1. Product Introduction

This product is a device for measuring the dissolved oxygen concentration of a solution. It uses the principle of fluorescence measurement, does not consume oxygen, and does not require electrolyte. Built in temperature transmitter with automatic temperature compensation function. The calibration function provides a simpler and more convenient way of calibration. It can be widely applied in industries such as water treatment, aquaculture, and environmental monitoring.

1.1 Functional Features

• The measurement range of dissolved oxygen is 0-20mg/L (0-200% saturation).
• RS485 communication interface: MODBUS RTU communication protocol can be easily connected to a computer for monitoring and communication.
• The ModBus communication address can be set and the baud rate can be modified.
• The equipment is powered by a wide voltage supply, ranging from 10 to 30V DC.
• Adopting the principle of fluorescence measurement, it does not consume oxygen and does not require electrolyte.

1.2 Equipment Technical Parameters

power supply	DC 10~30V
power consumption	0.2W
communication interface	RS485； Standard MODBUS-RTU protocol; Communication baud rate: default 4800 (2400, 4800, 9600 can be set)
Measuring principle	fluorescence method
measurement range	0~20mg/L (0~200% saturation)
measurement error	±3%FS； ±0.5℃（25℃）
resolution	0.01mg/L； 0.1%； 0.1℃
response time	≤60sec
Equipment working conditions	0~40℃
Fluorescent film lifespan	Normal use for 1 year
Storage conditions	-10~60℃
waterproof rating	IP68
Electrode wire length	Default 5m
Shell material	Corrosion resistant plastic, stainless steel

1.3 Product selection

S-				Company Code Name
	LDO-			Fluorescence dissolved oxygen transmitter
		N01-		RS485 (Modbus RTU protocol)
			1	First generation shell

1.4 Product List

◆ One fluorescence dissolved oxygen transmitter
◆ 5m cable
◆ Certificate of conformity, warranty card, etc

2.3 Calibration Instructions

2.3.1 Calibration Preparation

Preparation of zero oxygen standard solution: Prepare a beaker, take 200mL of distilled water and pour it into the beaker, then add anhydrous sodium sulfite while stirring until the anhydrous sodium sulfite is saturated. At this point, the standard solution is considered close to zero oxygen.
100% oxygen environment preparation: Prepare one beaker, pour 200mL of pure water (or distilled water) into the beaker, add an air pump, and fully expose the solution to air (at least 30 minutes). Note: If the on-site conditions do not allow or the usage requirements are not high, the sensor can also be directly placed in the air (calibration accuracy may deviate).

2.3.2 Calibration

Find the Dissolved Oxygen tab in the Water Quality Sensor tab in the configuration tool.

Place the sensor in a 100% oxygen environment, wait for the dissolved oxygen value to stabilize, and click the full-scale calibration button to complete the calibration of 100% oxygen saturation.
Place the sensor into the zero oxygen standard solution, gently stir to accelerate the response, and let it stand. After the dissolved oxygen value stabilizes, click the zero oxygen calibration button to complete the zero oxygen calibration.

2.3 ModBus Communication and Register Detailed Explanation

2.3.1 Basic parameters of equipment communication

code	8-bit binary
data bit	8 digits
parity bit	none
stop bit	1 person
Error verification	CRC (Redundant Cyclic Code)
Baud rate	2400bit/s, 4800bit/s, 9600 bit/s can be set, and the factory default is 4800bit/s

2.3.2 Definition of Data Frame Format

Adopting Modbus RTU communication protocol, the format is as follows:
The time for the initial structure to be ≥ 4 bytes
Address code=1 byte
Function code=1 byte
Data area=N bytes
Error check=16 bit CRC code
Time to end structure ≥ 4 bytes
Address code: It is the address of the transmitter and is unique in the communication network (factory default 0x01).
Function code: The instruction function indication issued by the host.
Data area: The data area contains specific communication data, please note that the high byte of 16 bits data comes first! CRC code: a two byte checksum.

