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'[EE] Tek Scope Calibration'
2010\01\05@053736 by Forrest W Christian

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Now I've got a second LCD DSO (aka I have a spare), I'm thinking of
sending out them one at a time to get them calibrated - something I've
never done, but in the past few years, I've been finding it very nice to
have reasonably-close readings on my scope for things like pulse width
and voltages....  It would be nice to

Having never done this I don't even know the price range to expect or
whether there are any third-party labs which do a good job - or if I
should just send these to Tek.

Just for reference, the two I'm talking about are a TDS1002 and a TDS2014.

Experiences, Ideas, Suggestions?

-forrest


2010\01\05@100639 by Mark Scoville

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We paid $210 to get our TDS2024 calibrated by Transcat. That cost included
test data required by our ISO-9000 manager. Sometimes calibration is less if
you don't need the test data. Shop around - there are plenty of places.

My rough estimate is that each calibration costs about 10% (roughly) of what
the equipment cost to purchase. So, after 10 years of calibrating the
equipment you have invested roughly 2x what the equipment initially cost to
purchase.

Hope this helps.

-- Mark

{Original Message removed}

2010\01\05@102222 by Mark Rages

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On Tue, Jan 5, 2010 at 9:08 AM, Mark Scoville
<spam_OUTMScovilleTakeThisOuTspamunicontrolinc.com> wrote:
> We paid $210 to get our TDS2024 calibrated by Transcat. That cost included
> test data required by our ISO-9000 manager. Sometimes calibration is less if
> you don't need the test data. Shop around - there are plenty of places.
>
> My rough estimate is that each calibration costs about 10% (roughly) of what
> the equipment cost to purchase. So, after 10 years of calibrating the
> equipment you have invested roughly 2x what the equipment initially cost to
> purchase.
>
> Hope this helps.

Is it worthwhile for a scope?  I can see calibration for a 6.5 digit
DMM, but for a scope I'm usually looking for ballpark waveforms.  This
is what I was taught in school as well (with analog scopes, where the
the knobs have "uncalibrated" sections).

I would think you can check the scope against a known-good DMM for
voltage accuracy, check against a precision oscillator (such as the
one in a frequency counter) for time base accuracy, then consider it
calibrated.

Regards,
Mark
markrages@gmail
--
Mark Rages, Engineer
Midwest Telecine LLC
.....markragesKILLspamspam@spam@midwesttelecine.com

2010\01\05@104017 by Mark Scoville

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Mark, *you* can compare a DMM to *your* scope and *consider* it calibrated -
and in many instances you would be fine. Our ISO certification *requires* us
to calibrate all instruments every year and to archive before/after test
data for all the manufacturers performance specs for ALL measuring
equipment. This is far from an inexpensive endeavor and I have fought for
more *resonable* requirements - but I get voted down by the ISO gurus.

I have heard stories about NASA calibrating instruments just before
disposing of them. Thought is that they need to verify that the instrument
*was* in calibration during it's last year of use.

So there are different levels of calibration "madness"

-- Mark

{Original Message removed}

2010\01\05@111244 by Mark Rages

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On Tue, Jan 5, 2010 at 9:42 AM, Mark Scoville
<MScovillespamKILLspamunicontrolinc.com> wrote:
> Mark, *you* can compare a DMM to *your* scope and *consider* it calibrated -
> and in many instances you would be fine. Our ISO certification *requires* us
> to calibrate all instruments every year and to archive before/after test
> data for all the manufacturers performance specs for ALL measuring
> equipment. This is far from an inexpensive endeavor and I have fought for
> more *resonable* requirements - but I get voted down by the ISO gurus.
>
> I have heard stories about NASA calibrating instruments just before
> disposing of them. Thought is that they need to verify that the instrument
> *was* in calibration during it's last year of use.
>
> So there are different levels of calibration "madness"
>
> -- Mark

What are you using a scope for that is that critical? Sounds like
madness to me -- like you're using the wrong tool for the job.

Regards,
Mark
markrages@gmail
--
Mark Rages, Engineer
Midwest Telecine LLC
.....markragesKILLspamspam.....midwesttelecine.com

2010\01\05@112943 by Forrest Christian

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For years, I was of the same opinion that you were.  Primarily because I
was doing a lot of low-precision analog work.  Even till today I'm still
somewhat of that opinion - for a lot of things, calibration isn't really
useful.   Especially if you can compare 'good' and bad.

