Does anyone know the relationship between CYA and NTU for the TF-100 test kit? If not, I guess a quick and dirty two point calibration could be done using the 50CYA standard and dilution.
NTU is a useful measurement of turbidity. Following is quoted from
http://en.wikipedia.org/wiki/Nephelometric_Turbidity_Unit>
A property of the particles — that they will scatter a light beam focused on them — is considered a more meaningful measure of turbidity in water. Turbidity measured this way uses an instrument called a nephelometer with the detector setup to the side of the light beam. More light reaches the detector if there are lots of small particles scattering the source beam than if there are few. The units of turbidity from a calibrated nephelometer are called Nephelometric Turbidity Units (NTU). To some extent, how much light reflects for a given amount of particulates is dependent upon properties of the particles like their shape, color, and reflectivity. For this reason (and the reason that heavier particles settle quickly and do not contribute to a turbidity reading), a correlation between turbidity and total suspended solids (TSS) is somewhat unique for each location or situation.
Another measurement of turbidity is OD or Optical Density. The following is quoted from
http://en.wikipedia.org/wiki/Optical_density
In spectroscopy, the absorbance (also called optical density[2][3]) of a material is a logarithmic ratio of the radiation falling upon a material, to the radiation transmitted through a material.[4] Absorbance measurements are often carried out in analytical chemistry.
In physics, the term spectral absorbance is used interchangeably with spectral absorptance or absorptivity. In this case it has a slightly different meaning: the fraction of radiation absorbed at a specific wavelengths.
Various companies manufacture instruments to measure the above, traceable to NIST. NIST is the National Institute of Standards and Technology.
http://en.wikipedia.org/wiki/NIST.
Hach
http://www.hach.com/ and Optek
http://www.optek.com/ instruments are used all over various industries for turbidity measurements. Typically, Optek are flow through, fixed installation systems, which are used as feedback in control systems. Hach, on the other hand, makes devices to measure samples or portable applications.
My personal experience is with the Hach 2100Q which we use as a spot check to measure centrifuge and filter performance in Biotech applications. In these purification applications, the molecule of interest (a protein manufactured by and engineered cell line) is in solution and the solids (cells and cell debris) are waste and must be removed.
So, the point of all of this is that I have a Hach 2100Q at the office and would like use it on samples of my pool water instead of the sight glass provided in the TF-100 test kit. The sample would be prepared according to the TF-100 instructions, just set into the 2100Q instead of put into the sight glass.
If anyone has done this kind of thing before and has a CYA to NTU conversion, I'd love to hear of it. Otherwise, I have the 50CYA standard (R-7065) and will use that as well as a 2:1 dilution (read 25CYA standard) to make a quick and dirty two point calibration. I say quick and dirty because we don't have purified water (DI or otherwise) at the office. The best available will be distilled water from the grocery store.
Notes on purified water: DI is DeIonized water and diluting with such would assure the purity of the standard.
http://en.wikipedia.org/wiki/Purified_water
I'll probably do this in the next week or two and will post results.
