Re: Conductivity sensors


mooseo wrote:

Why connect the grounds? Even if you have to connect them, use
inductors. The probes seems to be AC shorted.

I have the grounds connected simply because the A/D board is set up as
single-ended, i.e., it's reading each channel relative to common
ground. I can rewire some things to route the ground of each signal
through the multiplexer and run the board in differential mode.

I know you don't want to hear this. But the final solution might be
optically isolated multiple A2D units. That's why the commerical units
are so expensive.


I see what you are saying about AC noise, although I'm new enough at
this that I have a hard time wrapping my brain around AC. Why is it
that the current would drop in a shorted situation? I would have
guessed, though without knowing why, that it would have increased...

Your 555 circuit works by rapidly charging and discharging by a
reference voltage. If that reference voltage (from the probe) is
noisy, the basic assumptions are off.


Thanks for giving me some things to try.

.

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