Maker Pro
Maker Pro

Conductance of water versus frequency

  • Thread starter Klaus Kragelund
  • Start date
K

Klaus Kragelund

Jan 1, 1970
0
Hi

I'm working on a water sensor

The application is a pump which has a metallic surface connected to
the
earth wire. The sensor consists of a metal plate housed in a plastic
enclousure mounted on the chassis of the pump. The capacitance
measured
is the one from the metal plate to the chassis - growing in value
when
the water is present. The sensor plate is in direct contact with the
water

So with pure or low contaminated water we measure the capacitance
between the electrodes taking advantage of the dielectric constant of
80 for water.

When the water is polluted or is a salt solution we measure the
conductance of the water

But, I'm searching for theory/documentation for the conductance of
water with a salt solution at different frequencies. I have measured
the conductance using a network analyzer and have found that it seems
the conductance is lower at higher frequencies. So it seems at very
high frequencies (300MHz) the water begins to act as a capacitance
again without significant conductance.

But I want to be sure and don't want to measure all kinds of extremes.
So does anyone know of theory/books/links to descriptions of the
properties of water? (conductance, dielectric value etc)

Thanks

Klaus
 
I

Ian Stirling

Jan 1, 1970
0
In sci.electronics.design Klaus Kragelund said:
Hi

I'm working on a water sensor

The application is a pump which has a metallic surface connected to
the
earth wire. The sensor consists of a metal plate housed in a plastic
enclousure mounted on the chassis of the pump. The capacitance
measured
is the one from the metal plate to the chassis - growing in value
when
the water is present. The sensor plate is in direct contact with the
water

So with pure or low contaminated water we measure the capacitance
between the electrodes taking advantage of the dielectric constant of
80 for water.

When the water is polluted or is a salt solution we measure the
conductance of the water

But, I'm searching for theory/documentation for the conductance of
water with a salt solution at different frequencies. I have measured
the conductance using a network analyzer and have found that it seems
the conductance is lower at higher frequencies. So it seems at very
high frequencies (300MHz) the water begins to act as a capacitance
again without significant conductance.

But I want to be sure and don't want to measure all kinds of extremes.
So does anyone know of theory/books/links to descriptions of the
properties of water? (conductance, dielectric value etc)

What are you trying to do?
Are you trying to simply measure presence or absence of the water, or
its composition?

If it's simply presence or absence, then use an insulated sensor, and
trigger on capacitance increase at high frequency.
This works if the liquid is fully conductive - as the plate spacing of
the cap is now just the insulation, or if it's non-conductive - as the
dielectric constant of the capacitor formed by the electrode and the
motor case.
 
D

Don Lancaster

Jan 1, 1970
0
Klaus said:
Hi

I'm working on a water sensor

The application is a pump which has a metallic surface connected to
the
earth wire. The sensor consists of a metal plate housed in a plastic
enclousure mounted on the chassis of the pump. The capacitance
measured
is the one from the metal plate to the chassis - growing in value
when
the water is present. The sensor plate is in direct contact with the
water

So with pure or low contaminated water we measure the capacitance
between the electrodes taking advantage of the dielectric constant of
80 for water.

When the water is polluted or is a salt solution we measure the
conductance of the water

But, I'm searching for theory/documentation for the conductance of
water with a salt solution at different frequencies. I have measured
the conductance using a network analyzer and have found that it seems
the conductance is lower at higher frequencies. So it seems at very
high frequencies (300MHz) the water begins to act as a capacitance
again without significant conductance.

But I want to be sure and don't want to measure all kinds of extremes.
So does anyone know of theory/books/links to descriptions of the
properties of water? (conductance, dielectric value etc)

Thanks

Klaus

The usual reason for measuring water with ac rather than dc is to
prevent long term plating and electrochem corrosion effects.


The field is called EIS, short for electrochemical impedance spectrocsopy.

Intro at http://www.tinaja.com/glib/muse137.pdf

--
Many thanks,

Don Lancaster voice phone: (928)428-4073
Synergetics 3860 West First Street Box 809 Thatcher, AZ 85552
rss: http://www.tinaja.com/whtnu.xml email: [email protected]

Please visit my GURU's LAIR web site at http://www.tinaja.com
 
Hi

I'm working on a water sensor

The application is a pump which has a metallic surface connected to
the
earth wire. The sensor consists of a metal plate housed in a plastic
enclousure mounted on the chassis of the pump. The capacitance
measured
is the one from the metal plate to the chassis - growing in value
when
the water is present. The sensor plate is in direct contact with the
water

So with pure or low contaminated water we measure the capacitance
between the electrodes taking advantage of the dielectric constant of
80 for water.

