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Kamal:<br>
<br>
OK, I understand that you do not have a circulating system. I
suspect that this is a "once through" system where water goes
through a certain number of polishing beds, UV, and final filters
before heading directly to your DI taps. I've run systems of that
type.<br>
<br>
I personally don't think that calibration of your resistivity
monitors is the thing that you should worry about. Even if your
conductivity measures 0.04 uS/cm ... which, yes, is technically
impossible because at room temperature water can be no less than
0.055 uS/cm ... that is indicative of high-resistivity water. If
the conductivity increased to 0.08 uS/cm, however, then you know
that something has changed.<br>
<br>
I would suggest that you try to get the appropriate adapter in your
supply line so that you can install a permanent mounting point for
your resistivity monitor. In that way, you can look at your
conductivity any time that you are flowing water. You can also
answer the question in a once through system: how long after I begin
flowing water, does the conductivity fall to the point that I am
getting good resistivity water. Most importantly, if you normally
see a conductivity of 0.04 uS/cm, and it increases to 0.08 uS/cm,
for example, you know that something has changed. That might be
indicative, for example, that it is time to change your resin beds.<br>
<br>
While absolute calibration is nice, with all due respect to my
friends at NIST, not all instruments need to be fully calibrated to
provide useful diagnostic information. I believe that this may be
one of those cases where being able to detect a change in
conductivity may be more important than the absolute accuracy of the
conductivity measurement.<br>
<br>
Good luck,<br>
<br>
John<br>
<br>
<div class="moz-cite-prefix">On 2/2/2015 4:22 AM, Kamal Yadav wrote:<br>
</div>
<blockquote
cite="mid:CAOfoCyh2_1ER76rH-VjzsLkEZ_tUMBGbz5uRfh8Oi597zdbLrw@mail.gmail.com"
type="cite">
<div dir="ltr">Dear John, Noah, and Miller,
<div><br>
</div>
<div>Thank you for your response. I have gone through the
attachment sent by John and Noah, which is identical and
discusses about the topic in detail. I did not know this one
is going to be difficult as well...</div>
<div><br>
</div>
<div>We do not have a circulating DI water loop. We have a
conductivity meter using which we try to periodically check
the DI water resistivity in flowing condition in a beaker
waiting for sufficient time. I was happy as it was showing
0.04 uS/cm :) as that would be around 25 Mohm-cm much more
than 18.2 Mohm, until a faculty pointed out that it is
theoretically impossible at that temperature and is evident
from the attachments you sent.</div>
<div><br>
</div>
<div>We have another resistivity meter in Solar Cell Center,
that one is new and gives good reading something on which we
can believe, so far. Calibrating that meter after sometime
need to be identified as informed by the supplier [Merc
Millipore]. They do not know as of now!!</div>
<div><br>
</div>
<div><b>Two Options I can see: [John, Noah, Miller, please
comment].</b></div>
<div><br>
</div>
<div>1. These days 1 uS/cm standard is also available at NIST.
But still far from ~ 0.055. The attachment claims ASTM
standard even at 100 uS/cm can be used to calibrate UPW range
resistivity meter? I am little confused whether I can use the
standard, and whether it will be stable with its conductivity.
