I am using this DFRobot Turbidity sensor. The associated wiki page has some sample code that includes some sample code and some information about converting between voltage and NTU (Nephelometric Turbidity Unit)
But I would like to verify this relationship and explore how various factors effect its accuracy. To do that, I would like to have some way to calibrate these sensors.
It appears that distilled water should have a turbidity of less than .1 NTU. It appears that you can purchase Formazin solution for turbidity calibration that comes in a standard 4,000 NTU solution.
https://www.amazon.com/Hach-246142-Formazin-Turbidity-Standard/dp/B00N3ZS45C/ref=sr_1_fkmr0_1?keywords=4000+btu+turbidity&qid=1572274634&sr=8-1-fkmr0
Instructions that I have found on the internet say that you take this solution and "dilute it to the desired instrument range."
Is turbidity going to decrease linearly as I dilute this solution? So if I make a preparation of 1 part Formazin solution and 1 part distilled water, should it have a turbidity of 2,000 NTU?
Is this a good way to go about this calibration and testing? Are there other techniques I should look at?
Hi wmacfarl ,
I've been thinking about affordable ways to calibrate diy photometric devices without having to use commercial standards like formazin or polymer suspensions.
It is very important that the calibration technique is accessible so that it can be reproduced by others using other instruments so that the results can be compared.
An alternative would be to express the readings always with reference to distilled water readings (a more accessible material): Abs (sample) / Abs (distilled water)
But found an interesting tip in the paper: https://www.sciencedirect.com/science/article/pii/S2468067218300762
The authors suggest the use of neutral filters, widely used in photography.
These filters have known transmittance and could be used to calibrate DIY photometers.
I haven't read yet all the paper in detail, but I intend to evaluate this alternative to the photometer I'm mounting.
I hope it helps.
Best regards,
Markos
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