How does a pre-amplified pH sensor work?

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Bronze Marktheusch
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Posted by theusch: Tue. Sep 4, 2018 - 02:52 PM
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Consider a "pre-amplified" pH sensor such as

https://www.omega.com/pptst/PHE9...

 

There is only a single BNC connection.  Does the RTD temperature compensation as well as pre-amplification to turn high-impedance to low-impedance signal really work without a battery or other power source?

You can put lipstick on a pig, but it is still a pig.

I've never met a pig I didn't like, as long as you have some salt and pepper.

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Learning and Information, General Electronics, pH
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ki0bk
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Posted by ki0bk: Tue. Sep 4, 2018 - 03:00 PM
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IIRC those usually have a self contained battery (button cell) for power.

 

Jim

 

 

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ka7ehk
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Posted by ka7ehk: Tue. Sep 4, 2018 - 03:00 PM
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Does that BNC connection require DC bias like some microphones? Omega spec sheet says NOTHING about battery; no hint from the controller spec sheet.

 

YSI talks about  1 to 2 year battery life. https://www.ysi.com/File%20Libra...

 

Jim

 

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Last Edited: Tue. Sep 4, 2018 - 03:11 PM
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Bronze Marktheusch
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Posted by theusch: Tue. Sep 4, 2018 - 03:08 PM
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ka7ehk wrote:
Does that BNC connection require DC bias like some microphones?

Good thinking -- hadn't thought of that...

 

But I don't think that is the power source, as we just connected to the BNC, used some acid/base fluids, and got some hundreds of millivolts.

 

 

You can put lipstick on a pig, but it is still a pig.

I've never met a pig I didn't like, as long as you have some salt and pepper.

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ka7ehk
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Posted by ka7ehk: Tue. Sep 4, 2018 - 03:12 PM
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Intersting, as the spec sheet is totally silent about battery.

 

Jim

 

Until Black Lives Matter, we do not have "All Lives Matter"!

 

 

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Bronze Marktheusch
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Posted by theusch: Tue. Sep 4, 2018 - 03:33 PM
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ka7ehk wrote:
Intersting, as the spec sheet is totally silent about battery.

Indeed, thus our confusion.  The probe was pulled out of a box from Projects Past.  Is a pH probe like a resistor such that they are all alike and the datasheet doesn't give any gory details?

You can put lipstick on a pig, but it is still a pig.

I've never met a pig I didn't like, as long as you have some salt and pepper.

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Bronze Marktheusch
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Posted by theusch: Tue. Sep 4, 2018 - 03:48 PM (Reply to #6)
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theusch wrote:

... such that they are all alike ...

Follow-on related question:  The datasheeets for the pre-amplified sensors don't give a value of how many mV are a pH "count".  All the same -- "standard"?

You can put lipstick on a pig, but it is still a pig.

I've never met a pig I didn't like, as long as you have some salt and pepper.

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DocJC
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Posted by DocJC: Tue. Sep 4, 2018 - 04:10 PM
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All the same -- "standard"?

Maybe, don't know for sure.

 

 IIRC, a generic pH probe, (probe and front end driver), (dual probe, or whatever it is actually called, that also contains its own internal reference cell), outputs 0 V at pH 7, and +/- 60 mV / pH unit.

I don't recall if increasing pH gives increasing voltage, or vice versa.

That "standard" probe could then get plugged into any of several different display (analog dial or digital) and / or PC interfaces.

 

If the probe is old it won't be of much use.

pH probes have a life span, and are suppose to be kept wet at a neutral pH when not in use.

They have a reference electrode with a chemical in it, and the reference chemical and the glass membrane all age.

 

JC

 

edit: typo

 

 

 

 

 

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gchapman
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Posted by gchapman: Tue. Sep 4, 2018 - 08:29 PM (Reply to #8)
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DocJC wrote:
I don't recall if increasing pH gives increasing voltage, or vice versa.
It's proportional for this pH front-end (current amp) into an MCU (PIC18F14K22) :

https://www.atlas-scientific.com/_files/_datasheets/_oem/pH_oem_datasheet.pdf

(page 23)

Sensor Data

(uint32_t)

via

Atlas Scientific

pH OEM Circuit

https://www.atlas-scientific.com/product_pages/oem/oem_ph.html

(resolution is 1 milli-pH, 3.3..5.5V, 3..5mA, -40..+125C)

DocJC wrote:
pH probes have a life span, ...
and a calibration span; for industrial it's once per month or more often (harsh environment) (IIRC a 10degC change can greatly change the reaction rate)

DocJC wrote:
... and are suppose to be kept wet at a neutral pH when not in use.
Might be able to recover a mis-operated pH probe.

Atlas Scientific

pH Reconditioning Kit

https://www.atlas-scientific.com/product_pages/chemicals/ph_recon.html

 

Atlas Scientific

pH

https://www.atlas-scientific.com/ph.html

 

Edits: PIC18, typo

 

"Dare to be naïve." - Buckminster Fuller

Last Edited: Tue. Sep 4, 2018 - 08:35 PM
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