Conductivity Sensor

L

Luhan Monat

Guest
Hi,

I'm constructing a Hydroponics system, and need to monitor the
conductivity of the nutrient solution.

Any suggestions on what to use for the sensors for stable long-term
readings?

Thanks,
--
Luhan Monat: luhanis(at)yahoo(dot)com
http://members.cox.net/berniekm
"Any sufficiently advanced magick is
indistinguishable from technology."
 
Luhan Monat wrote:

Hi,

I'm constructing a Hydroponics system, and need to monitor the
conductivity of the nutrient solution.

Any suggestions on what to use for the sensors for stable long-term
readings?

Thanks,
Click to expand...
Here's what it looks like so far...

http://members.cox.net/berniekm/hydro2.jpg


--
Luhan Monat: luhanis(at)yahoo(dot)com
http://members.cox.net/berniekm
"Any sufficiently advanced magick is
indistinguishable from technology."
 
Hello Luhan,

I'm constructing a Hydroponics system, and need to monitor the
conductivity of the nutrient solution.

Any suggestions on what to use for the sensors for stable long-term
readings?
Click to expand...
I believe corrosion resistance is really important. Titanium is one of
the materials used. An example:

http://omega.com/manuals/manualpdf/M3696.pdf

Regarding your hydro tree in the picture, what happens when one of the
rubber bands snaps?

Regards, Joerg

http://www.analogconsultants.com
 
On Sat, 25 Jun 2005 20:44:27 GMT, in sci.electronics.design Joerg
<notthisjoergsch@removethispacbell.net> wrote:

Hello Luhan,


Regarding your hydro tree in the picture, what happens when one of the
rubber bands snaps?

Regards, Joerg

http://www.analogconsultants.com
The pro version will use cable ties or gaffer tape........
Click to expand...




martin
 
Hello Martin,

The pro version will use cable ties or gaffer tape........
Click to expand...
And I thought the pros use duct tape.

Regards, Joerg

http://www.analogconsultants.com
 
On Sat, 25 Jun 2005 21:09:44 GMT, in sci.electronics.design Joerg
<notthisjoergsch@removethispacbell.net> wrote:

Hello Martin,

The pro version will use cable ties or gaffer tape........

And I thought the pros use duct tape.

Regards, Joerg

http://www.analogconsultants.com
Hi Joerg
Click to expand...

Started life in the film industry, at Ealing Studios, So I call it
gaffer tape


martin
 
martin griffith wrote:
On Sat, 25 Jun 2005 21:09:44 GMT, in sci.electronics.design Joerg
notthisjoergsch@removethispacbell.net> wrote:


Hello Martin,


The pro version will use cable ties or gaffer tape........

And I thought the pros use duct tape.

Regards, Joerg

http://www.analogconsultants.com

Hi Joerg

Started life in the film industry, at Ealing Studios, So I call it
gaffer tape


martin
Click to expand...
The picture is a week out of date. I've gone to nylon ties with a piece
of mousepad between the jars and the PVC. We are running over 100 here
every day lately - the rubber bands were almost totally decomposed in
about 2 weeks.

--
Luhan Monat: luhanis(at)yahoo(dot)com
http://members.cox.net/berniekm
"Any sufficiently advanced magick is
indistinguishable from technology."
 
Joerg wrote:

Hello Luhan,

I'm constructing a Hydroponics system, and need to monitor the
conductivity of the nutrient solution.

Any suggestions on what to use for the sensors for stable long-term
readings?


I believe corrosion resistance is really important. Titanium is one of
the materials used. An example:

http://omega.com/manuals/manualpdf/M3696.pdf

Regarding your hydro tree in the picture, what happens when one of the
rubber bands snaps?

Regards, Joerg

http://www.analogconsultants.com
Click to expand...
Thanks, thats very informative.

--
Luhan Monat: luhanis(at)yahoo(dot)com
http://members.cox.net/berniekm
"Any sufficiently advanced magick is
indistinguishable from technology."
 
bill.sloman@ieee.org wrote:

Joerg wrote:

Hello Luhan,


I'm constructing a Hydroponics system, and need to monitor the
conductivity of the nutrient solution.

Any suggestions on what to use for the sensors for stable long-term
readings?

I believe corrosion resistance is really important. Titanium is one of
the materials used. An example:

http://omega.com/manuals/manualpdf/M3696.pdf


Platinum is traditional, and graphite has its devotees.

One of platinum's advantages is that it has much the same coefficient
of thermal expansion as soft soda glass, which can be handy.

-------
Bill Sloman, Nijmegen
Click to expand...
I may go for the 'poor mans' version of platinum/titanium - stainless
steel is one thing I have in stock here.

--
Luhan Monat: luhanis(at)yahoo(dot)com
http://members.cox.net/berniekm
"Any sufficiently advanced magick is
indistinguishable from technology."
 
Luhan Monat wrote:
Hi,

I'm constructing a Hydroponics system, and need to monitor the
conductivity of the nutrient solution.

