Re: Conductivity sensors


mooseo wrote:
linnix wrote:
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

Hmm, no, I really don't want to hear that! Given the realities of my
environment, I'm guessing these things will survive about 2 weeks
before they get destroyed by waves, so cheap is essential.

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.

I'll try some power filtering and see if that helps.

Otherwise, I guess it might be time to look for a new solution...

How many probes do you need in each unit and how many units are you
planning to build? If building enough units, a low impedence solid
ground plane circuit board would help.

.

Relevant Pages

  • Re: Conductivity sensors
    ... The probes seems to be AC shorted. ... That's why the commerical units ... this that I have a hard time wrapping my brain around AC. ... If that reference voltage is ...
    (sci.electronics.design)
  • Re: Conductivity sensors
    ... The probes seems to be AC shorted. ... optically isolated multiple A2D units. ... That's why the commerical units ... If that reference voltage is ...
    (sci.electronics.design)
  • Re: Conductivity sensors
    ... How many probes do you need in each unit and how many units are you ... ground plane circuit board would help. ... Each unit has a single probe, and for this stage of the experiment, ... I can't justify doing that (designing and building the loggers) ...
    (sci.electronics.design)
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