I don't have the manual here at home, but a standard I DL'd I at work --
and I had to hunt for it -- asks ("should") equipment be calibrated with a
signal of four times the accuracy specified for the device in question. If
that accuracy is unattainable, it requires justification be added and a
note in the calibration documents be added regarding the accuracy the
"calibrated" test equipment is good for, regardless of its specifications.
Given MIL-STD-461's generous accuracy requirements, that can't be hard to
live with.
(What I wonder about are requirements one be able to read 1% on a printed
plot!)
Cortland
KA5S
> [Original Message]
> From: Sundstrom, Michael <[email protected]>
> To: Ken Javor <[email protected]>; [email protected]
<[email protected]>
> Date: 8/11/2010 1:25:38 PM
> Subject: RE: Calibration supplier for signal generator with pulse
modulation
>
> Ken / Deniz,
> Speaking of significant digit's: I'm still looking for that EMI receiver
that will measure to 1/100 of a dB. So I can report to a 1/10 of a dB in
reports like I'm asked to.
>
>
>
> Michael Sundstrom
> OHD / TREQ Dallas
> Electronic Lab Analist, EMC Lead
> 2170 French Settelment Rd, Suite B
> Dallas, Texas 75212
> (214) 579 6312
>
>
> -----Original Message-----
> From: Ken Javor [mailto:[email protected]]
> Sent: Wednesday, August 11, 2010 11:59 AM
> To: [email protected]
> Subject: Re: [PSES] Calibration supplier for signal generator with pulse
modulation
>
> This gets back to Mr. Walton's differentiation between EMI testing and
> calibration laboratories.
>
> Clearly modulation, measured with an o'scope, can be measured to the
> tolerances available from the o'scope. That's plenty good enough. It
> strains credulity that there is one brand of scope that would give
sloppier
> results making it easier to pass a test.
>
> The essence of what Mr. Walton and I are saying is well-expressed by the
> rules for using significant digits: You don't get four digit accuracy as
the
> result of computations using two digit accuracy inputs.
>
> EMI limits are quite arbitrary; trying to meet them with accuracy
exceeding
> the limit placement process is unnecessary. As stated earlier, the only
> reason for MU control is on the basic facility chambers/OATS so that there
> is some repeatability from facility to facility, and so that it isn't
easier
> to pass at one facility than another.
>
> Anything beyond that is superfluous and an unnecessary expense.
>
> Regarding the example of the cable at 10 GHz. The MIL-STD-461 measurement
> system integrity check does indeed check that the cable is properly
> accounted for in terms of attenuation. Mr. Demirci is correct that the
> signal generator can be expected to be a better match to the cable than is
> the actual antenna used. However, to the limits of accuracy required for
> EMI testing, the antenna factor calibration takes care of the mismatch
> between antenna and cable, since the antenna is calibrated in a 50 Ohm
> system (albeit likely using pads between antenna and cable for
calibration).
> If further accuracy is desired, most manufacturers provide vswr
> characteristics for their antennas.
>
> Fear isn't the issue. The issue is a misapplication of a process where it
> isn't required, and the patina of precision and accuracy this dishonestly
> bestows on an inherently inaccurate and imprecise discipline.
>
> Ken Javor
>
> Phone: (256) 650-5261
>
>
> > From: Deniz Demirci <[email protected]>
> > Date: Wed, 11 Aug 2010 08:35:06 -0700
> > To: Untitled <[email protected]>
> > Conversation: Calibration supplier for signal generator with pulse
modulation
> > Subject: RE: Calibration supplier for signal generator with pulse
modulation
> >
> > Could you define how precise?
> >
> > What is your acceptance criteria for the modulation dept?
> > Let's say for basic 80 % AM modulation. Is your tolerance 0.1 % or
> > between 60 % to 90 % is good enough.
