Measurement Uncertainty is Overrated

[Duckbutta]

I can't believe the amount of otherwise intelligent people that bought into this uncertainty nonsense.    It is a practice that far exceeds the scope of the majority of your local cal lab's workload.    I can see where it would be useful at NIST where the margin for error is miniscule and the smallest systematic error could wreak havoc on your process.    But at Transcat or Simco? Give me a break.    I wouldn't dignify most of the garbage that comes through their doors with a statement of measurement uncertainty.     Look at the recent UL post as an example.    Someone is actually taking time out of his day to research whether or not a 5520A is adequate enough to do an 87.    Putting the capacitance measurement aside, you could use that calibrator with speaker wire and still have orders of magnitude to spare.    This whole accreditation thing has gotten way out of hand.    And these sanctioning bodies perpetuate their fiefdoms by requiring you to only use labs accredited by them, thereby ensuring a circuitous stream of steady revenues.    WAKE UP PEOPLE! The other thing that gets me is the pervasive use of Type Bs that are used to make up the majority of Uncertainty Budgets that I've seen.    These are just glorified accuracy statements.    That's why so many Scopes of Accreditation look virtually indistinguishable from one another.    You can only run a 3458A through RSS one way.    The numbers are virtually meaningless in most applications.    Overkill at best, a waste of valuable time and resources at worst.    The single largest contributor of uncertainty in any measurement is the person making it.    And these Type A uncertainties are rarely, if ever addressed.    That's why two people using the same standards can come up with vastly different results.    It's all in the technique.    Good measurements are like good porn, you know it when you see it.    You can have state of the art standards but if the guy using them only has a year of experience and is only making $15/hour, chances are you aren't getting a quality measurement.    That's like putting a $149 paint job on a Mercedes.    It just doesn't make sense.    There is no substitute for experience.    And the sooner these Cal Labs come to terms with that reality, the better off we'll be.   So while you're all busy feverishly punching in numbers on a calculator to come up with some arbitrary number that has little bearing on the measurement in question, I'll do an old school 4:1 and be on the bench.   .   .   .   .   Calibrating!

[flew-da-coup]

You are really poking a stick at a hornets nest now.

[Hawaii596]

Bzzzzzzzzzzz!!!!! (sound of bees in the hornet's nest getting riled).

[fwisdo]

The technicians should be on the bench calibrating.  The Metrologist or Calibration Engineer should do the uncertainty budgets. 
One problem is that as equipment gets more accurate it is harder to maintain a 4:1 all the way to NIST.  By stating known uncertainties NIST's standards do not have to be >64X more accurate than the equipment in the field.
I do, however, feel that measurement uncertainty can be way over done and waste a lot of time.  But it is the direction metrology is moving in so we will all have to deal with it.  Don't even look at Z540.3 you will really flip out. 

Process Measurement (1)
Working Metrology Laboratory (4X)
Reference Metrology Laboratory (16X)
National Laboratories. . . NIST (64X)
BIPM (256X)

Duckbutta. . . Your avatar rocks!!!

[Hawaii596]

Metrology has truly been cheapened by the Save-A-Buck mentality of too many these days.  It's unfortunate that so many less-than-reepectable labs have learned how to make uncertainty budgets look good.

But it is those same shoddy labs that created this need.  Oversimplifying the task of calibration in this technologically rapidly changing world (with such things is thinking uncertainty is nonsense) will likely one day cause the next "Challenger Disaster."

Let's take the example of the Fluke 5520A capacitance function.  If labs did good work all the time, every time with properly trained metrologists, proper procedures, proper standards, etc., then there would be no need for ISO17025.

Some use poor practices through ignorance; others through selfish motives.  Is the Fluke 5520A the correct standard to cal capacitance on a Fluke 87 DMM?  What is the cumulative uncertainty?  Is it 4:1 or better?

I don't quite understand the ignorance of belittling a scientifically valid analysis simply because you don't understand it.  If you don't know how to calculate expanded uncertainty to what ever [K] factor confidence level suits you, take a class, or pursue a different profession.  But don't cast dispersion upon something just because you don't understand it.

