RE: [compost_tea] Re: DO Meters

From: John Cowan <vivax_at_northlink.com>
Date: Tue, 23 Dec 2003 08:59:05 -0700

The Extech DO meter I got last summer made me crazy. The reading was highly
unstable. Their tech support is very friendly. They replaced mine and the
difference was night and day. Also, they have a three year warranty. I think
their spec is +-0.4. for ppm.

John Cowan

-----Original Message-----
From: kevin john richardon [mailto:kmagic_at_backpacker.com]
Sent: Monday, December 22, 2003 8:00 PM
To: compost_tea_at_yahoogroups.com
Subject: Re:[compost_tea] Re: DO Meters


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 To unsubscribe from this group, send an email to:
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Received on Tue Dec 23 2003 - 11:25:08 EST

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