Re:[compost_tea] Re: DO Meters

From: kevin john richardon <kmagic_at_backpacker.com>
Date: 23 Dec 2003 02:59:48 -0000

Changing the membrane did help in the device being able to be calibrated, yet the number reflecting DO in the tea may not be accurate; tuff to describe the prob with it, Ime not sure I understand it myself.

I have used three Extech DO meters at the same time, each one calibrated (reading 20.9 atmospheric O2) then put into the same batch of tea, and they each read differently, as much as 3.? off! ??? So, recal, test, still off, recal, test, still off, re... bs it wont hold calibration, can not be confident in collected data.

Little nuances that go along with the device (and components) are just too tedius to explain in writing. And it isn't even a complicated piece of equipment, it just does not perform (poor design?), which is critical when we are dealing with an O2 saturation point of 8.2ish and a lower threshold of 5.5 which the space in between can be very small depending on your air input and we are trying to figure out how much nutrient (organisms) is going to max out various cfm. Giavonni suggested to me that accurate readings have a price tag of $2500! ???

Ya asked about the membrane? I change it (sometimes I actually think it is working, then SOMETHING tells me it is'nt, like removing the probe from the the tea, measuring atmospheric DO and it NOT reading 20.9!); Ide rather change the whole piece of equipment in for something that works without any issues. I suggest against the Exctech (maybe I will make time to call them to discuss my issues; maybe probs will be cleared up and Ile let you know); I would try something else. Will be hip to hear more about other pieces of equip that are in the $500 or less price range?

~Kev
ps its the holidays, go out and love your neighbor!, I got 50 emails today from yall?!?

On Sun, 21 Dec 2003 23:27:31 -0000 chriscreid <reidchris_at_earthlink.net> wrote:
Judi,

I saw Kevin's post and have a question for him that I'll include
here. Tom Jaszewski has an Extech, the one with the 13 ft cable for
tracking the readings on a computer.

Here's what he told me about it:

1. The membrane goes bad often enough that he keeps several on
hand. When this happens, he gets squirrelly readings. (Kevin -- have
you changed the membrane on yours?)

2. The DO meter has a separate data logger available. Tom tried it
and his experience is that it was very buggy and glitchy. He took
the software sold with the DO, put it onto an old used PC that he
picked up for $50, and runs it that way. He told me recently that he
saw a similar PC for sale on E-Bay for $14 ( I can look up the specs
he gave me but they're not close at hand and I'm writing while
cooking dinner).

Other than the membrane problem, he's satisfied with it.

3. I see that Ted Peterson is using another brand entirely, so
there's another perspective to check out.

4. Not sure if this is the one Scott Alexander is using, but there
is one inexpensive DO that somebody told us about -- the company
told them that the thing worked great and only problems they had
were with people using them for compost tea! 9Well, I don't want it
for aquarium research, so...0

Hey Judy, if you want to research this for the list, I'll send you
everything I"ve got on DOs and aeration, and you can contact people
and companies, ask them questions and report back. What is not
clear from what I've gathered so far is what characteristics to be
looking for, and any special considerations that might relate
specifically to tea. Bob Pyke (the refractometer source) doesn't
sell these as I recall, but he might have some suggestions on people
to talk to about them. So far, it seems we are buying them based on
each others' experience, but we're not sure how really to select
them other than what worked for others on the list.

Let me know if you have any interest in pursuing.

In any case, I'll find you the PC specs if you decide you want to go
the data tracking route with Extech. I think price is about 360-
$450 range depending on whether you get the Extech with or without
the 13 ft cable for the data logging setup.

Hope this helps,

Chris


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Received on Mon Dec 22 2003 - 22:23:11 EST

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