[Duckbutta]

Dude,

You still don't get it. Even a cursory side by side ACCURACY comparison (forget uncertainty for a minute) between the 5520A and the 87 would have told you that you weren't making a 4:1 measurement. I don't need a calculator to figure that out. So while you're in the conference room, sipping tea with your pinkie in the air, talking with a fake British accent about Uncertain-teeee, I'll be on the bench maintaining a 4:1 ACCURACY ratio, employing good measurement practices, and KNOW that I'm making quality measurements. Meet you at the outgoing shelf....if you ever get there.

[flew-da-coup]

There are some good reasons for having measurement uncertainties. For example, you can have 2 standard resistors both spec'd @ 1%. I can have one cal'd with a 4:1 TAR and one cal'd with actual values with Measurement Uncertainties. Now I have a 1% resistor and another that is 5ppm. The same goes with the 5520A on capacitance. If I have my 5520a calibrated with measurement uncerts. for capacitance with data then my 5520a will have a higher accuracy when doing capacitance. I think the problem here is that many in our field do not understand how measurement uncertainty works. Calculating uncerts is one thing, knowing how to use them is another. It's not about having scopes making your lab look good. It is about having higher accuracy and measurement confidence. This does not effect most field or working labs like it does primary and secondary labs.

I am sure I will be blasted for my post, but I will be more than glad to explain myself if need be.

[Duckbutta]

Coup, I'm with you on that. Uncertainties definitely have their place. I never claimed that they didn't. I just said that their use in your local cal lab is usually, though not always, overkill. To utter the words Fluke 87 and Measurement Uncertainty in the same sentence is to me just preposterous. It's just making a mountain out of a mole hole and is a complete waste of time and resources. The Type B uncertainties are negligible in that case (excluding capacitance). Hell, you'd be hard pressed to find a Type A uncertainty that would have any noticeable effect on the calibration. What's a few uV amongst friends? A simple 4:1 TAR is MORE than sufficient in that instance. And I think that is basically the point you were trying to make, Coup, not to overthink this stuff. Face it, most of the work done in your local commercial cal lab isn't rocket science and no amount of uncertainty analysis is going to change that fact. Metrologists are analytical by nature and most have a healthy dose of ego (two good traits to have in this business). That's why I think so many are susceptible to falling into the Uncertainty Trap. They view it as a chance to show everybody that they're the smartest guy in the room but just wind up sounding foolish. Some advice to Hawaii596 and those like him, go back to your bush league cal lab, bang out your little handhelds and leave the uncertainty analysis to us, the big boys.

[flew-da-coup]

Coup, I'm with you on that. Uncertainties definitely have their place. I never claimed that they didn't. I just said that their use in your local cal lab is usually, though not always, overkill. To utter the words Fluke 87 and Measurement Uncertainty in the same sentence is to me just preposterous. It's just making a mountain out of a mole hole and is a complete waste of time and resources. The Type B uncertainties are negligible in that case (excluding capacitance). Hell, you'd be hard pressed to find a Type A uncertainty that would have any noticeable effect on the calibration. What's a few uV amongst friends? A simple 4:1 TAR is MORE than sufficient in that instance. And I think that is basically the point you were trying to make, Coup, not to overthink this stuff. Face it, most of the work done in your local commercial cal lab isn't rocket science and no amount of uncertainty analysis is going to change that fact. Metrologists are analytical by nature and most have a healthy dose of ego (two good traits to have in this business). That's why I think so many are susceptible to falling into the Uncertainty Trap. They view it as a chance to show everybody that they're the smartest guy in the room but just wind up sounding foolish. Some advice to Hawaii596, and those like him, go back to bangin' out your little handhelds and leave the uncertainty analysis to us, the big boys.

Thanks, that is close to what I am saying. I think that when it comes to MUA there are too many pokers in the fire. This is why we commonly hear different interpretations and understandings of MUA. The MUA Bible belongs to NCSLI and it is consistently evolving. I try not to give any validity to all those other MUA publications. I think all they do is muddy the water.

   I also agree that most of the time MUA will not be needed in the working lab. However, I am sure at times it has to be implemented for specific requirements at times.

This discussion is a real good one for us to have here. I think everyone should contribute their 2 cents on MUA. It will help us have a more clear understanding and help those who are in the dark see what it is all about. I cannot say that I am an expert, I just know what I have used and still use concerning MUA.