Unfortunately, I'm doing some testing which a lot of the 'I don't need a
calibrated instrument because of x' start to fail.  For instance, I'm
often comparing high-accuracy timing signals, and trying to determine
exactly how many microseconds (or nanoseconds) that a signal is leading
or lagging.   Just an example (and yes there are ways around it, but why
jump through hoops when a calibrated scope is quick and easy)

-forrest

On 1/5/10 8:22 AM, Mark Rages wrote:
{Quote hidden}

2010\01\05@113114 by Sean Breheny

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I agree with Mark R. You can just check the calibration yourself with
a few tests. Also, most modern scopes have a built-in
self-calibration. These are accurate enough for reasonable uses of the
scope. The paid calibration is really for users who have to have a
documentation trail for legal or certification purposes.

Sean


On Tue, Jan 5, 2010 at 10:22 AM, Mark Rages <EraseMEmarkragesspam_OUTspamTakeThisOuTgmail.com> wrote:
{Quote hidden}

>

2010\01\05@113247 by Alan B. Pearce

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>Mark, *you* can compare a DMM to *your* scope and *consider*
>it calibrated - and in many instances you would be fine.

This is not traceable calibration, whereas ISO certification is looking for
traceable calibration.

>Our ISO certification *requires* us to calibrate all instruments
>every year and to archive before/after test data for all the
>manufacturers performance specs for ALL measuring equipment.
>This is far from an inexpensive endeavor and I have fought for
>more *resonable* requirements - but I get voted down by the ISO gurus.

We have a similar requirement, and I moan about the requirement for having
power supplies 'calibrated', but when one thinks about it, such calibration
should be checking for hum and ripple as well ...

This reminds me of a story which would have occurred either side of WW2,
where a certain radio factory found that all its VOMs produced different
readings for a given voltage. So to stop the continual fights with the
development lab, it was agreed that on one particular day all the VOMs would
be gathered together in one place, one of them selected as being the
standard, and all the others were adjusted to correspond to that one by
adjusting the magnetic shunt on the meter. Everyone was then happy in the
lab and on the production floor, as any meter could be used to measure
anything within an acceptable accuracy without argument.

One day the inevitable happened, a new guy was employed, and he happened to
have as his favourite toy a nice brand new Avo Model 8. But he couldn't work
out why his nice brand spanking new meter which should be spot on for
calibration had a consistent error to every other meter in the place. No-one
was going to let on though ...

2010\01\05@113315 by Sean Breheny

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I think Mark S and Mark R actually agree in principle. The reason why
it was necessary to officially calibrate the scope is that ISO just
has a blanket rule which probably makes sense most of the time but is
a bit too broad. The calibration satisfies a rule - not an actual
physical need for accuracy.

Sean


On Tue, Jan 5, 2010 at 11:12 AM, Mark Rages <KILLspammarkragesKILLspamspamgmail.com> wrote:
{Quote hidden}

> -

2010\01\05@113415 by Mike Harrison

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On Tue, 5 Jan 2010 10:12:29 -0600, you wrote:

>On Tue, Jan 5, 2010 at 9:42 AM, Mark Scoville
><TakeThisOuTMScovilleEraseMEspamspam_OUTunicontrolinc.com> wrote:
>> Mark, *you* can compare a DMM to *your* scope and *consider* it calibrated -
>> and in many instances you would be fine. Our ISO certification *requires* us
>> to calibrate all instruments every year and to archive before/after test
>> data for all the manufacturers performance specs for ALL measuring
>> equipment. This is far from an inexpensive endeavor and I have fought for
>> more *resonable* requirements - but I get voted down by the ISO gurus.

Almost every ISO workshop I've been in has 'not calibrated' or 'for indication only' stickers on
many of the instruments.
Sounds like the ISO people are trying to justiify their own existance. How many more bits of test
gear could you afford if you had a more sensible cal regime...?

>What are you using a scope for that is that critical? Sounds like
>madness to me -- like you're using the wrong tool for the job.

Absolutely!



2010\01\05@113658 by Mark Scoville

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> What are you using a scope for that is that critical? Sounds like
> madness to me -- like you're using the wrong tool for the job.
>
> Regards,
> Mark
> markrages@gmail

Seems like madness to me too - I agree.

I don't believe we are using the wrong tool for the job. We are not, for
example, using the scope to measure mV, we have plenty of DMMs for that -
and all are calibrated once a year. The way our ISO manager thinks "if it is
in the building, it needs to be calibrated". So everything is calibrated...
DMMs, scopes, calipers, gage blocks, thermocoujple meters... everything.

So, the scope can sit in a cabinet for 11 months a year and still needs to
be calibrated once a year. It's nuts - and expensive.

