Salinity Conductivity TDS Probe AT-SB-PROBE-S-P-C1

Datasheet

1. Introduction

"The SENSBLUE RS-485 Salinity Conductivity TDS Probe (AT-SB-PROBE-S-P-C1) introduces a new generation of four-electrode conductivity sensor, adopts international leading four-electrode technology, RS485 digital interface, supports MODBUS protocol, and environmentally friendly design. Compared with the traditional two-electrode conductivity sensor, it has higher accuracy, wider measurement range and excellent stability. The four-electrode conductivity sensor also has a unique advantage in quantity: one is to completely solve the polarization problem in high conductivity test; the other is to solve the problem of inaccurate reading caused by electrode contamination.

2. Features

• Simultaneous output of conductivity, salinity, TDS, and temperature parameters;
• Corrosion-resistant housing with IP68 waterproof rating for long-term underwater operation;
• Built-in temperature sensor with automatic temperature compensation;
• Factory-calibrated with built-in calibration parameters for immediate installation and use

3. Technical Specifications

Model	KWS-300A	KWS-300B
Conductivity Range	0-200mS/cm (0-2mS/cm, 2-20mS/cm, 20-200mS/cm)
Accuracy	±1% or 0.01mS/cm (which is bigger)
Salinity Range	0 -175 ppt
Accuracy	±1 ppt
TDS Range	0 – 128000 mg/L
Response Time	＜10s
Ip Grade	IP68
Max. Pressure	6 bar
Sheath Material	Titanium
Operating Temperature	0~50℃ (no freezing)
Output	RS485, Modbus
Power Consumption	0.2W (Recommended power supply: DC 9–24V, >500mA)
Sensor Dimension	φ22mm*175.5mm	φ22mm*165.8mm
Assembly	NPT3/4 male thread	Connect with multi-parameter host
Cable Length	10 meters (default), customizable	None
Calibration	support one point or two-points calibration
Casing Material	Titanium + PEEK

Note:

The above technical specifications are based on laboratory standard solution conditions;

Sensor lifespan and calibration/maintenance frequency depend on actual site conditions.

4. Dimensions and Wiring

Pinouts
1 - Pin 12-24V DC	4 - RS485 B-
2 - GND	5 – NA
3 - RS485 A+	6 - NA
7 - NA

5. Installation

(1)Wiring and Power Tips

a.) Do not use the sensor cable to suspend the sensor. It is recommended to install a cable protection sleeve to ensure reliable power supply and waterproofing.

b.) Ensure that the connector between the sensor and the cable (or main unit) is properly aligned and securely tightened. Take care not to damage the sealing ring to maintain good waterproof performance.

c.) Before powering on, make sure the wiring sequence and supply voltage are correct.

(2) Sensor Installation

a.) It is recommended to install the sensor vertically with the electrodes facing downward. Avoid locations with excessive air bubbles.

b.) The sensor must be securely fixed to prevent impact or movement caused by water flow or other external forces.

c.) The sensor should be installed with sufficient clearance: the distance from the bottom should be ≥40 mm, and the distance from the side wall should be ≥20 mm (see reference diagram below). For pressurized pipeline installations, ensure the electrodes are used within their pressure tolerance range.

6. Maintenance Schedule and Method

6.1 Maintenance Schedule

Unlike traditional two-electrode conductivity sensors, the four-electrode probe offers strong antipolarisation capability and requires minimal maintenance. However, the electrodes must be kept clean. If solid buildup occurs on the optical window, soak the sensor in a suitable detergent, solvent, or diluted acid solution to dissolve and remove the deposits. You may also use a soft cotton swab to gently remove debris from the titanium electrodes, but do not scrub the electrode surface forcefully. Do not touch the surface of graphite or platinum-coated electrodes and always rinse the sensor thoroughly with deionized water after cleaning.

