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I've been toying around with the idea of automating the process of testing aquarium water for certain chemicals. Very briefly, salt water aquariums (reefs, specifically) require almost-daily testing for 3-4 chemicals (calcium, alkalinity, ammonia, phosphate). This is typically done by hand, using various kits. There are two main types

  • you combine several powders with a fixed amount of aquarium water, and then compare the color the mixture turns with a chart
  • you combine several liquids together with the aquarium water, and then add another liquid until the mixture turns a color. you then record how much of the final liquid you had to add for the color change to occur (titration).

Both methods are straightforward, but tedious. To maintain an aquarium well, you really do need daily readings of all of those metrics, which easily adds up to 30 minutes+ daily.

So - I'd like to be able to automate the process. The biggest question is, how do I reliably dispense the materials needed? We're talking in gram and milliliter UoM here. The kits come with plastic syringes and spoons of correct volume for the powders. I need a way to measure out and dispense both of these, and a way to queue up several days worth (refilling daily defeats the purpose).

Any ideas?

Edit this is different from How to measure and dispense a finite amount of powder or liquid because of the units of measure involved. I need to be able to reliably dispense ~ 1g +/- 5% of a powder, or 1ml +/- 5% of liquid.

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kolosy
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So here's a system commmonly used in portioning substances, but I don't know what it's called for you to look it up (sorry). I've included two pictures, one for reference for us to call things by the same name, and another for displaying principle of operation.

A portioner is a disc or other shape that has a hole. The hole is sized to contain the correct quantity of the substance you are trying to portion. Think of it like a measuring spoon.

The portioner goes into a portioner housing, which allows a hopper to attach. It also allows the material contained in the portioner to be released. The hopper allows you to hold as much stock as you would like. One sample, a day, a week - the size of the hopper is up to you.

As far as operation, the disc is configured with its hole aligned towards the hopper. When you want the required quantity of material, you just move the disc to align its hole with the outlet of the portioner housing. The material contained in the hole of the disc falls out.

Note that I've drawn this as a vertical-rotating system, but you could just as easily have a horizontal-translating system. This would look like a cigar cutter.

:EDIT:

To be clear, this setup works with any units of measure. It's as big or as small as you need it to be.

Parts Operation

Chuck
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  • Very interesting. I wonder what tolerances have to look like for the powder to not get into the seam of the portioner, and how to ensure that it actually gets filled (I assume vibration is the answer to the last part) – kolosy May 19 '15 at 15:57
  • You could always add a groove for an O-ring if you couldn't manufacture to a tight enough tolerance. With filling, as long as the powder doesn't get too sticky while exposed to air (like sugars would) and isn't too compacted before you put it into the hopper it shouldn't be an issue. You are correct, if you were very concerned, vibration would be an easy thing to add. You can buy small vibration motors for things such as cell phones that you could turn on during the fill/release sequence. – Chuck May 20 '15 at 18:10