Field-installation Type ORP Meter (Two-Wire Transmission)

HO-300 connects ORP sensor and measures ORP and temperature in the sample water. It is suitable for neutralization reaction treatment management of aeration tank, denitrification tank, etc.

Measurement range

ORP: -2000 - 2000 mV
Temperature: 0 - 100℃

Abteilung: Process Water
Produktionsfirma: HORIBA Advanced Techno Co., Ltd.


  • Responds to harsh conditions at the site process
      Operating temperature range(Transmitter):-20 - 55℃
      Rated voltage: DC 24 V
      Robust aluminum die cast (Protection code:IP65)
  • CE Marking and FCC Compliance suitable for use at overseas sites



  • Convenient function to display liquid temperature at the same time(Transmission output available)
  • Sensor error can be detected immediately by self-diagnosis function
  • Designed to be environmentally friendly (Pb-free) in response to WEEE and RoHS


Easy maintenance

  • Easy to view big display
  • Easy operation
  • Calibration log memory
  • Screw terminals that do not fall off are used in the terminal block for wiring


Product nameORP meter
Combined sensorORP electrode
ORP−2000 mV to 2000 mV (display range: −2200 mV to 2200 mV)
Temperature0℃ to 100℃
  • Display range :−10℃ to 110℃
    (the sensor types are detected automatically)
  • Display range :−20℃ to 130℃
    (the sensor types are input by manually)
PerformanceORPRepeatabilityWithin ±5mV (response for equivalent input)
LinearityWithin ±5mV (response for equivalent input)
TemperatureRepeatability±0.3℃ (response for equivalent input)
Linearity±0.3℃ (response for equivalent input)
Output type4 mA to 20 mA DC: input/output insulation type
Load resistanceMax.: 600Ω (case of 24 V DC power supply)*1
LinearityWithin ±0.08 mA (output only)
RepeatabilityWithin ±0.02 mA (output only)
Output rangeORP: Selection from preset ranges or free range input within measuring range.
Occasional out for errorHold or burnout to either 3.8 mA or 21 mA
Transmission holdIn the maintenance mode, transmission signal is held at the latest value or preset value.
In the calibration mode, transmission signal can be alive or held.
Contact inputNumber of input points1
Contact typeNo-voltage a-contact
ConditionsON resistance: 40 Ω
Open voltage: 1.2 V
Short-circuit current: 21 mA DC max.
Contact functionExternal input for transmission holding.
Applicable temperature
Platinum resistor: 1 kΩ (0℃)
Positive relation resistor with temperature:
500 Ω (25℃), 6.8 kΩ (25℃), 10 kΩ (25℃)
Element selection methodAutomatic temperature sensor type detection or manual selection (no temperature element is selectable)
CalibrationORP adjust functionAdjust (offset adjustment): −200 mV to 200 mV
Span sensitivity correction: 0.500 to 1.500
Temperature calibration1 point calibration comparing reference thermometer
Self-checkCalibration errorTemperature calibration error
Out of temperature calibration range (for ORP sensor with RTD).
Electrode diagnostic errorReference electrode impedance error (only applicable for differential circuit mode with a liquid contact electrode)
Temperature sensor short-circuit, temperature sensor disconnection, and out of the temperature measurement range
Converter errorCPU, ADC, and memory errors
Operating temperature range−20℃ to 60℃ (without freeze)
Operating humidity rangeRelative humidity: 5% to 90% (without condensation)
Storage temperature−25℃ to 65℃
Power supplyRated voltage24 V DC (operating voltage range: 21 V to 32 V DC)*1
Power consumption0.6 W or less.
CE marking 
 Compatible standardsEMC directive: EN61326-1
RoHS Directive: EN50581
ImmunityIndustrial electromagnetic environment
Electostatic dischargeIEC61000-4-2
Electromagnetic field of radiated radio frequencyIEC61000-4-3*2
Electric fast transient/burstIEC61000-4-4
Conducted interference induced by radio frequencyIEC61000-4-6*2
EmissionClass A
Radiated disturbanceCICPR 11 CLASS A
FCC RulesPart15 CLASS A
StructureInstallationOutdoor installation type
Installation methodMounted on 50 A pole or wall
Protection codeIP65IEC60529, JIS C0920
Case materialAluminum alloy (coated with epoxy-denatured melamine resin)
Material of fittingsSUS304
Material of hoodSUS304 (coated with epoxy modified melanine resin)
Material of windowPolycarbonate
Display elementReflective monochrome LCD
External dimensions180 (W) mm × 155 (H) mm × 115 (D) mm (excluding mounting brackets)
MassMain body: approx. 2.8 kg, Hood and mounting brackets: approx. 1 kg
  • *1:  The max. load resistance that can be connected is decided depending on the power-supply voltage.


Relation between power supply voltage and load resistance

Relation between power supply voltage and load resistance

  • *2:  The influence of the ORP reading by the electromagnetic field of radiated radio frequency or the conducted interference induced by radio frequency is within 6mV.
  • *3:  When the sensor cable, the transmission cable, or the contact input cable is extended by 30 m or more, the surge test under the EMC Directive for CE marking is not applied.


Though an arrester (spark over voltage: 400 V) is implemented for transmission output, use a most suitable surge absorption element on the connection lines in accordance with the ambient environment, the situation of equipment installed, and the externally connected equipment.


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