> > There is more than a dB peak difference in the signal for 60 % AM and 80
> > % AM modulations. You won't realize the difference with a field probe in
> > radiated immunity tests with modulated signal. (Simple math;
> > 20*Log(1.6/1.8) = -1.02 dB) It seems not very insignificant to me
> >
> > Another case;
> > If you are using 6 meter cable for radiated emission at 10 GHz, your
> > cable characterization uncertainty is more than 1.5 dB even with a quite
> > high grade cable (Experimental measurements). Check the cable vswr
> > figures in their specs measured in ideal conditions. Even a simple cable
> > is a significant uncertainty contributor.
> > Your measurement antenna is not exactly 50 Ohm at 10 GHz also. Site
> > imperfection is another story. Those figures are not accounted for in
> > the MIL-STD-461 RE102 verification. Everything seems to be very good
> > when you terminate the measurement cable with a signal generator (50
> > ohm) output. I don't agree with this <quote> an ultimate
> > "proof-of-the-pudding," </quote>
> >
> > You can use all your engineering skills for the tests but you have to
> > quantify your risk using type B measurement uncertainty analysis and do
> > the Type A if you can afford to see where you stand.
> >
> > As Mr. Gremmen said " MU is not difficult"
> > No need to be afraid,
> >
> > OOO (Own opinions only)
> >
> > Best regards,
> >
> > Deniz Demirci
> > National Technical Systems (NTS Canada)
> > Phone: 403-568-6605 ext 244
> > fax: 403-568-6970
> > email:[email protected]
> > web: http://www.ntscorp.com/about/locations
> >
> >
> >
> > -----Original Message-----
> > From: [email protected] [mailto:[email protected]] On Behalf Of Ken
> > Javor
> > Sent: Wednesday, August 11, 2010 7:55 AM
> > To: Untitled
> > Subject: Re: Calibration supplier for signal generator with pulse
> > modulation
> >
> > Precisely.
> >
> > Ken Javor
> >
> > Phone: (256) 650-5261
> >
> >
> >> From: Cortland Richmond <[email protected]>
> >> Reply-To: <[email protected]>
> >> Date: Wed, 11 Aug 2010 08:27:34 -0400
> >> To: emc-pstc <[email protected]>
> >> Subject: re: Calibration supplier for signal generator with pulse
> > modulation
> >>
> >> Not quite what you need to know but I've used signal taps or
> > directional
> >> couplers with a 'scope to watch the RF waveform and set modulation
> > depth,
> >> and a calibrated counter, or even a receiver or analyzer will for
> >> frequency. One always has recourse to calibrated devices to monitor
> >> another, uncalibrated one. It's a good idea anyway! If a detector must
> > be
> >> used whose linearity is unknown, one can use calibrated attenuators to
> > find
> >> out.
> >>
> >>
> >> Cortland Richmond
> >> KA5S
> >>
> >>
> >>> [Original Message]
> >>> From: Wendy Nya <[email protected]>
> >>> To: <[email protected]>
> >>> Date: 8/10/2010 4:23:29 AM
> >>> Subject: Calibration supplier for signal generator with pulse
> > modulation
> >>>
> >>> Dear All,
> >>>
> >>> I am looking for a calibration supplier that can provide accredited
> >> service for
> >>> AR SG6000. It has built-in pulse modulation option (for Radiated
> > Immunity
> >> use).
> >>>
> >>> By the way - Is anyone using this model? It seems to be OEM from
> > Agilent
> >> (it
> >>> came in an agilent box) but the equipment is marked AR
> >>> and works with Agilent N5181A driver. Agilent is saying that it is
> > not
> >> able to
> >>> provide accredited calibration service for this model.
> >>>
> >>> Thanks & Regards,
> >>> Wendy Nya
> >>
> >> -
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This message is from the IEEE Product Safety Engineering Society emc-pstc
discussion list. To post a message to the list, send your e-mail to
<[email protected]>
All emc-pstc postings are archived and searchable on the web at:
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For help, send mail to the list administrators:
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