When the water is polluted or is a salt solution we measure the
conductance of the water

But, I'm searching for theory/documentation for the conductance of
water with a salt solution at different frequencies. I have measured
the conductance using a network analyzer and have found that it seems
the conductance is lower at higher frequencies. So it seems at very
high frequencies (300MHz) the water begins to act as a capacitance
again without significant conductance.

But I want to be sure and don't want to measure all kinds of extremes.
So does anyone know of theory/books/links to descriptions of the
properties of water? (conductance, dielectric value etc)

The theory of the electrical conduction of water containing dissolved
ions has been worked out - at least for ionic concentrations up to
about 0.1 molar. The theory is good for higher concentration
solutions, but the math doesn't work too well.

Search on "Warburg Impedance", which dominates the conductive
impedance at low frequencies - up to about 10kHz IIRR. This has a
resistive component which decreases as the square root of frequency,
and a capacitative component which increases as the square root of
frequency. The resistance and reactive impedance is equal at any given
freuquency, so you get a constant 45 degree phase shift between
voltage and current over the frequencies where the Warburg effect is
dominant, which is to say where conductivity is dominated by the
diffusion of ions.

http://www.consultrsr.com/resources/eis/diffusion.htm

That web-site does recommend a book by Bard

http://www.consultrsr.com/bookstore/books01.htm#bard

but I've never come across it. I have used an other electrochemistry
text, cited here on the 6th March 2003

Bob Greef's "Instrumental Methods in Electrochemistry"
from the Ellis Horwood series in physical chemistry published by the
Halsted Press - now part of John Wiley and Sons - in 1985. ISBN
0-85312-875-8.

which was good enough for what I needed.
 
U

Uncle Al

Jan 1, 1970
0
Klaus said:
Hi

I'm working on a water sensor

The application is a pump which has a metallic surface connected to
the
earth wire. The sensor consists of a metal plate housed in a plastic
enclousure mounted on the chassis of the pump. The capacitance
measured
is the one from the metal plate to the chassis - growing in value
when
the water is present. The sensor plate is in direct contact with the
water

So with pure or low contaminated water we measure the capacitance
between the electrodes taking advantage of the dielectric constant of
80 for water.

When the water is polluted or is a salt solution we measure the
conductance of the water

But, I'm searching for theory/documentation for the conductance of
water with a salt solution at different frequencies. I have measured
the conductance using a network analyzer and have found that it seems
the conductance is lower at higher frequencies. So it seems at very
high frequencies (300MHz) the water begins to act as a capacitance
again without significant conductance.

But I want to be sure and don't want to measure all kinds of extremes.
So does anyone know of theory/books/links to descriptions of the
properties of water? (conductance, dielectric value etc)

At low frequencies the water molecules have time to realign dipoles in
opposition to the electric field, thereby showing a very large
dielectric constant. At frequencies higher than the reciprocal time
needed for reorientation you will see a pronounced drop in dielectric
constant. Then there's the Helholtz layer, ion clouds... stuff like

http://www.stanford.edu/group/Zarelab/pub links/741.pdf
http://ieeexplore.ieee.org/iel5/6822/18454/00848840.pdf
 
D

Dumbledore_

Jan 1, 1970
0
[snip river of shit]
Uncle Al said:
Newtonian physics is infinite lightspeed (instantaneous knowledge of
all aspects of a system),

You fuckin' ignorant, stoooopid, LYING bastard!

ROEMER,DOPPLER, MICHELSON, SAGNAC!
http://en.wikipedia.org/wiki/Ole_Rømer

"Cassini had observed the moons of Jupiter between 1666 and 1668, and discovered discrepancies in his measurements that, at first, he attributed to light having a finite speed."

http://www.androcles01.pwp.blueyonder.co.uk/mmx4dummies.htm
http://www.androcles01.pwp.blueyonder.co.uk/Sagnac/Sagnac.htm
http://www.androcles01.pwp.blueyonder.co.uk/Doppler/Doppler.htm


Einstein: "we shall, however, find in what follows, that the velocity of light in our theory plays the part, physically, of an infinitely great velocity."
http://www.fourmilab.ch/etexts/einstein/specrel/www/

Get the **** out of the river of shit, you are the biggest TORD in it, you lying fuckheaded ****!
Go and worship Nehemiah Scudder!
**** OFF and DIE!
 