-- Mark

2010\01\05@113703 by Mike Harrison

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On Tue, 05 Jan 2010 03:36:59 -0700, you wrote:

>Now I've got a second LCD DSO (aka I have a spare), I'm thinking of
>sending out them one at a time to get them calibrated - something I've
>never done, but in the past few years, I've been finding it very nice to
>have reasonably-close readings on my scope for things like pulse width
>and voltages....  It would be nice to
>
>Having never done this I don't even know the price range to expect or
>whether there are any third-party labs which do a good job - or if I
>should just send these to Tek.
>
>Just for reference, the two I'm talking about are a TDS1002 and a TDS2014.
>
>Experiences, Ideas, Suggestions?

DSOs just don't need timebase cal, as (a) it will be xtal controlled so highly unlikely to ever go
out of spec and (b) nobody uses scopes for timing measurements that need anything like crystal
accuracy.  

2010\01\05@115113 by Alan B. Pearce

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>DSOs just don't need timebase cal, as
>(a) it will be xtal controlled so highly unlikely to ever
>    go out of spec and
>(b) nobody uses scopes for timing measurements that need
   anything like crystal accuracy.

and (c) most DSOs have markers that you can move around to measure with so
you don't need to read the waveform on the screen, just the numbers given.
Cannot recall if this fits the Tek TDS1000 & TDS2000 series though.

2010\01\05@115207 by Sean Breheny

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Another thing that is madness is that I've come across so-called "cal
labs" which do not do a thorough job and still issue a NIST-traceable
cal certificate.

Sean


On Tue, Jan 5, 2010 at 11:39 AM, Mark Scoville
<RemoveMEMScovillespamTakeThisOuTunicontrolinc.com> wrote:
{Quote hidden}

> -

2010\01\05@115659 by Alan B. Pearce

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>The calibration satisfies a rule - not an actual
>physical need for accuracy.

Not quite correct. The rule might be that you count the swaps before and
after operating on someone, but the reason for doing so is rather important.

Similarly with calibrating instruments before use, and immediately before
disposal. At least then you know that measurements made between those times
are correct. If the calibration before disposal isn't done, and the UUT goes
out the door and has a problem, when was the error introduced, did it leave
uncelebrated due to faulty test gear, or is it an internal fault? Real
important to know when you cannot go service it - the guys that paid for
Hubble were just plain lucky.

2010\01\05@115713 by Carl Denk

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The ISO's are based on paperwork and procedures to ensure quality. When
an organization qualifies for ISO, that is a benchmark that they DO all
the things necessary to ensure quality. One of the results is some
unnecessary jumping through the hoop. The only real comparisons for
calibration are back to some standard at regular intervals. It may be
that the ISO approved procedure includes comparing 2 or more instruments
at a more frequent interval. With ISO, the intention is to provide high
quality without end of the line testing.

Mike Harrison wrote:
{Quote hidden}

2010\01\05@120834 by Alan B. Pearce

face picon face
>did it leave uncelebrated due to faulty test gear,
                ^^^^^^^^^

Argh, spelling checker strikes again ...

Should read 'uncalibrated' ...
--

2010\01\05@123258 by Sean Breheny

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I should have been more clear: I meant that, in the case of certain
instruments, like normal scopes being used for non-critical
measurements, calibration only satisfies a rule. Honestly, I've never
worked at a place which had to calibrate scopes, but I imagine that
the vast majority of scope calibrations are done because some
standards agency requires calibration of all instruments used at a
certain site. For example, imagine that you have a production line
which is ISO certified. In one step, a DMM is used to measure a
voltage to 0.1% accuracy. In another step, a scope is used just to
verify that an oscillator is running and is within +/- 10% of a
certain frequency. In reality, the DMM needs calibration and the scope
doesn't. However, I wouldn't be surprised if ISO required cal for the
scope, too, in this case.

As someone else pointed out, scopes aren't really precision measuring
devices. Voltage measurements are typically only good to about 1% at
best, due to ADC resolution and attenuator accuracy. Time measurements
are typically good to about 100 ppm, limited by the accuracy of the
timebase, which is often just a regular (non-ovenized) crystal
oscillator. Such an instrument is not likely to go out of these limits
unless there is a fault. Because the limits are rather wide to begin
with, it is not typically used to do things like precisely count
frequency or precisely measure amplitude. The only critical
application I can see which would truly require calibration would be
if gross inaccuracy would cause major problems, such as life-safety
critical applications. In this case the calibration is just a
formalized method for verifying that such a gross inaccuracy condition
has not occurred. Gross inaccuracy is unlikely enough that most
applications can assume that it has not occurred.