We are ok as long as it shows more than 16 or 17 MOhm,..but
certainly not 25 :). The good meter from Solar cell lab shows
around 15 Mohm-cm so we know it may be accurate. Since it is
flowing DI water in a beaker it would be little far from 18.2
compare to John's 17.5, I suppose!</div>
<div><br>
</div>
<div>2. Send out the meter to an outside agency, will work if
agency is in India, otherwise I need to see how much it cost,
which may be equal to buy a new one.</div>
<div><br>
</div>
<div><br>
</div>
<div>Thanks,</div>
<div>Kamal.</div>
<div><br>
</div>
<div><br>
</div>
<div><br>
</div>
<div><br>
</div>
<div><br>
</div>
<div><br>
</div>
<div><br>
</div>
<div><br>
</div>
<div><br>
</div>
<div><br>
</div>
</div>
<div class="gmail_extra"><br>
<div class="gmail_quote">On Sat, Jan 31, 2015 at 12:03 AM, Noah
Clay <span dir="ltr"><<a moz-do-not-send="true"
href="mailto:nclay@seas.upenn.edu" target="_blank">nclay@seas.upenn.edu</a>></span>
wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">
<div style="word-wrap:break-word">Kamal,
<div><br>
</div>
<div>Personally, I would send out your meter(s) for
calibration by an expert. That said, here’s a reference
from a company in the Boston area (google search:
"calibrate ultrapure water conductivity meter”)</div>
<div><br>
</div>
<div><a moz-do-not-send="true"
href="http://www.snowpure.com/docs/thornton-upw-resistivity-measurement.pdf"
target="_blank">http://www.snowpure.com/docs/thornton-upw-resistivity-measurement.pdf</a></div>
<div><br>
</div>
<div>Apparently, one can purchase standards from NIST for
this (as stated in the above link), but I’m not sure if
they have a standard in your range.</div>
<div><br>
</div>
<div>Here’s another link from the same search/query:</div>
<div><br>
</div>
<div><a moz-do-not-send="true"
href="http://www.thermoscientific.com/content/dam/tfs/ATG/EPD/EPD%20Documents/Application%20&%20Technical%20Notes/Water%20Analysis%20Instruments%20and%20Supplies/Lab%20Electrodes%20and%20Sensors/Ion%20Selective%20Electrodes/AN-PUREWATER-E%20RevA-HIGHRES.pdf"
target="_blank">http://www.thermoscientific.com/content/dam/tfs/ATG/EPD/EPD%20Documents/Application%20&%20Technical%20Notes/Water%20Analysis%20Instruments%20and%20Supplies/Lab%20Electrodes%20and%20Sensors/Ion%20Selective%20Electrodes/AN-PUREWATER-E%20RevA-HIGHRES.pdf</a></div>
<div><br>
</div>
<div>Best of luck,</div>
<div>Noah Clay</div>
<div><br>
</div>
<div><i>Director, Quattrone Nanofabrication Facility</i></div>
<div><i>School of Engineering & Applied Sciences</i></div>
<div><i>University of Pennsylvania</i></div>
<div><i><a moz-do-not-send="true"
href="http://nano.upenn.edu" target="_blank">nano.upenn.edu</a></i></div>
<div><i><br>
</i></div>
<div><br>
<div>
<blockquote type="cite">
<div>
<div class="h5">
<div>On Jan 30, 2015, at 11:12 AM, John Shott
<<a moz-do-not-send="true"
href="mailto:shott@stanford.edu"
target="_blank">shott@stanford.edu</a>>
wrote:</div>
<br>
</div>
</div>
<div>
<div>
<div class="h5">
<div bgcolor="#FFFFFF" text="#000000"> Kamal:<br>
<br>
Let me start by saying that I've never
actually tried to calibrate meters of this
type. Why? Because it is not easy. Here
is a good reference article from over 15
years ago that describes the process in
great detail including the fact that the
standard conductivity solutions only go down
to about 5 uS/cm ... which isn't very close
to the 0.06 uS/cm you are hoping to
measure. They also talk about separating
the whole calibration process into the steps
of calibrating the meter itself (easy), the
temperature probe (reasonably easy), and the
"cell constant" of the probe itself (hard).
