DODO AQUA CL
Amperometric Free Chlorine Sensor
Free Chlorine (HClO) · Temperature
- 0-2.000 mg/L free chlorine
- 0.001 mg/L resolution
- Response < 30 s
- Flow cell, 30-60 L/h
- RS-485 Modbus-RTU
- Flow cell included
Works with DODO LOGGER, the DODOTiK Platform and the DODOLINK app — see how.
Overview
DODO AQUA CL (DOT-FCS-200) measures free chlorine - the hypochlorous acid (HClO) that actually does the disinfecting - continuously, from 0 to 2.000 mg/L at 0.001 mg/L resolution, over RS-485 Modbus-RTU.
This is the measurement that regulators ask for and that a redox reading only approximates. ORP tells you a water is oxidising; free chlorine tells you how much disinfectant is in it, in the units the compliance report is written in. A sensor at the far end of a distribution network, or at the outlet of a treatment works, is what turns chlorine dosing from a scheduled job into a controlled one.
Measurement is amperometric, by the constant-voltage method: a fixed potential is held across the electrodes and the current that flows is proportional to the free chlorine reducing at the cathode. The membrane and electrolyte are PTFE and POM wetted; response is under 30 seconds.
Unlike the other four DODO AQUA sensors, this one is not an immersion probe. It is installed in the supplied flow cell with a controlled 30-60 L/h sample stream across the membrane - see Wiring.
Key features
- Free chlorine, directly - HClO in mg/L, not a redox proxy
- High resolution - 0.001 mg/L over a 0-2.000 mg/L span
- Fast - response under 30 seconds
- Compensated - automatic temperature compensation via Pt1000
- Flow cell included - the sample cell ships with the sensor
- Two-point calibration - zero in chlorine-free water, slope against a standard
- Low power - 0.2 W at 12 V
- Plug-in - 5 m cable with the DODO LOGGER GX12 connector fitted as standard
Measured parameters
| Parameter | Unit | Range | Accuracy | Resolution |
|---|---|---|---|---|
| Free chlorine (HClO) | mg/L | 0-2.000 mg/L | ±5 % of reading or ±0.05 mg/L | 0.001 mg/L |
| Temperature | °C | 5-50 °C | ±0.5 °C | 0.1 °C |
Technical specifications
Measurement
| Parameter | Value |
|---|---|
| Measured parameters | Free chlorine (HClO) and temperature |
| Measuring principle | Amperometric, constant-voltage method |
| Measuring range | 0-2.000 mg/L |
| Resolution | 0.001 mg/L |
| Accuracy | ±5 % of reading or ±0.05 mg/L; temperature ±0.5 °C |
| Response time | < 30 s |
| Medium pH range | 4-9 pH |
| Sample flow rate | 30-60 L/h |
| Temperature compensation | Automatic (Pt1000) |
| Calibration | Two-point - zero in chlorine-free water, slope against a standard |
Electrical
| Parameter | Value |
|---|---|
| Supply voltage | DC 12-24 V ±10 % |
| Power consumption | 0.2 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, 4-core shielded twisted pair, GX12 4-pin female fitted; other lengths on request |
Mechanical & environmental
| Parameter | Value |
|---|---|
| Body diameter | Φ30 mm |
| Overall length | 185 mm (see Dimensions) |
| Wetted material | POM and PTFE |
| Mounting | Flow cell - supplied with the sensor. Not an immersion probe |
| Working temperature | +5 … +50 °C |
| Working pressure | < 0.1 MPa |
| Ingress protection | IP68 |
Plug DA-CL 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-CL 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-CL 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 + temperature | Read | 4 registers: free chlorine, decimals, temperature, temperature decimals |
| 0x1000 | Zero calibration | Read / Write | In chlorine-free water, write 0; reading back returns the zero offset |
| 0x1004 | Slope calibration | Read / Write | In a 1-2 mg/L HClO standard; write actual concentration × 1000. Reading back returns slope × 1000 |
| 0x1010 | Temperature calibration | Read / Write | Write actual temperature × 10; read the stored offset × 10 |
| 0x2002 | Device address | Read / Write | Default 6, range 1-127 |
| 0x2020 | Factory reset | Write | Write 0 - restores factory calibration. Recalibrate after a reset |
Calibration
Calibration is performed over the bus — there is no handheld meter to carry and no transmitter to adjust.
