Calibration Of Electronic Equipment In The Home Workshop

[MassiveProng]

As alone as you on a Friday night?

I think there is a fly buzzing around the room. Perhaps it's only
flatulence.

Of no consequence either way.

 

[Anthony Fremont]

If you have used test gear, and you do not intend to PAY to have it
calibrated, you be best off leaving it all the **** ALONE!

You're amazing. You don't even know what equipment, qualifications or needs
he has, yet you're right there with THE answer. Lets take an example. I
have a 20 year old Hitachi scope as you know, the voltage cal is way off
(~20%) in a couple of ranges. Are you suggesting that I should drag it
across town, spend $200 and be without it for 2 weeks just to get it
adjusted by some obstinate, E-1 grade line tech, instead of using a brand
new DMM w .03% accuracy to tweak it myself? I'm quite sure that my Micronta
is up to the task to be honest.

If someone doesn't need traceable calibration, then why should they pay for
it? Especially if they have the resources to do it themselves. I'm
thinking of buying a cheap used Rb time base from e-bay so I can cal my old
Protek freq counter and adjust the timebase on my Hitachi scope, it's
certainly cheaper than having it done. Using a PIC driven by an ordinary
can xtal, and a quartz wristwatch of known accuracy, I was able to tweak the
xtal to within about 1-2ppm over the course of a week or two. Of course you
know that's impossible, don't you?

 

[MassiveProng]

For frequency, you can use WWV. You need:
A short wave radio with an audio output.
Perhaps an audio filter tuned to about 1KHz.
A generator you wish to calibrate near the WWV frequency.
A frequency counter that is not too far off.

Procedure:
Tune in WWV.
Put wire on generator and set it to WWV-1KHz
Listen for tone and move stuff around until it sounds good.
Feed tone into the filter.
Place the counter on the output of the filter.

The number on the counter is X Hz away from 1KHz when the generator is XHz
off from WWV-1KHz.

Joe Kane's audio video set up discs on Laser Disc, and DVD, and now
HD DVD are the bee's knees for a lot of audio spectrum sine wave
tones.

DVD $20, Player $40 TV and Audio gear already owned.

Catching it off some transmission has to be far more inaccurate.
Short wave receiver worth having $100 plus. Then add in audio gear?

Catching you thinking old is better than new after your brow beating
of BAH... priceless.

Hehehe... just kidding...

 

[MassiveProng]

LOL

You're a real ray of sunshine, aren't you?

Now go out and play in traffic while we adults talk about serious
stuff..

TMT

Serious? Look, dumbfuck, if you are concerned with calibration,
then you should be concerned enough to do it right. Asking here the
way you did means that you are beyond your depth to start with.

If you are too stupid to take your device to a place where freshly
calibrated devices are, and check it against them, you are too stupid
to be attempting to do it with some patched up method in the home
without cal manuals from the makers of all those devices. Far too
stupid.

So **** you, pops.

You prove that numeric age does not an adult make. The traffic I
play in runs at 30GHz, so you are screwed with that presumption as
well. I had calibrated meters back in 1970, and knew more then than
you do know.

 

[MassiveProng]

Thanks for the (positive) comments so far.

I look forward to any more you might want to offer.

Any circuits or examples others have done?

Any cal boxes that anyone have built?

TMT

All the circuits suggested here, while appearing good on the surface,
are all likely to introduce more error into your instruments than
correct.

THAT IS WHY REAL calibration services are used, and why I suggested
that if you do not intend to have it professionally calibrated, you...
YOU IN PARTICULAR, should just leave the gear alone, as you are too
fucking stupid to do it without introducing the aforementioned error.

In other words, they are better off UNcalibrated and still reliable,
than after any futzing around a twit like you will do with them. You
LACK the competence.

You want to attack my adulthood, fine, little boy. You are
BRAINLESS for this task.

I have worked in cal labs and in QA for years. You lose, sonny.

 

[MassiveProng]

True, 0.01% resistors are available, *but* they are extremely
expensive (over $100 each) and they are made when and if the
manufacturer sees fit to do so.

Or if the order is large enough.

 

[MassiveProng]

You're amazing. You don't even know what equipment, qualifications or needs
he has, yet you're right there with THE answer. Lets take an example. I
have a 20 year old Hitachi scope as you know, the voltage cal is way off
(~20%) in a couple of ranges. Are you suggesting that I should drag it
across town, spend $200 and be without it for 2 weeks just to get it
adjusted by some obstinate, E-1 grade line tech, instead of using a brand
new DMM w .03% accuracy to tweak it myself? I'm quite sure that my Micronta
is up to the task to be honest.

You are to be disappointed. The scale dial on that scope is likely
fitted with resistors, and one of them has shifted, which shifts all
the dividers on the dial below it.

It is not a calibration issue. It is a repair issue.

So shove it up your ass, you E-1 grade dipshit.

