pH sensors

FuzzyLogic

New member
Randy, I need to purchase a replacement electrode for a pH analyzer that I'm using. There is an option for these sensors that I am unfamiliar with, 'Solution Ground'. Do you know if this is a ground for the entire system or is it just for the analyzer and sensor? If I already have a ground probe in the system, will this cause a ground loop? I don't know if this option is really necessary. Have you ever used these kind of industrial sensors?
 

Randy Holmes-Farley

Reef Chemist
Premium Member
A ground is not necessary to measure pH, assuming you are measuring pH with a standard pH electrode that includes an internal reference electrode. I've never used one with a ground.

What brand?
 

Randy Holmes-Farley

Reef Chemist
Premium Member
I've never used such a system, but here's the claimed advantage:

http://www.aquametrix.com/productnews.html

"60 Series Differential pH Probes
(Same probes are available in ORP)
All P60 pH probes use the differential pH measurement technique, proven over almost three decades in thousands of applications worldwide. This design utilizes two glass electrodes to measure the pH differentially to a third metal (ground) electrode. The second glass electrode is protected from the process by a double junction replaceable salt bridge.
The resulting true differential measurement probe has several advantages over conventional probes:

Ground loop problem eliminated: Ground loop problems are virtually eliminated by sharing a common a ground electrode.
Extended Life: The salt bridge is easily replaced (with needle nosed pliers), greatly extending the life of the probe. If the internal solution becomes contaminated, the probe can be rejuvenated at modest cost by replacing the salt bridge and reference solution.
Automatic temperature compensation: Automatic temperature compensation is accomplished through the use of an exposed thermistor at the tip of the probe. This thermistor placement provides rapid response for process temperature variations.
Transmits up to 3000 feet: The encapsulated preamplifier provides an output signal that can be transmitted up to 3000 feet over inexpensive cable.
Built-in 4-20 mA Transmitter available. The P65 version encapsulates a blind 4-20 mA two-wire transmitter that can be wired directly into a PLC. "
 

Randy Holmes-Farley

Reef Chemist
Premium Member
Also:

http://www.faqs.org/faqs/sci/chem-faq/part6/preamble.html

Ground loops and spurious electrical currents may generate unexpected
electrical signals. Such signals can strongly influence pH measurements.
A pH reading in the range of -15 to +20 is possible, even if the pH is 7.
Ground loops can be eliminated by grounding the system according to the
manufacturer's instructions, and ensuring insulation is in good condition.
Often these problems can be extremely difficult to detect and remedy.
 
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