Dissolved Oxygen Probe AT-SB-PROBE-DO-P-C1
Datasheet
1. Introduction
SENSBLUE RS-485 Dissolved Oxygen Probe AT-SB-PROBEDO-P is an integrated online fluorescence dissolved oxygen sensor designed based on the quenching principle of excited fluorescence by specific substances in physics. When the excitation light shines on the fluorescent substance on the surface of the fluorescent membrane head, the substance becomes excited and emits fluorescence. The extinguishing time of this fluorescence is affected by the concentration of oxygen molecules on the surface of the fluorescent membrane head. The oxygen concentration can be calculated by detecting the phase difference between the fluorescence and the excitation light and comparing it with the internal calibration curve. The final value is then output after temperature and salinity compensation.
2. Features
- No electrolyte is required and it will not be polarized.
- No oxygen consumption; not affected by flow rate.
- Built‑in temperature sensor, automatic temperature compensation.
- Built‑in salinity compensation, flexible parameter settings.
- Free from interference by chemicals such as sulfides.
- Small drift, rapid reaction, for more accurate measurement.
- Long service cycle, lower cost of use.
- Simple replacement of fluorescent cap.RS‑485 interface, Modbus/RTU protocol.
- Low power consumption and anti‑interference
3. Technical Specifications
| Model | Pro | Ultra |
|---|---|---|
| Case material | POM, ABS/PC alloy, 316L stainless steel | 316L Titanium Alloy |
| Measurement principle | Fluorescence method | |
| Range | 0～20.00 mg/L (0～200% saturation, 25℃) | |
| Resolution | 0.01mg/L, 0.1℃ | |
| Accuracy | ±2%, ±0.3℃ | ±3% |
| Response time (T90) | ＜30s | ＜60s |
| Minimum detection limit | 0.08mg/L | |
| Calibration method | Two-point calibration | |
| Temperature compensation | Automatic temperature compensation (Pt1000) | |
| Output method | RS-485 (Modbus RTU) | |
| Storage temperature | -5~65℃ | |
| Working conditions | 0～50℃, ≤0.2MPa | |
| Installation method | Submersible installation, 3/4 NPT | Max Depth 30m |
| Power consumption | 10.1W@12V | |
| Power supply | 12~24V DC | |
| Protection level | IP68 | |
| Life of fluorescent membrane head | 1 year (under normal use) | |
| Cable length | 10 meters, other lengths can be customized | |
| Max water depth | 30m | |
4. Dimensions and Wiring
| Pinouts | |
|---|---|
| 1 - Pin +12V DC | 4 - RS485 B- |
| 2 - GND | 5 – NA |
| 3 - RS485 A+ | 6 - NA |
| 7 - NA | |
5. Installation
Install
The sensor needs to be installed below the liquid level. The installation and use should avoid any collisions or scraping against the surface of the fluorescent film head. The fluorescent film head should also be kept from contacting the bottom sediment. Remove the rubber cover when in use.
6. Maintenance
6.1 Use and maintenance
a) Maintenance schedule
Different from dissolved‑oxygen probe technology based on the electrochemical principle, the fluorescence dissolved‑oxygen probe does not consume oxygen and does not need to be cleaned frequently (except when used in viscous liquids).
| Maintenance Task | Recommended Maintenance Frequency |
|---|---|
| Cleaning sensor | Wash every 30 days |
| Check for damage to sensors and caps | Check every 30 days |
| Replace the fluorescent cap | Replace it once a year |
| Calibrate (if required by the competent authority) | According to the maintenance schedule required by the competent department |
Note: The maintenance frequency in the above table is only recommended, and the maintenance personnel shall clean the sensor according to the actual use of the sensor, however, the replacement frequency of the fluorescent cap is recommended once a year.
6.2 Maintenance method
a) Sensor outer surface:
Clean the outer surface of the sensor with tap water, if there is still debris residue, wipe with wet soft cloth, for stubborn dirt, you can add household washing liquid to clean.
b) Surface of fluorescent film head:
If there is dirt on the surface of the fluorescent film head, please rinse it with clean water or wipe it gently with a soft cloth. Pay attention to the cleaning intensity to avoid causing scratches in the measuring area and affecting measurement accuracy.
c) Inside the fluorescent film head:
It is generally unnecessary to clean. If water vapor or dust enters the fluorescent film head, the cleaning steps are as follows:
•Screw down the fluorescent film head;
•Rinse the inner surface of the fluorescent film head and the optical window of the sensor.
