Field-installation type residual chlorine meter

HORIBA's long-selling water quality meter that excels in indoor applications.

Ideal for measuring the concentration of free residual chlorine in tap water, swimming pools, spas and similar environments. By adopting physical polishing cleaning with rotating electrodes, long-term stable measurements can be achieved.

Division: Process Water
Manufacturing Company: HORIBA Advanced Techno Co., Ltd.

Parts can be replaced without the use of tools

Consumables (cathode electrode, filter, beads) can be replaced without the use of tools.

Equipped with rotation stop detection function and re-rotation function

If the rotating sensor stops, an error message will be displayed. Additionally, it will automatically initiate re-rotation.

Equipped with pH correction function

The HORIBA pH meter (HP-200) can be connected, applying pH correction to the residual chlorine measurement values.


Product nameResidual Chlorine Monitor
Sensor typeRA-30
Concentration0 mg/L to 3 mg/L (Display range: 0 mg/L to 5 mg/L)
Temperature0℃ to 50℃ (Display range: -10℃ to 110℃)
Concentration0.01 mg/L
PerformanceConcentrationRepeatabilityWithin ±0.05 mg/L (Equivalent input)
LinearityWithin ±0.05 mg/L (Equivalent input)
TemperatureRepeatability±0.5℃ (Equivalent input)
Linearity±0.5℃ (Equivalent input)
Number of current outputs2 (Negative terminals of each transmission output channel are connected inside and thus have the same electrical potential)
Output type4 mA to 20 mA DC, input/output isolated type
Load resistance900 Ω (Max.)
LinearityWithin ±0.08 mA (limited to the current linearity)
RepeatabilityWithin ±0.02 mA (limited to the current repeatability)
Output rangeOutput 1Residual chlorine concentration: An arbitrary value can be set within the range from 0 mg/L to 5 mg/L
Output 2Temperature: An arbitrary temperature can be set within the range from -10℃ and 110℃
Error outputProvided with burnout function (3.8 mA or 21 mA)
Hold functionSelectable from between the latest value hold and the preset value hold
Contact outputNumber of current outputs4
Output typeNo-voltage output contact
Contact typeRelay contact, R1 to R3: SPST (1a), FAIL: SPDT (1c)
Output capacityR1, R2, FAIL: 250 V AC 3 A/30 V DC 3 A (resistance load)
R3: 30 V DC 1 A (resistance load)
R1, R2, R3Selectable from among the upper limit alarm, lower limit alarm, ON/ OFF control, during transmission output hold, and during calibration
(closed at alarm operation, open under normal conditions and in a power-OFF state)
FAILError alarm (closed under normal conditions, open in an error or power-OFF state)
Description of alarm operation
  • Setting range: 0.00 mg/L to 3.00 mg/L
  • Delay time: 0 s to 600 s
Description of control operation
  • Setting range: 0.00 mg/L to 3.00 mg/L
  • Control width: 0.02 mg/L to 1.00 mg/L (±0.01 mg/L to 0.50 mg/L)
Contact inputNumber of input points2
Contact typeOpen collector no-voltage “a” contact
ConditionON resistance: 100Ω (max.)
Open-circuit voltage: 24 V DC
Short-circuit current: 12 mA DC (max.)
Contact functionSelectable from among the external input for transmission output hold, flow switch input for interlock (open when the flow rate drops), and calibration command
on function
Number of circuits1
Signal formTwo wire type, the power source of the communication is isolated from the power of measurement circuit (the power source of transmission and communication are not isolated).
pH correctionTypeConnected with expansion connector
pH correction range5.8 pH to 8.6 pH
Applicable temperature elementPt1000: 1 kΩ (0℃) (embedded in the detector unit)
Compensation range0℃ to 50℃
Calibration functionOne point calibration compared with reference temperature range
CalibrationCalibration methodZero calibration (with zero water)
Span calibration (comparative calibration with the value measured with the DPD method including electrical zero calibration)
Additional functionCalibration log (number of days elapsed since the zero or last calibration), calibration error automatic judgment (zero)
control output
Number of contact output1
Output typeVoltage contact output (connected power source voltage output)
Contact capacity250 V AC 0.5 A
Calibration cycle setting1 hour to 999 hour
CALR1Contact typeRelay contact, SPST (1a)
Contact functionZero water switching driven by solenoid valve
Self-checkCalibration errorZero calibration error, outside the temperature calibration range
Temperature sensor diagnosisTemperature sensor short-circuit, temperature sensor disconnection
Converter errorCPU abnormality, ADC abnormality, memory abnormality
Operating temperature range-20℃ to 55℃ (without freezing)
Operating humidity rangeRelative humidity: 5% to 90% (no condensation)
Storage temperature-25℃ to 65℃
Power supplyRated power supply voltage100 V to 240 V AC ±10% 50/60 Hz
Power consumption35 VA (max.)
OthersWith built-in power switch for maintenance
StructureInstallationOutdoor installation type
Installation methodPole-mounted or wall-mounted
Protection classIP65
Material of caseAluminum alloy (coated with epoxy-modified melamine resin)
Material of mounting bracketsSUS304
Material of sun shade hoodSUS304 (coated with epoxy-modified melamine resin)
Material of display windowPolycarbonate
Display elementReflective monochrome LCD
External dimensions180 (W) mm × 155 (H) mm × 115 (D) mm (excluding brackets)
MassMain frame: approx. 3.5 kg, Hood, bracket: approx. 1 kg


