RS485 Modbus Digital ORP Sensor IP68 ORP Probe with 10 m PUR Cable for Water Treatment

The DRH790 digital ORP sensor measures oxidation-reduction potential on the classic electrochemical principle, using a platinum ring electrode as the indicating element and a stable reference half-cell. ORP is the single most practical on-line indicator for disinfection strength, oxidant residual and chemical reaction state, and the DRH790 turns that measurement into a clean digital value that any PLC or controller can read over RS485 Modbus.

The measuring range is -2000 to +2000 mV with 1 mV resolution and ±2 mV accuracy, covering the full span needed for drinking water chlorination, wastewater disinfection, cyanide destruction, chromium reduction and oxidation towers. Sample temperature from 0 to 50 °C is measured by an integrated element and reported on the same Modbus register map, so the controller can log both ORP and temperature in a single poll.

Calibration is flexible: zero-point, slope and deviation calibration are all supported, which means you can correct an offset in the field with a single standard solution (typically 200 mV or 468 mV ORP buffer) without replacing the electrode. The ABS body is sealed to IP68 and can be immersed continuously, while the 1" NPT thread on each end fits side-wall brackets, top flanges, pipe tees, submerged holders and flow-through cells.

The sensor is powered from a wide 9 to 36 VDC input at about 0.2 W, so it suits 12 V battery systems, 24 V panel supplies and remote solar stations. Power and communication are electrically isolated inside the sensor, which removes ground-loop offsets that otherwise appear in plants where the probe and the controller sit on different earth potentials. The standard cable is a 10 m PUR-sheathed lead — PUR resists oil, UV and repeated flexing better than PVC — and cable length can be customized. Bare wire, M12 plug and waterproof aviation plug versions are all available, so the same probe can be integrated into new skids or dropped into an existing junction box.

1. Full ±2000 mV measuring range. One sensor covers both oxidising and reducing duties, from chlorination at +600 mV to chromium reduction at negative potentials, so a single spare part serves the whole plant.
2. Digital RS485 Modbus output. The ORP value is digitised inside the probe and transmitted as a Modbus RTU register, eliminating high-impedance signal loss over long cable runs and interference from motors and VFDs.
3. IP68 immersion rating. The ABS housing is sealed for continuous submersion, so the sensor can sit directly in a tank, channel or sump instead of being limited to a bypass line.
4. Three calibration modes. Zero-point, slope and deviation calibration let you correct drift quickly in the field with a single ORP standard solution, without pulling the probe out of service for long.
5. ±2 mV accuracy with 1 mV resolution. Fine enough to catch small shifts in disinfectant residual before a compliance limit is breached.
6. Wide 9–36 VDC supply, 0.2 W consumption. Works with 12 V batteries, 24 V panel supplies and solar-powered remote stations without a dedicated power module.
7. Internal electrical isolation. Power and communication are isolated inside the sensor, removing ground-loop error in large installations sharing one supply or one earthed metal tank.
8. 10 m PUR cable as standard. Polyurethane sheath resists oil, abrasion and UV, and the standard length is enough to reach most control panels without a junction box; custom lengths available.
9. Five mounting methods. 1" NPT threads at both ends support side-wall, top flange, pipeline, submerged and flow-through installation, with 100 mm insertion depth to suit standard fittings.

• Drinking water disinfection: chlorine and chlorine dioxide dosing control, residual verification and disinfection-by-product management.
• Wastewater treatment: effluent disinfection, cyanide destruction and sulphide oxidation control in industrial and municipal plants.
• Swimming pool and spa water: oxidant residual monitoring as a faster and more stable indicator than free chlorine alone.
• Cooling water and circulating water: oxidant programme control for biofouling and corrosion management.
• Electroplating and metal finishing: chromium reduction and oxidising bath control.
• Chemical, printing and dyeing, food and pharmaceutical process water: oxidation state monitoring in reaction and rinse stages.
• Surface water and pollution source monitoring: long-term remote stations powered by solar or battery.

Mount the sensor at an angle within ±30° of vertical; never install it horizontally or upside down, otherwise the reference chamber can trap air and the reading will drift. Keep the protective cap on during installation and remove it only after the probe is fixed. Insertion depth is 100 mm (115 mm including the cleaning connector), so standard 1" tees and immersion brackets fit directly.

Rinse the platinum ring with deionised water, then calibrate in an ORP standard solution (200 mV or 468 mV). If the reading is offset but the slope is healthy, use deviation calibration to correct it directly. A slow or noisy response usually means the platinum ring is coated — clean it and recalibrate before returning the probe to service.

If the electrode cannot communicate, check the wiring first and then the communication parameters (address, baud rate, parity bit, stop bit). If the measured value is abnormal, check whether the platinum ring is clean and whether the sensor is damaged, restore the factory calibration value, clean and recalibrate with standard buffer, and finally check the service life of the electrode.

Please confirm the cable length (10 m standard), the connection type (bare wire, M12 plug or waterproof aviation plug) and the Modbus slave address you need. OEM labelling is available for volume orders. Send us your process conditions — ORP range, temperature, pressure and installation method — and our engineers will confirm the right configuration for your project.