DODO AQUA ORP
Online ORP / Redox Potential Sensor
ORP (Redox Potential)
- −1500 … +1500 mV
- ±6 mV, 1 mV resolution
- RS-485 Modbus-RTU
- IP68, 3/4" NPT immersion
- DC 12-24 V, < 0.3 W
- 5 m cable, GX12 fitted
Works with DODO LOGGER, the DODOTiK Platform and the DODOLINK app — see how.
Overview
DODO AQUA ORP (DOT-RXS-200) measures oxidation-reduction potential - the net tendency of a water to oxidise or reduce - across the full −1500 to +1500 mV span, and reports it as a signed digital value on RS-485 Modbus-RTU.
ORP is the measurement that tells you whether a disinfection or reduction process is actually working, as opposed to whether the dosing pump is running. In a chlorinated system it tracks disinfecting power directly, which is why pool and drinking-water plants control on ORP rather than on dose rate; in wastewater it marks the aerobic/anoxic boundary that drives nitrification and denitrification; in metal finishing it is the endpoint indicator for cyanide oxidation and chromate reduction.
The platinum measuring electrode works against the same pressurised microporous-salt-bridge reference used in the DODO AQUA pH: the internal solution bleeds outward under at least 100 kPa for a rated 20+ months, about twice the life of a conventional industrial reference.
Key features
- Full bipolar span - −1500 to +1500 mV at 1 mV resolution, ±6 mV accuracy
- Signed digital output - RS-485 Modbus-RTU; no analog mV loop to protect
- Long-life reference - pressurised microporous salt bridge, 20+ months of forward bleed
- Fast - dual high-impedance differential front end, strong noise rejection
- Submersible - IP68, 3/4" NPT thread for tank, pipe or submerged mounting
- Single-point calibration - one standard solution, one command
- Plug-in - 5 m cable with the DODO LOGGER GX12 connector fitted as standard
Measured parameters
| Parameter | Unit | Range | Accuracy | Resolution |
|---|---|---|---|---|
| ORP (redox potential) | mV | −1500 … +1500 mV | ±6 mV | 1 mV |
Technical specifications
Measurement
| Parameter | Value |
|---|---|
| Measured parameters | ORP (oxidation-reduction potential) |
| Measuring range | −1500 … +1500 mV |
| Resolution | 1 mV |
| Accuracy | ±6 mV |
| Temperature compensation | None - ORP is reported uncompensated |
| Calibration | One-point, in a prepared ORP standard solution |
Electrical
| Parameter | Value |
|---|---|
| Supply voltage | DC 12-24 V ±10 % |
| Power consumption | < 0.3 W @ 12 V |
| Output | RS-485, Modbus-RTU |
| Baud rate | 9600 (default) |
| Frame format | 8 data bits, 1 stop bit, no parity (8N1) |
| Default slave address | 6 |
| Addressing | Field-changeable over the bus, range 1-127 |
| Cable | 5 m, Φ6 mm shielded, corrosion-resistant jacket, GX12 4-pin female fitted; other lengths on request |
Mechanical & environmental
| Parameter | Value |
|---|---|
| Body diameter | Φ30 mm |
| Overall length | 185 mm |
| Wetted material | POM |
| Mounting | Immersion, 3/4" NPT thread - tank, pipe or submerged |
| Working temperature | 0 … +65 °C |
| Working pressure | < 0.1 MPa |
| Ingress protection | IP68 |
Plug DA-ORP into DODO LOGGER and it is already on your phone
No firmware reflash, no driver to write, no backend deployment. The logger self-describes its schema to the platform, so a new sensor appears in the dashboard and in the app on its own.
1 · Plug in
The fitted GX12 4-pin connector screws onto the logger's Modbus RS-485 socket. No stripping, no terminal block, no tools. Up to four sensors per logger.
2 · Select it
DA-ORP is in the logger's no-code sensor library. Pick it in the web interface, assign a slot, and it starts logging.
3 · Logged locally
Every reading to microSD, always on, offline included. CSV download straight off the card.
4 · Live in the cloud
MQTT/TLS to the DODOTiK Platform — live dashboards, full history, alert thresholds, device management.
5 · On a phone
The same readings and alerts in DODOLINK for iOS and Android, for whoever is out in the field rather than at a desk.
Nothing here is lock-in. DA-ORP is a standard Modbus-RTU device on a standard RS-485 bus. The DODO LOGGER, the platform and the app are the fastest route from probe to dashboard, not the only one — the full register map is published below and in the datasheet, and the sensor can be ordered with bare leads for a PLC, DCS, SCADA or paperless recorder.
Dimensions
| Dimension | Value |
|---|---|
| Overall length | 185 mm |
| Body diameter | Φ30 mm |
| Electrode guard diameter | Φ22 mm |
| Process thread | 3/4" NPT, both ends |
| Wrench flat | 28 mm |
| Cable length | 5 m (standard) |
Wiring — GX12 4-pin connector
The cable is terminated in a GX12 4-pin female aviation connector, fitted as standard. It screws directly onto the DODO LOGGER Modbus RS-485 socket. For a third-party logger or a terminal block, order the bare-lead variant rather than cutting the connector off at the sensor's gland — the gland is part of the IP68 seal.
| Pin | Signal | Function |
|---|---|---|
| 1 | VCC | Power + (DC 12-24 V) |
| 2 | GND | Ground |
| 3 | A (D+) | RS-485 A |
| 4 | B (D−) | RS-485 B |
Modbus RTU register map
RS-485 Modbus-RTU, 9600 baud, 8 data bits, 1 stop bit, no parity. Default slave address 6. Published in full so the sensor can be read by any Modbus master — PLC, DCS, SCADA or a paperless recorder.
| Register | Value | Access | Notes |
|---|---|---|---|
| 0x0000 | Measured value | Read | 2 registers: ORP value (signed), decimals. No temperature channel |
| 0x1000 | Calibration | Write | In the standard solution; write the actual standard value in mV |
| 0x1006 | Calibration value | Read | Returns the stored calibration value |
| 0x2002 | Device address | Read / Write | Default 6, range 1-127 |
| 0x2020 | Factory reset | Write | Write 0 - restores factory calibration |
Calibration
Calibration is performed over the bus — there is no handheld meter to carry and no transmitter to adjust.
