GF Signet 2764-2767 Differential DryLoc pH_ORP Electrodes - Manual (Page 3)

3 Signet 275X, 276X, 277X Series pH and ORP Electrodes
2. Electrode Care and Application
Lubricate O-rings with a non-petroleum based, viscous, lubricant (grease) compatible with the system.
pH/ORP electrodes are similar to batteries; they age with time and usage. The following information will help maximize electrode life.
2.1 Conditions to Avoid:
• High temperatures, strong acids or caustics will accelerate electrochemical reactions and speed electrode aging.
• Coatings on the glass or junction surfaces (e.g., proteins) cause extended response time and inaccurate measurement.
• Never store the electrode tip in deionized (DI) water. Use pH 4 buffer solution to keep the glass wet when out of the process.
• Never expose electrode to temperatures below 0 °C (32 °F) or allow it to dehydrate. These conditions may damage the electrode.
• Never scrape or sand the glass electrode surface.
• Treat glass electrode surfaces with care to prevent accidental breakage.
2.2 Submersible Installation Tips:
• Choose a location that keeps the electrode glass completely submerged at all times.
• Mount electrodes in a location with ample clearance for removal.
• Place the electrode tip in pH 4 buffer during system maintenance or storage to avoid dehydration.
• Mount the electrode near tank outlets, away from reagent addition areas.
2.3 In-Line Installation Tips:
• pH and ORP electrodes respond best in moving fl uids.
• Differential (2764 series) electrodes must by mounted at a downward angle (> 15° from horizontal).
• 2774 and 2775 electrodes can be mounted at any angle.
3. pH Electrode Calibration
All pH electrodes are designed to provide linear output during their lifespan. The following sections
defi ne proper electrode operation.
3.1 Offset (STD)
Electrode offsets occur due to:
• Clogged reference junction
• Aged or contaminated reference electrochemical cell.
Check offsets in a pH 7 buffer @ 25 °C. The theoretical output is 0 mV.
Any deviation from 0 mV is the pH electrode offset.
pH electrode offset pH 7 buffer @ 25 °C. Theoretical: 7.0 pH (0.0 mV)
New electrode: pH 7 ± 0.25 pH (±15 mV)
Reliable: pH 7 ± 0.85 pH (± 50 mV)
Electrode offsets greater than 0.85 pH (50 mV) indicate the electrode requires cleaning or
replacement. See section 5: Maintenance and Cleaning.
Theoretical mV Values @ 25 °C
pH mV
2 +296 mV
3 +237 mV
4 +177 mV
5 +118 mV
6 +59 mV
7 0 mV
8 -59 mV
9 -118 mV
10 -177 mV
11 -237 mV
12 -296 mV