Summary: The out put of a LM35 is 10mV/Celsius degree. Design an op amp circuit which converts the output of LM35 to 10mV/Fahrenheit degree.
Test the LM35 and make sure it has a good output voltage.
The overall design is changing the LM35 output with a difference amplifier. Notice i0 should be less than 10mA according to the data sheet.
i0=Vref/R1.
Design calculation.
Vref=-0.4V is provided by a voltage divider. The complete schematic is:
Final setup. Before connect the circuit, both power supply were set to 10V, and the 10k pot was adjusted to give a -0.4V.
Results: the output of LM35 was 220mV, the output of the op amp was 720mV. 1.8*220+320=716mV. The circuit is giving the expected result. The multi-meter said the room temperature was 24 degree(240mV-752mV). The percent of difference is about 8%.
Notes:
1. R2/R1=0.8181 rather than 0.8 because the availability of resistors.
2. The output relationship between LM35 and the op amp is almost the same as calculation result; therefore, the circuit design was good. The percent of error completely depends on the performance of the LM35.
No comments:
Post a Comment