Simple salt-water detector, go/no-go type discrimination or

[N_Cook]

Any ideas. It will not be permanently immersed in salt-water, just the
odd sampling. Ancient unmaintained sewer system has breaches to tidal
sea-water at high tides from cracked and dislodged pipe-runs. Need a way
to monitor , firstly that it is partly at least seawater and then some
idea of concentration , to gauge how the situation worsens. At the
moment just the noise of the 1m fall at a manhole from the high-level
local system to the low-level district sewer , coincident with
high-tides, indicates it is mainly sea-water at thoe times. And
photographically to gauge the flow. Just needs a probe of some sort to
pass thru an air-balancing vent in a manhole, perhaps 1 inch x 4inches
and 6 to 10 feet below the surface.

--
Monthly public talks on science topics, Hampshire , England
<http://diverse.4mg.com/scicaf.htm>

 

[John Larkin]

On Fri, 09 Aug 2019 16:07:57 +0100, N_Cook <diverse@tcp.co.uk> wrote:

Any ideas. It will not be permanently immersed in salt-water, just the
odd sampling. Ancient unmaintained sewer system has breaches to tidal
sea-water at high tides from cracked and dislodged pipe-runs. Need a way
to monitor , firstly that it is partly at least seawater and then some
idea of concentration , to gauge how the situation worsens. At the
moment just the noise of the 1m fall at a manhole from the high-level
local system to the low-level district sewer , coincident with
high-tides, indicates it is mainly sea-water at thoe times. And
photographically to gauge the flow. Just needs a probe of some sort to
pass thru an air-balancing vent in a manhole, perhaps 1 inch x 4inches
and 6 to 10 feet below the surface.

A well-insulated toroidal inductor might be an interesting
conductivity probe.


--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

[whit3rd]

On Friday, August 9, 2019 at 8:08:02 AM UTC-7, N_Cook wrote:

Any ideas. It will not be permanently immersed in salt-water, just the
odd sampling. ... a probe of some sort to
pass thru an air-balancing vent in a manhole, perhaps 1 inch x 4inches
and 6 to 10 feet below the surface.

Sounds like a capacitive dipstick would do the job. Because salt water is conductive,
stray capacitance due to fringe fields will go 'way up. A 74HC14 R-C
oscillator (chip, battery, capacitor-probe, resistor) makes either an output frequency directly,
or (with a load resistor) signals frequency on its power supply lines.

I've used a charge-pump with capacitors and diodes to convert frequency
to current, comparator and set a trip point, but a multimeter that reads frequency would
be sufficient.

 

[Jan Panteltje]

On a sunny day (Fri, 09 Aug 2019 16:07:57 +0100) it happened N_Cook
<diverse@tcp.co.uk> wrote in <qik28c$1fp$1@dont-email.me>:

Any ideas. It will not be permanently immersed in salt-water, just the
odd sampling. Ancient unmaintained sewer system has breaches to tidal
sea-water at high tides from cracked and dislodged pipe-runs. Need a way
to monitor , firstly that it is partly at least seawater and then some
idea of concentration , to gauge how the situation worsens. At the
moment just the noise of the 1m fall at a manhole from the high-level
local system to the low-level district sewer , coincident with
high-tides, indicates it is mainly sea-water at thoe times. And
photographically to gauge the flow. Just needs a probe of some sort to
pass thru an air-balancing vent in a manhole, perhaps 1 inch x 4inches
and 6 to 10 feet below the surface.

Some of the ground water level meters here uses simply 2 electrodes,
enough conductivity to to trigger a pumping station controller.
I use the sampe principle for a water detector in a boat.
I guess the salter the water the better the conductivity,
so you could measure resistance perhaps,
but not sure that will work right with polluted water,
you need level too.
For water level pressure sensors are used in the sewer systems here.

Level on the sensor rods + conductivity?
You could use multiple sensor rods to give you height
and then also measure conductivity.


| | | |
|~|~|~|~~~~
| | |
| |
|


Maybe better use a commercial product?
google 'salinity sensor' first hit:
https://www.vernier.com/products/sensors/sal-bta/
ebay has stuff too.

