[volt-nuts] Calibration and Certification - Trust and detail

[Dr. David Kirkby]

On 11 August 2013 15:39, Robert Atkinson <robert8rpi at yahoo.co.uk> wrote:
> On a related issue to the 3457A calibration, I was asked to review an item at work last week (sorry can't say what or why). Looking at compliance certification by two fully qualified, internationally recognised labs, all looked well until I looked at the detail. Things like "..all RELEVANT requirements of.." (my capitals) with no list of what was relevant or any test report., details of only one test when the standard needed a number under different conditions, no record of the part or serial numbers of the unit tested. Others had accepted the "certification" at face value.

I think it depens why you want the cal certificate.

1) If it to keep the BSI person happy to keep your ISO 9001
acreditation, then I guess as long as it has a cal certificate that is
ok, so use the cheapest dodgy cal lab.

2) If the purpose of the cal certificate is to get the highest price
when selling something, then a cal certificate by some dodgy cal lab
is probably all you need. 99% of buyers are not going to question who
did the cal, and their ability to do it.

3) If you want to know the instrument works correctly, and have it
adjusted for best performance, then it is a very different matter. One
is probably better sending it to the manufacturer in many cases.

I want to know my VNA works properly, so that is going to Agilent this
week. The cal cost on my VNA is about 5% of what I paid for the VNA.
It would be much more difficult to justify sending my 3457A to
Agilent, when the cal cost will probably be more than what I paid for
the instrument.

How useful is this

http://www.ebay.com/itm/281149723636 ?

On the fact of it, the device would give one a reasonly high
confidence something is working readlably well. I wonder if that is
good enough for a 3457A.

> Unfortunatly if the test house "customer" says "just do this bit" and the test house is happy to put weasely words on the certifcate, then user beware.

As I wrote earlier, I think there is a very cosy relationship between
cal labs and test equipment dealers. It is in both their interests to
get cal certificates on items even if they are not 100%. A T+M dealer
is not likely to use a cal lab that keeps sending items back marked
"Out of specification" or similar. A cal lab does not want to lose a
customer.

> Robert G8RPI.

Dave, G8WRB.