Field-installation Type Dissolved Oxygen Meter (Four-Wire Transmission, Optical Type)

Optical dissolved oxygen sensor with no electrolyte replacement and rugged membrane.
Highly intelligent, including automatic recognition of membrane properties when replacing the sensor cap.

The HD-200FL is an optical (fluorescent) dissolved oxygen meter suitable for monitoring aeration tanks used for sewage treatment, effluent treatment, and other processes. Compared to conventional membrane polarographic type sensors, there is no need for electrolyte (internal fluid) replacement or warming, up. Characteristics of optical sensors are utilized to realize unequaled, improvement in ease of maintenance and reduction in running costs. Moreover, it features enhanced user-friendliness, with sensor caps that have built-in memory and a membrane replacement notification function.

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


  • Rugged membrane
  • Flow independent
  • Less affected by interference
  • Long-life LED light source
    (10 years or longer)


Easy maintenance

  • Longer sensor cap replacement cycle
  • Electrolyte-free
    ▶No worry about replacement and degradation
  • Longer calibration cycle
    ▶Low drift
  • No warming-up time



  • Sensor cap replacement notification function
    ▶Counts number of light emissions
  • Self-diagnosis function
    ▶Light source errors, sensor cap detection errors
  • Automatic recognition of parameters  
    after replacing sensor cap (fluorescent membrane)
    ▶Sensor cap with built-in memory


Optical DO sensor Principles and structure

* Lifetime of sensor caps may vary with the environment in which they are used.
DO:Dissolved Oxygen

Measurement principles

Exposing an oxygen sensing membrane that contains a special fluorescent substance with excitation light causes fluorescent light to be emitted.
The light emission intensity will be strongest in the absence of oxygen, and will decrease by quenching if oxygen molecules are present. Light emission time shows the same relationship as strength of light emission intensity, being the longest in the absence of oxygen, and shortest in its presence. Oxygen concentration and light emission time are inversely related, as shown in the diagram below. Light emission time measurement employs the phase difference detection method, which is mostly unaffected by dirt on the sensor surface and changes in sensitivity.


IC built-in memory sensor cap

Automatic recognition of parameters eliminates the need to input a distinctive membrane count when replacing the sensor cap (fluorescent membrane).

Example field test

In the aeration tank (without feedback by DO)




Float holder
Accumulation of dirt is prevented with its self-cleaning function that uses flow rate of the measurement liquid.
Immersion holder


The nose shape of the float
is free of large bumps,
keeping dirt and floc from
clinging to the sensor part.

FH-101 (Vertical type)


SFH-201 (Slanted type)


DH-151 series (insertion type)
NH-15 series (drop type)




Immersion jet washerImmersion jet washerRelay boxMounting brackets

JDH series
JH-15 (for drop type)





Indication converter specifications

Measuring methodOptical (fluorescent)
Measuring rangeDO: 0 to 20 mg/L      Resolution: 0.01 mg/L
Saturation: 0 to 200%    Resolution: 0.1%
Temperature: 0 to 50°C   Resolution: 0.1°C
RepeatabilityWithin ± 1% of full scale
LinearityWithin ±2% of full scale
2 points 4 mA to 20 mA DC output isolated type Maximum load resistance 900 Ω
 Range 1: DO concentration: Freely selectable within the measurement range
 Range 2: Temperature: Freely selectable within the range from -10.0 to 110.0°C
 Alarm: Burnout function (3.8 mA or 21 mA)
 Hold: Selectable from previous value hold, optional value hold
3 points Dry contact output Relay contact, SPDT (1c)
 Signal R1, R2: upper limit alarm, lower limit alarm,
        hold, Cleaning (selectable)
      FAIL : Alarm
 Control operation Control width: 0.02 to 4.00 mg/L (±0.01 to ±2.00 mg/L)
On cleaning
1 point Wet contact output (connecting power supply voltage output) Relay contact, SPST (1a)
 Contact function: Solenoid Valve Control
External input1 point Contact shape: Open connector dry ‘a’ contact
 Contact function: Cleaning Unit Control
Communication functionRS-485 2-line, insulated input/output (transmission output is not insulated)
compensation range
0 to 50°C
compensation device
Calibration methodAtmosphere span calibration, zero liquid (sodium sulfite) calibration, span liquid (atmosphere saturation liquid) calibration
Self-diagnosis functionCalibration error, sensor diagnosis error, converter alarm
Operating temperature range-20 to 55°C (Should not be frozen)
Power supply90 to 264 V AC 50/60 Hz Power consumption: 15 VA (max)
StructureIP65 : 50 A pole or wall mounting
Case: Aluminum alloy Mounting brackets, hood: SUS304
MassMain unit body: Approx. 3.5 kg   Hood, mounting brackets: Approx. 1 kg
Regulatory complianceCE marking, FCC
Compatible sensorDO-2000

*1     When extending the sensor cable, transmission cable, or contact input cable 30 m or more, the CE marking EMC directive surge test does not apply.
*2     An arrestor (inception voltage: 400 V) is mounted on the unit for transmission output, contact input, and communications. However, an optimal surge absorber should be installed on the connecting line depending on the surrounding environment, equipment setup, externally connected devices, etc.

Probe specifications

Measurement principlesOptics (fluorescence)
Sample water0 to 50°C
Wetted materialSUS316、NBR、PVC
Response time90% response: Within 30 s  95% response: Within 60 s
MassApprox. 3.0 kg (incl. 10 m cable)

Sensor cap specifications (replaceable)

Wetted materialNBR, PMMA
MassApprox. 5.0 g
Membrane memoryBuilt-in memory in the membrane unit, automatic recognition

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