Although an arrestor (400 V discharge starting voltage) is mounted for the transmission output, contact input, and communication, install an optimum surge absorber element on the connection line, depending on the surrounding environment, device installation conditions, and externally connected devices.

Detector and measuring cell

Product nameRotating electrode polarographic residual chlorine sensor
Measurement methodRotating electrode polarographic method
Measurement targetFree residual chlorine in sample water
Measurement range0 mg/L to 3.00 mg/L
Temperature compensationAutomatic temperature compensation using Pt1000
PerformanceLinearityWithin ±5% full-scale range
RepeatabilityWithin ±2% full-scale range or ±0.05 mg/L, whichever is larger
Response timeWithin 120 s from the inlet of the measuring cell (90% response)
Zero driftWithin ±1% full-scale range/month
Span driftWithin ±10% full-scale range/month
Temperature0℃ to 45℃
Flow rateMeasuring cell flow rate: 0.1 L/min to 0.5 L/min*1
Primary pressure0.01 MPa to 0.15 MPa*2
pH value5.8 pH to 8.6 pH (with no fluctuation over 1.0 pH)*3
Electrical conductivity8 mS/m or more*4
CalibrationZero calibrationZero water calibration, electrical zero calibration
Span calibrationComparative calibration with the value measured with the DPD method
(including electrical zero calibration)
Material of
liquid contact
ElectrodeAu, AgCI
BeadsCeramic beads
sample inletφ6 mm × φ8 mm tube or Rc1/8
sample outletVP16
Cleaning methodPhysical cleaning with beads
Cable lengthProvided standard cable: 1.5 m, max. extension distance: 10 m
Operating temperature range0℃ to 45℃*5
Operating humidity rangeRelative humidity: 5% to 90% (no condensation)
Storage temperature0℃ to 45℃
StructureInstallation method50 A pole-mounted or wall-mounted
Protection classIP53
External dimensions110 (W) mm × 340 (H) mm × 110 (D) mm (excluding brackets)
MassApprox. 1.5 kg
Standard accessoriesBeads, abrasive paper, mesh filter (2 types), O-ring

1: If use our designated flow switch (RA-FS30), regulate flow rate in 0.3 L/min to 0.5 L/min.
2: The measurement section is under an open air environment.
3: If pH of the measured sample varies, the value of residual chlorine also varies. Perform measurement in an environment in which pH variations are less likely to occur.
4: Measurement cannot be performed correctly when the electrical conductivity falls below 8 mS/m (80 μS/cm). Be sure to perform measurement in this conditions.
5: If the electrode is exposed to the direct sunlight, the anode and cathode electrode could deteriorate. Install the instrument where it is not exposed to direct sunlight (indoors).
6: If a reducing agent or oxidizer exists in a sample, it affects the reading. Do not use a sample containing a reducing agent such as thiosulfate or sulfite, or oxidizer such as O3, hydrogen sulfide or chlorine dioxide, as measurement cannot be performed correctly.

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