Re: [APD] dropchecker setup

[Carlo Flores <wet at petalphile_com>]

Hey Steve.

Sorry, you caught a bug.  Most folks using the calculator do it for
two drop checkers, and I missed this at some point.  Fixed.

The error check is still in place but more strictly matches the proper
condition.  That condition is when the drop checker solution is under
1dKH, which isn't a very strong buffer, and so subject to pH swings
and fluctuation that won't keep the drop checker necessarily accurate.
 But as you stated above, this is not an issue when calculating 30ppm
CO2.  More an issue when  calculating, say, 5ppm CO2.

"Also, this seems to imply that the standard recommendation for dropcheckers
is highly inaccurate?

When using a 4.0 dKH ref. soln. we know...

 yellow, ph 6.0, 4 dKH -> 120 ppm co2
 yellow-green, ph 6.4, 4 dKH -> 47 ppm co2
 green, ph 6.6, 4 dKH -> 30 ppm co2
 blug-green, ph 6.8, 4 dKH -> 19 ppm co2
 light blue, ph 7.0, 4 dKH -> 12 ppm co2

...which seems pretty useful, at least for indicating co2 > 20 ppm and
< 47 ppm?"

I don't think most folks would consider 20-47ppm -- a range of 135% --
accurate and rather "highly inaccurate"

Try out the calculator again and see what happens with two drop
checkers and your +/- 2.5ppm original target.  This will even make a
test chart for you.  Notice what happens
when you make sure *both* drop checkers are green.

Here's a sample:
http://dropcheck.petalphile.com/chart.png

Hope this helps, and thanks again for finding that bug.
Carlo

On Thu, Mar 29, 2012 at 9:23 AM,  <rader at hep_wisc.edu> wrote:
>
> Carlo,
>
> The standard dropchecker recommendation seems to be to use a 4 dKH reference
> solution so "perfect green" indicates 30 ppm CO2.  But when I plug that
> value and +/- 2.5 into your calculator at http://dropcheck.petalphile.com/
> I get an error/warning msg that doesn't make sense to me...
>
>  Your values are such that we cannot accurately measure CO2, since the
>  resulting low range and high range would be less than 1dKH.
>
> What does "less than 1dKH" refer to in this context?  Isn't the dKH of the
> ref. soln. invariant and set at 4??
>
> Also, this seems to imply that the standard recommendation for dropcheckers
> is highly inaccurate?
>
> When using a 4.0 dKH ref. soln. we know...
>
>  yellow, ph 6.0, 4 dKH -> 120 ppm co2
>  yellow-green, ph 6.4, 4 dKH -> 47 ppm co2
>  green, ph 6.6, 4 dKH -> 30 ppm co2
>  blug-green, ph 6.8, 4 dKH -> 19 ppm co2
>  light blue, ph 7.0, 4 dKH -> 12 ppm co2
>
> ...which seems pretty useful, at least for indicating co2 > 20 ppm and
> < 47 ppm?
>
> steve
> --

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