Maintenance Task	Recommended Maintenance Frequency
Clean the sensor	Recommended every 3 - 4 weeks. (shorter if the water body is dirty);
Calibrate the sensor	Recommended every 3 - 4 weeks. (depending on the working conditions)

6.2 Maintenance Methods

a.) Sensor Surface Cleaning: The sensor is made of chemically resistant materials and can be cleaned using most diluted cleaning agents, acidic substances, or other suitable solvents for removing scaling or coating. Warning: If hazardous cleaning materials are used, appropriate safety precautions must be taken. For coatings between the metal electrodes, a cotton swab can be used to gently wipe the surface. However, do not use brushes and do not touch the electrodes directly, as this may smooth the intentionally roughened surface and result in inaccurate low conductivity readings.

b.) Sensor Storage: After cleaning, the conductivity sensor can be placed in a flow cell and kept moist for several days. However, if the equipment will be out of service for an extended period, it is recommended to remove the sensor and let it dry to prevent microbial growth.

c.) Cable Inspection: During normal operation, the cable should not be under tension. Excessive strain may cause internal wire breakage, resulting in sensor malfunction.

d.) Casing Inspection: Check whether the sensor housing has been damaged due to corrosion or other causes.

7. Calibration

7.1 Standard solution configuration

1. Conductivity standard solution configuration:

Potassium Chloride: Analytical reagent grade; dry at 220–240 °C for 2 hours, then cool to room temperature in a desiccator.

Water: Use laboratory-grade Type I water, or distilled/deionized water with a conductivity not exceeding 0.2 × 10⁻⁶ S/cm at 25 °C.

Solution code	Approximate concentration mol/L	Conductivity values S/cm
		15℃	18℃	20℃	25℃	35℃
A	1	0.09212	0.09780	0.10170	0.11131	0.13110
B	0,1	0.010455	0.011163	0.011644	0.012852	0.015353
C	0,01	0.0011414	0.0012200	0.0012737	0.0014083	0.0016876
D	0,001	0.0001185	0.0001267	0.0001322	0.0001465	0.0001765

Solution number	Approximate molar concentration Mol/L	Potassium chloride required to prepare 1 L of solution g
A	1	74.2457
B	0,1	7.4365
C	0,01	0.7440
D	0,001	Dilute 100 mL of Solution C to a final volume of 1,000 mL

8. Modbus Protocol

The RS485 communication protocol uses MODBUS communication protocol, and the sensors are used as slaves.

Data byte format:

Baud rate	9600
Starting position	1
Data bits	8
Stop bit	1
Check digit	N

Read and write data (standard MODBUS protocol).

The default address is 0x01, the address can be modified by register

Reading data

Host call (hexadecimal)

01 03 00 00 00 01 84 0A

Code	Function Definition	Remarks
01	Device Address
03	Function Code
00 00	Start Address	See register table for details
00 01	Number of registers	Length of registers (2 bytes for 1 register)
84 0A	CRC checksum, front low and back high

Slave answer (hexadecimal)

01 03 02 00 xx xx xx xx

Code	Function Definition	Remarks
01	Device Address
03	Function Code
02	Number of bytes read
XX XX	Data (front low and back high DCBA)	See register table for details
XX XX	CRC checksum, front low and back high

Writing data

Host call (hexadecimal)

01 10 1B 00 00 01 02 01 00 0C C1

Code	Function Definition	Remarks
01	Device Address
10	Function Code
1B 00	Register Address	See register table for details
00 01	Number of registers	Number of read registers
02	Number of bytes	Number of read registersx2
01 00	Data (front low and back high DCBA)
0C C1	CRC checksum, front low and back high

Slave answer (hexadecimal)

01 10 1B 00 00 01 07 2D

Code	Function Definition	Remarks
01	Device Address
10	Function Code
1B 00	Register Address	See register table for details
00 01	Returns the number of registers written
7D 2D	CRC checksum (front low and back high)

9. Calculating CRC Checksum

a.) Preset a 16-bit register as hexadecimal FFFF (i.e., all 1s), and call this register the CRC register;

b.) XOR the first 8-bit binary data (the first byte of the communication information frame) with the lower 8 bits of the 16-bit CRC register, and placing the result in the CRC register, leaving the upper eight bits unchanged;

c.) Shift the contents of the CRC register one bit to the right (toward the low bit) to fill the highest bit with a 0, and check the shifted-out bit after the right shift;

d.) If the shifted-out bit is 0: repeat step 3 (shift one bit to the right again); if the shifted-out bit is 1, XOR the CRC register with the polynomial A001 (1010 0000 0000 0001);

e.) Repeat steps 3 and 4 until the right shift is made 8 times, so that the entire 8-bit data is processed;

f.) Repeat steps 2 through 5 for the next byte of the communication information frame;

g.) Exchange the high and low bytes of the 16-bit CRC register obtained after all bytes of this

communication information frame have been calculated according to the above steps.

h.) The final content of the CRC register is CRC code.

