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LISST-25X marks a generational advance in the measurement of suspended sediments. Unlike all prior sediment or turbidity sensors, optical or acoustic, the LISST-25X maintains its calibration over a 200:1 range of particle sizes.  This is the only sensor capable of holding calibration for sediment concentration regardless of particle color or size within this broad a range.  Depending on grain size, the LISST-25X is suitable for operations in an approximate concentration range of 1 to 2000 mg/l.

Essentially, the LISST-25X offers capabilities between those of an OBS, which suffers calibration changes due to changes in grain size or color and the LISST-100X, which provides the detailed size distribution. In short: The LISST-25X overcomes the OBS’s shortcomings, but does not provide the full size distribution of the LISST-100X.

An anti-fouling accessory BioBlock is available for this instrument (see LISST accessories page).  The picture on the left shows the LISST25X with the BioBlock installed.

BioBlock is very strongly recommended for deployments in biologically productive waters.

The instrument is self-contained, with memory and batteries. It is fully programmable to set sample rate. Data can be internally stored or captured in real time.  A depth sensor is included as standard. Windows software for data offload and display is provided.

The idea behind the LISST-25X is to use shaped focal plane detectors. These detectors (see figure) derive their shape from the physics of light scattering. The shape is found such that for any size of particle in the 2.5 to 500 micron range, the instrument reports the correct volume concentration. A different shape is found to yield area concentration.The ratio of volume to area is called the Sauter Mean Diameter. The instrument employs 2 pairs of shaped detectors. One pair measures particles in the 2.5 to 63 micron range, the other in the 63-500 micron range.