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'[OT] Looking for PH sensor (fish tank)'
2000\05\01@233229 by Damon Hopkins

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Jim Ruxton wrote:
>
> I was wondering if anyone can recommend a PH sensor that is fairly
> simple to interface with a PIC either through A/D or serial etc. I'm not
> looking for anything too fancy. I want to be able to monitor the PH of
> the water in a fish tank I'll also be measuring temperature so if there
> is something that does both that would be a bonus.
> Thanks for any suggestions.
> Jim
http://www.coleparmer.com

Be aware that MOST PH probes are not intended for saltwater use I'd
suggest picking up a PH probe from somewhere that sells the PH equipment
for fish tanks such as
http://www.premiumaquatics.com (if that site is down try
www.algaeworkers.com/cgi-bin/loadpage.cgi?13828+/volts/probes.html
)
or one of these
http://www.jensalt.com
http://www.acropora.com
http://www.exoticfish.com
http://www.marinedepot.com

there are 2 really good all inclusive controllers, the Neptune and the
octopus check them out for more ideas.

2000\05\03@033425 by Stephan Kotze

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Jim,

Interfacing a pH probe to PIC is not a simple exercise as I have found over
the last three months.

The best types are the glass refillable type. Most manufacturers have them.
The gel filled electrodes are not refillable and  have a finite lifespan of
about one year. If the fish tank  is saline, you will need a special prode.
Regardless you will need a special probe for very long life as the junction
tends to clog up with protiens (common in the tank).

Probes marked as ATC probes have a seperate temperature sensor in them
usually Pt100 or Pt1000. To interface with a PIC you will either need a
pre-amplified probe or you have to provide a FET input stage as the pH probe
has an impedance of about 10^9 Ohms ( yes 1000 MOhms).

I can recommend http://www.omega.com and http://www.orionres.com . Both have an excellent
range with lots! of useful information on selection and interfacing.

Stephan

{Original Message removed}

2000\05\03@043717 by Vasile Surducan

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On 3 May 00, at 9:36, Stephan Kotze wrote:

> Jim,
>
> Interfacing a pH probe to PIC is not a simple exercise as I have found over
> the last three months.

I'm agree with this conclusion...( I'm interfere here like fly's in the
milk...)
>
> The best types are the glass refillable type. Most manufacturers have them.
> The gel filled electrodes are not refillable and  have a finite lifespan of
> about one year. If the fish tank  is saline, you will need a special prode.

You may use here metallic electrodes (with bad liniarity out of
4...11pH)

> Regardless you will need a special probe for very long life as the junction
> tends to clog up with protiens (common in the tank).
>
> Probes marked as ATC probes have a seperate temperature sensor in them
> usually Pt100 or Pt1000. To interface with a PIC you will either need a
> pre-amplified probe or you have to provide a FET input stage as the pH probe
> has an impedance of about 10^9 Ohms ( yes 1000 MOhms).
>
  If money are not a very important thing, you can use a uniFET-
electrodes with small output impedance direct conectable to a AD-
PIC (output impedance in 1..100kohm) from Norel.inc USA fax:609-
625-0526 or in Europe 02633/8198
  If no money, no fear...a FET operational amplifier not to expensive
like LF411 can solve your problem. Connect the electrodes between
in- and output and use a 100ohm + 47uF( not polarized )filter from
output to ground. The in+ can be connected to a offset reglage;
large value  resistors (10M) must be added to in+ and in- to
echilibrate bias current...
  If tank gradient temperature do not exceed few grades a manual
temperature compensation it's enough...
By the way what pH precision you need and what is exactly the
saltwater content ( % ) in your tank?
Vasile

*********************************************
Surducan Vasile, engineer
mail: spam_OUTvasileTakeThisOuTspaml30.itim-cj.ro
URL: http://www.geocities.com/vsurducan
*********************************************

2000\05\03@091547 by Robert A. LaBudde

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<x-flowed>At 09:36 AM 5/3/00 +0200, Stephan wrote:
>Regardless you will need a special probe for very long life as the junction
>tends to clog up with protiens (common in the tank).

This can be cleaned by soaking in 10% HCl/methanol.

>pre-amplified probe or you have to provide a FET input stage as the pH probe
>has an impedance of about 10^9 Ohms ( yes 1000 MOhms).

This seems high. Maybe 100 MOhm. You can read a voltage with a DMM (10 Mohm
input).

================================================================
Robert A. LaBudde, PhD, PAS, Dpl. ACAFS  e-mail: .....ralKILLspamspam@spam@lcfltd.com
Least Cost Formulations, Ltd.                   URL: http://lcfltd.com/
824 Timberlake Drive                            Tel: 757-467-0954
Virginia Beach, VA 23464-3239                   Fax: 757-467-2947

"Vere scire est per causas scire"
================================================================

</x-flowed>

2000\05\04@005547 by Vasile Surducan

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On 3 May 00, at 9:14, Robert A. LaBudde wrote:

> At 09:36 AM 5/3/00 +0200, Stephan wrote:
> >Regardless you will need a special probe for very long life as the junction
> >tends to clog up with protiens (common in the tank).
>
> This can be cleaned by soaking in 10% HCl/methanol.
>
> >pre-amplified probe or you have to provide a FET input stage as the pH probe
> >has an impedance of about 10^9 Ohms ( yes 1000 MOhms).
>
> This seems high. Maybe 100 MOhm. You can read a voltage with a DMM (10 Mohm
> input).
>
   No Robert, Stephan has perfectly right, a good pH-meter with
glass electrodes has 10^9 to 10^10 Ohms, smallest input impedance
will give big measurement errors (non-linearities) . Building an
electrometer input stage is not an easy job, DVM no
way...electrometer DVM yes.
  But now that I understand the purpose of this pH-meter (to check
the salt contain into a fish aquarium with sensitive fish) solution is no
pH measured but conductivity - a little convenient problem
Vasile
*********************************************
Surducan Vasile, engineer
mail: vasilespamKILLspaml30.itim-cj.ro
URL: http://www.geocities.com/vsurducan
*********************************************

2000\05\06@160523 by Damon Hopkins

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Vasile Surducan wrote:
> By the way what pH precision you need and what is exactly the
> saltwater content ( % ) in your tank?
>  Vasile
>
> *********************************************
> Surducan Vasile, engineer
> mail: .....vasileKILLspamspam.....l30.itim-cj.ro
> URL: http://www.geocities.com/vsurducan
> *********************************************

In my tank I keep it at 82 degrees F and the salinity @ 35ppt (1.025
sg). some people may keep the temp as low as 70-72 and salinity around
1.020. depending on the tank and what the owner believes is right :)

temp swings range from 78-85 over a 12 month period.

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