Bioreactor pH Sensors: EasyFerm, OneFerm, and Sterile Service Selection
Reusable (autoclave, SIP, CIP) and single-use pH sensors for fermentation and cell culture: differences, comparison table, and selection criteria.
Three Families, Three Use Cases
- Stainless steel bioreactor, industrial/chemical-pharmaceutical process: EasyFerm Plus, PHI or HB glass, 0–140 °C, 6 bar, autoclave + SIP + CIP.
- Food, brewing, gelatin, or cytotoxicity-sensitive bioprocess: EasyFerm Bio, certified biocompatible Foodlyte electrolyte.
- Single-use bag: OneFerm, gamma-sterilized, factory-calibrated at pH 4 and 7, pH 3–10.
A Central Parameter in Bioprocessing
All biological processes depend on enzyme activity, and enzymes have a pH optimum; when pH is too low or too high, they lose their function. In most processes, pH is measured with a glass electrode: in aqueous solution, the glass forms a thin gel layer highly selective to protons, and the pH-dependent potential of this layer is measured against a built-in reference of constant potential. In a bioreactor, this measurement is affected both by sterilization (autoclaving, SIP) and by media and protein load during the run; sensor selection therefore rests on reference, electrolyte, and diaphragm design.
The distinguishing design of Hamilton's EasyFerm family is its pre-pressurized reference and clog-resistant HP Coatramic diaphragm: pre-pressurization prevents process liquid from entering the reference, while the Everef-F reference incorporates a silver-ion barrier that protects the reference electrolyte from silver and protein precipitation. The result is stable readings, low drift, and long sensor service life.
EasyFerm Plus, EasyFerm Bio, and OneFerm
| Feature | EasyFerm Plus | EasyFerm Bio | OneFerm |
|---|---|---|---|
| Type | Reusable, steel vessel | Reusable, steel vessel | Single-use (bag) |
| Process temperature | 0–140 °C (0–110 °C on Arc analog output) | 0–140 °C | 4–50 °C |
| Pressure | 6 bar | 6 bar | 1 bar |
| Sterilization | Autoclave (130 °C), SIP (140 °C), CIP | Autoclave, SIP, CIP | Gamma or X-ray, up to 50 kGy |
| pH range | 0–14 (recommended 2–12) | 0–14 (recommended 2–13) | 3–10 |
| Electrolyte | Phermlyte | Foodlyte (certified biocompatible) | - |
| Reference | Everef-F, pre-pressurized | Everef-F, pre-pressurized | - |
| Diaphragm | HP Coatramic | HP Coatramic | Non-clogging diaphragm, very low drift |
| O-ring | EPDM | VMQ (silicone) | - |
| Recommended min. conductivity | 100 µS/cm | 100 µS/cm | - |
| Glass | PHI or HB | PHI or HB | Glass electrode |
| Connector | VP, S8, Arc, Memosens, K8, LEVP | VP, S8, Arc, Memosens, K8, LEVP | VP6, K8 |
| Shaft length (12 mm) | 120–425 mm (360 mm PHI only, excluding Arc) | 120, 160, 200, 225, 325, 425 mm | VP6: 70–425 mm; K8: 120–425 mm |
| Typical application | Bioprocess, industrial processes | Bioreactor, brewing, gelatin, downstream | SUB/SUF, single-use mixer, SU downstream |
Source: Hamilton Process Analytics Catalog 2026 and Hamilton product documentation. OneFerm temperature sensor options: PT100, PT1000, or NTC.
Autoclave, SIP, CIP: What Can the Sensor Withstand?
EasyFerm Plus withstands up to 130 °C in an autoclave, up to 140 °C in steam-in-place (SIP) sterilization, and up to 6 bar pressure, enduring repeated CIP and SIP cycles. With its low drift, PHI glass is recommended for bioreactor upstream and downstream lines exposed to frequent SIP/autoclaving, while HB glass is intended for frequent CIP and autoclaving. The sensor must not be used in lines where pressure exceeds the nominal rating of 6 bar.
EasyFerm Bio is in the same sterilization class but contains certified biocompatible Foodlyte electrolyte specifically for food and biopharma sanitation. In clinical and commercial-scale single-use lines, OneFerm is used; it provides a +12 month shelf life pre-mounted in the bag under dry storage and a +18 month usable life after commissioning.
Headplate Port, Housing, and Flow Cell
| Mounting type | Hamilton product | Note |
|---|---|---|
| Hygienic fixed housing | FlexiFit Bio (Ingold G1¼"), FlexiFit TC50 (Tri-Clamp 1.5"), FlexiFit VV (Varivent) | 120 mm, PG13.5 threaded sensor; 0–16 bar(g), -10…140 °C; autoclave, CIP, SIP |
| Removal and cleaning without stopping the process | Retractex / RetractoFit Bio | Retractable housing; sensor can be withdrawn for maintenance |
| Pipeline, by-pass | FlowCell, FlowCell XL, FlowCell UR | pH and conductivity; low dead volume, self-draining; FlowCell internal volume approx. 8 mL, XL approx. 25 mL |
| Single-use bag | OneFerm (pre-installed in bag at factory) | With Arc Module SU pH or VP6 / K8 connector |
Details: Hamilton housings, flow cells, and Retractex retractable housings. In a pressurized housing, the Hamilton manual requires the pressure applied to the sensor to be approximately 0.5 bar above the process pressure.
