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toroidal conductivity sensor

One other comment: With this sort of arrangement, there is no need to have the two toroids right against each other. If it helps to eliminate any cross talk between them (any output signal when the sample loop is full of air, for example) you can place them anywhere around the sample loop. for instance, one may be on the top horizontal pipe and one on the bottom horizontal pipe. They need to be closely stacked only for the direct immersion application as is common with the commercial probes. The important thing is that one core induce current in the loop, and the other core measure that loop current.

Reply to
John Popelish
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Good suggestions, except that you don't need to worry about the shorted turn. The hole does not have any flux passing through it. The plane is at right angles to the current circulating in the liquid loop.

Reply to
jpopelish

I read in sci.electronics.design that John Popelish wrote (in ) about 'toroidal conductivity sensor', on Tue, 23 Aug 2005:

I would move the toroids further apart, so as to reduce any stray direct coupling, unless the conductivity is very low. A Faraday shield between them would be good, too. A sheet of, preferably, copper 0.5 mm thick or more, with a hole for the pipe, connected by a narrow slit to the edge so as not to make a shorted turn. Make it at least twice the outside diameter of the toroids.

--
Regards, John Woodgate, OOO - Own Opinions Only.
If everything has been designed, a god designed evolution by natural selection.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk
Reply to
John Woodgate

I read in sci.electronics.design that snipped-for-privacy@rica.net wrote (in ) about 'toroidal conductivity sensor', on Tue, 23 Aug 2005:

True IF the toroids are perfectly uniformly wound, so there is zero leakage flux. But in practice.... Since I don't know who wound the toroids, I wanted to be prudent.

In any case, the slit allows the installation of the screen without splitting the pipework. Been there, etc.

Yes.

--
Regards, John Woodgate, OOO - Own Opinions Only.
If everything has been designed, a god designed evolution by natural selection.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk
Reply to
John Woodgate

hi again well i was just wondering ,if i use a op-amp for the driver circuit,and supply 8khz(3v max) can i still get the desired output to mesure conductivity.And if i can assume that the resistance of the water at

27.7CF in that pipe is of the order of 500 Ohms. The voltage induced into the water loop will be of the order of 10mV. And so can i now work out the current and therefore the Ampere turns energising the pickup coil. From there can estimate the flux and hence the induced emf per turn of pickup.

If this emf is very small, and small in comparison with noise induced in the water loop then you may need to consider using a synchronous rectifier together with a sensitive amp at the pickup. I will leave it to you to research how this can extract the required signal whilst eliminating the noise.

John P> > hi

Reply to
timmy

hi again well i was just wondering ,if i use a op-amp for the driver circuit,and supply 8khz(3v max) can i still get the desired output to mesure conductivity.And if i can assume that the resistance of the water at

27.7CF in that pipe is of the order of 500 Ohms. The voltage induced into the water loop will be of the order of 10mV. And so can i now work out the current and therefore the Ampere turns energising the pickup coil. From there can estimate the flux and hence the induced emf per turn of pickup.

If this emf is very small, and small in comparison with noise induced in the water loop then you may need to consider using a synchronous rectifier together with a sensitive amp at the pickup.

John P> > hi

Reply to
timmy

The induced voltage will be about what you have across 1 turn of the powered toroid. Your value lets me guess that your toroid has 300 turns on it (3V/.01V).

Well, the water completes 1 turn, so the water amperes are the output ampere turns.

Not quite. The output toroid should pass current through a short circuit (virtual ground of an inverting opamp) so its only EMF will be the voltage drop across its own wiring resistance. The ampere turns of the winding should approximate the ampere(turn) of the water loop.

Is that a question?

Reply to
John Popelish

Reply to
timmy

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