Fiber Optic Turbidity Probes

Spectrophotometers and photometers can provide alarms in the event of filter breakthrough or pump cavitation, where the clear liquid work solution becomes cloudy. This is critical because a cloudy solution will likely impair any chemical measurement. In a spectrophotometer, this results in a rise in the spectral baseline. In a photometer, the signal at the reference wavelength will decrease. These can be continuously monitored and alarmed.

However, there are times when a more quantitative measurement of turbidity is required. For this reason, Guided Wave provides an insertion probe and flow cell designed to measure light scattered 90º from the transmitted beam of light. This type of light scattering provides quantitative turbidity information in units of NTU (nephelometric turbidity unit).

The tip of our 1" diameter insertion probe is shown above (left). It is a modification of our insertion transflectance probe. The transmitted beam crosses the "gap" and is internally reflected back through the probe to the analyzer. However, we additionally include a third optic in this turbidity probe in the flat area at the back of the "gap". This picks up light scattered 90º from the transmitted beam.

A similar modification has been engineered into our multi-purpose flow cell show above (right), wherein a third optic (left side of probe) detects light scattered 90º from the transmitted beam.

A typical installation for the turbidity insertion probe is shown below, including a ball valve and a "union cross" where the probe can be positioned and calibrated with a minimum of a calibration standard. This is an advantage over process turbidimeters using a welded-spool piece that becomes part of the main process pipe.

The turbidity flow cell is often used on bypass lines at petroleum pipelines to measure color and haze (turbidity due to water saturation). A typical installation is shown below, where the third optic for turbidity is pointing back toward the shed (flexible conduit pointing back).

This picture shows the addition of a Saybolt color calibration standard into the probe for validation.

The Optical Solutions' brand Clearview and ChemView photomters are designed to accept the 3 fibers needed by these probes (light source, transmitted light, scattered light).

Specifications

Optical Path	20 mm
Materials	316 SS, Kalrez^© o-rings, sapphire windows
Turbidity Range	0-900 NTU
Maximum Temperature	150 150º
Maximum Pressure	500 p.s.i
Insertion Probe Dimensions	1" diameter; 18" long
Flow Cell Dimensions	Same as 20 mm multi-purpose flow cell
Fiber optic connections	SMA905
Fiber Cables for Flow Cell	3 separate cables required
Fiber Cable for Insertion Probe	Tri-furcated fiber bundle with one cable separating into 3 at each end within the probe and analyzer