pH Electrode Selection Guide: Glass, Diaphragm, Temperature, Pressure, and Connector
Process pH sensor selection in seven steps: medium, glass, reference, diaphragm, operating conditions, connector, and housing.
Seven-Step Selection
- Medium: Bioprocess, chemical, water-wastewater, or ultra-low conductivity; determines the sensor family to select.
- Glass: PHI, HB, H, HF, or F.
- Reference and electrolyte: Everef-F, Everef-L, polymer gel (Polisolve), liquid 3 M KCl, or gel.
- Diaphragm: Single Pore, HP ceramic, HP Coatramic, PTFE sleeve.
- Conditions: Temperature, maximum pressure, sterilization (CIP/SIP/autoclave), sample conductivity.
- Connector and length: 12 mm shaft; VP6, S8, Arc, K8, Memosens; 120–425 mm a-length.
- Housing: Static, immersion, flow cell, or retractable housing.
Sensor Family by Medium
| Medium | Family | Key characteristics |
|---|---|---|
| Bioreactor, fermentation (CIP/SIP/autoclave) | EasyFerm Plus / Bio | 0–140 °C, 6 bar; pre-pressurized Everef-F reference; HP Coatramic diaphragm |
| Single-use bioreactor | OneFerm | pH 3–10, 4–50 °C, 1 bar; gamma sterilized, factory calibrated |
| Chemical, acid, base, solvent | Polilyte Plus, ChemoTrode, MecoTrode | 0–130 °C; polymer gel, liquid electrolyte, or viscous KCl; H or HF glass for extreme pH |
| Water treatment and wastewater | Polilyte Plus, InchTrode, EasyControl | Maintenance-free polymer gel; Single Pore in fibrous media; economical entry-level option |
| Boiler feedwater, drinking water, low conductivity | IonoTrode | F glass, PTFE sleeve diaphragm, 0.2 µS/cm |
| Pulp and paper | InchTrode | 1 inch PEEK shaft, NPT threaded connection |
| Laboratory and quality control | Laboratory electrodes | S7 connector or BNC/DIN/Lemo cable; 39+ models by sample type |
Glass Type: Hamilton Selection Table
| Requirement | Glass | Example |
|---|---|---|
| CIP, SIP, autoclave, chemical durability | PHI | EasyFerm Plus PHI, Polilyte Plus PHI |
| CIP, SIP, autoclave, fast response time | HB | EasyFerm Plus HB, Polilyte Plus HB |
| Low conductivity, low alkali error, high temperature | H | Polilyte Plus H, MecoTrode H |
| Hydrofluoric acid in medium, low temperature | HF | Polilyte Plus HF (-10…100 °C), MecoTrode HF |
| High pressure | H (XP) | Polilyte Plus XP: 50 bar at 60 °C, 20 bar at 100 °C, 16 bar at 130 °C |
| Ultra-low conductivity (low-resistance glass) | F | IonoTrode, Liq-Glass PG |
Reference, Electrolyte, and Diaphragm
Refillable or maintenance-free? ChemoTrode uses refillable liquid electrolyte and can be pressurized up to 6 bar via its port; it provides fast response and high accuracy in exchange for electrolyte maintenance. The Polisolve polymer gel of Polilyte Plus, Polilyte Pro, and InchTrode requires no refilling and slows the ingress of chemicals. The gel electrolyte of EasyControl is non-refillable and maintenance-free.
Pressurized reference. In the EasyFerm family, the reference is pre-pressurized, preventing process fluid from entering the reference system and ensuring stable readings. The Everef-F reference includes a silver-ion barrier so the electrolyte remains free of silver and protein precipitates. Everef-L provides extended reference lifetime in Polilyte Plus and InchTrode.
Diaphragm. Single Pore is a single wide pore where the sample contacts the polymer electrolyte directly, and it does not clog in fibrous, viscous, or particulate media (in the Hamilton laboratory catalog, the single-pore cross-sectional area is described as approximately 200 times larger than the fine pores in a ceramic diaphragm). HP Coatramic is a non-clogging ceramic design. MecoTrode's 3 HP ceramic diaphragms reduce drift caused by streaming potential in viscous fluids and pipeline installations. IonoTrode's removable PTFE sleeve serves to adjust and control electrolyte outflow.