Digital Sensors: Arc, ArcAir, and PCS Integration
Arc moves the transmitter function to a microprocessor in the sensor head. The sensor delivers a signal fully compensated for factors such as temperature, pressure, and salinity directly to the process control system via digital Modbus or 4-20 mA, and stores its last calibration data, diagnostic information, and configuration internally. The ArcAir application provides wireless configuration and calibration and generates automated verification and documentation; Hamilton states that ArcAir Advanced is ready for compliance with FDA CFR 21 Part 11 and EudraLex Volume 4 Annex 11.
If the existing infrastructure is Profibus, Profinet, or OPC, Hamilton's Arc Modbus converter portfolio is used. Unused DuraCal pH buffer solution is required for sensor calibration.
Related Pages
Bioreactor pH Sensors: Frequently Asked Questions
Reusable and single-use sensors, EasyFerm Plus and Bio, glass type, shaft length, calibration, and Arc.
Should a reusable or single-use pH sensor be selected for a bioreactor?
In stainless steel bioreactors and fermenters, a reusable sensor (EasyFerm) withstands repeated autoclave, SIP, and CIP cycles. In a single-use bioreactor (SUB) or fermenter (SUF) bag, OneFerm is pre-installed into the bag at the factory, sterilized together with the bag by gamma irradiation, and disposed of with the bag at the end of the process; it requires no permanent piping, autoclaving, or field calibration. The decision depends on your equipment type and your batch-to-batch cross-contamination policy.
What is the difference between EasyFerm Plus and EasyFerm Bio?
Both are 0–140 °C, 6 bar, autoclave/SIP/CIP-compatible families with PHI or HB glass. EasyFerm Plus uses Phermlyte electrolyte and an EPDM O-ring; it is presented as suitable for all industries across industrial and bioprocess applications. EasyFerm Bio uses certified biocompatible Foodlyte electrolyte and a silicone (VMQ) O-ring; it is designed for bioprocesses sensitive to cytotoxicity risk, as well as food, brewing, and gelatin applications. The recommended pH range is 2–12 for Plus and 2–13 for Bio.
How do I choose between PHI and HB glass?
According to Hamilton's selection table: choose PHI when CIP, SIP, autoclaving, and chemical resistance are required; choose HB when CIP, SIP, autoclaving, and a fast response time are required. With its low drift, PHI is recommended for bioreactor lines exposed to frequent SIP/autoclave cycles.
Which length and connector are selected for a bioreactor sensor?
The shaft diameter is 12 mm. For EasyFerm Plus, shaft lengths are 120, 160, 200, 225, 325, and 425 mm (plus 360 mm in PHI glass, excluding Arc); for EasyFerm Bio, 120–425 mm. Connector options are VP, S8, Arc, Memosens, K8, and LEVP (LEVP only in 120 and 225 mm). The length is determined by the immersion depth in the headplate port or housing; the measuring tip must remain submerged in the liquid.
Can the OneFerm pH sensor be used without calibration?
OneFerm is factory-calibrated at pH 4 and pH 7 at 25 °C, and the calibration values are documented with the sensor; the user does not recalibrate it prior to connecting it to the process. Conditioning in media for less than 1 hour before connecting to the process, followed by a single-point check measurement, is sufficient. Accuracy after gamma irradiation and dry storage is specified as plus/minus 0.15 pH together with the factory calibration values.
What does an Arc digital sensor bring to a bioprocess?
In Arc sensors, the function of a conventional transmitter is moved to a microprocessor inside the sensor head; the last calibration data, diagnostic information, and configuration are stored in the sensor, and the signal goes directly to the process control system via Modbus and 4-20 mA. Wireless configuration and calibration are performed with the ArcAir app; Hamilton states that ArcAir Advanced is ready for compliance with FDA CFR 21 Part 11 and EudraLex Volume 4 Annex 11.
Which measurements are performed alongside pH in a bioreactor?
pH, dissolved oxygen, conductivity, ORP, CO2, cell density, and glucose are frequently monitored parameters. Hamilton offers Conducell SU in bags or FlowCell COND in flow lines for conductivity, VisiFerm for dissolved oxygen, and FlowCell COND 4UPtF Arc (+ pH) for combined conductivity and pH measurement in a single flow cell.
Send the make and model of your current instrument to [email protected] — our engineers will propose the equivalent with the same connection and measuring range.
Planning a project? Send us your flow rate, feed water source and target water quality to [email protected] — our engineers will reply with a technical proposal.