I've noticed there are a couple different methods for monitoring turbidity:
- Secchi disks: where users putting a disk into a body of water and measuring the distance in the water until the disk is no longer visible.
- Turbidity tubes: which require a sample of water to be viewed by the naked eye through the tube, and
- Turbidity meters: which requires a sample of water put into a meter that measures the amount of scattered light that sample produces (when with a light is shown through a sample at 90 degrees).
I'm wondering, under what conditions would I choose between these different methods? And, are there other methods?
DFRobot makes a Turbidity Sensor For Arduino (SKU:SEN0189). It's sitting in my forge right now and integrating it with a Mini-Pearl logger ( @cfastie ) is on my growing list of things to do. My goal is monitoring mountain streams associated with mining runoff and identifying time and duration of events. This really precludes either Secchi disks or turbidity tubes.
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In the lab where both epa and fda testing was done, we always used the turbidity meter. We used color comparison tubes, too, just not for turbidity.
It depends on the requirements of the government. In the US, this is the EPA. If both tubes and meters are ok, then it breaks down to cost and speed.
I haven't seen a commercial lab that uses tubes.
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