ORP needs one calibration point. Rinse the probe thoroughly before moving between solutions - carry-over is the dominant error source.
Preparing the standard. Dissolve 2.1 g of hydrazine in 200 mL of pH buffer:
- pH 4.00 buffer → +256 mV standard - pH 6.86 buffer → +86 mV standard - pH 9.18 buffer → −40 mV standard
Make up 250 mL of the pH buffer and use 200 mL of it. Stand the probe in the prepared standard for 3-5 minutes; if the settled reading is not the standard value, write the calibration command for that standard.
> Hydrazine is toxic and a suspected carcinogen. Prepare these standards only with appropriate ventilation, gloves and eye protection, or buy ready-made ORP standard solution.
Calibration commands
| Operation | Request | Response |
|---|---|---|
| Calibrate in the +86 mV standard | 06 06 10 00 00 56 0C 83 | 06 06 10 00 00 56 0C 83 |
| Calibrate in the +256 mV standard | 06 06 10 00 01 00 8D 2D | 06 06 10 00 01 00 8D 2D |
Applications
Drinking water and swimming pools - disinfection control on redox rather than dose rate
Wastewater treatment - aerobic / anoxic boundary, nitrification and denitrification control
Metal finishing - cyanide oxidation and chromate reduction endpoints
Cooling-tower circuits - biocide effectiveness monitoring
Aquaculture - redox as an early indicator of water-quality collapse
Bleaching and process chemistry - oxidant strength in the bath
Before you specify it
Limits worth knowing before the order goes in, rather than after the sensor is in the ground.
- Signed output: an integrator decoding the value as unsigned reads −40 mV as 65496.
- Two registers, not four - the ORP has no temperature channel.
Ordering information
| Order code | Description |
|---|---|
| DA-ORP | DODO AQUA ORP (DOT-RXS-200), −1500 … +1500 mV, RS-485 Modbus-RTU, 5 m cable with GX12 4-pin female connector |
| DA-ORP-L10 | As DA-ORP, 10 m cable |
| DA-ORP-L20 | As DA-ORP, 20 m cable |
| DA-ORP-BL | As DA-ORP, bare leads instead of the GX12 connector |
What's in the box
- DODO AQUA ORP sensor with 5 m cable, GX12 4-pin female connector fitted
- Test certificate
Quality and warranty
- IP68 sealed body, POM wetted parts
- 72-hour burn-in and stability test on every unit before shipment
- Warranty: 1 year from date of sale, excluding damage from improper use
- The platinum electrode is a wearing part; reference life is rated at 20+ months of continuous service
Handling and maintenance
- Rinse the platinum in distilled or deionised water before measuring and blot with filter paper. Immerse about one third of the electrode in the sample.
- Store the probe wet - protective sleeve or vessel filled with 3.5 mol/L potassium chloride. Never store it dry.
- Avoid prolonged immersion in distilled water or protein solutions, and keep silicone grease off the electrode.
- A dulled or coated platinum surface can be cleaned with dilute hydrochloric acid followed by a water rinse.
- Keep the terminal dry; wipe with absolute alcohol if contaminated.
- If the probe will no longer calibrate after cleaning, the electrode has reached end of life. Replace it.
Frequently asked questions
Does DODO AQUA ORP work with a PLC, SCADA or a third-party data logger?
Yes. DA-ORP is a standard RS-485 Modbus-RTU device at 9600 baud, 8N1, so any Modbus master can read it - PLC, DCS, SCADA or a paperless recorder. The full register map is published in the datasheet, and the sensor can be ordered with bare leads instead of the GX12 connector for terminal-block wiring. There is no proprietary driver and no lock-in.
What is the default Modbus address of DA-ORP?
6. The address is changeable in the field over the bus, so several sensors can share one RS-485 pair as long as each has a unique address.
How do I connect DODO AQUA ORP to DODO LOGGER?
Screw the fitted GX12 4-pin connector onto the logger's Modbus RS-485 socket - no stripping, no terminal block, no tools. DA-ORP is in the logger's no-code sensor library, so an installer selects it in the web interface and it begins logging to microSD and publishing to the DODOTiK Platform and the DODOLINK app. No firmware reflash, no backend change.
What does DA-ORP measure, and how accurately?
ORP (redox potential): −1500 … +1500 mV, accuracy ±6 mV.
How do I order DA-ORP, and what does it cost?
DA-ORP is sold direct and through distributors. Pricing depends on configuration and quantity, so request a quote with the order code and the quantity you need and DODOTiK will come back with export pricing and volume tiers. Available configurations: DA-ORP; DA-ORP-L10; DA-ORP-L20; DA-ORP-BL.
Is there anything to watch out for when specifying DA-ORP?
Signed output: an integrator decoding the value as unsigned reads −40 mV as 65496. Two registers, not four - the ORP has no temperature channel.
More from DODO AQUA
Request a quote for DA-ORP
Sold direct and through distributors. Tell us the order code, the quantity and the destination country and we will come back with export pricing, volume tiers and lead time.