Yokogawa Model FU20 Widebody Type PH/ORP Sensor 12mm PH Sensor SC25V PH21 PH4/OR4 Sensor FU20-05-T1-NPT

What Are FU20 and FU24

• Both FU20 and FU24 are combined pH + ORP (redox) sensors — they integrate multiple measurement elements (pH electrode, reference electrode, ORP (redox) electrode, and temperature sensor) in a single sensor body.
• They are designed for industrial/liquid-analysis applications (water & wastewater treatment, chemical processing, power generation, etc.), where reliable measurement of pH and ORP (plus temperature compensation) is needed.

Key Design & Technical Features

• Multi-element design: Each sensor includes a pH glass electrode, a saturated Ag/AgCl double-junction reference system, a solid platinum ORP electrode, and an integral Pt1000 for temperature measurement.
• Robust body materials: The sensor bodies are made of chemically resistant materials (PPS 40GF / Ryton for FU20 and FU24; and sometimes PVDF for certain FU20 variants) to withstand harsh, aggressive or corrosive fluids.
• Extended lifetime & reliability: The sensors use a double-junction reference system with a large volume polymerized electrolyte and a porous PTFE diaphragm to minimize poisoning or contamination of the reference — this prolongs the sensor life in demanding chemical environments.
• Temperature compensation: Because of the built-in Pt1000 temperature sensor, pH and ORP measurements are automatically temperature-compensated, improving accuracy over a range of operating conditions.
• Installation flexibility: These sensors can be installed in-line, as immersion probes, or off-line (in flow fittings). The FU20 especially supports quick-release adapters and easy removal for cleaning or calibration.

Differences: FU20 vs FU24 — When to Choose Which

* Exact operating limits may depend on sensor variant (dome vs flat, standard vs high-temperature, sample conductivity, etc.) — always check the manufacturer’s datasheet for your application conditions.

In short: use FU20 for standard, stable liquid conditions where ease of installation/maintenance and accuracy suffice; use FU24 when you expect pressure or temperature fluctuations, or chemical stress, and need maximum robustness and stability.

Typical Applications & Use Cases

• Water and wastewater treatment — monitoring pH and ORP to control chemical dosing, disinfection, neutralization, etc.
• Chemical-/process-industry streams — handling corrosive or aggressive fluids, requiring robust sensor construction.
• Power generation / boiler-cooling / steam-cycle water — where pH/ORP must be monitored under variable temperature/pressure.
• Industrial process control, water-treatment plants, neutralization tanks, or any setup needing simultaneous pH + redox (ORP) + temperature measurement with minimal maintenance.

Why Engineers / Industry Choose FU20 / FU24

• Because they integrate pH, ORP, and temperature in a single compact sensor, reducing the number of probes needed and simplifying installation.
• Because the double-junction reference + polymerized electrolyte + PTFE diaphragm significantly improves lifetime and reliability, even in chemically harsh or contaminated fluids.
• Because of built-in temperature compensation, ensuring measurement accuracy over varying temperature; and in the case of FU24, built-in pressure compensation, ensuring stability under dynamic pressure or temperature conditions.
• Because of versatility of installation (inline, immersion, flow-fitting, hot-tap possible with FU20), making them suitable for both new installations and retrofits.