pH sensor
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I am looking for a pH sensor to use with a BS basic stamp. Anyone know of a
good one?
Thanks,
Kevin
good one?
Thanks,
Kevin
Comments
On Monday 02 June 2003 11:01 am, Kevin A. Nesmith wrote:
> I am looking for a pH sensor to use with a BS basic stamp. Anyone know of
> a good one?
>
>
> Thanks,
> Kevin
>
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It depends hugely on where you are going to use the pH sensor. Lab?
Aquarium? Industry? Field site? And other instrumentation present
in the same environment, in relation to instrumentation ground loops,
and accuracy and longevity requirements. One good source for
industrial quality is
http://www.sensorex.com
for hobby or school use, check out,
http://www.vernier.com/probes/index.html
-- best regards
Thomas Tracy Allen PhD
electronically monitored ecosystems
http://www.emesystems.com
mailto:tracy@e...
>Sorry, I have a BS2 chipset.
>
>On Monday 02 June 2003 11:01 am, Kevin A. Nesmith wrote:
>> I am looking for a pH sensor to use with a BS basic stamp. Anyone know of
>> a good one?
>>
>>
>> Thanks,
> > Kevin
soil. If you have any advise on the best one for a hobby, please let me
know. I am very open to suggestions.
Thanks,
Kevin
On Monday 02 June 2003 12:22 pm, Tracy Allen wrote:
> Hi Kevin,
>
> It depends hugely on where you are going to use the pH sensor. Lab?
> Aquarium? Industry? Field site? And other instrumentation present
> in the same environment, in relation to instrumentation ground loops,
> and accuracy and longevity requirements. One good source for
> industrial quality is
> http://www.sensorex.com
> for hobby or school use, check out,
> http://www.vernier.com/probes/index.html
>
> -- best regards
> Thomas Tracy Allen PhD
> electronically monitored ecosystems
> http://www.emesystems.com
> mailto:tracy@e...
>
> >Sorry, I have a BS2 chipset.
> >
> >On Monday 02 June 2003 11:01 am, Kevin A. Nesmith wrote:
> >> I am looking for a pH sensor to use with a BS basic stamp. Anyone know
> >> of a good one?
> >>
> >>
> >> Thanks,
> >>
> > > Kevin
>
> To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@yahoogroups.com
> from the same email address that you subscribed. Text in the Subject and
> Body of the message will be ignored.
>
>
> Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
Are these hydroponic tomatoes? If so, maybe you can drip some of the
irrigation water into a free-standing cup and measure the pH of that.
The usual way to measure pH of soil is to take a sample of the soil
in a cup, mix it with an equal amount of distilled H2O, wait a few
minutes, and then stick in a piece of Hydrion paper (color change) or
a pH electrode. If you are using an electrode, you then wash it and
put it back into the storage solution, until next time.
Electrodes in continuous contact with the medium require careful
maintenance. Industrial electrodes for process monitoring often are
constructed with a flat sensing surface so that they can be easily
cleaned. You can see some of those at the sensorex.com site.
There is another issue of instrumentation that can make pH monitoring
very tricky. If the electrode is in intimate contact with a large
body of water or an extensive system of pipes, or the soil out of
doors, it is in effect connected to a huge antenna for 60hz pickup
and all kinds of galvanic currents. In those cases, the pH signal can
be overwhelmed by noise, unless it is equipped with a so-called
isolation amplifier.
It is not a problem if your electrode is a simple handheld instrument
contacting the system at one point. And, it is not a problem if you
take a sample of liquid out of the system and hold it in a separate,
electrically isolated cup. That is why I was wondering if you could
drip irrigation water into a separate cup?
The experimenters pH electrode from Vernier includes a built-in
amplifier (not isolated!), offset to read 1.75 volts at pH 7, so you
could apply that directly to the input of an analog to digital
converter, to the BASIC Stamp. Read up on pH instrumentation in the
manual for the Vernier electrode, and also at the
http://www.omega.com site, and others through a web search. You
cannot apply the signal from a pH electrode directly to an analog to
digital converter, because of the high output resistance of the
electrodes' glass membrane.
