, LM135A/LM235A/LM335A
Precision Temperature Sensors
General Description
The LM135 series are precision, easily-calibrated, integrated
circuit temperature sensors. Operating as a 2-terminal zener,
the LM135 has a breakdown voltage directly proportional to
absolute temperature at +10 mV/˚K. With less than 1dy-
namic impedance the device operates over a current range
of 400 µA to 5 mA with virtually no change in performance.
When calibrated at 25˚C the LM135 has typically less than
1˚C error over a 100˚C temperature range. Unlike other sen-
sors the LM135 has a linear output.
Applications for the LM135 include almost any type of tem-
perature sensing over a −55˚C to +150˚C temperature
range. The low impedance and linear output make interfac-
ing to readout or control circuitry especially easy.
The LM135 operates over a −55˚C to +150˚C temperature
range while the LM235 operates over a −40˚C to +125˚C
temperature range. The LM335 operates from −40˚C to
+100˚C. The LM135/LM235/LM335 are available packaged
in hermetic TO-46 transistor packages while the LM335 is
also available in plastic TO-92 packages.
Features
n Directly calibrated in ˚Kelvin
n 1˚C initial accuracy available
n Operates from 400 µA to 5 mA
n Less than 1dynamic impedance
n Easily calibrated
n Wide operating temperature range
n 200˚C overrange
n Low cost
Schematic Diagram
DS005698-1
© 1999 National Semiconductor Corporation DS005698
www.national.com

1 page

LM235AH pdf
Typical Performance Characteristics (Continued)
Thermal Response in Stirred Oil Bath
Forward Characteristics
Application Hints
DS005698-36
CALIBRATING THE LM135
Included on the LM135 chip is an easy method of calibrating
the device for higher accuracies. A pot connected across the
LM135 with the arm tied to the adjustment terminal allows a
1-point calibration of the sensor that corrects for inaccuracy
over the full temperature range.
This single point calibration works because the output of the
LM135 is proportional to absolute temperature with the ex-
trapolated output of sensor going to 0V output at 0˚K
(−273.15˚C). Errors in output voltage versus temperature are
only slope (or scale factor) errors so a slope calibration at
one temperature corrects at all temperatures.
The output of the device (calibrated or uncalibrated) can be
expressed as:
where T is the unknown temperature and To is a reference
temperature, both expressed in degrees Kelvin. By calibrat-
ing the output to read correctly at one temperature the output
at all temperatures is correct. Nominally the output is cali-
brated at 10 mV/˚K.
Typical Applications
DS005698-37
To insure good sensing accuracy several precautions must
be taken. Like any temperature sensing device, self heating
can reduce accuracy. The LM135 should be operated at the
lowest current suitable for the application. Sufficient current,
of course, must be available to drive both the sensor and the
calibration pot at the maximum operating temperature as
well as any external loads.
If the sensor is used in an ambient where the thermal resis-
tance is constant, self heating errors can be calibrated out.
This is possible if the device is run with a temperature stable
current. Heating will then be proportional to zener voltage
and therefore temperature. This makes the self heating error
proportional to absolute temperature the same as scale fac-
tor errors.
WATERPROOFING SENSORS
Meltable inner core heat shrinkable tubing such as manufac-
tured by Raychem can be used to make low-cost waterproof
sensors. The LM335 is inserted into the tubing about 12"
from the end and the tubing heated above the melting point
of the core. The unfilled 12" end melts and provides a seal
over the device.
Basic Temperature Sensor
Calibrated Sensor
Wide Operating Supply
DS005698-2
*Calibrate for 2.982V at 25˚C
DS005698-9
5
DS005698-10
www.national.com

5 Page

LM235AH arduino
Typical Applications (Continued)
Differential Temperature Sensor
Variable Offset Thermometer
DS005698-14
Adjust for zero with sensor at 0˚C and 10T pot set at 0˚C
*Adjust for zero output with 10T pot set at 100˚C and sensor at 100˚C
Output reads difference between temperature and dial setting of 10T pot
11
DS005698-15
www.national.com

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