[MIRCS]

The Type B uncertainties are negligible in that case (excluding capacitance). Hell, you'd be hard pressed to find a Type A uncertainty that would have any noticeable effect on the calibration. What's a few uV amongst friends?

Actually those Type B's can make all the difference in the world.  If the manufacturer would give all their data, less type B's would be needed.  Also a Type A does make a very large noticeable difference in the uncert. just by lowering the student number.

Some advice to Hawaii596 and those like him, go back to your bush league cal lab, bang out your little handhelds and leave the uncertainty analysis to us, the big boys.

Who are you to be saying that you're the "big boys", could very well be a bush lab compared to many else out here.

[Duckbutta]

MIRCS,

You're proving my point for me. If you read my prior posts, you'll see that I talk about the pervasive lack of Type A use in most Scopes. Type As are a critical part of ANY uncertainty analysis. A purely Type B analysis only tells half the story. The measurement is only as good as the person making it. And to omit this factor, to me, defeats the whole purpose of the analysis in the first place. Anything else is inadequate and substandard. So before you come off half-cocked, I suggest you put the calculator down, read all the pertinent threads, and then comment.

[MIRCS]

MIRCS,

You're proving my point for me. If you read my prior posts, you'll see that I talk about the pervasive lack of Type A use in most Scopes. Type As are a critical part of ANY uncertainty analysis. A purely Type B analysis only tells half the story. The measurement is only as good as the person making it. And to omit this factor, to me, defeats the whole purpose of the analysis in the first place. Anything else is inadequate and substandard. So before you come off half-cocked, I suggest you put the calculator down, read all the pertinent threads, and then comment.

Maybe just a little civility in the previous 15 post that you have and people wouldn't come off as half cocked.

I give a sh!t about other places scopes.  We are really talking two different things here. 

1. Uncertainity budgets

2. Scopes of companies that shouldn't be in the field at all

I personally don't like and disagree with almost every cert that has an uncertainity associated with that measurement.  I believe in the uncertainity budget over the rest.

How and or why someone couldn't take the measurements for a Type A is beyond me.  I guess I'm with the big boys as that never happens with us and we actually do budgets

[flew-da-coup]

Where's the love? Come on guys we can discuss this in a little better way.

[Kalrock]

This argument seems kind of out of hand.   I think that most cal labs don't require every tech to be able to do Uncertainty analysis.   They have a few people that will take care of that for them.   I know that Transcat is in the process or has already complete their attempt to go ahead and have the uncertainties figured out for every standard so that their system Caltrack automatically inputs the Uncertainties.   I do think that Uncertainties are a way for the industry to set some kind of standard to try and keep people on the same page.   I mean we all are suppose to be using the same procedures it's not that different.

That being said it does seem like somebodies Uncle came up with this thing to make some money.   I mean we all know that ESD is just made up bullsh!t.   Just like we all know that resistors have magic smoke.   I still haven't managed to get high off smoking a resistor, but I try everyday.   

On the serious side if a quick check of the TAR is greater than 4:1 can't you just add 15% to your accuracies have had a solid TUR.   If I'm wrong go ahead and let me know because I'm know expert at Uncertainties.

Later

[Duckbutta]

Kalrock,

Did you read the threads? I don't think you did because you wouldn't have trotted that tripe out there like that. That's a hangin' curve ball if I ever saw one.

That fact that Transcam is listing the uncertainties of their standards in Caltrak is the type of deception that I have been harping on. Though I don't like to admit it, I have intimate first hand knowledge of this company (Disclaimer: I was desperate and needed the money). Their uncertainties are based on the standards only, not the bush-league "techs" they hire to carry out the process. And judging by your post, Kalrock, you're one of them. Of the 10 techs at the Transcam lab where I worked, only 2 of us had formal PMEL training. The rest were your basic garden variety electronics techs. And as anyone who knows this business will tell you, that's not gonna get it. Their labs are plagued by incompotence and piss-poor management. If you are a customer seeking a legitimate cal on anything other than a handheld, I strongly suggest that you seek another provider. Transcam is in the business of selling certs, plain and simple. You can throw Simco in there too. I don't know about Davis and Sypris but I suspect it's more of the same. If you want to save yourself some money, download the accredited logo du jour, invest in a nice printer, and print your own. The ones that you print will be worth the same as the ones they print, nothing.