strange readings

[Acetronics2]

Hi,

The LM 35 problem ...

Simply the output range : 0v for 0°C ...250 mV for 25°C !!!

IF you use the 5v ref voltage ... 250 mV/ 5v = 1/50 of the usable range ...


3 Solutions ...

1) use a Vref just a bit Higher than your max input ( say 500 mv for 50°C ) - not so good !
2) use a voltage amplifier that will allow 5v output for your max input temp.
3) use a LM 335 that offers a 2.73 offset voltage @ 0°C

The more you input on Analog inputs, the less parasitic signals you see ...

Now, the LM 35 has a +/- 1.0 to 1.5 °C Guaranteed max error ..., add the A/D and calculation errors ( PbP works with INTEGERS !!! ) and your couple of degrees is here !!!

as an eyeblick ... how precise is your temp ref ???? ... LOL !!! remember getting the true degree is not so easy ..., and getting the true 1/10 of degree is a really a performance.

Back to the Input problem itself ... What about the comparators settings ???

Alain ... Thermics engineer ...