Temperature, Pressure, Sterilization, and Sample Conductivity
| Sensor | Temperature | Max. pressure | Sterilization | Recommended min. conductivity |
|---|---|---|---|---|
| EasyFerm Plus / Bio | 0–140 °C | 6 bar | Autoclave, SIP, CIP | 100 µS/cm |
| Polilyte Plus (H, HB, PHI) | 0–130 °C | 10 bar | Autoclave (H, HB, PHI); CIP (HB, PHI); SIP (H, HB, PHI) | 5 µS/cm |
| Polilyte Plus HF | -10…100 °C | 16 bar | Not specified in catalog | 5 µS/cm |
| ChemoTrode | 0–130 °C | 6 bar | SIP, CIP | 20 µS/cm |
| MecoTrode H | 0–130 °C | 6 bar (16 at 25 °C) | Not specified in catalog | 50 µS/cm |
| InchTrode | -10…130 °C (flat), 0–130 °C (cylindrical) | 6 bar (10 at 25 °C) | Not specified in catalog | 5 µS/cm |
| IonoTrode | -10…40 °C | 0.5 bar (higher with side arm) | Not specified in catalog | 0.2 µS/cm |
| EasyControl | 0–60 °C | 2 bar | Not specified in catalog | 20 µS/cm |
| OneFerm | 4–50 °C | 1 bar | Gamma or X-ray, up to 50 kGy | - |
Source: Hamilton Process Analytics Catalog 2026, "Sensor Comparison" and product pages. A high-pressure sensor should not be immediately exposed to high temperature (above 80 °C) after prolonged operation above 10 bar (Hamilton manual).
Connector, Shaft Length, and Ordering Code
12 mm shaft is the standard diameter of Hamilton process pH sensors; the a-length (length) is selected before choosing the housing, vessel port, or retractable assembly. VP6: 6-contact connector with Pt100 or Pt1000 temperature sensor option; S8 and K8: analog connectors without a temperature sensor; LEVP: for 120 and 225 mm EasyFerm only; Arc: digital, Modbus and 4-20 mA; Memosens (MS): digital option in certain families; S7: laboratory and IonoTrode, ChemoTrode.
| Family and ordering code | Glass | Connector | Length (a-length) | Temperature sensor |
|---|---|---|---|---|
| EasyFerm Plus 238633- | 1 PHI, 2 HB | 1 VP, 2 S8, 3 Arc, 4 Memosens, 5 K8, 6 LEVP (120 and 225 mm) | 1: 120; 2: 160; 3: 200; 4: 225; 5: 325; 6: 360 (except Arc, PHI only); 7: 425 mm | 1 Pt100, 2 Pt1000 (VP, LEVP); 3 none (S8, K8) or built-in (Memosens, Arc) |
| EasyFerm Bio 243632- | 1 PHI, 2 HB | Same coding as Plus | 120, 160, 200, 225, 325, 425 mm | Same as Plus |
| Polilyte Plus 242428- | 1 H, 2 HB (except MS), 3 HF, 4 PHI | 1 VP, 2 S8, 3 Arc, 4 Memosens | 1: 120; 2: 225; 3: 325; 4: 360 (except Arc, MS in H glass only); 5: 425 mm | 1 Pt100, 2 Pt1000 (VP); 3 none (S8) or built-in (MS, Arc) |
| MecoTrode | H or HF | S8, VP6, MS, Arc | 120 mm; 225 mm for Memosens H and HF | VP: Pt100; Arc: NTC 22 kΩ; MS: NTC 30 kΩ |
| ChemoTrode | PHI | S7, VP6 | 120, 150, 200, 250 mm | VP6: Pt1000 or Pt100 |
| InchTrode | HF or PHI | VP6 or fixed cable | 140–150 mm; N75: 3/4" NPT, N100: 1" NPT | VP6: Pt1000; fixed cable: Pt100 |
Length selection. Hamilton housings (FlexiFit, Hygienic Socket) are designed for 120 mm sensors with a PG13.5 thread. On the Safety Socket, the O-ring position (OP 25/50/55) and angle (0° or 15°) are selected separately. Compatibility of longer sensors is verified against the housing and retractable assembly table; see our Hamilton page for details on housings, flow cells, and Retractex assemblies.
