IP68 Digital ORP Sensor with Replaceable ORP Head and 316 Stainless Steel Body for Online ORP Probe Monitoring

The DRH890 digital ORP sensor is the heavy-duty model in our digital ORP range. Instead of a plastic shell it uses a 316 stainless steel outer body combined with a POM (polyoxymethylene) sensor head, which gives it the mechanical strength to survive rough handling, high-solids wastewater and outdoor installations while keeping the wetted front end chemically compatible with typical process water. The result is a probe that survives knocks, cable pulls and years of immersion rather than being treated as a consumable.

ORP is the practical control variable for oxidation and disinfection. The DRH890 covers -2000 to 2000 mV with 1 mV resolution and an accuracy of 0.1% of range or ±2 mV (whichever is greater), plus ±0.5 °C temperature accuracy. That range spans chlorination and ozone disinfection at strongly positive potentials as well as chromium reduction and other reducing reactions at negative potentials, so one model serves the whole plant.

The most important maintenance feature is the replaceable ORP head. When the platinum electrode reaches end of life, you do not scrap the whole instrument: the stainless steel body, the cable and the electronics stay in service and only the head is replaced. On a plant with dozens of ORP measuring points this turns an annual capital cost into a much smaller consumable cost, and it shortens downtime because the replacement is a mechanical swap rather than a full re-installation.

Electrically the sensor runs on 9 to 24 VDC at about 0.2 W and communicates over RS485 Modbus RTU, with power and communication isolated inside the body to remove ground-loop offset. Calibration is fully supported over Modbus: write value 256 to register 200 for slope calibration, 86 to register 206 for zero calibration, and 99 to register 400 to restore settings. The 1" NPT thread at both ends supports side-wall, top-flange, pipeline, submerged and flow-through installation, and the standard cable is 10 m of oil- and UV-resistant PUR.

1. 1316 stainless steel body. Far stronger than plastic housings: it resists impact, vibration, cable pull and years of outdoor UV exposure, and it will not crack in high-solids or gravel-laden wastewater.
2. 2Replaceable ORP head. Only the POM head and electrode are renewed, so the stainless body, cable and electronics stay in service — a major reduction in total cost of ownership for multi-point plants.
3. 3Full ±2000 mV range. Covers both oxidising duties (chlorination, ozone) and reducing duties (chromium reduction, cyanide destruction) with one model number.
4. 4High accuracy. 0.1% of range or ±2 mV, plus ±0.5 °C temperature accuracy, which is tight enough for compliance-grade disinfection control.
5. 5Digital RS485 Modbus RTU. No high-impedance analog signal, no signal loss on long cable runs, no interference from VFDs and large motors.
6. 6Calibration over Modbus. Slope, zero and offset calibration are performed by writing defined registers, so integrators can automate routine calibration from the control system instead of walking to the probe.
7. 7IP68 continuous immersion. Sealed for permanent submersion in tanks, channels, sumps and wet wells.
8. 8Internal electrical isolation. Power and communication isolation removes ground-loop error where probe and controller sit on different earth potentials.
9. 910 m PUR cable standard. Polyurethane resists oil, abrasion, plating mist and UV, and custom lengths are available.
10. 10Five mounting methods. 1" NPT threads at both ends allow side-wall, top flange, pipeline, submerged and flow-through installation with no adapters.

• Municipal and industrial wastewater: effluent disinfection, cyanide destruction, sulphide oxidation and oxidation ditch control.
• Surface water and pollution source monitoring: outdoor stations and remote platforms where a stainless body resists impact and UV.
• Drinking water treatment: chlorine and chlorine dioxide dosing control and residual verification.
• Circulating and cooling 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.
• Aquaculture and industrial ponds: oxidant and water treatment control in outdoor, high-humidity environments.

Note: the waterproof aviation plug version is factory terminated and does not require the user to connect individual wires. The M12 plug version uses the M12 pin-out printed on the connector body.

Install the sensor within ±30° of vertical — never horizontally and never inverted, or air can be trapped in the reference chamber. Keep the protective cap fitted during mechanical installation and remove it only when commissioning starts. Because the body weighs about 500 g, support the cable with a strain relief when the probe is suspended in a channel.

Rinse the platinum electrode, then calibrate in an ORP standard solution (200 mV or 468 mV). Calibration can be triggered either from the controller or directly over Modbus using the registers below.

Factory reset does not restore the communication parameters. With slave address 11 the host frame for restoring settings is [0B 06 01 90 00 63 C8 98].

Common problems and solutions: 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 surface is clean and whether the sensor is damaged, restore the factory calibration value, clean and recalibrate with standard buffer, and check the electrode service life.

Please confirm the cable length (10 m standard), connection type (bare wire, M12 plug or waterproof aviation plug), Modbus slave address and whether spare ORP heads should be included in the first order. OEM labelling is available for volume orders. Send your process conditions — ORP range, temperature, pressure and chemical environment — and our engineers will confirm the configuration.