HO-300, Field-Installation Type ORP Meter HO-300, HORIBA

The HO-300 is a 2-wire loop-powered field-installation type ORP transmitter from HORIBA, the ORP counterpart to the HP-300 pH transmitter. It provides reliable continuous monitoring of oxidation-reduction potential for managing neutralization reaction processes including aeration tanks and denitrification tanks. Powered from the 4–20 mA signal loop without a separate AC supply, the HO-300 simplifies wiring, reduces installation costs, and is particularly well suited to retrofitting existing installations. It shares the same proven H-1 Series platform and IP65-rated aluminium alloy housing as its siblings in the lineup, ensuring long-term durability in demanding indoor and outdoor environments. A wide range of compatible HORIBA cleaning devices — including drop-in ultrasonic cleaners requiring neither water nor air — further simplifies electrode maintenance on site.

Key Features HO-300

• 2-wire loop-powered design: operates from 24 V DC signal loop (0.6 W max.) — no separate AC power supply wiring required.
• ORP measurement range −2000 to +2000 mV (display −2200 to +2200 mV); resolution 1 mV; repeatability and linearity within ±5 mV.
• Single isolated 4–20 mA DC transmission output; max. load resistance 600 Ω at 24 V DC (voltage-dependent — see load curve); linearity ±0.08 mA; repeatability ±0.02 mA.
• Temperature measurement 0–100 °C; supports Pt 1 kΩ and NTC thermistors (500 Ω, 6.8 kΩ, 10 kΩ at 25 °C); automatic or manual sensor type selection.
• ORP calibration: offset adjustment ±200 mV; 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/memory errors.
• Contact input (1 × no-voltage a-contact) for external transmission hold.
• 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, RoHS EN50581; FCC Part 15 Class A.

Applications

The HO-300 is well suited to continuous ORP monitoring in municipal and industrial wastewater treatment — particularly aeration tanks and denitrification tanks — as well as chemical neutralization process control, environmental water monitoring, and any application where simplified 2-wire installation is preferred over a fully featured 4-wire transmitter.

Installation and Safety Notes

Power the HO-300 from a 24 V DC source (operating range 21–32 V DC) via the 4–20 mA loop. Maximum load resistance depends on supply voltage — consult the power supply voltage vs. load resistance curve in the product documentation. When sensor, transmission, or contact input cables are extended by 30 m or more, additional surge absorption elements must be fitted 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 the transmission output terminal. Operating temperature: −20 to 60 °C; storage: −25 to 65 °C; humidity: 5–90% RH non-condensing.

Technical Specifications