-- best regards
Tracy Allen
electronically monitored ecosystems
http://www.emesystems.com
mailto:tracy@e...
>It is for a hobby of growing tomato plants. So the sensor would be in the
>soil. If you have any advise on the best one for a hobby, please let me
>know. I am very open to suggestions.
>
>Thanks,
>Kevin
>
>On Monday 02 June 2003 12:22 pm, Tracy Allen wrote:
>> Hi Kevin,
>>
>> It depends hugely on where you are going to use the pH sensor. Lab?
>> Aquarium? Industry? Field site? And other instrumentation present
>> in the same environment, in relation to instrumentation ground loops,
>> and accuracy and longevity requirements. One good source for
>> industrial quality is
>> http://www.sensorex.com
>> for hobby or school use, check out,
>> http://www.vernier.com/probes/index.html
>>
>> -- best regards
>> Thomas Tracy Allen PhD
>> electronically monitored ecosystems
>> http://www.emesystems.com
>> mailto:tracy@e...
>>
>> >Sorry, I have a BS2 chipset.
>> >
>> >On Monday 02 June 2003 11:01 am, Kevin A. Nesmith wrote:
>> >> I am looking for a pH sensor to use with a BS basic stamp. Anyone know
>> >> of a good one?
>> >>
>> >>
>> >> Thanks,
>> >>
>> > > Kevin
>>
>> To UNSUBSCRIBE, just send mail to:
>> basicstamps-unsubscribe@yahoogroups.com
>> from the same email address that you subscribed. Text in the Subject and
>> Body of the message will be ignored.
>>
>>
>> Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
>
>
>To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@yahoogroups.com
>from the same email address that you subscribed. Text in the
>Subject and Body of the message will be ignored.
>
>
>Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
On Monday 02 June 2003 06:16 pm, Tracy Allen wrote:
> Kevin,
>
> Are these hydroponic tomatoes? If so, maybe you can drip some of the
> irrigation water into a free-standing cup and measure the pH of that.
>
> The usual way to measure pH of soil is to take a sample of the soil
> in a cup, mix it with an equal amount of distilled H2O, wait a few
> minutes, and then stick in a piece of Hydrion paper (color change) or
> a pH electrode. If you are using an electrode, you then wash it and
> put it back into the storage solution, until next time.
>
> Electrodes in continuous contact with the medium require careful
> maintenance. Industrial electrodes for process monitoring often are
> constructed with a flat sensing surface so that they can be easily
> cleaned. You can see some of those at the sensorex.com site.
>
> There is another issue of instrumentation that can make pH monitoring
> very tricky. If the electrode is in intimate contact with a large
> body of water or an extensive system of pipes, or the soil out of
> doors, it is in effect connected to a huge antenna for 60hz pickup
> and all kinds of galvanic currents. In those cases, the pH signal can
> be overwhelmed by noise, unless it is equipped with a so-called
> isolation amplifier.
>
> It is not a problem if your electrode is a simple handheld instrument
> contacting the system at one point. And, it is not a problem if you
> take a sample of liquid out of the system and hold it in a separate,
> electrically isolated cup. That is why I was wondering if you could
> drip irrigation water into a separate cup?
>
> The experimenters pH electrode from Vernier includes a built-in
> amplifier (not isolated!), offset to read 1.75 volts at pH 7, so you
> could apply that directly to the input of an analog to digital
> converter, to the BASIC Stamp. Read up on pH instrumentation in the
> manual for the Vernier electrode, and also at the
> http://www.omega.com site, and others through a web search. You
> cannot apply the signal from a pH electrode directly to an analog to
> digital converter, because of the high output resistance of the
> electrodes' glass membrane.
>
> -- best regards
> Tracy Allen
> electronically monitored ecosystems
> http://www.emesystems.com
> mailto:tracy@e...