 

[George Herold]

On Friday, August 9, 2019 at 11:08:02 AM UTC-4, N_Cook wrote:

Any ideas. It will not be permanently immersed in salt-water, just the
odd sampling. Ancient unmaintained sewer system has breaches to tidal
sea-water at high tides from cracked and dislodged pipe-runs. Need a way
to monitor , firstly that it is partly at least seawater and then some
idea of concentration , to gauge how the situation worsens. At the
moment just the noise of the 1m fall at a manhole from the high-level
local system to the low-level district sewer , coincident with
high-tides, indicates it is mainly sea-water at thoe times. And
photographically to gauge the flow. Just needs a probe of some sort to
pass thru an air-balancing vent in a manhole, perhaps 1 inch x 4inches
and 6 to 10 feet below the surface.

--
Monthly public talks on science topics, Hampshire , England
http://diverse.4mg.com/scicaf.htm

Simplest might be some stainless steel probes and AC conductivity..
at ~1kHz or something. Maybe a SS tube with SS rod down the center,
or some other way to fix the geometry.

George h.

 

[Phil Hobbs]

On 8/9/19 11:07 AM, N_Cook wrote:

Any ideas. It will not be permanently immersed in salt-water, just the
odd sampling. Ancient unmaintained sewer system has breaches to tidal
sea-water at high tides from cracked and dislodged pipe-runs. Need a way
to monitor , firstly that it is partly at least seawater and then some
idea of concentration , to gauge how the situation worsens. At the
moment just the noise of the 1m fall at a manhole from the high-level
local system to the low-level district sewer , coincident with
high-tides, indicates it is mainly sea-water at thoe times. And
photographically to gauge the flow. Just needs a probe of some sort to
pass thru an air-balancing vent in a manhole, perhaps 1 inch x 4inches
and 6 to 10 feet below the surface.

I'd probably do a capacitive conductivity gauge--look for the salt water
shorting out the E field even more than fresh water. That way you don't
have to expose the wiring to the water.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

[Rick C]

On Friday, August 9, 2019 at 12:48:17 PM UTC-4, Phil Hobbs wrote:

On 8/9/19 11:07 AM, N_Cook wrote:
Any ideas. It will not be permanently immersed in salt-water, just the
odd sampling. Ancient unmaintained sewer system has breaches to tidal
sea-water at high tides from cracked and dislodged pipe-runs. Need a way
to monitor , firstly that it is partly at least seawater and then some
idea of concentration , to gauge how the situation worsens. At the
moment just the noise of the 1m fall at a manhole from the high-level
local system to the low-level district sewer , coincident with
high-tides, indicates it is mainly sea-water at thoe times. And
photographically to gauge the flow. Just needs a probe of some sort to
pass thru an air-balancing vent in a manhole, perhaps 1 inch x 4inches
and 6 to 10 feet below the surface.


I'd probably do a capacitive conductivity gauge--look for the salt water
shorting out the E field even more than fresh water. That way you don't
have to expose the wiring to the water.

Is "fresh water" the appropriate term here? I say that only partly in jest because the various contaminants may make the sewer water as conductive as salt water.

--

Rick C.

- Get 1,000 miles of free Supercharging
- Tesla referral code - https://ts.la/richard11209

 

[piglet]

On 09/08/2019 16:07, N_Cook wrote:

Any ideas. It will not be permanently immersed in salt-water, just the
odd sampling. Ancient unmaintained sewer system has breaches to tidal
sea-water at high tides from cracked and dislodged pipe-runs. Need a way
to monitor , firstly that it is partly at least seawater and then some
idea of concentration , to gauge how the situation worsens. At the
moment just the noise of the 1m fall at a manhole from the high-level
local system to the low-level district sewer , coincident with
high-tides, indicates it is mainly sea-water at thoe times. And
photographically to gauge the flow. Just needs a probe of some sort to
pass thru an air-balancing vent in a manhole, perhaps 1 inch x 4inches
and 6 to 10 feet below the surface.

Length of graduated hose with a hydrometer at the end?

piglet

 

[Klaus Kragelund]

I did something similar once

In principle applying an ac signal to the electrodes

Measured the capacitance with a dV/dt measurement

Then used energy consumption of the sensor to detect conductivity, that is salt concentration

 

[Sjouke Burry]

On 09.08.19 17:07, N_Cook wrote:

Any ideas. It will not be permanently immersed in salt-water, just the
odd sampling. Ancient unmaintained sewer system has breaches to tidal
sea-water at high tides from cracked and dislodged pipe-runs. Need a way
to monitor , firstly that it is partly at least seawater and then some
idea of concentration , to gauge how the situation worsens. At the
moment just the noise of the 1m fall at a manhole from the high-level
local system to the low-level district sewer , coincident with
high-tides, indicates it is mainly sea-water at thoe times. And
photographically to gauge the flow. Just needs a probe of some sort to
pass thru an air-balancing vent in a manhole, perhaps 1 inch x 4inches
and 6 to 10 feet below the surface.

