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Aquametrix Products


pH and ORP Probes

pH and ORP Probes






Combination Probes



P/R65 4-20 mA Output Differential pH/ORP Sensors

USA Toll Free: 1-800-730-0302 Tel: 416-240-1920 -

P/R65 4-20 mA Output Differential pH/ORP Sensors

AquaMetrix pH and ORP differential probes stay in service and provide accurate measurements under conditions that often render conventional pH probes inoperable. Now for added versatility, these probes, field-proven in hundreds of installations, are available with an integral encapsulated 4-20 mA two-wire transmitter to feed directly to a PLC or a DCS.

The P65 pH and R65 ORP probes employ a differential measurement technique. Unlike conventional combination probes, the differential probe has two high impedance measurement circuits containing a common metallic return electrode. One circuit includes the process measurement electrode which generates a potential E1 proportional to the process pH. The second circuit includes an internal measurement electrode immersed in a stable buffer solution which generates a standard reference potential, E2. Both circuitshave a common potential E3 developed at the return electrode. The two circuits are fed into amplifiers which provide an output representing the differential between them:
(E1 - E 3) - (E2 - E3). The common potential E3 is cancelled out electronically, greatly reducing inaccuracies caused by ground loops which may exist between process and instrument grounds. Ground loop current willflow through the low impedance path of the return electrode, affecting the potential E3, but not the differential measurement.

The differential probe maintains its accuracy and stability in aggressive process applications long after a combination-style probe’s performance begins to deteriorate.

Maintenance costs are reduced and the life of the probe is increased. The internal reference electrode is electrically connected to the process solution by means of a field-replaceable double junction salt bridge which greatly reduces the possibility of contamination of the buffer solution in the reference circuit. Although seldom required, the reference solution may be easily replaced by removing the screw-out salt bridge. A salt bridge and buffer kit is available for this purpose.

Another advantage of the 65 series is the semi-flush face which is easily cleaned and avoids solution materials gathering on protrusions found in competitive probes. The domed glass electrode, the protective metal electrode and the temperature sensor protrude only about 1/8 inch while the salt bridge is flush. A flat-face version of the pH probe is also available.

The 65 series can be provided in any of the physical configurations in the P60/R60 series differential probes: 65C-8 with 1-1/2” threaded body style, 65C-6 “Easy-In, Easy-Out” variable insertion depth version with 1- 1/4” NPT compression fitting

  • Integral two-wire 4-20 mA transmitter can be fed directly to PLC, DCS

  • Accurate differential measurement

  • Eliminates ground loop interference

  • Built-in pre-amp supports up to 3,000' sensor-to-analyzer distance

  • 15 ft. (5m) standard cable length

  • Replaceable saltbridge for extended service life

  • Flow-thru, Hot-tap or submersible mounting

  • Automatic temperature compensation on pH versions

  • Semi-flush face available: reduced buildup

  • Long-lasting

  • Low Maintenance Cost

  • Field-proven

  • 2 year warranty

PR65 Datasheet
PR65 Series pH/ORP Probe Manual



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Metex Corporation Limited has been providing superior products and services to the process control, chemical treatment, waste water, industrial and manufacturing industries for over 25 years. It is our goal to continually provide our customers with the best possible equipment, technology, and service.


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