2.3.3 Register Address

register address	operation	Instructions
0000H、0001H	03	Dissolved oxygen saturation (%; floating point high end)
0002H、0003H	03	Dissolved oxygen concentration (mg/L; floating point high end)
0004H、0005H	03	Temperature (℃; floating point big end)
1010H	06	Calibration (write 0x0001 calibration zero point, Write 0x0002 to calibrate 100% saturation point)
1020H	03/06	Salinity (‰; default 0)
1022H	03/06	Atmospheric pressure (kPa; default 101.33, actual value increased by 100 times)

2.3.4 Communication Protocol Examples and Explanations

Example 1: Read the current dissolved oxygen saturation (%), dissolved oxygen concentration (mg/L), and temperature of the device with address 01
Issued frame:

address code	function code	register address	Register content	Low-order check digit	high-order check digit
0x01	0x03	0x00 0x00	0x00 0x06	0xc5	0xc8

Response frame:

address code	function code	valid byte count	Register content	Low-order check digit	high-order check digit
0x01	0x03	0x0c	0x3f 0x6a 0xeb 0x52 0x40 0xe2 0x48 0xb0 0x41 0xe5 0x85 0xc5	0xa7	0x49

The floating-point number 3f 6a eb 52 is 0.917653, indicating a dissolved oxygen saturation of 91.8%
Floating point number big end 40 e2 48 b0 is 7.071373 Dissolved oxygen concentration is 7.07mg/L
The floating-point number 41 e5 85 c5 is 28.690317, indicating a temperature of 28.7 ℃

Example 2: Writing atmospheric pressure
Issue frame: Write atmospheric pressure 101.35kPa to the device with address code 1
Write 10135 to the 0x1022 register and convert it to hexadecimal 2797

address code	function code	register address	Register content	Low-order check digit	high-order check digit
0x01	0x06	0x10 0x22	0x27 0x97	0x77	0x5e

Response frame: (according to the MODBUS standard, the response is a mirror message of the issued frame)

address code	function code	register address	Register content	Low-order check digit	high-order check digit
0x01	0x06	0x10 0x22	0x27 0x97	0x77	0x5e

Example 3: Zero point calibration
After the sensor stabilizes in anaerobic water, write 0x0001 to the 1010H register

address code	function code	register address	Register content	Low-order check digit	high-order check digit
0x01	0x06	0x10 0x10	0x00 0x01	0x4d	0x0f

Response frame: (according to the MODBUS standard, the response is a mirror message of the issued frame)

address code	function code	register address	Register content	Low-order check digit	high-order check digit
0x01	0x06	0x10 0x10	0x00 0x01	0x4d	0x0f

3. Precautions and Maintenance

When the equipment shows obvious malfunctions, please do not open it for self repair and contact us as soon as possible!
The fluorescent film on the front end of the device should avoid collision or scratching, as any damage will result in a decrease in measurement accuracy or even render it unusable.
◆ Avoid using in organic solvents and avoid cleaning the fluorescent cap with organic solvents.
During equipment installation, try to avoid cables being too tight or subjected to stress.
Equipment cleaning:
For the external surface of the equipment; You can clean it with tap water and wipe it with a damp soft cloth. For stubborn dirt, you can add some household detergent to tap water to clean it;
For the outer surface of the fluorescent cap; Rinse the dirt on the sensor light window with clean water; If wiping is necessary, gently wipe with a soft cloth and do not rub hard to prevent damage to the fluorescent film, which may result in inaccurate measurement settings and inability to measure.
If dust or water vapor enters the fluorescent cap: unscrew the fluorescent cap and rinse the inner surface of the fluorescent cap and the optical glass window of the device with tap water. If there is oily dirt, it can be cleaned with tap water mixed with household detergent. Then rinse the detergent clean, dry all cleaned surfaces with a lint free soft cloth, and place it in a dry place to completely evaporate the moisture.