Reagent Type Residual Chlorine Sensor Unit RC800D

Providing reliable chlorine measurements in Water Treatment Plants since 1959
No.1 Process analyzer supplier to Japanese market*

"Reliable Chlorine monitoring and minimize Chlorine injection"

"Continuous automatic cleaning and achieved less maintenance time"

"Maintenance remotely and reduce maintenance time"

Many of our customers face these challenges - Yokogawa Chlorine Analyzers resolve them.

The RC800D residual chlorine analyzer employs a polarographic system that uses rotating platinum electrodes to provide a continuous online measurement of residual chlorine concentration.  It is possible to separate residual chlorine (free chlorine + combined-chlorine) from free chlorine for measurements by appropriate use of reagents. 

The RC800D is suitable for various water condition measurements and gives you a stable and high-quality measurement thanks to the rotation electrodes and superior reagent pump.

The RC800D is intended for water distribution measurements at pumping stations, water delivery points, schools, and public facilities.
*Based on a Yokogawa survey in 2019


Easy to clean cell structure, Module motor unit, and Sensor health and motor check

  • Amperometric measurement of free chlorine or total chlorine (polarographic method)
  • Measure Free chlorine or residual chlorine (total chlorine) continuously in water
  • Unique rotation electrode method keeps sensor clean and reduces maintenance cycle
  • Superior reagent pump realizes stable measurement regardless of sample conditions
  • Easy maintenance structure, modularized motor unit, and diagnostics functions strongly support regular maintenance
  • Remote wash and calibration functions are available
  • RC800D is equipped with Manual calibration and Auto Calibration, 2 points correction, Basic (reference) sensitivity calibration, and circuit open Zero calibration
  • Remote range switching is available
RC800D Left

RC800D display:easy to use touch screen


TC8000D Structure


Each process at treatment plant: from reservoir to treated water, distribution system

Water Purification Treatment

  • Stabilization 
  • Flocculation 
  • Settling Basins 
  • Chlorination 
  • Clean water reservoir 
  • Distributing pump 
  • Distribution tank & Piping


Use case



Measured Object Free chlorine or residual chlorine (total chlorine) in water
Measuring System Amperometric method (Polarographic method) using rotating electrode
Measuring Range 0-10 mg/L
Sample Conditions Temperature 0 to 50°C (Temperature compensation is effective within 0 to 40°C)
pH 3 to 9
Flow Rate 1 to 4 L/min, for pure water or municipal water application.
5 to 10 L/min, for raw water or sea water application.
10 to 20 L/min, for secondary sewage treatment application.
Pressure 20 to 500 kPa
Power Supply 100 to 240 V DC, 50/60 Hz
Digital Communication Modbus TCP/IP, Modbus RTU
Installation Indoor (Outdoor use requires protection against rain. Direct sunlight must be avoided.)



Linearity ±3% of reading or ±0.03 mg/L whichever is greater
Repeatability ±1% of reading or ±0.01 mg/L whichever is greater


About OpreX

OpreX is the comprehensive brand for Yokogawa’s industrial automation (IA) and control business and stands for excellence in the related technology and solutions. It consists of categories and families under each category. This product belongs to the OpreX Analyzers family that is aligned under the OpreX Measurement category.  


FLXA 402T Multi Sensor variation 1st module TB820D FC800D FC800D FC800D FC800D TB820D TB820D 2nd module TB820D FC800D TB820D Analog pH Analog Conductivity Analog pH sensor Analo...
You don't need to do any difficult setting. The FLXA402T configurations have already optimized for selected measurement when it is shipped.
Maximum digit is three decimal points, default is 2 decimal points.
PH4, pH7 and pH9 tables complied by NIST, DIN and US standards are available.
The FLXA402T can connect a pH sensor, but an ORP sensor is not available. For ORP measuring, please select the FLXA402. (Not FLXA402T)
Static conductivity sensor is available. Inductive conductivity sensors are not available. For inductive conductivity sensor measuring, please select the FLXA402. (Not FLXA402T)
Conductivity measuring is available in the FLXA402T. For resistivity measuring, please select the FLXA402. (Not FLXA402T)
Maximum 20m is available. If you want to use more than 20m cable, please contact us.
Yes, you can save and copy the FLXA402T configurations by SD card. It realizes easy installation and replacement.
Rotation electrode will get damaged in case there is no water in the measurement cell. To avoid this situation, the FC800D and the RC800D measurement electrode rotation is automatically stopped. This function makes rotation electrode lifetime longer ...
Air purging is required for electrode unit and liquid pump by air pump or compressor air (industrial air). It is required to protect electrode from chlorine gasses which will affect the metal parts.
The FC800D and the RC800D are not suitable for outdoor installation. Strongly recommend installing inside because of pump structure. If you want to install outside, a separate rainproof cover is required and take care install place environment (no co...
Within ordered range, you can set the FLXA402T analog output range seamlessly. Cannot change ordered analyzer measurement range.
Beads become gradually smaller because of friction, and decreases cleaning efficiency. So, we recommend replacing beads once a year.
Parts No. Name Remarks QTY Recommended Replacement Interval - Primary acetic acid (CH3COOH) grade: over 99.0+% For reagent preparation -   - Sodium acetate (CH3COONa) grade: over 98.0%...




Smart Water Management System providing clean and safe water.
Yokogawa provides total water management system including Turbidity and Free Chlorine measurement.

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