Solving the problems of signal saturation and poor repeatability in high-concentration suspended solids measurement

The YEX-S2-MLSS-A Online Sludge Concentration Sensor adopts the backscattered light measurement principle, combined with fiber optic optical structure and infrared LED light source, effectively suppressing external stray light interference and maintaining stable signal response across the wide 0~20.000g/L range. No frequent calibration required. Pt1000 automatic temperature compensation simplifies on-site operation and maintenance.

• Reliable Measurement: Backscattered technology + fiber optic structure, resistant to ambient light interference, suitable for high-concentration mixed liquor

• Easy Integration: RS-485 Modbus RTU + 4-20mA dual output, compatible with various PLC and data acquisition systems

• Harsh Environment Adaptation: IP68 (20m water depth), ABS + 316L composite housing, 0~50℃ operating temperature, corrosion resistant

YEX-S2-MLSS-A Online Sludge Concentration Sensor Product Overview

Yexsensor YEX-S2-MLSS-A is an integrated online sludge concentration (MLSS) sensor specially designed for continuous monitoring of suspended solids concentration in the activated sludge process of wastewater treatment. The product uses backscattered light technology — when an infrared beam enters the water sample, the intensity of backscattered light produced by suspended particles is positively correlated with sludge concentration. After internal linearization processing, the concentration value is directly output.

Compared with traditional MLSS measurement methods, this product focuses on solving three major engineering pain points: signal saturation in high concentration areas, data drift caused by optical window contamination, and sensor corrosion in mixed liquor. The fiber optic structure physically isolates and optimizes the light source and receiving optical path. Even when installed in strong bubble interference environments such as aeration tanks, it can still maintain stable readings. It has undergone 72-hour aging and stability testing before shipment to ensure long-term reliable operation on site.

Core Advantages and Technical Features

1. Backscattered Principle + Fiber Optic Structure, Strong Anti-Interference

Adopts backscattered light measurement principle optimized for high-concentration suspended solids. The scattering light receiving angle is specially designed to provide good linear response in the 0~20.000g/L range. Combined with fiber optic optical structure, it effectively isolates crosstalk between light source and receiver while reducing the influence of external ambient light (such as sunlight and lighting) on measurement results. No additional light shield is needed even when installed on the surface of aeration tanks or open channels.

2. Wide Range and High Resolution

• Range: 0～20.000g/L, covering most working conditions from low-concentration return sludge to high-concentration mixed liquor

• Resolution: 0.001g/L (1mg/L), clearly reflecting subtle concentration changes during process adjustments

• Accuracy: ±5% (depending on sludge homogeneity), meeting conventional requirements of the wastewater treatment industry for online MLSS monitoring

3. Dual Output Interfaces, Easy Integration

• RS-485 (Modbus RTU) is standard configuration, can be directly connected to distributed IO, data collectors, and touch screens

• 4-20mA analog output is provided simultaneously as standard (no extra option needed)

• Modbus registers allow reading of sludge concentration value and temperature value, and support writing calibration coefficients

4. Pt1000 Automatic Temperature Compensation

Built-in Pt1000 temperature sensor automatically corrects the influence of water temperature changes on scattered light intensity and electronic components. Operating temperature 0～50℃, accuracy ±0.3℃. Accurate temperature compensation data can be obtained without additional temperature probes.

5. Corrosion-Resistant Composite Housing

The main housing body uses ABS (chemical corrosion resistant and lightweight), while the measuring end face and fastening parts use 316L stainless steel (wear-resistant and resistant to biological attachment). It balances cost and corrosion resistance of key parts, suitable for municipal sewage, industrial wastewater and other weakly acidic/alkaline environments.

YEX-S2-MLSS-A Online Sludge Concentration Sensor Technical Specifications

YEX-S2-MLSS-A Online Sludge Concentration Sensor Typical Application Scenarios

• Wastewater Treatment Plant Aeration Tanks: Continuous monitoring of mixed liquor suspended solids (MLSS) to guide sludge discharge and return ratio adjustment, avoiding sludge bulking or over-oxidation.

• Secondary Sedimentation Tanks and Return Sludge Channels: Monitor return sludge concentration, calculate sludge return ratio and sludge age (SRT), and optimize biological system load distribution.

