Semiconductor
temperature sensors offer high accuracy and high linearity over an operating
range of about –55°C to +150°C. The output is scaled to give sensitivity of 10mV/°C.
They are also useful in cold-junction compensation circuits for wide temperature
range thermocouples.
All semiconductor
temperature sensors make use of the relationship between a bipolar junction
transistor's (BJT) base-emitter voltage to its collector current:
where k is Boltzmann's
constant, T is the absolute temperature, q is the charge of an electron, and Is
is a current related to the geometry and the temperature of the transistors.
The LM35/36/37 are voltage
output temperature sensors with a 10mV/°C (LM35/36) or 20mV/°C (LM37) scale
factor. Supply current is below 50µA, providing very low self-heating (less
than 0.1°C in still air). The LM35 provides a 250mV output at +25°C and reads
temperature from +10°C to +125°C. LM35 have an output scale factor of +10mV/°C.
LT1167
Single Resistor Gain Programmable, Precision Instrumentation Amplifier
As the output from LM35
is very low (typically 300 mV at 30°C), it is susceptible to distortion due to
noise. The signal is amplified using an amplifier to a suitable level so as to utilize
the full input range of ADC of Arduino. It improves the measurement
sensitivity.
We are using LT1167
precision In-amp from Linear Technologies (now Analog Devices).
Supply
voltage: ±15 VDC
Setup
and connection
REF pin (5) is to be
connected to Ground.
We have selected Rg=8.2kΩ.
So the gain is 7.02.
The amplified output is
fed to analog input channel of an Arduino UNO board. The data is read on
LabVIEW using Makerhub example program for Single Channel AI read. I tweaked
the program to display temperature in degree C.
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