The sensor is calibrated at the factory. Preparing a chlorine standard to a known concentration is genuinely difficult - the solution decays while you work - so do not recalibrate unless the reading is demonstrably wrong, verified against a DPD test on the same sample.
Zero, in chlorine-free water. Place the probe in chlorine-free water, wait for the value to settle, then write the zero command.
Slope, against a standard. Run a residual-chlorine standard through the flow cell - 1 to 2 mg/L HClO is recommended - and once the value is stable write the slope command with the actual concentration × 1000. Determine the standard's true concentration by the national-standard residual-chlorine method, not by assuming what was made up.
Calibration commands
| Operation | Request | Response |
|---|---|---|
| Zero, in chlorine-free water | 06 06 10 00 00 00 8C BD | 06 06 10 00 00 00 8C BD |
| Slope, 2.000 mg/L standard | 06 06 10 04 07 D0 CE D0 | 06 06 10 04 07 D0 CE D0 |
Applications
Drinking-water treatment works - final-stage disinfection control and compliance
Distribution networks - residual at the far end of the network, where it matters
Swimming pools and leisure water - continuous free-chlorine control
Bottling and canning plants - process-water disinfection
Cooling circuits - biocide residual monitoring
Water-reuse and treatment skids - disinfection verification before discharge
Before you specify it
Limits worth knowing before the order goes in, rather than after the sensor is in the ground.
- Flow cell only. This is not an immersion probe.
- The electrode is a 6-month consumable, not a 1-year part.
Ordering information
| Order code | Description |
|---|---|
| DA-CL | DODO AQUA CL (DOT-FCS-200), 0-2.000 mg/L free chlorine, flow cell included, RS-485 Modbus-RTU, 5 m cable with GX12 4-pin female connector |
| DA-CL-L10 | As DA-CL, 10 m cable |
| DA-CL-L20 | As DA-CL, 20 m cable |
| DA-CL-BL | As DA-CL, bare leads instead of the GX12 connector |
| DA-CL-EL | Replacement electrode only |
What's in the box
- DODO AQUA CL sensor with 5 m cable, GX12 4-pin female connector fitted
- Flow cell
- Test certificate
Quality and warranty
- IP68 sealed body, POM and PTFE wetted parts
- 72-hour burn-in and stability test on every unit before shipment
- Warranty: 1 year on the sensor body from date of sale
- Warranty: 6 months on the electrode, which is a consumable - order replacements as DA-CL-EL
Handling and maintenance
- Activate before first use. A new electrode, or one that has been out of service for a long period, must stand in tap water for 24 hours before it will read correctly.
- Keep the sample flow in the 30-60 L/h window. Most 'sensor drift' on an amperometric chlorine cell is a sample-flow problem.
- Check the membrane for deposits, biofilm or bubbles whenever the reading goes sluggish. A bubble on the membrane stops the measurement.
- Recalibrate zero and slope if the value is wrong after cleaning. If it still cannot be calibrated, the electrode has reached end of life.
- Do not let the cell run dry between the sample pump stopping and starting. Repeated drying shortens electrode life sharply.
Frequently asked questions
Does DODO AQUA CL work with a PLC, SCADA or a third-party data logger?
Yes. DA-CL 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-CL?
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 CL 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-CL 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-CL measure, and how accurately?
Free chlorine (HClO): 0-2.000 mg/L, accuracy ±5 % of reading or ±0.05 mg/L; Temperature: 5-50 °C, accuracy ±0.5 °C.
How do I order DA-CL, and what does it cost?
DA-CL 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-CL; DA-CL-L10; DA-CL-L20; DA-CL-BL; DA-CL-EL.
Is there anything to watch out for when specifying DA-CL?
Flow cell only. This is not an immersion probe. The electrode is a 6-month consumable, not a 1-year part.
More from DODO AQUA
Request a quote for DA-CL
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.