Sean


On Tue, Jan 5, 2010 at 11:56 AM, Alan B. Pearce
<Alan.B.PearceEraseMEspam.....stfc.ac.uk> wrote:
{Quote hidden}

> -

2010\01\05@123436 by Mike Harrison

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On Tue, 05 Jan 2010 11:56:56 -0500, you wrote:

>The ISO's are based on paperwork and procedures to ensure quality. When
>an organization qualifies for ISO, that is a benchmark that they DO all
>the things necessary to ensure quality. One of the results is some
>unnecessary jumping through the hoop. The only real comparisons for
>calibration are back to some standard at regular intervals. It may be
>that the ISO approved procedure includes comparing 2 or more instruments
>at a more frequent interval. With ISO, the intention is to provide high
>quality without end of the line testing.

But ISO does not necessarily require  that all instruments must be calibrated, externally or
otherwise.
ISO is ONLY about documenting processes to acheive the required quality, not the quality itself.
As long as uncalibrated instruments are suitably labelled, and your procedures state what procedures
require the use of calibrated instruments there is no problem.

Any instrument used for production testing obviously needs traceable calibration, but that
traceability could be achieved by checks against other instruments, provided suitable 'de-rating' is
applied. e.g. if you have an externally cal'd voltage source accurate to 0.01%, this can happily be
used to check instruments to 0.1% accuracy.
Of course there is a potential 'eggs in one basket' situation if you rely on too few  externally
cal'd instruments to calibrate others, in the situation where the externally cal'd kit is found out
of spec before re-cal, but even then, unless it is faulty it is unlikely to be an order of magnitude
out of spec unless it's actually faulty or you're dealing at extremes of measurement ranges.

Most test equipment is typically used for development, debug and repair, most of which do not
require super-accuracy or  traceability.

{Quote hidden}

2010\01\05@124554 by Dave Tweed

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Carl Denk wrote:
> The ISO's are based on paperwork and procedures to ensure quality. When
> an organization qualifies for ISO, that is a benchmark that they DO all
> the things necessary to ensure quality.

That's a very common misperception.

Actually, the only thing that ISO guarantees is *consistency* -- you
have to document your procedures and processes, and then follow the
documentation consistently. As you say, that should reduce the need for
end-of-line testing, because there should be less variation among the
units to begin with.

It's up to each organization to come up with processes and procedures
that actually result in high-quality products and services. Customers
may ask to see your ISO documentation, and of course, they will make
their own judgement as to whether your processes meet their needs for
quality. Or else, they'll test your product and assume, based on ISO
certification, that you're going to consistently produce product at
that level of quality.

ISO certification is *only* about the paperwork, not the actual level
of quality.

-- Dave Tweed

2010\01\05@124816 by Ruben Jönsson

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> The ISO's are based on paperwork and procedures to ensure quality. When
> an organization qualifies for ISO, that is a benchmark that they DO all
> the things necessary to ensure quality. One of the results is some
> unnecessary jumping through the hoop. The only real comparisons for
> calibration are back to some standard at regular intervals. It may be
> that the ISO approved procedure includes comparing 2 or more instruments
> at a more frequent interval. With ISO, the intention is to provide high
> quality without end of the line testing.
>

We are an ISO9000 certified firm and we have set the procedures up so that we
only need to calibrate 1 DMM. All quality (and ex safety) measurements and
verifications are done with that DMM. However, the audition (review) this year
resulted in some mechanical measurement instruments that needs to be calibrated
also.

We also use oscilloscopes, other DMM's, temperature instruments and som others
that are not calibrated and that is OK.

/Ruben
==============================
Ruben Jönsson
AB Liros Electronic
Box 9124, 200 39 Malmö, Sweden
TEL INT +46 40142078
FAX INT +46 40947388
EraseMErubenspampp.sbbs.se
==============================

2010\01\05@134251 by Mark Scoville

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> Another thing that is madness is that I've come across so-called "cal
> labs" which do not do a thorough job and still issue a NIST-traceable
> cal certificate.
>
> Sean

I have run into this too. In one instance we had sent a device out to be
calibrated by TransCat. They came back and told us the unit was out of
calibration and could not be repaired. TransCat supplied us a "quote" with
suitable devices they suggested we purchase to replace the "bad" unit. We
elected to simply get the unit back. I tested it - it seemed to work fine.
So I then sent it back to the manufacturer for repair and calibration. The
manufacturer checked it out and certified that it was recieved "in-spec" -
the manufacturer could find nothing wrong with the unit.