Any suggestions on what to use for the sensors for stable long-term
readings?

Thanks,
My favorite kind of sensor is a toroidal transformer type. It is
Click to expand...
completely enclosed in insulating material and is very resistant to
fouling. Unfortunately, the electronics are fairly expensive. I
think that Cole Parmer has some units for $360. But it might be fun
to try to make one of these sensors from simple parts.

The concept is that you excite a toroidal core (high permeability)
with AC through a winding. Then you place a second toroid beside that
one with another winding. The two cores are enclosed in insulation,
with a hole passing through both cores. When submersed, the first
core induces 1 turn's worth of voltage around the liquid loop that
passes through the hole. The current that voltage moves through the
liquid is sensed by the second core, acting as a current transformer.
You amplify the AC current from the second core, rectify it, and the
result represents the conductivity of the solution.
 
John Popelish wrote:
Luhan Monat wrote:

Hi,

I'm constructing a Hydroponics system, and need to monitor the
conductivity of the nutrient solution.

Any suggestions on what to use for the sensors for stable long-term
readings?

Thanks,

My favorite kind of sensor is a toroidal transformer type. It is
completely enclosed in insulating material and is very resistant to
fouling. Unfortunately, the electronics are fairly expensive. I think
that Cole Parmer has some units for $360. But it might be fun to try to
make one of these sensors from simple parts.

The concept is that you excite a toroidal core (high permeability) with
AC through a winding. Then you place a second toroid beside that one
with another winding. The two cores are enclosed in insulation, with a
hole passing through both cores. When submersed, the first core induces
1 turn's worth of voltage around the liquid loop that passes through the
hole. The current that voltage moves through the liquid is sensed by
the second core, acting as a current transformer. You amplify the AC
current from the second core, rectify it, and the result represents the
conductivity of the solution.
Click to expand...
Hey, that sounds interesting. I see why it would work.

Alternativly, maybe using the fluid as part of an 'air core' inductor.
Conductive water may change the inductance. Easy to test by using the
inductor in an oscillator configuration and using the Micro as a crude
frequency counter.

Also, making an 'air core' capacitor using two closely spaced insulated
plates. Capacitors are known to be sensitive to the dielectric used
between the plates.

--
Luhan Monat: luhanis(at)yahoo(dot)com
http://members.cox.net/berniekm
"Any sufficiently advanced magick is
indistinguishable from technology."
 
In article <_crve.3416$Qo.1737@fed1read01>,
Luhan Monat <x@y.z> wrote:

Also, making an 'air core' capacitor using two closely spaced
insulated plates. Capacitors are known to be sensitive to the
dielectric used between the plates.
Click to expand...
A Co I once worked for used coaxial tubes as a capacitor
for a liquid level sensor, with conductive liquids.

The designer didn't use the change in capacitance though,
he used the change in the tuned circuit losses. In fact
he kept the amplitude constant with an agc loop, and
measured the change in agc voltage.

--
Tony Williams.
 
Tony Williams wrote:
In article <_crve.3416$Qo.1737@fed1read01>,
Luhan Monat <x@y.z> wrote:


Also, making an 'air core' capacitor using two closely spaced
insulated plates. Capacitors are known to be sensitive to the
dielectric used between the plates.


A Co I once worked for used coaxial tubes as a capacitor
for a liquid level sensor, with conductive liquids.

The designer didn't use the change in capacitance though,
he used the change in the tuned circuit losses. In fact
he kept the amplitude constant with an agc loop, and
measured the change in agc voltage.
Click to expand...
Circuit losses were probably due to the lowered resistive component that
is part of the resonance formula. Hence, it probably has much the same
flaw as conductance systems as the electrodes become contaminated.

By the way, I'm defining 'success' of a hydroponic system as one that
needs attention once per week or less often. My previous system used a
horizontal section of 2 inch PVC pipe with holes every few inches on top
for plant placement. This actually works well, but leaves a big mess of
roots inside the pipe. The current jar system is designed to allow
easy replacement of plants over time.

--
Luhan Monat: luhanis(at)yahoo(dot)com
http://members.cox.net/berniekm
"Any sufficiently advanced magick is
indistinguishable from technology."
 
Luhan Monat wrote:
The picture is a week out of date. I've gone to nylon ties with a piece
of mousepad between the jars and the PVC. We are running over 100 here
every day lately - the rubber bands were almost totally decomposed in
about 2 weeks.
Click to expand...
Use stainless steel hose clamps - cheap and readily available from
automotive suppliers. Nylon ties die fairly quickly if exposed to UV.
So do most tapes.

Ted
 
John Popelish wrote:
My favorite kind of sensor is a toroidal transformer type. It is
completely enclosed in insulating material and is very resistant to
fouling. Unfortunately, the electronics are fairly expensive. I think
that Cole Parmer has some units for $360. But it might be fun to try to
make one of these sensors from simple parts.

