Yokogawa FLXA21 Two-Wire pH/ORP Analyzer with FU20 Sensor
The Yokogawa FLXA21D/S/D/AA/P1/NN/A/N/LA/N/NN/CD4/SCT/U combined with FU20/VP/T1/FSM represents a configured two-wire liquid-analysis package for pH, oxidation-reduction potential, and temperature measurement. The FLXA21 platform uses a modular input design, loop-powered operation, local touch-screen access, and digital diagnostics. The specified P1 input code identifies a pH/ORP measurement channel, while the included FU20 reference indicates a combined process sensor package that must be verified as a complete analyzer-and-sensor system.
Yokogawa publishes the FLXA21 as a 24 VDC two-wire analyzer with an isolated 4–20 mA output and HART communication for applicable configurations. The family can accept up to two compatible detectors for pH/ORP, contacting conductivity, inductive conductivity, or dissolved oxygen, depending on the input modules ordered. This requested configuration uses one pH/ORP input and no second input according to the listed suffix. Exact housing, coating, approvals, cable glands, sensor accessories, and special options require order-code confirmation.
Process Applications
A pH/ORP analyzer package can support neutralization, chemical dosing, water and wastewater treatment, scrubber control, fermentation, food processing, utility water, and general process monitoring. The analyzer converts the sensor signal into a standard loop output for the PLC or DCS while giving operators local access to measurement, temperature, calibration, and diagnostic information. The FU20 combined sensor concept can simplify a field installation by integrating measuring and reference functions in one assembly.
Reliable pH measurement depends on more than the analyzer. The process sample must keep the sensor wetted, the mounting position must suit the electrode design, and the holder must allow safe removal and cleaning. High temperature, aggressive chemicals, coating, low conductivity, pressure changes, or frequent sterilization can affect sensor life and response. Engineering should review the exact FU20 materials and limits against the application.
Key Product Data
| Verification point | Information for this product page |
|---|---|
| Analyzer family | Yokogawa FLXA21 two-wire modular liquid analyzer |
| Configured measurement | P1 pH/ORP input; FU20 combined sensor referenced in the package |
| Power and output | Nominal 24 VDC loop power; 4–20 mA with HART for the A communication code |
| Published pH input range | −2 to 16 pH for the family, subject to selected sensor and settings |
| Published ORP input range | −1500 to +1500 mV |
| Housing protection | FLXA21 family rated IP66/NEMA 4X-class, subject to regional configuration |
| Order verification | Full analyzer suffix, FU20 sensor suffix, cable, holder, cleaning, and calibration accessories |
Installation and Wiring
Mount the FLXA21 where the display can be read and where vibration, direct heat, and chemical exposure remain within the selected enclosure rating. Maintain correct cable-entry sealing and separate sensor wiring from power cables and variable-frequency-drive outputs. Sensor cable length, junction-box use, shielding, and grounding should follow Yokogawa instructions. Confirm that the loop power supply provides adequate voltage after accounting for the receiving load and any intrinsic-safety barrier.
The analyzer housing and hazardous-area code must match the site classification. If the package is used in an intrinsically safe loop, verify the analyzer, sensor, associated apparatus, cable parameters, and entity values as one system. Do not assume that an approval shown for another FLXA21 suffix automatically applies to this configuration.
Calibration, Diagnostics, and Maintenance
Commissioning should include sensor inspection, temperature-element selection, buffer calibration, output scaling, HART address or device setup, and verification at the control system. Use fresh traceable buffer solutions appropriate to the expected measuring range. Rinse between buffers and allow the reading to stabilize. Record the slope, asymmetric potential, calibration date, and operator information so later maintenance can identify gradual sensor aging.
The FLXA21 platform can monitor electrode impedance, slope, asymmetric potential, and other diagnostic indicators for compatible pH sensors. Diagnostics help maintenance teams plan cleaning or replacement, but they do not replace process knowledge. A drifting measurement can result from coating, depleted reference electrolyte, damaged glass, ground loops, poor sample flow, temperature error, or an unsuitable calibration procedure.
Photo and Configuration Verification
The reused photograph shows a Yokogawa FLXA-series field analyzer under protective wrapping and does not reveal the full configured nameplate or the FU20 sensor suffix. It is a family-level reference only. Final supply must be checked against FLXA21D/S/D/AA/P1/NN/A/N/LA/N/NN/CD4/SCT/U and FU20/VP/T1/FSM, including every option and accessory.
For a quotation, provide the complete analyzer and sensor codes, process liquid, temperature, pressure, expected pH/ORP range, mounting method, cable length, cleaning requirement, hazardous-area classification, communication, quantity, and delivery destination. This information supports accurate selection of the analyzer, FU20 sensor, holder, glands, and calibration accessories.
