Turbidity Sensors

A turbidity sensor works by measuring the optical clarity of a liquid. The instrument emits a light beam into the process medium, where suspended particles or colloidal matter either scatter or obstruct the light's transmittance. The sensor then measures the light based on two primary principles:

• Forward scattered light/absorption: This technology is designed for low to medium turbidity levels and is commonly used for phase separation.
• Backscattered light: Used for high particle concentrations (up to 250 g/L), this technology measures the light that is reflected back to the sensor.

Turbidity is measured using a system of integrated equipment designed for continuous, in-line measurement:

• In-line Turbidity Sensors: These are the primary analytical instruments, such as the InPro 8000 series or InPro 86x0ie.
• Transmitters: A transmitter, such as the M800, is an all-in-one device that powers the sensor, processes measurements, and enables on-site monitoring and control, including calibration, through an intuitive touchscreen interface.
• Sensor Housings: Various housings secure the sensor into the process. These include stationary housings, retractable housings for removal during active processes, or immersion housings for basins and tanks.

Turbidity sensors should be installed in a vertical pipe with an upward flow to ensure the pipe remains full and free of air bubbles, which can cause erroneous readings.

If horizontal installation is necessary, position the sensor at the 3 or 9 o'clock position to avoid air pockets or settling sediment. Use of a Varinline(R) housing enables seamless integration into existing systems without requiring major piping modifications or system downtime. This allows for quick mounting and connection, significantly reducing installation time and complexity.

Before operation, perform a two-point calibration. Once calibrated and integrated into your monitoring system, the sensor will provide real-time, continuous data. Recalibrate the sensor as required by your specific quality assurance plan to compensate for potential sensor drift.

Turbidity sensors are designed for in-line installation, allowing for continuous, real-time measurement of particle concentrations directly within the process flow. The precise installation point depends on the specific industry and the goals of the measurement:

• Brewing: Sensors are placed in the lauter tun and whirlpool to monitor hot wort clarity, as well as in filtration, blending, and filling lines to ensure product consistency. They are also installed before the filler line to manage beer/water phase separation, which helps reduce product loss.
• Pharmaceuticals and Chemicals: Sensors are typically installed in fermentation vessels to monitor biomass growth or in vessels used for crystallization and purification to track crystal formation and purity levels.
• Industrial Wastewater: Sensors are often located at raw water intake points to monitor incoming water quality or within various treatment stages to ensure effluent meets environmental discharge regulations.

Fouling can affect turbidity sensor accuracy by obstructing light transmittance or reflection, which interferes with the sensor's ability to precisely measure liquid clarity.

To prevent these inaccuracies, METTLER TOLEDO optical fiber turbidity sensors feature an unbroken surface structure design to reduce the occurrence of sensor fouling during measurement.

The primary difference between low-range and high-range sensors lies in the optical technology used and the particle concentrations they measure:

• Low to Medium Range Sensors: These sensors use forward-scattered light or absorption technology. They are optimized for high sensitivity in clearer liquids, such as beer filtration or phase separation, and many models can simultaneously measure color.
• High Range Sensors: These sensors use backscattered light technology to handle dense samples with up to 250 g/L  suspended solids. They provide a wide, linear measuring range (up to 4,000 FTU) and feature a uniform surface structure that resists fouling in processes like biomass/cell growth or crystallization.

The difference between TDS and turbidity is the physical state of the solids they measure:

• TDS (Total Dissolved Solids): Measures substances that have completely dissolved into the liquid at a molecular or ionic level (such as salt, sugar, or minerals). These are invisible to the naked eye, meaning a liquid can have high TDS and still be perfectly clear.
• Turbidity: Measures the concentration of suspended particles that have not dissolved (such as silt, algae, or organic matter). These particles scatter light, causing the liquid to appear cloudy or hazy.

In the brewing industry, turbidity is an optical measurement of beer clarity. Turbidity is caused by suspended particles or colloidal matter (such as proteins, yeast, and glucanes) that scatter or obstruct light. Using specific optical angles, sensors (InPro 8630ie) can detect both small-particle haze (90° angle) and filter breakthrough (25° angle) to ensure product consistency.

Monitoring is critical at several stages:

• Hot Brew House: Sensors monitor clarity in the lauter tun and whirlpool.
• Filtration and Filling: Continuous in-line measurement ensures quality during post-filtration and final packaging.
• Phase Separation: In-line systems identify the interface between beer and water, significantly reducing product waste and increasing yield.
• Color Measurement: Advanced sensors use dual light sources to measure turbidity and yellowness (color) simultaneously, ensuring the beer meets its specific visual profile.