The concept is that you excite a toroidal core (high permeability) with
AC through a winding. Then you place a second toroid beside that one
with another winding. The two cores are enclosed in insulation, with a
hole passing through both cores. When submersed, the first core induces
1 turn's worth of voltage around the liquid loop that passes through the
hole. The current that voltage moves through the liquid is sensed by
the second core, acting as a current transformer. You amplify the AC
current from the second core, rectify it, and the result represents the
conductivity of the solution.
Click to expand...
Very interesting! What frequency do you use/recommend and why?

Ted
 
Ted Edwards wrote:
Luhan Monat wrote:

The picture is a week out of date. I've gone to nylon ties with a
piece of mousepad between the jars and the PVC. We are running over
100 here every day lately - the rubber bands were almost totally
decomposed in about 2 weeks.


Use stainless steel hose clamps - cheap and readily available from
automotive suppliers. Nylon ties die fairly quickly if exposed to UV.
So do most tapes.

Ted
Click to expand...
If the nylon dies, I'll definitely go to the steel hose clamps.

--
Luhan Monat: luhanis(at)yahoo(dot)com
http://members.cox.net/berniekm
"Any sufficiently advanced magick is
indistinguishable from technology."
 
Ted Edwards wrote:
John Popelish wrote:

My favorite kind of sensor is a toroidal transformer type. It is
completely enclosed in insulating material and is very resistant to
fouling. Unfortunately, the electronics are fairly expensive. I
think that Cole Parmer has some units for $360. But it might be fun
to try to make one of these sensors from simple parts.

The concept is that you excite a toroidal core (high permeability)
with AC through a winding. Then you place a second toroid beside that
one with another winding. The two cores are enclosed in insulation,
with a hole passing through both cores. When submersed, the first
core induces 1 turn's worth of voltage around the liquid loop that
passes through the hole. The current that voltage moves through the
liquid is sensed by the second core, acting as a current transformer.
You amplify the AC current from the second core, rectify it, and the
result represents the conductivity of the solution.


Very interesting! What frequency do you use/recommend and why?
Click to expand...
I haven't actually built one of these, yet, so I haven't thought too
much about that. This is the way commercial toroidal conductivity
probes work. I think I once measured a Yokagowa unit and it operated
around 5 kHz. I would choose a frequency that allowed the two high
permeability cores to operate with low losses. If the excitation core
has high losses, they subtract a little of the voltage per turn the
liquid receives. If the current transformer core has losses, it
subtracts from the conductivity signal. I think any frequency in the
mid to upper audio range will work pretty well with a pair of 10,000
relative permeability ferrite cores. If you have a couple tape would
permoly or hypermoly cores, the frequency could be lower.
 
On Sat, 25 Jun 2005 12:44:30 -0700, Luhan Monat wrote:

Luhan Monat wrote:

Hi,

I'm constructing a Hydroponics system, and need to monitor the
conductivity of the nutrient solution.

Any suggestions on what to use for the sensors for stable long-term
readings?

Thanks,

Here's what it looks like so far...

http://members.cox.net/berniekm/hydro2.jpg
Click to expand...
Why so tall? And where do the plants go?

And where do you buy a jar of "Medium"? ;-)

Thanks,
Rich
 
On Sat, 25 Jun 2005 12:39:29 -0700, Luhan Monat wrote:

Hi,

I'm constructing a Hydroponics system, and need to monitor the
conductivity of the nutrient solution.

Any suggestions on what to use for the sensors for stable long-term
readings?

I'm wondering why conductivity, specifically. Is it really a good
Click to expand...
indication - well, I know it would be a good indication of concentration
of _every_ kind of ion, but wouldn't distinguish between nutrient A
and nutrient B; or then again, are you using a premix and just need
to know when to add a teaspoon of mix or whatever?

But for plain ordinary conductivity, I was going to say platinum,
but that two-toroid idea sounds pretty intriguing.

Good Luck!
Rich
 
Rich Grise wrote:
On Sat, 25 Jun 2005 12:39:29 -0700, Luhan Monat wrote:


Hi,

I'm constructing a Hydroponics system, and need to monitor the
conductivity of the nutrient solution.

Any suggestions on what to use for the sensors for stable long-term
readings?


I'm wondering why conductivity, specifically. Is it really a good
indication - well, I know it would be a good indication of concentration
of _every_ kind of ion, but wouldn't distinguish between nutrient A
and nutrient B; or then again, are you using a premix and just need
to know when to add a teaspoon of mix or whatever?

But for plain ordinary conductivity, I was going to say platinum,
but that two-toroid idea sounds pretty intriguing.

Good Luck!
Rich


Yo,
Click to expand...

Measuring conductivity is standard procedure for hydroponics. My tests
so far, show only about a 10% change in conductivity between water and a
specified nutrient solution. From further study of Hydro systems, I
may just start with a standard mixture and have the system add plain
water to maintain the concentration.

Once I get some plants in, I'll post some more pictures.

--
Luhan Monat: luhanis(at)yahoo(dot)com
http://members.cox.net/berniekm
"Any sufficiently advanced magick is
indistinguishable from technology."
 
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