About the properties of salt water:
https://pdfs.semanticscholar.org/5d6b/b9f16308f62f368943f5f17383da9b57e071.pdf

Put two isolated plates in water, use them as cap in an oscilator,
and examine the frequency.
(1.5 minute result from google).

 

[Bill Sloman]

On Saturday, August 10, 2019 at 1:38:55 AM UTC+10, John Larkin wrote:

On Fri, 09 Aug 2019 16:07:57 +0100, N_Cook <diverse@tcp.co.uk> wrote:

Any ideas. It will not be permanently immersed in salt-water, just the
odd sampling. Ancient unmaintained sewer system has breaches to tidal
sea-water at high tides from cracked and dislodged pipe-runs. Need a way
to monitor , firstly that it is partly at least seawater and then some
idea of concentration , to gauge how the situation worsens. At the
moment just the noise of the 1m fall at a manhole from the high-level
local system to the low-level district sewer , coincident with
high-tides, indicates it is mainly sea-water at thoe times. And
photographically to gauge the flow. Just needs a probe of some sort to
pass thru an air-balancing vent in a manhole, perhaps 1 inch x 4inches
and 6 to 10 feet below the surface.

A well-insulated toroidal inductor might be an interesting
conductivity probe.

The classic conductivity probe is two non-progressively wound toroids, stacked.

You drive one toroid, and monitor the current out of the other toroid. In air - if you've got the windings non-progressive - there nothing coming from the second toroid.

In conductive water, the water forms a single turn winding linking both toroids, and the current you can detect coming oout of the second winding is proportional (including turns ratio) to the current circulating through the water.

The sensitivity is calculable, but you just dunk the toroid pair in a solution of known conductivity and calibrate that way.

Getting small diameter toroids isn't difficult. Getting them wound non-progresively might be - you have wind around clockwise for half the turns you put on and wind back for the other half. Even better to wind one way for a quarter of the turns, wind back over the top for half the turns then wind back for the last quarter of the turns. Twist the leads together too.

Doing it by hand is probably priactical, if tedious.

https://www.amazon.com.au/Coaxial-AC-Bridges-B-Kibble/dp/0852743890/ref=sr_1_1?keywords=Rayner+and+Kibble&qid=1565399987&s=books&sr=1-1

does talk about non-progressive windings. It's national standards lab book - the Kibble is the Kibble in the Kibble balance - so there's nothing about measuring the conductivity of liquids in it.

--
Bill Sloman, Sydney

 

[John Miles, KE5FX]

On Friday, August 9, 2019 at 6:22:52 PM UTC-7, Bill Sloman wrote:

You drive one toroid, and monitor the current out of the other toroid. In air - if you've got the windings non-progressive - there nothing coming from the second toroid.

Why non-progressive? Ordinary toroids should behave that way too, no?

-- john, KE5FX

 

[Jeff Liebermann]

On Fri, 09 Aug 2019 16:07:57 +0100, N_Cook <diverse@tcp.co.uk> wrote:

Any ideas. It will not be permanently immersed in salt-water, just the
odd sampling. Ancient unmaintained sewer system has breaches to tidal
sea-water at high tides from cracked and dislodged pipe-runs. Need a way
to monitor , firstly that it is partly at least seawater and then some
idea of concentration , to gauge how the situation worsens. At the
moment just the noise of the 1m fall at a manhole from the high-level
local system to the low-level district sewer , coincident with
high-tides, indicates it is mainly sea-water at thoe times. And
photographically to gauge the flow. Just needs a probe of some sort to
pass thru an air-balancing vent in a manhole, perhaps 1 inch x 4inches
and 6 to 10 feet below the surface.

"Remote Detection of Saline Intrusion in a Coastal Aquifer Using
Borehole Measurements of Self-Potential"
<https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2017WR021034>
Note that this report was done in UK.