A number of you will recognize that the
author of this paper works for a company
that makes and sells resistivity probes and
monitors. This is not intended to be an
endorsement of that, or any other, company
... but, I think, indicates that detailed
calibration of DI resistivity monitoring
systems is typically found primarily in the
companies that make and sell such
instrumentation rather than by the folks
that use such instrumentation.<br>
<br>
Their solution for high-precision
calibration was to measure UHP water over a
range of temperatures as a means of
determining and/or calibrating the cell
constant. If you read this article,
however, you will conclude that this is not
a procedure for the faint of heart.<br>
<br>
In recirculating DI systems, I believe that
it is more common to have continuous
resistivity monitoring on both the supply
side and return side of the system. In our
case, we typically see supply and return
resistivity readings about 17.7 MOhm-cm or
higher ... but that rarely, if ever, read
the theoretically expected 18.2 MOhm-cm. In
fact, it is not uncommon to see a return
resistivity that is slightly higher than the
supply-side resistivity ... which would seem
unlikely.<br>
<br>
Then, on an occasional basis ... probably
not as frequently as we should ... we (well,
a third-party analytical laboratory) collect
samples and have them measured for particle
content, bacteria grown, total oxidizable
carbon, dissolved silica, and a 30-element
mass-spec analysis for metal levels in the
ppt range that is commonly used for DI
systems. In short, there are lots of things
that CAN be wrong with DI water that are not
seen by even an accurate resistivity
measurement. In other words, as long as our
resistivity readings are on the order of
17.5 MOhm-cm or above on both supply and
return lines, I, for one, don't worry about
the resistivity aspects of our water. In
fact, earlier this week, I was comparing
these DI analytical test results with
another frequent contributor to this forum
from the Bay Area institution with the
longest history as a university laboratory
in this field.<br>
<br>
Finally, when you say "periodic monitoring"
do you mean that you have a probe in a
continuously recirculating loop and you want
to look at the resistivity of that
periodically ... or that you occasionally
collect a sample of water and are trying to
measure it's resistivity? If it is the
latter, that can be tricky: when exposed to
air, DI water absorbs CO2 which forms
carbonic acid that can cause your
resistivity numbers to degrade.<br>
<br>
My guess is some of the folks that run newer
labs than ours will have more details about
the way that they monitor the DI water in
these newer operations.<br>
<br>
Let me know if you have any additional
questions.<br>
<br>
John<br>
<br>
<div>On 1/30/2015 2:01 AM, Kamal Yadav
wrote:<br>
</div>
<blockquote type="cite">
<div dir="ltr">Dear All,
<div><br>
</div>
<div>What is the best way to calibrate
conductivity meters for DI water
resistivity periodic monitoring.</div>
<div><br>
</div>
<div>Standard known conductivity
solutions are available but which one
is good and stable for this range of
measurement. [18 MOhm-cm or ~ 0.06
uS/cm]</div>
<div><br>
</div>
<div>Thanks a lot!<br clear="all">
<div><br>
</div>
-- <br>
<div>
<div dir="ltr">
<div>Thanks,<br>
</div>
<div>Kamal Yadav</div>
<div>Sr. Process Technologist<br>
</div>
<div>IITBNF, EE Department,
Annexe,</div>
<div>IIT Bombay, Powai</div>
<div>Mumbai 400076</div>
<div>Internal: 4435</div>
<div>Cell: 7506144798</div>
<div>Email: <a
moz-do-not-send="true"
href="mailto:kamal.yadav@gmail.com"
target="_blank">kamal.yadav@gmail.com</a>,
<a moz-do-not-send="true"
href="mailto:kamalyadav@ee.iitb.ac.in"
target="_blank">kamalyadav@ee.iitb.ac.in</a></div>
</div>
</div>
</div>
</div>
<br>
<fieldset></fieldset>
<br>
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</blockquote>
</div>
<br>
<br clear="all">
<div><br>
</div>
-- <br>
<div class="gmail_signature">
<div dir="ltr">
<div>Thanks,<br>
</div>
<div>Kamal Yadav</div>
<div>Sr. Process Technologist<br>
</div>
<div>IITBNF, EE Department, Annexe,</div>
<div>IIT Bombay, Powai</div>
<div>Mumbai 400076</div>
<div>Internal: 4435</div>
<div>Cell: 7506144798</div>
<div>Email: <a moz-do-not-send="true"
href="mailto:kamal.yadav@gmail.com" target="_blank">kamal.yadav@gmail.com</a>,
<a moz-do-not-send="true"
href="mailto:kamalyadav@ee.iitb.ac.in" target="_blank">kamalyadav@ee.iitb.ac.in</a></div>
</div>
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