HO-200, Field-Installation Type ORP Meter HO-200, HORIBA

The HO-200 is HORIBA's long-selling field-installation type ORP meter, widely used for continuous monitoring and control of oxidation-reduction potential in industrial and municipal water treatment processes. It is particularly suited to managing neutralization reaction processes — including aeration tanks, denitrification tanks, and chemical dosing control — where real-time ORP feedback is critical for process efficiency and regulatory compliance. The HO-200 is the ORP equivalent of the HP-200 pH meter and shares the same H-1 Series platform, offering two isolated 4–20 mA transmission outputs, three relay contact outputs with flexible alarm and control functionality, an integrated cleaning output for automated electrode maintenance, and RS-485 serial communication for SCADA/DCS integration. A broad lineup of cleaning devices — including ultrasonic cleaners that require neither water nor air — makes on-site retrofitting straightforward. The IP65-rated aluminium alloy housing with SUS304 stainless steel fittings and a reflective monochrome LCD display ensures reliable performance in demanding indoor and outdoor environments.

Key Features HO-200

• ORP measurement range −2000 to +2000 mV (display −2200 to +2200 mV); resolution 1 mV; repeatability and linearity within ±5 mV.
• Temperature measurement 0–100 °C (display up to 130 °C); resolution 0.1 °C; supports Pt 1 kΩ and NTC thermistors; automatic or manual sensor type selection.
• Two isolated 4–20 mA DC transmission outputs (max. load 900 Ω): output 1 for ORP (preset or free range), output 2 for temperature; hold and burnout options.
• Three relay contact outputs (SPDT 1c, 250 V AC / 30 V DC, 3 A): R1 and R2 selectable as upper/lower limit alarm, ON/OFF control, transmission hold, or cleaning output; FAIL alarm contact.
• Integrated cleaning output (SPST 1a, 250 V AC 0.5 A) with programmable period (0.1–168 h), cleaning time (2–600 s), and hold time (2–600 s); internal timer or external trigger modes.
• RS-485 serial communication (2-wire, isolated from input circuit) for integration into plant control systems.
• ORP calibration: offset adjustment ±200 mV and span sensitivity correction 0.500–1.500; 1-point temperature calibration against reference thermometer.
• Self-diagnostics: reference electrode impedance error, temperature sensor short-circuit/disconnection/range deviation, CPU/ADC/EEPROM errors.
• IP65 protection (IEC60529 / JIS C0920); pole (50 A) or wall mount; aluminium alloy housing with epoxy-denatured melamine resin coating; SUS304 fittings and hood.
• CE marked: EMC EN61326-1 Class A, Safety EN61010-1, RoHS EN50581; FCC Part 15 Class A.

Applications

The HO-200 is suited to continuous ORP monitoring and closed-loop control in municipal wastewater treatment (aeration tanks, denitrification tanks, disinfection), industrial process water management, chemical and petrochemical neutralization processes, environmental water monitoring, and any application requiring reliable real-time oxidation-reduction potential measurement in demanding field conditions.

Installation and Safety Notes

Connect the HO-200 to a 100–240 V AC ±10%, 50/60 Hz supply (15 VA max.). Mount on a 50 A pole or wall in a location free from vibration and direct impact. When sensor, transmission, or contact input cables are extended by 30 m or more, additional surge absorption elements must be installed on all connection lines — the CE marking surge test does not apply to extended cable runs. An internal arrester (spark-over voltage 400 V) is provided for transmission output, contact input, and communication terminals. Operating temperature: −20 to 55 °C; storage: −25 to 65 °C; humidity: 5–90% RH non-condensing.

Technical Specifications