• Sludge Thickening Tanks and Dewatering Rooms: Monitor bottom sludge concentration in thickening tanks and inlet sludge concentration to dewatering machines to evaluate dewatering efficiency.

• Industrial Wastewater Treatment: Suspended solids monitoring in biochemical sections of chemical, food, papermaking, printing & dyeing and other industries to warn of abnormal shocks.

• River Dredging and Slurry Monitoring: Real-time feedback of slurry concentration in dredging projects to assist control of dredging pumps and concentration ratio.

• Flocculation Dosing Optimization: Used with coagulation sedimentation processes to dynamically adjust flocculant dosing according to inlet suspended solids concentration.

FAQ

Q1: Can the sensor be used in oily water or water with a large number of bubbles?

Backscattered signals will be interfered with by oil films and bubbles. It is recommended to add pretreatment (such as air flotation for oil removal) in oily conditions. In aeration tanks with severe bubbles, adjust the installation position to avoid strong aeration areas or add a stilling zone.

Q2: How does the accuracy of the online sensor compare with laboratory gravimetric method?

The ±5% accuracy is obtained based on comparison with homogeneous sludge. Due to factors such as sludge floc size, bubbles, and flow velocity in actual field applications, it is recommended to perform comparative sampling calibration every 1~2 weeks to eliminate systematic deviation.

Q3: Is the 4-20mA output standard? Does it require extra option?

The 4-20mA output of YEX-S2-MLSS-A is a standard feature and is provided simultaneously with RS-485. No additional payment is required. The output range is 4mA corresponding to 0g/L and 20mA corresponding to 20.000g/L.

Q4: Is there a cleaning brush or automatic cleaning device?

This model is not equipped with an automatic cleaning brush. It mainly relies on the flow field scouring of the optical window itself. If the sludge has strong adhesion on site, it is recommended to use external compressed air or high-pressure water for regular flushing, or manual wiping (frequency depends on attachment speed).

Q5: How deep can the sensor be submerged? How to handle cable extension?

IP68 protection rating, maximum submersion depth 20 meters. Standard cable is 5 meters and can be customized longer (recommended not to exceed 50 meters). Extension cables should use shielded twisted pair wire, and wiring points must be waterproof sealed.

Q6: How to prepare standard solution for calibration?

Zero-point calibration can use deionized water or supernatant (field water sample filtered through 0.45μm membrane). Slope calibration is recommended to use known concentration samples prepared from concentrated field sludge (calibrated by laboratory gravimetric method). Commercial formazin turbidity standard solutions can also be purchased, but note that the conversion relationship may not be completely consistent with MLSS.

Q7: Can concentrations greater than 20g/L be measured?

Signals tend to saturate beyond the range, and accuracy cannot be guaranteed. For higher concentrations (such as the bottom of sludge storage tanks), dilution measurement is recommended, or other range models should be selected.

Q8: What are the distance requirements from side walls and bottom during installation?

It is recommended to maintain more than 5cm from side walls and more than 10cm from the bottom. Avoid close proximity to walls forming stagnant zones or sediment interference. When installed in pipelines, ensure the sensor is in a uniform flow velocity section (5 times pipe diameter upstream and 3 times downstream of straight pipe section).

Summary

The Yexsensor YEX-S2-MLSS-A Online Sludge Concentration Sensor provides a simple, stable, and easy-to-integrate measurement solution for municipal wastewater treatment, industrial wastewater treatment, and slurry monitoring. Backscattered technology + fiber optic structure overcomes common problems of signal saturation and external light interference in high-concentration suspended solids measurement. Infrared LED light source and Pt1000 temperature compensation ensure long-term repeatability. Dual output interfaces (Modbus RTU + 4-20mA) allow smooth integration into new or renovation projects.

Although it does not have an automatic cleaning function, the ABS+316L corrosion-resistant housing and low power consumption design (0.2W) make it particularly suitable for solar-powered remote sites. The main on-site variables users need to pay attention to are sludge homogeneity and window contamination. Reliable data meeting process control requirements can be obtained through reasonable installation positions and regular comparative calibration.