Register Table

Register Starting Address	Function Definition	Number of registers	Data format (hexadecimal)
0x3000H	Device Address (Read / Write)	1	2 bytes in total 00~01: Device address The settable range is 1~247 For example, the data obtained is 02 00 (low first, which means the address is 2) Taking address 15 as an example, write 0F 00 (low first) to the corresponding address. When the current device address is unknown, FF can be used as the general device address to query the current device address.
0x2600H	Temperature, Conductivity and Salinity Value Acquisition	8	16 bytes in total 00~03: Temperature value 04~07: Conductivity value 08~11: TDS 12~15: Salinity value Continuously read temperature / conductivity / TDS / salinity value, each is 4 bytes of data. (The low first, DCBA format, this data needs to be converted to floating point number)
0x2000	Temperature Calibration TK/TB (Read/Write)	4	8 bytes in total 00~03: TK 04~07: TB To read TK for example, readout is 4 bytes of data (the low first, DCBA format, this data needs to be converted to floating point number) To write TK for example, TK needs to be converted to 32-bit floating point first and written in according to (DCBA format) Note: TK and TB need to be read and written together.

Register Starting Address	Function Definition	Number of registers	Data format (hexadecimal)
0x1100H	User Calibration K/B (Read / Write)	12	24 bytes in total 00~03：K1 04~07：B1 08~11：K2 12~15：B2 16~19：K3 20~24：B3 User calibration is divided into three sections: 0~2mS/cm corresponds to K1 and B1, default K1=1 B1=0 2~20mS/cm corresponds to K2 and B2, default K2=1 B2=0 20~200mS/cm corresponds to K3 and B3, default K3=1 B3=0 Taking reading K1 as an example, the data read out is 4 bytes (lower bit first, DCBA format, this data needs to be converted into floating point number). Taking writing K1 as an example, k1 needs to be converted into a 32-bit floating point number first, and written in (DCBA format). Note: The writing process requires 24 bytes to be written at the same time
0x1200H	User calibration K1/B1 (read and write)	4	8 bytes in total 00~03: K1 04~07: B1 User calibration corresponds to 0~2mS/cm Take reading K1 as an example, the readout is 4 bytes of data (low bit first, DCBA format, this data needs to be converted to floating point) Take writing K1 as an example, K1 needs to be converted to 32-bit floating point first, and written in (DCBA format) Note: K1 and B1 need to be read and written together
0x1300H	User calibration K2/B2 (read and write)	4	8 bytes in total 00~03: K2 04~07: B2 User calibration corresponds to 2~20mS/cm Take reading K2 as an example, the readout is 4 bytes of data (low bit first, DCBA format, this data needs to be converted to floating point) Take writing K2 as an example, K2 needs to be converted to 32-bit floating point first, and written in (DCBA format) Note: K2 and B2 need to be read and written together
0x1400H	User calibration K3/B3 (read and write)	4	8 bytes in total 00~03: K3 04~07: B3 User calibration corresponds to 20~200mS/cm Take reading K3 as an example, the readout is 4 bytes of data (low bit first, DCBA format, this data needs to be converted to floating point) Take writing K3 as an example, K3 needs to be converted to 32-bit floating point first, and written in (DCBA format) Note: K3 and B3 need to be read and written together

10. Applicable Accessories

	Name	Requirements
PA000000076	SENSBLUE MONARCH Solar Panel 1 Probe
PA000000079	SENSBLUE MONARCH Solar Panel 2 Probes
PA000000080	SENSBLUE MONARCH Solar Panel 1 Probe External Antenna
PA000000074	SENSBLUE MONARCH Solar Panel 2 Probes External Antenna
PA000000081	SENSBLUE MONARCH Opaque Case 1 Probe
PA000000082	SENSBLUE MONARCH Opaque Case 2 Probes
PA000000083	SENSBLUE MONARCH Opaque Case 1 Probe External Antenna
PA000000084	SENSBLUE MONARCH Opaque Case 2 Probes External Antenna
PA000000020	SENSBLUE MONARCH RS485 Probe Splitter Box (1 input -> 2 outputs)

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12. 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