-- Mark


2010\01\05@135452 by Sean Breheny

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Wow, that's bad, although not what I meant. I encountered a place
which cal'd a spectrum analyzer for me and when I did the calibration
check as described in the manual, it failed. They provided me with a
certificate listing all their equipment and its traceability, etc.
However, all that doesn't do any good if you fail to go through all of
the cal steps (it is very involved for this item, it would probably
take all day to perform).

Sean


On Tue, Jan 5, 2010 at 1:45 PM, Mark Scoville
<RemoveMEMScovilleEraseMEspamEraseMEunicontrolinc.com> wrote:
{Quote hidden}

> -

2010\01\05@150603 by Carl Denk

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Have to agree with what was said, just didn't go into all the words. :)

Dave Tweed wrote:
{Quote hidden}

2010\01\05@153055 by M. Adam Davis

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On Tue, Jan 5, 2010 at 11:33 AM, Mike Harrison <RemoveMEmikespam_OUTspamKILLspamwhitewing.co.uk> wrote:
> Almost every ISO workshop I've been in has 'not calibrated' or 'for indication only' stickers on
> many of the instruments.

I skipped the previous calibration cycle at work with my power supply,
and right before the ISO audit it was given a shiny new "CALIBRATION
NOT REQUIRED" sticker.

Now I don't ever have to worry about it again for this piece of equipment.

However, I bought a bunch of used equipment from a surplus auction
last year, and it all had calibration stickers on it that told me when
it was last done - some within the last year.  It's nice buying old
equipment that has been recently calibrated.

So it's a double edged sword.  As long as I don't have to pay for it,
or my measurements are non-critical, I don't worry about it.

However, there are some very good reasons for yearly traceable
calibration in ISO-9000 shops, so don't knock it until you understand
it.  Keep in mind that ISO 9000 isn't about doing the right thing or
having an ideal process - it's about documention and traceability with
the end result being consistency.

2010\01\05@181912 by Mark Scoville

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Hi Sean, I realized after I had sent my story that it was not the same thing
as what you were relating. We've not yet encountered anyplace that has
neglected to cal a unit , but sent a certificate anyway. In addition to our
TransCat episode we had another vendor cal a multimeter and send the test
data for someone elses unit. You have to watch closely - the calibration
people are human too.


{Original Message removed}

2010\01\05@201016 by Peter van Hoof

face picon face
This also depends on wich ISO certification
My company is ISO 9001:2000 certified and this means that only
equipment directly used to verify end product quality has to be calibrated

Not for example the multimeter or scope of the tech that repairs production
equipment.

Peter van Hoof



{Original Message removed}

2010\01\06@040627 by Alan B. Pearce

face picon face
>In reality, the DMM needs calibration and the scope doesn't.
>However, I wouldn't be surprised if ISO required cal for the
>scope, too, in this case.

However the internal rules that the ISO certification is issued against
could allow internal calibration of such scopes, against a unit with
traceable calibration, or against other standards (e.g. crystal oscillator).
To get such changes to the internal procedures it probably needs a case to
the management to show how much money they could save by not getting
expensive external calibration done (but on the other hand, a persons time
to do the calibration may make the external fee much cheaper ...).

2010\01\08@170826 by Clint Sharp

picon face
In message <RemoveMEE1NSDTP-0006rp-SLTakeThisOuTspamspamelasmtp-dupuy.atl.sa.earthlink.net>, Dave
Tweed <EraseMEpicspamspamspamBeGonedtweed.com> writes
>Carl Denk wrote:
>> The ISO's are based on paperwork and procedures to ensure quality. When
>> an organization qualifies for ISO, that is a benchmark that they DO all
>> the things necessary to ensure quality.
>
>That's a very common misperception.
>
>Actually, the only thing that ISO guarantees is *consistency* -- you
>have to document your procedures and processes, and then follow the
>documentation consistently.
The way our consultant explained it was thus;

If you say in your procedure that you slap the customer across the face
left cheek first then right cheek you better damn well do it that way
round when you get audited.

It doesn't matter *what* the procedure is, as long as you adhere to it.

--
Clint Sharp

2010\01\08@170826 by Clint Sharp

picon face
In message <RemoveMEWorldClient-F201001051139.AA39170109KILLspamspamunicontrolinc.com>,
Mark Scoville <MScovilleSTOPspamspamspam_OUTunicontrolinc.com> writes
>So, the scope can sit in a cabinet for 11 months a year and still needs to
>be calibrated once a year. It's nuts - and expensive.
Can you not just mark it 'for indication only' in that case? It's the
way we got around having to have scopes calibrated when we went for ISO.
>
>-- Mark

--
Clint Sharp

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