They used electrokinetic potential (two dissimilar electrodes to form
a battery). See Table 1 for some differences in electrical
characteristics of sea water and fresh water which you should be able
to detect. For example:

Rock electrical conductivity seawater 5.2-5.75 (5.2measured) mS/cm
Rock electrical conductivity groundwater 0.06-0.25 (0.25measured)mS/cm

EK coupling coefficient groundwater -0.575 ą0.080 mV/mH2O
EK coupling coefficient seawater -0.0101 ą0.0020 mV/mH2O

I don't know what you're going to do about the sewage in the
measurements. It could be anything from conductive (ionic) chemicals
to corrosives that will eat or coat your electrodes. That's why this
kind of testing is normally by collecting samples, and doing the
analysis in a laboratory.

In food analysis, salt content is measured by titration. It can
probably be adapted to testing concentration in your sewage plus
saltwater mix.
<https://www.foodqualityandsafety.com/article/determining-salt-in-food/3/>

If you're just measuring dissolved salt concentration, and ISE (ion
selective electrode) probe and salt meter should be able to produce
usable numbers. It's commonly used for salt water aquariums:
<https://www.youtube.com/watch?v=XPNKyarScm8>
<https://wiki.ezvid.com/best-salt-meters>

If you're cheap, use salinity test paper:
<https://preclaboratories.com/product/salinity-test-strips/>

Again, all these tests assume that the salt will be diluted, not
contaminated by sewage. Good luck.
--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

 

[Bill Sloman]

On Saturday, August 10, 2019 at 12:52:25 PM UTC+10, Jeff Liebermann wrote:

On Fri, 09 Aug 2019 16:07:57 +0100, N_Cook <diverse@tcp.co.uk> wrote:

Any ideas. It will not be permanently immersed in salt-water, just the
odd sampling. Ancient unmaintained sewer system has breaches to tidal
sea-water at high tides from cracked and dislodged pipe-runs. Need a way
to monitor , firstly that it is partly at least seawater and then some
idea of concentration , to gauge how the situation worsens. At the
moment just the noise of the 1m fall at a manhole from the high-level
local system to the low-level district sewer , coincident with
high-tides, indicates it is mainly sea-water at thoe times. And
photographically to gauge the flow. Just needs a probe of some sort to
pass thru an air-balancing vent in a manhole, perhaps 1 inch x 4inches
and 6 to 10 feet below the surface.

"Remote Detection of Saline Intrusion in a Coastal Aquifer Using
Borehole Measurements of Self-Potential"
https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2017WR021034
Note that this report was done in UK.

They used electrokinetic potential (two dissimilar electrodes to form
a battery). See Table 1 for some differences in electrical
characteristics of sea water and fresh water which you should be able
to detect. For example:

Rock electrical conductivity seawater 5.2-5.75 (5.2measured) mS/cm
Rock electrical conductivity groundwater 0.06-0.25 (0.25measured)mS/cm

EK coupling coefficient groundwater -0.575 ą0.080 mV/mH2O
EK coupling coefficient seawater -0.0101 ą0.0020 mV/mH2O

I don't know what you're going to do about the sewage in the
measurements. It could be anything from conductive (ionic) chemicals
to corrosives that will eat or coat your electrodes. That's why this
kind of testing is normally by collecting samples, and doing the
analysis in a laboratory.

In food analysis, salt content is measured by titration. It can
probably be adapted to testing concentration in your sewage plus
saltwater mix.
https://www.foodqualityandsafety.com/article/determining-salt-in-food/3/

There are electrodes that are sodium-ion concentration specific, and food analysts are going to use them - rather than titration - for all but pickiest customers.

How long they might last if exposed to raw sewage is an open question

If you're just measuring dissolved salt concentration, and ISE (ion
selective electrode) probe and salt meter should be able to produce
usable numbers. It's commonly used for salt water aquariums:
https://www.youtube.com/watch?v=XPNKyarScm8
https://wiki.ezvid.com/best-salt-meters

If you're cheap, use salinity test paper:
https://preclaboratories.com/product/salinity-test-strips/

Again, all these tests assume that the salt will be diluted, not
contaminated by sewage. Good luck.

The contamination question is the one that suggests to me that an inductive conductivity measurement might be the way to go.

John Larkin mentioned usinga single toroid to induce a current in the surrounding (dirty) water. Two stacked non-progressively wound toriods do the job a whole lot more easily - you could pick out the current induced in the conductive liquid threadig a single toroid, but it wouldn't be easy.

Toroids would stop working if lumps of - non-conducting - sludge block up the hole in the toroid (or the stacked toroids) but nylon netting would prevent that.