•For oily dirt, you can use household cleaning solution;
•Gently dry the water with a clean cloth and let dry;
Reinstall the fluorescent film head.
d) Check the cables of the sensor:
There should be no damage to the skin and root of the cables;
Terminals should not be submerged in water; When the sensor is normally installed, the cable should not be tensioned, otherwise the internal wire of the cable will easily break, and the sensor cannot work normally.
e) Check whether the casing of the sensor is damaged by corrosion or other causes.
f) Daily storage of fluorescent film head:
When not in use, a rubber protective cover with a wet sponge should be placed over the fluorescent film head to keep the surface of the measuring area wet. If the surface of the measuring area of the fluorescent film head becomes chronically dry, measurement errors or data instability may occur, and it needs to be soaked in water for 48 hours before use.
6.3 Frequently asked questions
| Wrong | Probable Cause | Solution |
|---|---|---|
| The operating interface cannot connect or does not display the measurement results | Error connecting controller to cable | Reconnect the controller and cable |
| Cable failure | Please contact us. | |
| The fluorescent cap is not tightened or damaged | Refit and tighten the fluorescent cap or replace the fluorescent cap. | |
| The measured value is too high, too low, or the numerical value | The outer surface of the fluorescent cap is attached to the outer object | Clean the outer surface of the fluorescent
film head and agitate the film head during measurement. |
| The fluorescent cap was damaged | ||
| remains unstable. | The fluorescent cap has exceeded
its service life |
Replace the fluorescent cap |
| Temperature measurements change slowly. | The temperature measuring area
(stainless steel housing) is attached to the exterior |
Gently brush the attachment with a soft brush |
6.4 Calibration of sensors
a) Zero Calibration
Weigh 5 g of sodium sulphite using a balance, add 95 mL of water into a 250‑mL measuring cylinder, pour the water into a beaker, add the previously weighed sodium sulphite, and stir with a glass rod until fully dissolved to obtain a 5% sodium sulphite solution. Place the sensor in the solution and perform the zero‑point calibration after the reading has stabilized for three minutes. Refer to the Appendix for instructions.
Slope Calibration
The sensor probe is placed in air‑saturated water, and the slope is calibrated after 3 minutes of numerical stability. The instructions refer to the appendix.
Preparation of Air Saturated Water:
Add 2/3 volume of fresh distilled water to the constant‑temperature water bath to allow the porous plastic sheet to float on the water surface (see figure below). At the same time, use the bubbler (air pump) to aerate the water continuously for more than 1 hour. Then stop aeration and obtain air‑saturated water after approximately 20 minutes. Place the sensor into the water and calibrate the slope once the reading has stabilized.
Note: As an alternative, slope calibration can also be performed in water‑saturated air. Pour pure water into the calibration cup, keeping the liquid level column height slightly below 1 mm. After the sensor’s fluorescent membrane head is dipped in water, shake it lightly (to ensure that the surface of the fluorescent membrane is moist and there are no water droplets), and place the sensor vertically on the calibration cup column (as shown in the figure below, ensuring that the water surface does not touch the fluorescent membrane). Wait for 3 minutes for the value to stabilize before calibrating the slope.
6.5 Precautions
- Avoid exposing the inner surface of the fluorescent film head to sunlight
- Please do not touch the fluorescent film with your hands
- Avoid bubbles adhering to the surface of the fluorescent film during measurement and calibration
- Avoid applying any mechanical stress (pressure, scratches, etc.) directly to the fluorescent film during use
7. Appendix data communication
7.1 Data Format
The default data format for Modbus communication is: 9600, n, 8, 1 (baud rate 9600bps, 1 start bit, 8 data bits, no parity, 1 stop bit).