J

Jim Thompson

Jan 1, 1970
0
[snip river of shit]
Uncle Al said:
Newtonian physics is infinite lightspeed (instantaneous knowledge of
all aspects of a system),

You fuckin' ignorant, stoooopid, LYING bastard!

ROEMER,DOPPLER, MICHELSON, SAGNAC!
http://en.wikipedia.org/wiki/Ole_Rømer

"Cassini had observed the moons of Jupiter between 1666 and 1668, and discovered discrepancies in his measurements that, at first, he attributed to light having a finite speed."

http://www.androcles01.pwp.blueyonder.co.uk/mmx4dummies.htm
http://www.androcles01.pwp.blueyonder.co.uk/Sagnac/Sagnac.htm
http://www.androcles01.pwp.blueyonder.co.uk/Doppler/Doppler.htm


Einstein: "we shall, however, find in what follows, that the velocity of light in our theory plays the part, physically, of an infinitely great velocity."
http://www.fourmilab.ch/etexts/einstein/specrel/www/

Get the **** out of the river of shit, you are the biggest TORD in it, you lying fuckheaded ****!
Go and worship Nehemiah Scudder!
**** OFF and DIE!

PLONK

...Jim Thompson
 
D

Dumbledore_

Jan 1, 1970
0
Jim Thompson said:
[snip river of shit]
Uncle Al said:
Newtonian physics is infinite lightspeed (instantaneous knowledge of
all aspects of a system),

You fuckin' ignorant, stoooopid, LYING bastard!

ROEMER,DOPPLER, MICHELSON, SAGNAC!
http://en.wikipedia.org/wiki/Ole_Rømer

"Cassini had observed the moons of Jupiter between 1666 and 1668, and discovered discrepancies in his measurements that, at first, he attributed to light having a finite speed."

http://www.androcles01.pwp.blueyonder.co.uk/mmx4dummies.htm
http://www.androcles01.pwp.blueyonder.co.uk/Sagnac/Sagnac.htm
http://www.androcles01.pwp.blueyonder.co.uk/Doppler/Doppler.htm


Einstein: "we shall, however, find in what follows, that the velocity of light in our theory plays the part, physically, of an infinitely great velocity."
http://www.fourmilab.ch/etexts/einstein/specrel/www/

Get the **** out of the river of shit, you are the biggest TORD in it, you lying fuckheaded ****!
Go and worship Nehemiah Scudder!
**** OFF and DIE!

PLONK

*plonk*
 
J

Jim Thompson

Jan 1, 1970
0
Jim Thompson said:
[snip river of shit]
Newtonian physics is infinite lightspeed (instantaneous knowledge of
all aspects of a system),

You fuckin' ignorant, stoooopid, LYING bastard!

ROEMER,DOPPLER, MICHELSON, SAGNAC!
http://en.wikipedia.org/wiki/Ole_Rømer

"Cassini had observed the moons of Jupiter between 1666 and 1668, and discovered discrepancies in his measurements that, at first, he attributed to light having a finite speed."

http://www.androcles01.pwp.blueyonder.co.uk/mmx4dummies.htm
http://www.androcles01.pwp.blueyonder.co.uk/Sagnac/Sagnac.htm
http://www.androcles01.pwp.blueyonder.co.uk/Doppler/Doppler.htm


Einstein: "we shall, however, find in what follows, that the velocity of light in our theory plays the part, physically, of an infinitely great velocity."
http://www.fourmilab.ch/etexts/einstein/specrel/www/

Get the **** out of the river of shit, you are the biggest TORD in it, you lying fuckheaded ****!
Go and worship Nehemiah Scudder!
**** OFF and DIE!

PLONK

*plonk*

Aha! A first class turd... changes address at each posting.

No problem, I have my ways ;-)

TURD!