Your micronta? Bwuahahahahahah!

 

[Anthony Fremont]

You are to be disappointed. The scale dial on that scope is likely
fitted with resistors, and one of them has shifted, which shifts all
the dividers on the dial below it.

Given that the symptom is not as you describe, then I figure you are
probably wrong, again. If so, I imagine I can fix it.

It is not a calibration issue. It is a repair issue.

You just know it all don't you?

So shove it up your ass, you E-1 grade dipshit.

Just had to get that anal jab in there, huh?

Your micronta? Bwuahahahahahah!

Since 3% accuracy is considered good in the scope world, I think it would do
fine.

 

[Tim Shoppa]

I have a well stocked test bench at home containing a range of analog,
digital and RF test equipment as I am sure most of you also do.

Well the question I have is how do you handle the calibration of your
equipment? What do you use for calibration standards for resistance,
voltage, current and frequency?

It depends entirely on what you need the equipment for.

If for any legal reason you need NBS traceability, then the question
of how and how often is already answered by your regulatory agencies.

If you don't, then I cannot imagine that a couple off-the-shelf
precision resistors, voltage references, and frequency references
(total cost: $10) would not be good enough for sanity checking for
almost any pedestrian uses.

If you're the sort who keeps equipment on your bench just to calibrate
equipment on your bench just to calibrate equipment on your bench,
then any rational argument about traceability is pointless because
you've already set yourself up in an infinite circular loop.

Tim.

 

[Ken Smith]

This works if you only need about 1 part in a million.

One PPM is enough for almost all the test equipment you will find on
places like ebay.

You can do better if you average over longer periods.

[.....]

just use it for the timebase all the time. Alternately, use a Rb
source. They were also used in cell sites and are available easily.
They cannot move more than about a part in 100 million and they make
excellent time bases for frequency counters.

I thing someone messed up a decimal. You just made a Rb clock 100 times
worse that WWV.

 

[Jim Yanik]

<snippety>

I could post pictures... ;-)


Hmm. Excellent question.

For frequency, I actually have three different references, all
GPS-
locked. One is my primary reference, an HP Z3801, as retired from a
cellphone site. The second and third ones are both combination clocks
and freq-references, one from Trak Systems (now Trak Microwave) and
the other from Odetics/Zypher. All three use a very stable OCXO that
is constantly disciplined by the GPS receiver.

Long-term accuracy is on the order of 1E10 -11th or so. In other
words, about as good as you can get without being NIST certified.

I don't have good primary voltage or current references as yet.
That's on the 'Acquire' list for scrounging this year. For resistance,
simple Pomona plugs with 0.01% tolerance resistors work pretty well
for 2-wire. For anything more, I will probably have to rent one of the
Fluke all-in-ones.

I'm just beginning to gather the goodies I need for calibrating
my
O-scope collection. That will eventually consist of Tektronix leveled
sine-wave generators, and one of their CG5xxx series calibration
generators.

Keep the peace(es).

TEK sold their TM500/5000 line to TEGAM years ago,they may still make some
calibration products. www.tegam.com

 

[Jim Yanik]

reminds me of the local TV station techs who insisted that the video gear
of theirs I serviced and calibrated was off,and it turned out their 75 Ohm
termination was 87ohms.Other techs double-terminated monitors and
complained of low brightness,tried to tweak it in,screwed it all up.
Or they would have a "reference" generator at the end of 100's of feet of
coax and complain it was a few percent off.

A lot of good points have been made already so I'll just add a small
one.

Don't mess with calibration of quality equipment unless you have
reason to believe the calibration is off AND THAT IS ADVERSELY
AFFECTING YOUR WORK PRODUCTS. An amazing amount of electronics work
has been done using equipment with non-current calibration stickers,
some of which was out of calibration.

If metrology is something that interests you as a hobby, then jump
into it and have fun. Tim's last paragraph ought to be printed and
framed.

Chuck

this is good advice,because without a service manual and cal procedure,you
have no way of knowing what adjustments INTERACT with others.
Adjust a power supply,and gain and timing goes out the window.
Freq.response tweaks can affect more than one area of the signal.


for example,
TEK 475s have multiple vertical gain adjustments,and different adjustments
for the 2/5-10mv ranges.And the gain affects F-response.

 

[krw]

this is good advice,because without a service manual and cal procedure,you
have no way of knowing what adjustments INTERACT with others.
Adjust a power supply,and gain and timing goes out the window.
Freq.response tweaks can affect more than one area of the signal.


for example,
TEK 475s have multiple vertical gain adjustments,and different adjustments
for the 2/5-10mv ranges.And the gain affects F-response.

A *real* good example of calibration adjustments that interact is
the trigger delay lines used in 60's era scopes. Without a
program, calibrating one was impossible (hard enough with).

