Digital ORP Probe ORP Sensor with Modbus RTU Register Calibration, 1 inch NPT Thread and IP68 Continuous Immersion

The DRH890 digital ORP probe is designed for engineers who integrate sensors into control systems. It is a 1" NPT ORP sensor with a stainless steel 316 body and POM head that speaks RS485 Modbus RTU natively — including Modbus-triggered calibration — so commissioning and routine calibration can be handled from the PLC or SCADA instead of by hand at the probe.

The measurement range is -2000 to 2000 mV with 1 mV resolution, and accuracy is specified as 0.1% of range or ±2 mV, whichever is greater, with ±0.5 °C temperature accuracy. Sample temperature from 0 to 50 °C is measured continuously and reported alongside the ORP value, so the control system can compensate and log both variables from a single polling cycle.

Calibration is register-driven, which is the feature that separates the DRH890 from cheaper probes. Writing 256 to register 200 performs a slope calibration, writing 86 to register 206 performs a zero calibration, and writing 99 to register 400 with function code 06 restores the setting parameters without touching the communication parameters. This makes the probe suitable for OEM skids and remote stations, where a technician cannot easily reach the sensor every month.

The 1" NPT thread at both ends accepts standard imperial fittings for side-wall, top-flange, pipeline, submerged and flow-through installation, with a φ37 mm × 261 mm profile. The body is sealed to IP68 for continuous immersion, and the PUR cable (10 m standard, customizable) resists the oils, cleaning agents and UV exposure found in purified water plants, pharmaceutical facilities and cooling systems. Power is 9 to 24 VDC at about 0.2 W, with electrical isolation inside the sensor to eliminate ground-loop error.

1. 1Modbus RTU with register-based calibration. Slope, zero and restore-setting functions are all addressable from the control system, enabling automated or guided calibration sequences without local access to the probe.
2. 2True 1" NPT thread at both ends. Fits standard imperial tees, flanges and immersion holders directly, with no adapters and no custom machining.
3. 3Stainless steel 316 + POM construction. A strong, dimensionally stable body with a chemically compatible wetted head, built for continuous immersion rather than occasional dipping.
4. 4Replaceable ORP head. Renew only the head at end of life and keep the stainless body, cable and electronics in service.
5. 5Full ±2000 mV measuring range. One probe covers disinfectant residual monitoring and reducing reaction control, simplifying spares across a multi-process site.
6. 6High accuracy, fine resolution. 1 mV resolution and 0.1% FS or ±2 mV accuracy support tight disinfection and oxidation control loops.
7. 7IP68 continuous immersion. Permanently submersible in tanks, loops and wet wells with a properly tightened gland or factory plug.
8. 8Internal electrical isolation. Isolated power and communication remove ground-loop offset in plants with multiple earth references.
9. 910 m PUR cable, factory terminated. Oil-, abrasion- and UV-resistant sheath, with custom lengths available from the factory to preserve the IP68 seal.
10. 10Five mounting options and three connection types. Side wall, top flange, pipeline, submerged or flow-through, with bare wire, M12 plug or waterproof aviation plug termination.

• Pure water and purified water systems: RO permeate, EDI outlet and loop oxidation state monitoring where a stainless body and sealed cable entry are preferred.
• Pharmaceutical and biotechnology facilities: process water, CIP rinse water and WFI loop oxidant monitoring.
• Food and beverage plants: CIP sanitizer control and process water oxidation state verification.
• Circulating water and cooling towers: oxidant programme control for biofouling and corrosion.
• Drinking water treatment: chlorine and chlorine dioxide dosing and residual verification.
• Wastewater treatment: effluent disinfection, cyanide destruction and sulphide oxidation control.
• OEM skids and remote monitoring stations: Modbus-native design for automated calibration and unattended operation.
• Electroplating, chemical and printing/dyeing process water: oxidation and reduction reaction monitoring.

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.

The installation angle must be within ±30° of vertical; horizontal and inverted mounting are not permitted. Keep the protective cap on until mechanical installation is complete. In pure water loops where the probe sits in a low-pressure bypass, install it so that the platinum surface always stays wetted, and keep working pressure at or below 1 Bar.

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].

Important: the sensor seal must be serviced by the manufacturer's service department every two years. If seal maintenance is skipped, water can enter the sensor body and cause irreparable damage.

If communication fails, verify the wiring and then the communication parameters (address, baud rate, parity bit, stop bit). If the value is abnormal, check whether the platinum surface is clean and the sensor undamaged, restore the factory calibration value, clean and recalibrate with standard buffer, then check electrode service life.

Please specify the connection type (bare wire, M12 plug or waterproof aviation plug), cable length (10 m standard), Modbus slave address and mounting method. Spare ORP heads can be supplied with the first order so your maintenance team has them in stock. OEM labelling and custom cable lengths are available for volume orders.