...Jim Thompson
 
C

chuck

Jan 1, 1970
0
Klaus said:
Hi

I'm working on a water sensor

The application is a pump which has a metallic surface connected to
the
earth wire. The sensor consists of a metal plate housed in a plastic
enclousure mounted on the chassis of the pump. The capacitance
measured
is the one from the metal plate to the chassis - growing in value
when
the water is present. The sensor plate is in direct contact with the
water

So with pure or low contaminated water we measure the capacitance
between the electrodes taking advantage of the dielectric constant of
80 for water.

When the water is polluted or is a salt solution we measure the
conductance of the water

But, I'm searching for theory/documentation for the conductance of
water with a salt solution at different frequencies. I have measured
the conductance using a network analyzer and have found that it seems
the conductance is lower at higher frequencies. So it seems at very
high frequencies (300MHz) the water begins to act as a capacitance
again without significant conductance.

But I want to be sure and don't want to measure all kinds of extremes.
So does anyone know of theory/books/links to descriptions of the
properties of water? (conductance, dielectric value etc)

Thanks

Klaus
Conductance of salt water is nil at radio frequencies. At those
frequencies, skin depth is generally the more relevant consideration.
Submarines use radio frequencies below 30 kHz with usable penetration to
about 20 meters. Attenuation, rather than conductance, may be the
property you are interested in. Try a Google search on "attenuation
radio waves salt water" and you should see some links of interest.

Good luck.

Chuck
 
D

Dumbledore_

Jan 1, 1970
0
Uncle Al said:
Dumbledore_ wrote:
[snip]

Nothing
[snip river of shit from Schwartzcyst]
Schwartz:
http://tinyurl.com/ck9r2

Uncle Al said:
Newtonian physics is infinite lightspeed (instantaneous knowledge of
all aspects of a system),

You fuckin' ignorant, stoooopid, LYING bastard!

ROEMER,DOPPLER, MICHELSON, SAGNAC!
http://en.wikipedia.org/wiki/Ole_Rømer

"Cassini had observed the moons of Jupiter between 1666 and 1668, and discovered discrepancies in his measurements that, at first, he attributed to light having a finite speed."

http://www.androcles01.pwp.blueyonder.co.uk/mmx4dummies.htm
http://www.androcles01.pwp.blueyonder.co.uk/Sagnac/Sagnac.htm
http://www.androcles01.pwp.blueyonder.co.uk/Doppler/Doppler.htm


Einstein: "we shall, however, find in what follows, that the velocity of light in our theory plays the part, physically, of an infinitely great velocity."
http://www.fourmilab.ch/etexts/einstein/specrel/www/

Get the **** out of the river of shit, you are the biggest TORD in it, you lying fuckheaded ****!
Go and worship Nehemiah Scudder!
**** OFF and DIE!
 
D

Dumbledore_

Jan 1, 1970
0
Uncle Al said:
Dumbledore_ wrote:
[snip]

Nothing
[snip river of shit from Schwartzcyst]
Schwartz:
http://tinyurl.com/ck9r2

Uncle Al said:
Newtonian physics is infinite lightspeed (instantaneous knowledge of
all aspects of a system),

You fuckin' ignorant, stoooopid, LYING bastard!

ROEMER,DOPPLER, MICHELSON, SAGNAC!
http://en.wikipedia.org/wiki/Ole_Rømer

"Cassini had observed the moons of Jupiter between 1666 and 1668, and discovered discrepancies in his measurements that, at first, he attributed to light having a finite speed."

http://www.androcles01.pwp.blueyonder.co.uk/mmx4dummies.htm
http://www.androcles01.pwp.blueyonder.co.uk/Sagnac/Sagnac.htm
http://www.androcles01.pwp.blueyonder.co.uk/Doppler/Doppler.htm


Einstein: "we shall, however, find in what follows, that the velocity of light in our theory plays the part, physically, of an infinitely great velocity."
http://www.fourmilab.ch/etexts/einstein/specrel/www/

Get the **** out of the river of shit, you are the biggest TORD in it, you lying fuckheaded ****!
Go and worship Nehemiah Scudder!
**** OFF and DIE!
 
