Below is an email I sent to EXTECH. I thought I would post it here to get some additional feedback. I have not yet heard from them but when I do I will post their reply as well.

Good afternoon,

We have just purchased an EXTECH Oyster-10 to use to check pH of our Phosphate and Cleaning solutions for a cleaning unit we recently purchased. My question is regarding calibration of the Oyster.

What is an acceptable frequency for calibration for the unit? Daily Weekly? Monthly? 100 Uses? I am not sure since this is not stated clearly in the manual. We will be conducting 2 tests daily and the pH range of the tests will vary from about 4-8 on the pH scale.


Thanks,
RWest
QA Manager
Golden Precision LLC

Info: http://www.ambientweather.com/exoyoysephme.html

We have several ph/mv meters used by our Chemical Lab, and some by production. What we do in calibration is to calibrate the meter only. The user should check the meter before each use with standard fluids. With meters like this that are not that expensive, they usually come with a plastic probe. You will find yourself replacing those on a regular basis.

As for calibration frequency, most of ours are on a 6 month interval, while the good meters are on 12 months as stated by the mfg. Again, we check only the meter. The user needs to check and dial in the reading with standard ph fluids before each use.

Charles,

It appears since I am sending the gage out to be calibrated I would also have to relpace the reference liquids at a predetermined interval in order to be able to make accurate measurments. (Did I say that right??) Come to think of it I think they had an expiration right on the package.

Thanks for the input!


Here is the email I received from EXTECH today. I have to say that they did respond quickly and with a direct answer.



Hi Robert,

Thank you for your most recent email inquiry. Extech model Oyster 10
will need to be calibrated when first used. You should calibrate using
pH buffer 7 then pH buffer 4. The electrode should stay calibrated for a
day or two. The electrode will most likely need to be calibrated every
other day base on your usage stated below. If the meter & electrode is
not used for a long period you will need to calibrate the
meter/electrode each time you use it.

I hope that you find this information helpful. Thanks.

Best Regards,

Brian J. McAuley - Extech Technical Support

Brian.McAuley@Extech.com
www.Extech.com
Phone: (781) 890-7440 X147
Fax: (781) 890-2987