From time to time, Sequoia will update the US and other International Standards known to us, that relate to our products. We invite visitors to our website to send us information on relevant standards that need to be included on this page.

ISO-7027  This is a turbidity standard, reporting results in FNU (Formazin Nephelometric Units). It is based on monochromatic light scattering at 90-degrees plus or minus 2.5-degrees. Like the USEPA turbidity standard below, this standard has no relationship to suspended sediment mass or volume. The conversion to suspended sediment concentration changes with changes in sediment grain size, color, ligth wavelength, and particle shape. For more details, we recommend visiting http://www.omega.com/techref/ph-6.html.

US EPA 180.1 This is the US version of the ISO standard mentioned above. The results are reported in NTU (Nephelometric Turbidity Units), again with Formazin as the standard. This method, unlike ISO-7027, this standard is more lax (and therefore, even less reliable). The scattering angle can be 90 +/- 20-degrees. The lamp need not be monochromatic, etc. Fundamentally, this method suffers from all the ills of the ISO method.

ISO-13320-1 This standard describes the laser diffraction method. Click here to go to the standard.

AWWA-2560D The American Water Works Association has proposed a standard based on laser diffraction technology. Status unknown.

EPA Drinking Water Standards: go to http://www.epa.gov/OGWDW/mcl.html

OBTAINING STANDARD PARTICLES

For extremely precisely sized polystyrene spheres, go to http://www.dukescientific.com/

To obtain glass beads for laboratory calibrations, visit http://www.whitehousescientific.com

To obtain natural particle standards (Arizona dust, also called AC Spark Plug Powder, and also used as a standard by USGS, ISO-12103-1, contact Powder Technology Inc., Burnsville, MN, Tel: 952-894-8737

To obtain Turbidity Standards in NTU units, visit http://www.voigtglobal.com/turbidity.htm