>
> >It is for a hobby of growing tomato plants. So the sensor would be in the
> >soil. If you have any advise on the best one for a hobby, please let me
> >know. I am very open to suggestions.
> >
> >Thanks,
> >Kevin
> >
> >On Monday 02 June 2003 12:22 pm, Tracy Allen wrote:
> >> Hi Kevin,
> >>
> >> It depends hugely on where you are going to use the pH sensor. Lab?
> >> Aquarium? Industry? Field site? And other instrumentation present
> >> in the same environment, in relation to instrumentation ground loops,
> >> and accuracy and longevity requirements. One good source for
> >> industrial quality is
> >> http://www.sensorex.com
> >> for hobby or school use, check out,
> >> http://www.vernier.com/probes/index.html
> >>
> >> -- best regards
> >> Thomas Tracy Allen PhD
> >> electronically monitored ecosystems
> >> http://www.emesystems.com
> >> mailto:tracy@e...
> >>
> >> >Sorry, I have a BS2 chipset.
> >> >
> >> >On Monday 02 June 2003 11:01 am, Kevin A. Nesmith wrote:
> >> >> I am looking for a pH sensor to use with a BS basic stamp. Anyone
> >> >> know of a good one?
> >> >>
> >> >>
> >> >> Thanks,
> >> >>
> >> > > Kevin
> >>
> >> To UNSUBSCRIBE, just send mail to:
> >> basicstamps-unsubscribe@yahoogroups.com
> >> from the same email address that you subscribed. Text in the Subject
> >> and Body of the message will be ignored.
> >>
> >>
> >> Your use of Yahoo! Groups is subject to
> >> http://docs.yahoo.com/info/terms/
> >
> >To UNSUBSCRIBE, just send mail to:
> > basicstamps-unsubscribe@yahoogroups.com
> >from the same email address that you subscribed. Text in the
> >Subject and Body of the message will be ignored.
> >
> >
> >Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
>
> To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@yahoogroups.com
> from the same email address that you subscribed. Text in the Subject and
> Body of the message will be ignored.
>
>
> Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
works well with a BS2?
Thanks,
S.
unit referenced to pH7. So pH7 gives 0mV, pH6 = -70mV and pH8= +70mV.
Most sensors have very high impedance outputs so you would require a
preamp before measuring the voltage with an AD converter. However
there is a really good sensor that has the preamp built in. It is
called an AmpHel sensor and is manufactured by Hanna Instruments.
You can buy them from www.labsales.com
All you need then is the right AD converter for the resolution that
you require.
--- In basicstamps@yahoogroups.com, "Sarah" <nursesarah1996@y...>
wrote:
> Can anyone recommend a pH sensor and interface circuit (if
required) that
> works well with a BS2?
>
> Thanks,
>
> S.
>works well with a BS2?
>Thanks,
>S.
Hi Sarah,
Ph probes require a very high impedance pre-amplifier, and since the
voltage output is usually positive in acids (pH<7) and negative in
bases (pH>7), there may also be a need to shift the level so that it
can be read by positive voltage ADC.
If it is for a school project, take a look at
http://www.vernier.com/probes/index.html
I think their pH probe has the interface circuit built in.
Another source of pH probes is
http://www.omega.com
or
http://www.sensorex.com/
The probe itself will be either a laboratory probe optimized for
accuracy and speed of response, but delicate, or "process" or
"environmental" probes optimized for ruggedness and anti-fouling.
If the probe will be used in contact with a large scale system (as
opposed to a beaker or sampler hooked up to a hand-held meter), it
may well need an isolation amplifier or transmitter.
I have a little written on a stamp interface to a pH probe at
http://www.emesystems.com/OL2ph.htm
For a quick & dirty Stamp interface, this circuit might work with RCtime:
http://www.emesystems.com/BS2rct.htm#SmallV
If the op-amp in the first circuit there is a mos input op-amp.
-- Tracy