J

Joerg

Jan 1, 1970
0
Klaus said:
Hi

I'm working on a water sensor

The application is a pump which has a metallic surface connected to
the
earth wire. The sensor consists of a metal plate housed in a plastic
enclousure mounted on the chassis of the pump. The capacitance
measured
is the one from the metal plate to the chassis - growing in value
when
the water is present. The sensor plate is in direct contact with the
water

So with pure or low contaminated water we measure the capacitance
between the electrodes taking advantage of the dielectric constant of
80 for water.

When the water is polluted or is a salt solution we measure the
conductance of the water

But, I'm searching for theory/documentation for the conductance of
water with a salt solution at different frequencies. I have measured
the conductance using a network analyzer and have found that it seems
the conductance is lower at higher frequencies. So it seems at very
high frequencies (300MHz) the water begins to act as a capacitance
again without significant conductance.

But I want to be sure and don't want to measure all kinds of extremes.
So does anyone know of theory/books/links to descriptions of the
properties of water? (conductance, dielectric value etc)

I've only heard about such technique in soil water content sensing or
when they wanted to gauge water content in crude oil. This contains some
of the basics:
http://www.sowacs.com/sensors/capacitance.html
http://www.sowacs.com/sensors/whatistdrfdr.html

A little more indepth:
http://www.wileywater.com/Contributor/Sample_2.htm

A lab meter, don't know how good it is though:
http://www.labsearch.ie/pdf_files/MeterLab/CDM230FE.pdf

An article about contactless sensing of sea water with different salinity:
http://rfmicro.eng.usf.edu/Papers/Paper_1165_Natarajan.pdf

Let us know what the goal of the sensing is. Just the presence of water?
Bottomline I believe anything that is in contact with the water won't
last long. I just had my dose of reality this weekend. Part of our
irrigation system broke and I thought it was only due to frost damage.
Well, when ripping it out frost must have indeed torn the stem of an
electric valve. However, I also found that the chlorine in our water had
seriously eaten away at lots of metal and rubber that it got in contact
with.
 
J

Jean

Jan 1, 1970
0
[email protected] a écrit dans le message
basics:http://www.sowacs.com/sensors/capacitance.htmlhttp://www.sowacs.com/s
ensors/whatistdrfdr.html

The sensor is made of stainless steel, so it won't corrode. We will
only be detecting the presence of water or not. But since the sensor
is in contact with the water we have the time constant of the
capacitance and the conductance of the water to fight. With the
present sensor size (about 20mm dia), the capacitance is about 60pF if
in contanct with water and a 5% NaCL (salt solution) has about 10ohms
of conductance (expressed in ohms)

So the timeconstant is very low demanding a very fast sensor. We are
however investigating if the 5% solution is likely, we don't want to
design something to be way overspec'ed.

We have two signals coming from the sensor. The capacitance and the
conductance. So when we have high capacitance we say we have "water",
and also when the conductance is high we also have "water". The only
problem is if some wet paper shorts the sensor (sensor plates about
5cm apart), the the conductance will be medium and we have to have a
well defined limit there. So therefore we are making the sensor so it
can measure capacitance in very high conductance water

Regards

Klaus

I think you need to go back to the basics. Conductivity is measured in
(micro) siemens (S) older units were micromhos per centimeters.
deciSiemens per metre are used also.
Resistivity of water is measured in ohms/cm.
Conductivity meters are commonly used in hydrology, hydrogeology, soil
sciences, chemistry
and a host of other fields.
There are also various geophysical methods for
measuring different kinds of conductance and or resistance of water or soils
and rock. What
kind of instrument you would want to use depends on what you want to measure
and for what purpose.
For meters that use capacitance see the links below for examples

http://www.iop.org/EJ/abstract/0957-0233/11/6/318/
http://home.btconnect.com/mjweb/RRC/ect.html
http://pasture.ecn.purdue.edu/~abe305/moisture/html/page31.htm
http://www.tomography.manchester.ac.uk/captom.shtml
http://www.earthsystemssolutions.com/assets/capacitance.htm


JL
 
KlausKragelundwrote:







I've only heard about such technique in soil water content sensing or
when they wanted to gauge water content in crude oil. This contains some
of the basics:http://www.sowacs.com/sensors/capacitance.htmlhttp://www.sowacs.com/sensors/whatistdrfdr.html

A little more indepth:http://www.wileywater.com/Contributor/Sample_2.htm

A lab meter, don't know how good it is though:http://www.labsearch.ie/pdf_files/MeterLab/CDM230FE.pdf

An article about contactless sensing of sea water with different salinity:http://rfmicro.eng.usf.edu/Papers/Paper_1165_Natarajan.pdf

Let us know what the goal of the sensing is. Just the presence of water?
Bottomline I believe anything that is in contact with the water won't
last long. I just had my dose of reality this weekend. Part of our
irrigation system broke and I thought it was only due to frost damage.
Well, when ripping it out frost must have indeed torn the stem of an
electric valve. However, I also found that the chlorine in our water had
seriously eaten away at lots of metal and rubber that it got in contact
with.