--
Bill Sloman, Sydney

 

On Friday, 9 August 2019 22:13:04 UTC+2, Klaus Kragelund wrote:

I did something similar once

In principle applying an ac signal to the electrodes

Measured the capacitance with a dV/dt measurement

Then used energy consumption of the sensor to detect conductivity, that is salt concentration

My patent from many years ago:

https://patents.google.com/patent/US8610309/en

 

[N_Cook]

On 09/08/2019 18:09, George Herold wrote:

On Friday, August 9, 2019 at 11:08:02 AM UTC-4, N_Cook wrote:
Any ideas. It will not be permanently immersed in salt-water, just the
odd sampling. Ancient unmaintained sewer system has breaches to tidal
sea-water at high tides from cracked and dislodged pipe-runs. Need a way
to monitor , firstly that it is partly at least seawater and then some
idea of concentration , to gauge how the situation worsens. At the
moment just the noise of the 1m fall at a manhole from the high-level
local system to the low-level district sewer , coincident with
high-tides, indicates it is mainly sea-water at thoe times. And
photographically to gauge the flow. Just needs a probe of some sort to
pass thru an air-balancing vent in a manhole, perhaps 1 inch x 4inches
and 6 to 10 feet below the surface.

--
Monthly public talks on science topics, Hampshire , England
http://diverse.4mg.com/scicaf.htm

Simplest might be some stainless steel probes and AC conductivity..
at ~1kHz or something. Maybe a SS tube with SS rod down the center,
or some other way to fix the geometry.

George h.

Thanks all, I'll go with this simplest one first, I've got some s/s tube
and rod.



--
Monthly public talks on science topics, Hampshire , England
<http://diverse.4mg.com/scicaf.htm>

 

On Saturday, 10 August 2019 09:07:17 UTC+1, N_Cook wrote:

On 09/08/2019 18:09, George Herold wrote:
On Friday, August 9, 2019 at 11:08:02 AM UTC-4, N_Cook wrote:

Any ideas. It will not be permanently immersed in salt-water, just the
odd sampling. Ancient unmaintained sewer system has breaches to tidal
sea-water at high tides from cracked and dislodged pipe-runs. Need a way
to monitor , firstly that it is partly at least seawater and then some
idea of concentration , to gauge how the situation worsens. At the
moment just the noise of the 1m fall at a manhole from the high-level
local system to the low-level district sewer , coincident with
high-tides, indicates it is mainly sea-water at thoe times. And
photographically to gauge the flow. Just needs a probe of some sort to
pass thru an air-balancing vent in a manhole, perhaps 1 inch x 4inches
and 6 to 10 feet below the surface.

--
Monthly public talks on science topics, Hampshire , England
http://diverse.4mg.com/scicaf.htm

Simplest might be some stainless steel probes and AC conductivity..
at ~1kHz or something. Maybe a SS tube with SS rod down the center,
or some other way to fix the geometry.

George h.


Thanks all, I'll go with this simplest one first, I've got some s/s tube
and rod.

Don't be tempted to put one inside the other, makes keeping them usably clean a problem. A flat surface with both conductors on is best.
SS is generally coated with nonconductive oxide, not a good choice for conductivity measurement.


NT

 

[Jeff Liebermann]

On Fri, 9 Aug 2019 21:13:47 -0700 (PDT), Bill Sloman
<bill.sloman@ieee.org> wrote:

There are electrodes that are sodium-ion concentration specific, and
food analysts are going to use them - rather than titration - for all
but pickiest customers.

How long they might last if exposed to raw sewage is an open question

Both sodium and chlorine ion sensors can be contaminated by a wide
variety of substances found in sewage. That's why the collection is
done with a sampler and analysis is done in a lab.

I did some work for Manning Environmental when they were located in
Santa Cruz CA:
<https://www.manningenvironmental.com>
Helping design a refrigerator that fit in a manhole was not exactly
the high point of my design career. The reason for the refrigeration
was that many of the pollutants found in sewage are volatile. The
only way to keep them in solution was to arrest evaporation by cooling
the samples. The EPA wanted everything cooled to 0C - 4C. Preventing
the collected samples from freezing was a major challenge. One
ancient product, not found on the current web site, was a rotary
sampler that resembled a miniature bottling plant, where sewage was
sampled on a timed schedule, bottled, capped, tagged, and refrigerated
for later analysis.

