Re: [core] Proposed new SenML Units

[Michael Koster <[e-mail]>]

> On Nov 9, 2020, at 7:12 AM, Carsten Bormann <[e-mail]> wrote:
> 
>> 
>> +===========+================================+=======+
>> | Symbol    | Description                    | Type  |
>> +===========+================================+=======+
>> | NTU       | Nephelometric Turbidity Unit   | Float |
>> +-----------+--------------------------------+-------+
>> | mg/l      | milligrams per liter           | Float |
>> +-----------+--------------------------------+-------+
> 
> 
>> NTU is the most common way to measure turbidity.
> 
> This one is interesting.  There are several Turbidity units, which are not in a simple linear relationship, so I would like to get some input from domain experts which ones we should have (and which are more of a historical interest).
> 
> 

FWIW

While I'm not specifically a domain expert, I do have experience in a water turbidity measurement program.

I was responsible for process control and measurement systems in a large number of oil & gas installations in Alaska in the 1980s (please no "historical interest jokes...)

One of the installations was a water injection facility that needed to be accountable for the purity of the water injected into the ground over a period of decades. We maintained a fleet of "Surface-Scatter Turbidimeters" which measured turbidity in NTU. I was responsible for calibration of the machines and "certification" of the measurement record.

Turbidity is an indirect measure of suspended solids in water or other fluid, measured according of the amout of light blocked from transmission through the fluid. The Surface-Scatter Turbidimeter, or Nephelometer, measures the diffraction of light from surface roughness caused by the suspended solids. Standard solutions or cards (for field calibration) are used to calibrate the measurements.

A quick check on Wikipedia and discussion with an acquaintance who is a (retired) water treatment consultant (chemical salesman) confirms that NTU is still the metric of choice, though some facilities that know what their contaminants are can convert it to a concentration unit like ug/l for "internal" use.

Best regards,

Michael