Sequoia Scientific


  • Stop sediment sampling, measure!
  • 100% calibration-free
  • Measure total concentration and mean particle size at 1Hz

LISST-25X marks a generational advance in the measurement of suspended sediment concentrations and size. 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 2,000 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.

Please note:  The LISST-25X is no longer being manufactured.  Contact Sequoia for more information about it potential availability in the future.


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.

  • Small angle forward-scattering laser diffraction technology (also called laser diffraction)
  • Self-contained with internal batteries and built-in programmable datalogger, holds up to 27,000 samples
  • Solid state red diode laser @ 670 nm
  • RS232C serial data interface
  • Programmable data collection
  • Integrated BioBlock connection
  • Internal battery (4 x 9V, alkaline or lithium)
  • External power option 6-12VDC @ max 250mA


Specifications (subject to change without notice)
Parameters Measured
  • Sauter mean diameter [µm] (what is the Sauter mean diameter?)
  • Total volume concentration [µl l-1]
  • Sauter mean diameter in 63-500 µm sub-range [µm]
  • Total volume concentration in 63-500 µm sub-range [µl l-1]
  • Optical transmission [%]
  • Depth [m]
  • Date and Time
Size ranges
  • 2.5-500 µm for the full range
  • 63-500 µm for the sub-range
Concentration ranges
  • Concentration range 2-1,600 mg/l. NOTE: Actual range is dependent on the grain-size and size distribution of the suspended particles. See table below for details and examples of concentration ranges based on measurements using ISO particle standards and easily obtained reference materials. SMD: Sauter Mean Diameter.
  • Resolution < 1 mg/l

SSC [mg/l] @ 98% optical transmission

SSC [mg/l] @ 30% optical transmission 





ISO Fine
(ISO 12103-1,A2)







ISO Coarse
(ISO 12103-1,A4)







Whitehouse 20-30 µm glass beads







Sieved sand 75-125 µm







Accuracy and Resolution

Accuracy Resolution
Concentration 2% for fixed shape factor 0.025% of full-scale
Size 20% 1 µm
Transmission 0.1% 0.1%

Optical Path Lenghts and Maximum Concentration

Path Length
A4 Test Dust
200 µm sand
2.5 cm (standard) 500 mg l-1 25,000 mg l-1
1.0 cm (optional) 1250 mg l-1 67,500 mg l-1
0.5 cm (optional) 2500 mg l-1 125,000 mg l-1

Weight and Dimensions

  • Dimensions: 10.0 cm diameter x 61.7 cm long (3.95″ x 24.3″)
  • Weight: 4.5 kg (10 lbs) in air; 1.4 kg (3 lbs) in water
  • 300 m depth rating
  • Serial interface: RS232C @ 9600 baud
  • Internal battery pack: 4 × 9V batteries, alkaline or lithium
  • External power input (optional): 6-12VDC @ max 250 mA
  • Power drain: 147 mA/3.5 mA/140 µA (measuring/quiescent/sleeping)


BIOBLOCK – a mechanical anti-fouling accessory for the LISST-100X and LISST-25X. Sliding copper shutters in front of the windows limit fouling to a minimum. BIOBLOCK is controlled by the LISST-100X or LISST-25X to open before a measurement takes place and close again after the measurement.
Replacement Large volume test chamber
Custom Optical paths