If you're just measuring dissolved salt concentration, and ISE (ion
selective electrode) probe and salt meter should be able to produce
usable numbers. It's commonly used for salt water aquariums:
https://www.youtube.com/watch?v=XPNKyarScm8
https://wiki.ezvid.com/best-salt-meters

If you're cheap, use salinity test paper:
https://preclaboratories.com/product/salinity-test-strips/

One thing nice about test strips is that they're not clogged by
sewage. Just dip them in the flow, and take a digital photo to
determine the color. However, I'm not sure what they'll do in the
presence of the chemical cocktail found in industrial sewage.

Again, all these tests assume that the salt will be diluted, not
contaminated by sewage. Good luck.

Oops. That should read:
Again, all these tests assume that the salt will be diluted by
clean and neutral pH water and not contaminated by sewage.

The contamination question is the one that suggests to me that
an inductive conductivity measurement might be the way to go.

John Larkin mentioned usinga single toroid to induce a current
in the surrounding (dirty) water. Two stacked non-progressively
wound toriods do the job a whole lot more easily - you could
pick out the current induced in the conductive liquid threadig
a single toroid, but it wouldn't be easy.

I'm not sure how that would look, but in my very limited experience in
sampling sewage, it will stick to anything that is not a smooth
surface. Direct pumping is also problematic. Ask anyone who has a
basement toilet pump:
<https://www.google.com/search?q=sewage+ejector+pump&tbm=isch>
However, pumping raw sewage through one or two torroid orifices would
be easy if the torroids were wrapped around a smooth teflon sampling
pipe that does not present an obstruction. My guess(tm) is that pipe
would need to be the same size as a typical toilet drain pipe (3in or
4in), which would require two rather huge torroidal cores.

Toroids would stop working if lumps of - non-conducting - sludge
block up the hole in the toroid (or the stacked toroids) but
nylon netting would prevent that.

Perforated silicone tubing is what's typically used for collector and
vacuum collector hoses. Not much sticks to it or attacks it. For the
nasty stuff, there's Teflon. If long life is not necessary, there's
PVC. If there's a strainer screen, it's either disposable PVC, or
stainless steel:
"Manning Flex Strainer"
<https://youtu.be/hBh9r7ZclfI>
For the various pump types, there is usually a "purge" cycle, which
reverses the action, pressurizes the sampler strainer, and hopefully
dislodges any obstructions.


--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

 

[John Larkin]

On Fri, 9 Aug 2019 20:35:52 -0700 (PDT), "John Miles, KE5FX"
<jmiles@gmail.com> wrote:

On Friday, August 9, 2019 at 6:22:52 PM UTC-7, Bill Sloman wrote:
You drive one toroid, and monitor the current out of the other toroid. In air - if you've got the windings non-progressive - there nothing coming from the second toroid.


Why non-progressive? Ordinary toroids should behave that way too, no?

-- john, KE5FX

I was thinking that conductive water would present a resistive shunt
load to a single toroid. The circuit could be simple.


--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

[Bill Sloman]

On Saturday, August 10, 2019 at 9:06:57 PM UTC+10, Jeff Liebermann wrote:

On Fri, 9 Aug 2019 21:13:47 -0700 (PDT), Bill Sloman
bill.sloman@ieee.org> wrote:

snip>

The contamination question is the one that suggests to me that
an inductive conductivity measurement might be the way to go.

John Larkin mentioned usinga single toroid to induce a current
in the surrounding (dirty) water. Two stacked non-progressively
wound toriods do the job a whole lot more easily - you could
pick out the current induced in the conductive liquid threadig
a single toroid, but it wouldn't be easy.

I'm not sure how that would look, but in my very limited experience in
sampling sewage, it will stick to anything that is not a smooth
surface. Direct pumping is also problematic. Ask anyone who has a
basement toilet pump:
https://www.google.com/search?q=sewage+ejector+pump&tbm=isch
However, pumping raw sewage through one or two torroid orifices would
be easy if the torroids were wrapped around a smooth teflon sampling
pipe that does not present an obstruction. My guess(tm) is that pipe
would need to be the same size as a typical toilet drain pipe (3in or
4in), which would require two rather huge torroidal cores.

The toriodal core pair conductivity probe doesn't work like that. The current flows through the hole in both toriods, but also flows back around the outsides of both toroids - it's current loop thaqt threads both toroids.

The wholen thing has to be immersed in the liquid whose conductivity is to be measured.

The OP was looking for 4"x1" package to go on the end of a stick.

<snipped useful stuff about screens>

--
Bill Sloman, Sydney