Substitution of Standards - Pipe UP!!!!!!!111

flamy78 · 03-05-2005 -- 10:10:10

Figure this best fits here. Okay everybody that knows the answer jump in. This applies to all of us. I knew the answer recently but couldn't prove it exactly because of lack of understanding.

When a spec. an. is called for and the spec is 600kHz to 250 MHz +/- 1 dB what specification in the spec an k-pro would I refer to to validate that my substitute is acceptable? I have a few ideas but would rather not say.

Now in my case I had two items - one called for +/-1 the other called for +/- 1.6 . The one that called for 1 called for a B model - I grabbed the kpro and noted the areas where the A and B had differing specs. None of them were amplitude related so I knew that the A would be good enough for the 1.6 but did not know the real name of the spec. This is referring to looking at harmonics dBc.

Another example: a spec an is called for with a +/- 3 Hz accuracy up to 40 MHz. Would that be the time base accuracy x 40 E6 has to be <=3 hz?

For items being calibrated and what was being used as a sub PM me. Gotta love the lack of alternates being listed and the specs not explained to the point where somebody that doesn't calibrate the standard can understand it.

howiesatwork · 03-09-2005 -- 16:21:17

Well, it seems some that write cal procedures like to randomly pick a spec and include that.

Looking at the tests where it is used might help narrow it down as to what specs you really need to look at.
Just because there are two different spec-ans with differing specs in the function required does not mean they cannot be used to do the same test if the TUR is sufficient to adequately check the DUT.
When some peoplle put a spec in a procedure, they put in what the spec for the test equipment is in the book, versus what is required for the actual test being made.
To write the procedure correctly, the TUR has to be determined for each test function and spec, which is a long, drawn out way to go, but it should be done most of the time...
Timebase accuracy, for example, is a non-issue, as you can phase lock that to the DUT, as is done in phase noise measurement.

flamy78 · 03-09-2005 -- 22:28:33

Nooooo , I cleared my reply by refreshing. Be back in a few . Because I may have exceeded my bandwidth on my avatar pic.

<edit -close to what I had before>
K pros to ref: k3 1549 and k3 3215

There is no TUR or TAR in this case. We are checking distortion via harmonics.

my $.02 If said spec an was used in k3-3215 The procedure should specify <41.6 dBc - since std accy is 1.6 dB - this would ensure the UUT meets specs - but this could be me overthinking it.

howiesatwork · 03-15-2005 -- 02:35:53

Okay.
You're checking harmonic distortion.
The spec is a < value...
The analyzer called for has a spec of ±1dB in Freq Resp. accuracy?
That's probably what the procedure is referring to as accuracy, seeing as you stated the Equip Required accuracy was 600kHz to 250 MHz ±1dB. This would be freq resp.
You could just subtract(add) the extra .6dB from the DUT spec. and essentially test it to a tighter spec.
This would insure the accuracy of the SA does not give a false pass.
f the DUT pass is marginal (-.6dB of spec), the actual condition of the DUT cannot be determined. It may be good, and yet it may be bad. It depends on where the response of the SA is.
If the SA response is + at that freq, and the DUT checks good, it is.
If the SA response is - at that freq, and the DUT checks good, it might be bad.
If the SA response is - at that freq, and the DUT checks good at the tightened spec, it is.

Did any of that make sense?

flamy78 · 03-15-2005 -- 10:26:23

Well since you responded I'll say - somewhat.
But what me and the spec an guys came up with was - scale fidelity or display accuracy.

howiesatwork · 03-16-2005 -- 20:21:43

Nope on both counts.

flamy78 · 03-16-2005 -- 22:31:56

Nope what? You say that neither of those are the spec that is being used? Really? Well they don't say which is the big pile of dooky. But I spoke to ... oh 3 guys here. Guessing I could contact an engineer ... oh wait I still don't have a fracking e-mail accoutn here.

Thraxas · 07-23-2005 -- 10:24:42

Quote from: flamy78 on 03-16-2005 -- 22:31:56
Nope what? You say that neither of those are the spec that is being used? Really? Well they don't say which is the big pile of dooky. But I spoke to ... oh 3 guys here. Guessing I could contact an engineer ... oh wait I still don't have a fracking e-mail accoutn here.

Fracking? Do you watch a lot of Battlestar Galatica?

Sorry I have no answer. I stay away from spec an's like the plague.

flamy78 · 07-23-2005 -- 12:12:54

Yes I watch the new bsg. And now I'm seeing in some kpros (scale fidelity) behind the spec. The problem with previous methods was if you could find a spec on your std that was = to or better than what was listed you could use it.

Stupid kpro mistake of last night : connect to counter with feedthrough termination then set both channels to 50 ohms.

DER!

Why choose to do symmetry at 120k 1.2M and 12M - Numbers involving 3333 can be a pain in the arse. Why perform an asymmetry calculation when you want symmetry? (they won't answer this one)

flew-da-coup · 11-16-2005 -- 11:28:47

Flamy I am wondering if your in the wrong career. Substitution of standards is common practice in our field. It's not knowledge, but more like common sense. I would take great effort to THINK before I post if I were you. By the way, metrology is not a K-PRO.

howiesatwork · 11-23-2005 -- 05:24:47

Metrology is not a K-Pro...?
Ever work AF PMEL? I guess not.
It was by the book when I was NCOIC of QA at Clark.
There was a set of equipment to choose from, some substitution could be made, but we had procedures that were almost able to be followed verbatim.
Not the case where I work now in a commercial lab setting.
We use some K, NA, TB procedures, but mostly MFR provcedures.
Substitution is done in many cases, but it's not common sense that allows you to substitute, it's knowledge of metrology.
Common sense will not translate into TUR knowledge.
Common semse is a requirement in some of the job, but in substitution of standards?

flew-da-coup · 11-23-2005 -- 06:59:15

I have worked Air Force PMEL. I have been in the field for 16 years. My comment about " A K-Pro is not Metrology" only means that I know Flamy and he cannot get through a calibration without one that is flawless. As for my comment about subing standards, well it is not that complicated. If you have the MFR Specs of your standard and the MFR Specs of your TI then what's the problem? To me it's common sense if you can sub. Yes, it does depend if you are doing 4 to 1 or a total uncertinty ratio. However, I know Flamy works for the PMEL at Robins AFB and he is only required to have a 4 to 1. To many people over complicate these things. What is so hard about dividing numbers? I learned that in third grade. Now I would agree that if you are actually working out a Total Uncert. Ratio it does take knowledge. Before you bust my balls, let's keep my comments in context.

flew-da-coup · 11-23-2005 -- 07:06:12

also, I have worked under the NRC for Georgia Powers Nuclear Primary Lab ( Juliette Metrology Lab Ga. Power) and I am currently working for a A2LA Primary Standards Lab now. I am not ignorant of Metrology as you implied.

flew-da-coup · 11-23-2005 -- 07:10:43

It also sounds to me that you are confusing a T.A.R with a T.U.R. and they are by no means the same thing. A 4:1 is not a T.U.R. it is a T.A.R. and there is a hugh difference.

flew-da-coup · 11-23-2005 -- 07:13:15

I apologize. Please disregard my last post. I did not read your other post.