Description

• Model: FLXA21
• Brand: Yokogawa Electric
• Series: FLEXA
• Core Function: Continuous two-wire liquid analysis
• Type: Modular Process Liquid Analyzer
• Key Specs: 2 sensor inputs, 4 measurement types, 4–20 mA + HART

Product Introduction

Yokogawa FLXA21 is a modular two-wire liquid analyzer built for continuous online process measurement. One housing can be configured for pH/ORP, contacting conductivity, inductive conductivity, or dissolved oxygen, with one or two sensor modules installed.

The practical advantage is flexibility. Two sensors of the same measurement type can be combined for calculated values or redundant measurement, while the loop-powered design uses a nominal 24 V DC supply and provides an isolated 4–20 mA output with HART communication. The enclosure is rated IP66 / NEMA 4X in applicable configurations, and hazardous-area approvals include ATEX, IECEx, FM, CSA, NEPSI, and KCs depending on the selected suffix.

Key Technical Specifications

Yokogawa’s specifications confirm the modular architecture, 24 V DC loop power, 4–20 mA output, and environmental ratings. Exact input, communication, housing, and hazardous-area options depend on the complete suffix code.

Yokogawa FLEXA21

Application and Selection Notes

The analyzer suits continuous liquid monitoring in process plants, water and wastewater systems, power generation, petrochemical facilities, and other installations where measurement data must remain available during routine sensor maintenance. Yokogawa specifically notes applications involving pH/ORP, conductivity, inductive conductivity, and dissolved oxygen.

A useful field detail: two identical sensor types can form a redundant arrangement, allowing the main measurement to switch to the second sensor when a failure condition is detected. That is a different proposition from simply adding another input channel.

Do not order by “FLXA21” alone. Input module, output type, enclosure, mounting option, hazardous-area approval, and communication interface are encoded in the full model configuration.

Quality Inspection and Pre-Shipment Checks

1. Incoming inspection: Verify the Yokogawa nameplate, full suffix code, serial number, housing condition, display, terminals, and supplied accessories.
2. Functional test: Where a suitable test setup is available, power the analyzer, confirm startup diagnostics, sensor-module recognition, display operation, and output behavior.
3. Electrical checks: Verify supply-path continuity, grounding, terminal integrity, and insulation condition as applicable to the test procedure.
4. Configuration verification: Record sensor-module type, communication option, output setting, and installed configuration before shipment.
5. Final QC: Photograph the identification label, seal the unit in suitable ESD-safe protection where required, add shock protection, and retain the inspection record.

Test photographs and available Test Reports should be supplied with the shipment when requested.

Technical Replacement Risks

Full configuration mismatch. A FLXA21 with the wrong sensor module is not a practical plug-and-play substitute.

Communication mismatch. The standard 4–20 mA + HART configuration differs from FOUNDATION Fieldbus and PROFIBUS PA versions. Verify the host system before ordering.

Hazardous-area approval mismatch. The applicable certification depends on the exact suffix and installation area. For China, current Yokogawa documentation lists NEPSI compliance for specified FLXA21 output configurations.

Sensor wiring matters. pH/ORP, SC, ISC, and DO modules use different measurement hardware. Match the sensor technology before commissioning.

And one old technician’s rule still works: photograph the old configuration before pulling the analyzer out. It takes seconds.

Purchase and Logistics Notes

For international procurement, state the complete FLXA21 configuration code rather than only the family name. The commercial description should identify the analyzer type, installed measurement module, communication option, enclosure, and hazardous-area configuration when applicable.

For China-bound shipments, the importer should verify the required conformity and hazardous-location documentation against the exact delivered configuration. Yokogawa’s current safety documentation was updated in February 2026, including revisions to the EU Declaration of Conformity and China/Korea explosion-protection information.

For export packaging, protect the display and enclosure corners against impact, keep the unit dry, and ensure the commercial invoice, packing list, and product identification carry consistent model information.

Quick Conclusion

• FLXA21 is a modular two-wire liquid analyzer for continuous process measurement.
• It supports pH/ORP, contacting conductivity, inductive conductivity, and dissolved oxygen measurement.
• Up to two same-type sensor modules can be used for dual measurement and redundancy functions.
• The standard architecture uses 24 V DC loop power, 4–20 mA output, and HART communication.
• Exact replacement suitability depends on the full suffix code and sensor/communication configuration, not the family name alone.

FAQ

What is the Yokogawa FLXA21 used for?

It is a two-wire online liquid analyzer for measuring pH/ORP, contacting conductivity, inductive conductivity, or dissolved oxygen with the appropriate sensor module.

Can it use two sensors?

Yes. Two sensors of the same measurement type can be installed, enabling dual measurement, calculated values, and redundant operation.

What is the power requirement?

The standard system is nominally 24 V DC loop powered. Actual minimum voltage depends on the installed sensor and configuration.

Does it support HART?

Yes. The 4–20 mA configuration supports HART communication. Separate FOUNDATION Fieldbus and PROFIBUS PA configurations are also available.

Is FLXA21 suitable for hazardous areas?

Selected configurations carry ATEX, IECEx, FM, CSA, NEPSI, and KCs approvals. The exact certification must be checked against the full suffix code and installation requirements.

What should be checked before buying a replacement?

Confirm the complete model code, sensor module type, communication method, enclosure material, mounting hardware, and hazardous-area certification. Those details can change the actual specification even when the base model remains FLXA21.