[labnetwork] Conductivity Standard Solution

Mon Feb 2 07:22:35 EST 2015

Dear John, Noah, and Miller,

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...

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.

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!!

*Two Options I can see: [John, Noah, Miller, please comment].*

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!

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.

Thanks,
Kamal.

On Sat, Jan 31, 2015 at 12:03 AM, Noah Clay <nclay at seas.upenn.edu> wrote:

> Kamal,
>
> 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”)
>
> http://www.snowpure.com/docs/thornton-upw-resistivity-measurement.pdf
>
> 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.
>
> Here’s another link from the same search/query:
>
>
> 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
>
> Best of luck,
> Noah Clay
>
> *Director, Quattrone Nanofabrication Facility*
> *School of Engineering & Applied Sciences*
> *University of Pennsylvania*
> *nano.upenn.edu <http://nano.upenn.edu>*
>
>
> On Jan 30, 2015, at 11:12 AM, John Shott <shott at stanford.edu> wrote:
>
>  Kamal:
>
> 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.
>
> 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.
>
> 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.
>
> 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.
>
> 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.
>
> 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.
>
> Let me know if you have any additional questions.
>
> John
>
> On 1/30/2015 2:01 AM, Kamal Yadav wrote:
>
> Dear All,
>
>  What is the best way to calibrate conductivity meters for DI water
> resistivity periodic monitoring.
>
>  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]
>
>  Thanks a lot!
>
>  --
>  Thanks,
>  Kamal Yadav
> Sr. Process Technologist
>  IITBNF, EE Department, Annexe,
> IIT Bombay, Powai
> Mumbai 400076
> Internal: 4435
> Cell: 7506144798
> Email: kamal.yadav at gmail.com, kamalyadav at ee.iitb.ac.in
>
>
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>
>  <thornton-upw-resistivity-measurement.pdf>
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>

-- 
Thanks,
Kamal Yadav
Sr. Process Technologist
IITBNF, EE Department, Annexe,
IIT Bombay, Powai
Mumbai 400076
Internal: 4435
Cell: 7506144798
Email: kamal.yadav at gmail.com, kamalyadav at ee.iitb.ac.in
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