The sensor is made of stainless steel, so it won't corrode. We will
only be detecting the presence of water or not. But since the sensor
is in contact with the water we have the time constant of the
capacitance and the conductance of the water to fight. With the
present sensor size (about 20mm dia), the capacitance is about 60pF if
in contanct with water and a 5% NaCL (salt solution) has about 10ohms
of conductance (expressed in ohms)

So the timeconstant is very low demanding a very fast sensor. We are
however investigating if the 5% solution is likely, we don't want to
design something to be way overspec'ed.

We have two signals coming from the sensor. The capacitance and the
conductance. So when we have high capacitance we say we have "water",
and also when the conductance is high we also have "water". The only
problem is if some wet paper shorts the sensor (sensor plates about
5cm apart), the the conductance will be medium and we have to have a
well defined limit there. So therefore we are making the sensor so it
can measure capacitance in very high conductance water

Regards

Klaus
 
J

Joerg

Jan 1, 1970
0
The sensor is made of stainless steel, so it won't corrode. We will
only be detecting the presence of water or not. But since the sensor
is in contact with the water we have the time constant of the
capacitance and the conductance of the water to fight. With the
present sensor size (about 20mm dia), the capacitance is about 60pF if
in contanct with water and a 5% NaCL (salt solution) has about 10ohms
of conductance (expressed in ohms)

If it's good stainless it may not corrode but what can happen over a
period of a few years is that mineral deposits build up on that sensor
plate. Water almost always contains some solids and they'll slowly
roughen up the surface even of polished stainless steel. That can speed
up the mineral deposit process.

Even on our pool pump we have that happen. It only sees rather clean
water but every 5 years or so the presure sensor quits and I have to
scrape off the mineral deposits. Now I do that on a regular schedule so
I don't have to go out there when it's freezing and come back with blue
hands.

So the timeconstant is very low demanding a very fast sensor. We are
however investigating if the 5% solution is likely, we don't want to
design something to be way overspec'ed.

We have two signals coming from the sensor. The capacitance and the
conductance. So when we have high capacitance we say we have "water",
and also when the conductance is high we also have "water". The only
problem is if some wet paper shorts the sensor (sensor plates about
5cm apart), the the conductance will be medium and we have to have a
well defined limit there. So therefore we are making the sensor so it
can measure capacitance in very high conductance water

If you'd pulse it in bipolar fashion you should always get a signal.
Probably you have to arrive at some compromise with the rise times and
the level, for a balance between capacitive effect and conductivity.
Plus some amplitude margin in the comparator to accommodate the wet
paper situation. I'd start with a Schmitt version where the threshold
would determine the amplitude limit.

There are some more esoteric approaches here. One that I have seen in
proximity sensors was based on magnetic coupling but it should also work
with a combined capacitive/conductive situation. The sensor would become
part of a resonant section or the feedback path of an oscillator. The
oscillator is set up so that it quits oscillating beyond a certain
limit. That would become your output signal. In our case its current was
used which dropped to a lower limit (set by a parallel resistor) when
the oscillator quit. Kind of like a 4-20mA loop. So we always had a
minimum current to be able to detect a broken wire and stop the unit
when that happened.
 
R

RST Engineering \(jw\)

Jan 1, 1970
0
Hah. You ought to be about 30 miles north of where you live. We've got the
white stuff fairly thick on the ground and more coming down.

Is the only question whether there is or is not water in a particular
vessel? Drop a diode into the vessel and run some significant current
through it. Monitor the voltage across the diode. When the water hits the
case of the diode it will cool it significantly and remove some of the 2.5
mV/°C drop with temperature. An identical diode outside the vessel with the
same current ought to take care of the ambient temperature problem.

Jim


Now I do that on a regular schedule so
 
Top