Mounting, Maintenance, and Fault Symptoms
| Topic | Information in the manufacturer manual |
|---|---|
| Upside-down mounting | Permitted only for Polilyte Plus (VP, MS) and Polilyte Pro (VP); not permitted in other families |
| Pressurized housing | In a housing where the sensor is pressurized, the applied pressure must be approximately 0.5 bar above the process pressure |
| Preparation | Remove the watering cap carefully, rinse the sensor with water, and if an air bubble is present inside the glass membrane, shake gently to remove it |
| Storage | The watering cap contains 3 M KCl (Hamilton REF 238036) or storage solution (REF 238931); a dry-stored sensor exhibits temporary drift, and a dried-out sensor should be soaked overnight in storage solution |
| Refillable sensor | Open the reservoir plug before measurement, close it after measurement, and check the level |
| Regeneration | 10 minutes in 0.1–1 M NaOH, followed by 10 minutes in 0.1–1 M HCl; then at least 15 minutes in storage solution. For ORP, clean the metal surface with a mildly abrasive material |
| Protein fouling | Soak for several hours in 0.4 % HCl + 5 g/L pepsin |
| Blackened diaphragm (silver compounds) | Immerse the electrode in a 0.4 % HCl + 76 g/L thiourea solution |
| Erratic signal, weak slope, long response time | May indicate a damp or dirty connector; clean the VP connector head with a paper towel moistened with ethanol and dry it |
| After cleaning | The electrode may respond slowly for a while; keep it in storage solution for 15 minutes after cleaning |
| O-ring | Wear part; must be in place and intact so it is not damaged during threading |
IonoTrode manages electrolyte outflow in low-conductivity water via its side arm: remove the black cap of the side arm, attach a soft tube with a 6–7 mm inner diameter (such as silicone), connect the other end to a 500 mL bottle of 3 M KCl (REF 238936), and position the bottle upside down above the side arm; electrolyte outflow increases noticeably as temperature rises. Unused DuraCal pH or ORP buffer is used for calibration.
Overview of online pH and ORP analyzers: online analyzers. For bioprocess selection: bioreactor pH sensor. For Walchem differential sensors on boiler, cooling tower, and water applications: Walchem.
pH Electrode Selection: Frequently Asked Questions
Selection sequence, 12 mm and a-length, connectors, diaphragm, sterilization, and low conductivity.
In what order should I proceed when selecting a pH electrode?
First the medium (sterile/bioprocess, chemical, water-wastewater, ultra-low conductivity), then the glass type, reference and electrolyte, diaphragm, temperature-pressure-sterilization limits, and finally the connector and shaft length. The medium largely determines the sensor family, while the connector and length are configured via the ordering code of that family.
What do 12 mm shaft and 120 mm length mean?
The standard shaft diameter of Hamilton process pH sensors is 12 mm; the a-length is the length of the portion of the shaft that enters the housing or vessel, and for EasyFerm it is selected between 120–425 mm. Hamilton housings (FlexiFit, Hygienic Socket) are designed for 120 mm sensors with a PG13.5 thread. A sensor must only be used in a housing matching its a-length.
What is the difference between VP6, S8, K8, and Arc connectors?
VP6 and S8 are traditional (analog mV) connectors; VP6 can include a Pt100 or Pt1000 temperature sensor, whereas S8 and K8 do not. Arc is digital: a microprocessor, temperature compensation, and calibration data are built into the sensor head, providing Modbus and 4-20 mA outputs. Memosens (MS) is a connector option in certain families. An NTC 22 kΩ temperature sensor is built into Arc, and an NTC 30 kΩ sensor is built into MS.
How do I prevent a clogged diaphragm?
The diaphragm type is selected according to the medium. Single Pore (Polilyte, InchTrode) establishes direct contact between the sample and the polymer electrolyte; clogging is virtually impossible, making it suitable for fibrous, particulate, and viscous media. HP Coatramic (EasyFerm) resists clogging and keeps drift very low. HP ceramic (ChemoTrode, MecoTrode) reduces streaming potential effects in viscous liquids. In protein-containing media, an Everef-F reference and protein cleaning (see below) are required to prevent silver and protein precipitation.
Which pH electrode withstands CIP, SIP, and autoclaving?
EasyFerm Plus and EasyFerm Bio are suitable for autoclaving, SIP, and CIP. In Polilyte Plus, autoclaving is possible with H, HB, and PHI glasses; CIP with HB and PHI; and SIP with H, HB, and PHI. ChemoTrode is suitable for SIP and CIP. For HF-glass and other families, no sterilization method is specified in the catalog. For single-use bags, OneFerm is sterilized by gamma irradiation (up to 50 kGy).
How long does a pH electrode last, and when is it replaced?
According to the Hamilton manual, sensor lifetime is governed by response time, zero point, and slope requirements; the user is responsible for calibration, maintenance, and regular replacement. When the slope weakens, response slows down, or the zero point drifts, cleaning and regeneration are attempted, and if it does not recover, the sensor is replaced. High-quality cables also contribute to service life and measurement stability.
Which electrode is used in low-conductivity water?
According to the recommended minimum conductivity values in the catalog: IonoTrode 0.2 µS/cm, Liq-Glass PG 2 µS/cm, InchTrode, Polilyte Plus, and Polilyte Pro 5 µS/cm, ChemoTrode and EasyControl 20 µS/cm, MecoTrode H 50 µS/cm, EasyFerm 100 µS/cm. IonoTrode uses low-resistance F glass and a side-arm reservoir with 3 M KCl; a soft tube with a 6–7 mm inner diameter is attached to the side arm.
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