(MM) wild temp sensor readings


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TassyJim

Guru

Joined: 07/08/2011
Location: Australia
Posts: 4447
Posted: 10:48pm 14 Jan 2012      

Pete,
The difference between 1.5k and 1.8k for R1 is insignificant.
It will change the current through the 335Z slightly but not enough to change the voltage output.
Also, small changes in the 5V supply wouldn't make much difference.
The LM335Z output changes slowly by design so any sudden changes in voltage are caused by interference etc.

Eliminate the fluctuations first then worry about getting the true value.
Then:
X=(T+273)/V
where X is the multiplier we are looking for
T is the actual temperature in deg C
V is the voltage at the Maximite input.

In your program:
T = pin(1) * X - 273

In my situation I put a recording thermometer in the sensor location for 24 hours and adjusted for best fit. That's why my maths doesn't look quite right.

Using your 0.001 capacitor would be OK as an RF filter. My choice usually depends on the first one I find in the box. Usually a ceramic. You can do all sorts of calculations to come up with a correct value if you know the frequency you are trying to eliminate but in this case its easier to use what you have.

Jim

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