Calibration of spectrometer - Master sample as reference

Ettore

Quite Involved in Discussions
#11
qsmso said:
I got confused with the calibration room in my company.
QSMSO
Hello , I'm confused too. Could anybody suggest to me the error acceptance level for spectrometer used for chemical analysis in foundry. Should be one error acceptance level for every element (C,Mn,Si,P,S,Cr,Ni, etc) or only one for the instrument. Who is able to answer obtains from me charma points :tg: By.
 
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D

Dale D. Barnes

#12
Calibration of Spectrometer

We have had questions about the calibration of our spectrometer in our plant also. It seems that every time a master sample is burned the machine has to be re-adjusted. We use the spectrometer to add alloy to our melt furnances and this always seems to come up as an audit issue. I have actually had to put a calibration sticker on the spectrometer every 6 months when the pm is done. I would also appreciate any thoughts on this subject.

Thanks
Dale :confused:
 
L

Lyn N Iles

#13
Calibration of spectrometer

I spent 35 years as an analytical chemist, but no longer work in this field. However, I was involved with Optical Emission Spectrometers for about 10 years and I'm casting my mind back as to what practices we used .....

The instrument was profiled on a daily basis using setting-up samples (we didn't work shifts).

The initial calibration of the instrument had been carried out using nationally/internationally recognised standards for each programme related to a type of alloy (e.g. low alloy and carbon steels on one programme, high alloys on another, tool steels on yet another). The calibrations were carried out using the ratio % element/% base element vs the ratio of voltage element/voltage base element.

The calibration standards were certified and analysis had been carried out by a number of organisations using varying techniques. The certficates stated the standard deviation for each element. On a daily basis, we used to run a certified calibration standard applicable to each of the programees to be used - if the result for each element was within 3 standard deviations of the average stated on the certificate, then that was considered acceptable. If the result varied from the average by more than that amount, the instrument profile was carefully repeated and the standardisation rechecked - if this didn't bring the instrument back in line, then the matter would have to be ivestigated.

We used to keep a control chart for each element of the calibration standard used per programme to keep track of the variation and identify any trends.

The use of nationally/internationally certified standards in such a manner can be expensive. One route to consider is getting together with organisations in the same field, finding a reasonably large quantity of homogenous material typifying the alloy(s) you are concerned with and collaborating on carrying out exhaustive chemical and statistical analysis. An agreement would have to be reached on how to share costs, of course.

The parameter that has the greatest effect on these types of instruments on a routine basis (e.g. not power cuts, or if applicable, vacuum pump failure) is temperature - good stable room temperature control is a must.

Hope this may be of help.

Lyn
 

Ettore

Quite Involved in Discussions
#14
Lyn N Iles said:
if the result for each element was within 3 standard deviations of the average stated on the certificate, then that was considered acceptable. If the result varied from the average by more than that amount, the instrument profile was carefully repeated and the standardisation rechecked - if this didn't bring the instrument back in line, then the matter would have to be ivestigated.

Lyn
Thank a lot. Anyway what Could I Write for spectrometer Acceptance level in a table like Attached
 

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K

Kevin H

#15
Cavanna - some thoughts that may help. In my last position I ran a Mechanical testing lab. Our tensile and Rockwell testing equipment was calibrated twice a year by an outside vendor. We verified the equipment at the beginning of each turn prior to use. For the Rockwell testers we used certified test blocks for the scale we were testing on that were provided by an external vendor, and simply recorded results in a log. If we needed to switch Rockwell hardness scales during a turn, we'd reverify after making the appropriate changes to the tester. For the tensile test equipment we used internally developed standards and SPC charts. We would pull 2 tensile specimens and plot average and range for ultimate tensile strength, 0.2% offset yield strength, and % elongation over a 2" gauge length.

Our chemistry laboratory also used spc charts and standards to verify prior to the beginning of the turn, depending on the grades of steel being produced. (We produced electrical steels, PH grades of stainless steel, 300 series grades of stainless, and 400 series of stainless.) Some of the standards used were purchased and traceable to NIST (The US government body responsible for standards, measurements, etc.) Others had been developed through interlaboratory cooperative testing arrangements. (One lab would take it upon itself to produce a set of samples that were sent to other producing using labs, and they would do multiple rounds of analyses until a consensus agreement was reached regarding the level of various elements in the sample. Then all labs would use the new standard as part of their verification/calibration activities.) For carbon and sulfur, we typically used special analyzers developed by Leco that were more accurate than a spectrometer in the ranges we measured. Standards for verification of Leco instruments were purchased from Leco.

For your spectrometer, I'd probably be interested in seeing accuracy versus analytical ranges by element. For example: iron based alloys, Cr range of 0.40 % to 18.00 % with an accuracy of+/- 10% of reading over the entire range, or whatever might be appropriate if accuracy varies over the range of alloys you produce.

To help quantify lab competency, our chem lab took part on a regular basis in interlaboratory comparison testing that was managed by an external company, whose whole business was managing and reporting interlaboratory tests for many different types of labs. I used the same service for both tensile and B & C scale rockwell hardness testing. Hope the info helps some.
 

Hershal

Metrologist-Auditor
Staff member
Super Moderator
#17
CRM and other standards

It appears that at least some of the discussion centers around the items used to check the spectrophotometer.

As has been stated, these are generally a CRM (Certified Reference Material) or SRM (Standard Reference Material). These should be available from the National labs.

If the Thai National lab does not have CRM/SRM for the use, then look at the APLAC (Asia Pacific Laboratory Accreditation Cooperation) for suppliers of CRM/SRM or APLAC signatories that accredit suppliers of CRM/SRM. Those accrediting bodies will have lists of the accredited labs. http://www.aplac.org

Consensus standards (e.g. Rockwell blocks used as an example) have also been mentioned. At times the consensus standards are necessary, but they tend to be non-traceable.....just something to watch for.

Hershal
 

Caster

An Early Cover
Trusted Information Resource
#18
Another idea - inter lab correlation

Dale D. Barnes said:
We have had questions about the calibration of our spectrometer in our plant also. It seems that every time a master sample is burned the machine has to be re-adjusted. We use the spectrometer to add alloy to our melt furnances and this always seems to come up as an audit issue. I have actually had to put a calibration sticker on the spectrometer every 6 months when the pm is done. I would also appreciate any thoughts on this subject.Thanks Dale :confused:
We also use spectrometers in the foundry for receiving metal inspection and melt chemistry.

Most auditors/customers have no idea what the equipment is or how it works so they just ask for "calibration records"

I have a set speech about this...It takes about 5 minutes to educate them. Some can't be educated so I just show them the cert for the masters to shut them up.

Another thing to consider is inter lab correlation studies. How do your burns compare to your supplier, customer, and competitors?

ASTM has several programs

http://www.astm.org/cgi-bin/SoftCart.exe/STATQA/index.html?L+mystore+frvt4284+1110356023

Consider asking your raw material supplier about this..they would likely love to help. We work with our Aluminum ingot suppplier and they are all over this topic..they have experts in this...people who do nothing but this.

It is fascinating and humbling to get involved in this...there is a lot to know about spectrometers and the test sample. Every little thing matters.

Good luck!
 

Hershal

Metrologist-Auditor
Staff member
Super Moderator
#19
Caster,

Great reply.....have you considered putting in to deliver a paper at Measurement Science Conference (MSC)?

http://www.msc-conf.com

If you have not, then let me encourage you.....of course this type of equipment is a bit unique, but then, Metrologists love strange toys......... :agree1:

Hershal
 
#20
Good am Sir may i ask i receive new Master material sample ingot it is possible verify does material without reference from spectrometer machines?
 
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