Hello everyone,

I am in the process of developing a quality system for ISO17025 accreditation for the calibration of electronic weighing scales. At the moment, I am extracting the best measurement capability of our lab by considering the uncertainties during calibration due to external influences like temperature variation, relative humidity, other ambient conditions, instrument repeatability, instrument resolution and uncertainty for the masses used. We have a set of OIML E2 masses, calibrated by the manufacturer.

My querry is this, I am trying to maintain the same ambient conditions as stated in the masses calibration certificate, that is; same temp, air density and RH so that I can assume the same uncertainty as stated by the manufacturer. In the meantime, I am trying to eliminate any electromagnetic interference, any variation in supply voltage, any draught and any vibration. I am taking the combined uncertainty (type B) contributors as the instrument resolution (0.5R/3½ rectangular), repeatability (s/3½ rectangular) plus the quoted masses uncertainty/2 (certificate).

I am relatively new to these things, so can you please illuminate me on what am I leaving out, what other influences I need to consider, where am I wrong, is there something that makes sense in what I wrote?

cheers and thanks
goro

Any help here that someone can provide?

Some influences that must be considered include:

local acceration of gravity (g), barometric pressure (which changes), and essentricity are some to keep included in the uncertainty analysis

Hope this helps.

Hello
Thanks for your replies. Regarding gravity acceleration, since the whole calibration will be at the same location wouldn't the acceleration remains constant throughout the process? If it varies, how should it be included in the uncertainty budget?
Barometric pressure will be measured and the value used to determine the air density during calibration. Is this sufficient or should there be anything else, please?
Regarding eccentricity, since the scales are supposed to be loaded always at the centre of the platform as instructed by manufacturers, shouldn't it be omitted out of the uncertainty budget? If not, how should it be included, please?

Can you please tell me, with regards to measurement devices like thermometer, barometer, hygrometer, etc, should they be also calibrated through a 17025 accredited lab and traceable to a reference standard?

Thanks goro

hello

You need to bifurcate the UCM into Type A and Type B, If you tell me which accreditation you seeking I can send you clear guidelines

Ananth

QUOTE=goro89129;307227]Hello everyone,

I am in the process of developing a quality system for ISO17025 accreditation for the calibration of electronic weighing scales. At the moment, I am extracting the best measurement capability of our lab by considering the uncertainties during calibration due to external influences like temperature variation, relative humidity, other ambient conditions, instrument repeatability, instrument resolution and uncertainty for the masses used. We have a set of OIML E2 masses, calibrated by the manufacturer.

My querry is this, I am trying to maintain the same ambient conditions as stated in the masses calibration certificate, that is; same temp, air density and RH so that I can assume the same uncertainty as stated by the manufacturer. In the meantime, I am trying to eliminate any electromagnetic interference, any variation in supply voltage, any draught and any vibration. I am taking the combined uncertainty (type B) contributors as the instrument resolution (0.5R/3½ rectangular), repeatability (s/3½ rectangular) plus the quoted masses uncertainty/2 (certificate).

I am relatively new to these things, so can you please illuminate me on what am I leaving out, what other influences I need to consider, where am I wrong, is there something that makes sense in what I wrote?

cheers and thanks
goro[/QUOTE]

Hi

I'm going for ISO17025 accreditation for calibration of electronic weighing scales. I hope this is what you asked for? If you need any more info please tell me.

Thanks a lot for your help
Goro

Hello
Thanks for your replies. Regarding gravity acceleration, since the whole calibration will be at the same location wouldn't the acceleration remains constant throughout the process? If it varies, how should it be included in the uncertainty budget?
Barometric pressure will be measured and the value used to determine the air density during calibration. Is this sufficient or should there be anything else, please?
Regarding eccentricity, since the scales are supposed to be loaded always at the centre of the platform as instructed by manufacturers, shouldn't it be omitted out of the uncertainty budget? If not, how should it be included, please?

Can you please tell me, with regards to measurement devices like thermometer, barometer, hygrometer, etc, should they be also calibrated through a 17025 accredited lab and traceable to a reference standard?

Thanks goro


True, the load should always be at the center, but achieving that perfectly every time is unlikely, so essentricity must be considered. This is often an assigned value.

Gravity if all in one location is ok, but if you then go to a different location that has a different gravity, such as calibration in San Diego and the next day in Phoenix for example, the gravity will change and that does affect uncertainty.

Barometric pressure considered as you describe should be fine. Remember that you may also have bouyancy as an influence.

Do calibrate your instruments like the hygo-thermometer and the barometric pressure gage. You need to have their uncertainty just as you have the uncertainty of your mass standards.

Hope this helps.

Hi,

this can help you:
Guidelines on the Calibration of Non-Automatic Weighing Instruments

http://www.dkd.eu/dokumente/Richtlinien/EURAMET_cg-18_v.02.pdf

http://ts.nist.gov/WeightsAndMeasures/upload/NISTIR6919.pdf


This is a very straight forward, simplified method for determining uncertainties for balances and scales both in controlled (laboratory) environments as well as unstable (field) environments. It is NIST's recommended practices so it is very widely accepted. Worked for us.