7.2 Modbus Frame Format (xx represents a byte)
a) Read data instruction frame
| 05 | 03 | xx xx | xx xx | xx xx |
| Address | FC | Register start
address |
Number of Registers | CRC check code (low bytes in front) |
b) Read data response frame
| 05 | 03 | xx | xx xx | xx xx |
| Address | FC | Number of Bytes | Response data | CRC check code (low bytes in front) |
c) Write data instruction frame
| 05 | 06 | xx xx | xx xx | xx xx |
| Address | FC | Register address | Read-in data | CRC check code (low bytes in front) |
d) Data response frame
| 05 | 06 | xx xx | xx xx | xx xx |
| Address | FC | Register address | Read-in data | CRC check code (low bytes in front) |
7.3 Register Address
| Register Address | Name | Instruction | Number of Registers | Access Method |
|---|---|---|---|---|
| 40001 (0x0000) | Measured value + temperature | Four double-byte integers: measured value, measured decimal places, temperature value, and temperature decimal places. | 4 (8 bytes) | Read |
| 40005 (0x0004) | Dissolved oxygen saturation (0–200%) | Two double-byte integers: saturation value and decimal places. | 2 (4 bytes) | Read |
| 44097 (0x1000) | Zero calibration | Calibrated in anoxic water. Write value 0; read returns zero offset. | 1 (2 bytes) | Write / Read |
| 44101 (0x1004) | Slope calibration | Calibrate in air-saturated water. Write value 0; read returns slope value × 1000. | 1 (2 bytes) | Write / Read |
| 44113 (0x1010) | Temperature correction | In solution, write the actual temperature value ×10. Read returns the temperature calibration offset ×10. | 1 (2 bytes) | Write / Read |
| 44129 (0x1020) | Salinity compensation | Read/write value is salinity (PSU) ×10 used for compensation. Default = 0 (no compensation). Range: 0–500 (0–50.0 PSU). | 1 (2 bytes) | Write / Read |
| 48195 (0x2002) | Sensor address | Default value is 5. Range: 1–255. | 1 (2 bytes) | Write / Read |
| 48196 (0x2003) | Baud rate | Default: 9600. 0 → 9600 1 → 19200 | 1 (2 bytes) | Write / Read |
| 48225 (0x2020) | Reset sensor | Restores calibration values to default. Write value 0. Sensor must be recalibrated after reset. | 1 (2 bytes) | Write |
7.4 Command example
a) Measurement command:
Function: Get the dissolved oxygen value and temperature measured by the sensor; the unit of dissolved oxygen is mg/L, and the unit of temperature is ℃.
Request frame: 05 03 00 00 00 04 45 8D
Response frame: 05 03 08 01 02 00 02 00 B0 00 01 DB 0C
Reading example:
| DO value | temperature scale |
|---|---|
| 01 02 00 02 | 00 B0 00 01 |
For example, the DO value 01 02 indicates the hexadecimal DO reading, and 0002 indicates the dissolved oxygen value with 2 decimal places, which is converted to a decimal value of 2.58. The temperature value 00B0 represents the hexadecimal temperature reading, and 0001 indicates the temperature value with 1 decimal place, converted to a decimal value of 17.6.
b.) Calibration instruction：
Zero calibration
Function: set the calibration value of dissolved oxygen zero point of electrode； Request frame：05 06 10 00 00 00 8C 8E
Acknowledgement frame ：05 06 10 00 00 00 8C 8E Slope calibration
Function: set the slope calibration value of dissolved oxygen for the electrode; here the slope value is calibrated in air saturated water。
Request frame：05 06 10 04 00 00 CD 4F
Response frame: 05 06 10 04 00 00 CD 4F
c) Set the device ID address：
Function: set the MODBUS device address of the electrode;
Change the device address 05 to 01, with the following example Request frame
：05 06 20 02 00 01 E3 8E
Response frame: 05 06 20 02 00 01 E3 8E
d) Salinity compensation command:
Function: Set the salinity compensation of the sensor;
Measure the water body with a salinity of 35.0 PSU and add salinity compensation.
The example is as follows:
Request frame: 05 06 10 20 01 5E 0D 2C
Response frame: 05 06 10 20 01 5E 0D 2C
7.5 Error response
If the sensor does not execute the upper‑computer command correctly, the following format of information is returned:
| Definition | Address | FC | CODE | CRC check |
| data | ADDR | COM+80H | xx | CRC 16 |
| Number of bytes | 1 | 1 | 1 | 2 |
a) CODE：
01 – Functional code error
03 – Data error
b) COM：Received function code
8. Applicable Accessories
| Name | Requirements | |
9. Similar Products
| Name | Requirements | |
10. Applicable certifications and standards
EMC Directive 2014/30/EU.
- EN IEC 61326-1: 2021
- EN 55011: 2016+A2: 2021
- EN IEC 61000-3-2: 2019+A1: 2021
- EN 61000-3-3: 2013+A2: 2021