Sequoia Scientific


Sediment Monitor for Protecting Hydro Turbines from Abrasive Damage

Abrasion of turbines by sediments causes losses in millions of dollars. The loss can be avoided by installing this instrument. When dangerous conditions arise, it generates alarms so plant operators may shut power production. 

This instrument is based on laser diffraction technology (LD). This technology separates measured sediment concentration into harmless fines and harmful coarse grains. Coarse grain concentration data can be used to set off alarms when abrasive conditions arise. LD technology avoids false alarms and loss of generation revenue. Click here for how it all works.

View the Installation Requirements, Responsibilities, Warranty document.


The LISST-Infinite instrument is designed to generate ALARMS for plant operators to enable them to take action during dangerous conditions. Guidelines for when to shut down a plant have only recently begun to evolve. For example, see the first such guideline suggested by our President at an IAHR hydro abrasion symposium in Grenoble, France, July 2016. A very similar idea was presented at the same session by Swiss scientists.

Damage to turbines only occurs due to large and hard grains, travelling at high velocity. In short, grain size is important. Sensors such as turbidity type do not distinguish harmless fine grains from harmful large grains. Thus, they can lead to false alarms. False alarms can result in loss of power generation revenue.

Sequoia’s laser diffraction technology built into the LISST-Infinite instrument is the only technology that reports total suspended sediment concentration into 3 size classes (fine, medium, and coarse). A continuously updated stripchart displays time-series of concentrations in these size classes, and the total. Sampling interval is set by the operator. Sequoia provides the software and (optional) a computer with pre-installed software.

Sequoia provides the complete solution – from instrument delivery and installation to data delivery at the Control Room. Operators choose and set concentration levels for audible alarms. The alarms have some ability to forecast dangerous conditions, and similarly, to forecast ‘all clear’ conditions.

Some of the requirements for installation, e.g. civil works are the responsibility of the customer. For more details of customer responsibilities, please click here. A Features summary is provided below:

Concentration Limits: ~10 ppm to ~ 30,000 ppm. [actual limits may be higher for larger grains; ask us.]

Advance Warning: The software anticipates onset of dangerous sediment levels, and issues warning. Also, vice versa for clearing.

Sample Interval: 15 min. and longer.

Power Supply:    110VAC or 220VAC.

Communication: RS-232, fiber-optic cable for long lengths from instrument installation to data display station.

Software: Powerful Windows software is provided for viewing strip-charts of concentrations at multiple stations on a common server or by placing data on cloud.

Alarm Settings: User selected. Alarms can be based on either of the 3 size classes, although only the largest class is recommended, 75-381 microns. Alarm levels are user selected. Algorithm includes false-alarm prevention logic.

Data Archive: Data are archived for report preparation by the customer.

Water requirement: The instrument needs a clean-filtered water supply for regular ‘zeroing’ of output. Ask us about our water filtration and storage tank, available as a complete system.


For further information, write us at


Updated 10 Jan. 2017


Data are transmitted and displayed in the control room. Alarm levels can be defined by plant operators. These levels can be based on either total sediment concentration, or concentration in a particular size range (e.g. the size bins covering 75-500 microns). When concentration of sediments reaching the turbine crosses this threshold, an visible and audible alarm is sounded on the monitor screen. At this point, plant operators may choose to initiate action such as a plant shutdown. Power production can resume when danger passes, for which an ‘all clear’ is sounded.

For both conditions, advance warnings are displayed, (e.g. “Sediment Concentration will reach danger level in 3 hours”, or that it will “…clear in 2 hours..”). The particle size distribution (PSD) can be viewed by clicking on a data point on the strip chart. The PSD display shows concentration (units: mg/liter) of grains in 32 size classes. Data are archived on PC or network for later viewing on-site or off-site or for report preparation.

Damage to turbines occurs by the scouring action of large grains. Thus, the data requirement is for concentration of the coarser grains. Although no set threshold exists, only grains larger than 200 microns are considered harzardous by some plant operators. In research in progress, it appears that the abrasion potential depends on grain size, velocity, and hardness. The LISST-Infinite provides real-time data on concentration of sediment in 32 size classes, from 2 to 400 microns (for other requirements, please contact us). Operator defined danger thresholds can be built in via the software.

  • Auto-dilution system for continued operation in high-concentration environments (concentration in excess of 2,000 mg/l).
  • The auto-dilution system consists of a dilution chamber, a mixer pump and a pinch valve system. The pinch valves enable the LISST-Infinite to capture a small sample of turbid water, transfer it to the dilution chamber where it is diluted 10:1, and then recirculated using the mixer pump through the optics system for a second measurement.
  • With the dilution, the upper concentration range is extended to about 30,000 mg/l (ppm by mass).


LISST-Pump for LISST-StreamSide and LISST-Infinite