 

[Bud--]

For frequency, you can use WWV. You need:
A short wave radio with an audio output.
Perhaps an audio filter tuned to about 1KHz.
A generator you wish to calibrate near the WWV frequency.
A frequency counter that is not too far off.

Procedure:
Tune in WWV.
Put wire on generator and set it to WWV-1KHz
Listen for tone and move stuff around until it sounds good.
Feed tone into the filter.
Place the counter on the output of the filter.

The number on the counter is X Hz away from 1KHz when the generator is XHz
off from WWV-1KHz.

I believe the color subcarrier in a color TV is phase locked to the
transmitted signal and, for network studio transmissions, is derived
from a cesium clock. From what I have read it is more accurate than WWV
and doesn't require extra equipment other than a TV displaying an image
with a studio source. Frequency is 3.579545 MHz.

 

[Clint Sharp]

Joe Kane's audio video set up discs on Laser Disc, and DVD, and now
HD DVD are the bee's knees for a lot of audio spectrum sine wave
tones.

DVD $20, Player $40 TV and Audio gear already owned.

Aren't you reliant on the stability of the DVD player reference clock
for the stability of the test tones? I would suspect a GPS reference
would be considerably better. Of course, I could be wrong!

 

[doug]

This works if you only need about 1 part in a million.

One PPM is enough for almost all the test equipment you will find on
places like ebay.

You can do better if you average over longer periods.

[.....]

just use it for the timebase all the time. Alternately, use a Rb
source. They were also used in cell sites and are available easily.
They cannot move more than about a part in 100 million and they make
excellent time bases for frequency counters.

I thing someone messed up a decimal. You just made a Rb clock 100 times
worse that WWV.

No. One part in 100 million (10^-8) is 100 times better than wwv
(10^-6). There is lots of excellent equipment on ebay that can take
advantage of this level of accuracy. The main point is that you do
not have to think about it very often. The low cost counters that have
uncompensated or poorly compensated timebases are basically useless for
any serious work. The other nice part about the high stability
references is that you can distribute it to all the synthesizers on your
bench and everything is coherent.
Of course it depends on what you do. For my ham work, one ppm is fine.
I do other work where the Rb source is not good enough.

 

[clifto]

I agree with Prong on this one. I've worked in repair and broadcast
for 35 years. Unless you have a compelling reason to change it, leave
it alone. Of course, this assumes it's good stuff to begin with like
Fluke and Tek.

A few years ago I got stuck with the Telequipment scope, the last junk
available. It was sadly out of calibration. I whipped up a few voltage
dividers and took other stuff and spent an hour calibrating the vertical
channels and horizontal timebase. I got my work done. The head tech
wanted to know how, and I told him, and he hit the ceiling, ran to the
other room, grabbed the scope and sent it out for calibration.

He was strangely silent when the scope came back. When I asked him
outright about it, he didn't look up from his work when he mumbled
something about the vertical being 0.4% off reference.

Mission-critical? Send it out. Need for extreme precision? Send it out.
But if 2-5% is good enough and you've got some time and imagination,
you can get it awfully close to where you need it.

 

[clifto]

I believe the color subcarrier in a color TV is phase locked to the
transmitted signal and, for network studio transmissions, is derived
from a cesium clock. From what I have read it is more accurate than WWV
and doesn't require extra equipment other than a TV displaying an image
with a studio source. Frequency is 3.579545 MHz.

I've seen that discussed elsewhere, and although it would take me a week
to find the particulars, (1) the frequency can be off as much as 10 Hz
by FCC standards, (2) from what I've read it's frequently off by more
than that, even on network feeds, (3) IIRC they don't even use the good
clocks on the networks any more, (4) NIST clocks are going to be a couple
of orders of magnitude better than the best a network would buy for the
purpose of meeting FCC regulations, (5) IIRC the frequency should
actually be 3,579,545.454545454545..... Hz, and (6) Doppler shift on
the incoming television signal could potentially cause the subcarrier
frequency to vary up and down.

 

[Chris Jones]

If someone doesn't need traceable calibration, then why should they pay
for
it? Especially if they have the resources to do it themselves. I'm
thinking of buying a cheap used Rb time base from e-bay so I can cal my
old Protek freq counter and adjust the timebase on my Hitachi scope, it's
certainly cheaper than having it done. Using a PIC driven by an ordinary
can xtal, and a quartz wristwatch of known accuracy, I was able to tweak
the
xtal to within about 1-2ppm over the course of a week or two. Of course
you know that's impossible, don't you?

I don't think the oscillator on a PIC would be good to 2ppm absolute
accuracy even with a very good xtal, unless you FIRST calibrate it against
something that has already been calibrated, therefore it doesn't get you
far. It will however be good enough to calibrate your scope since that
would only need 1% or so, and any old crystal should achieve that, even
with a fairly primitive oscillator. For frequency calibration, your best
bet is to receive an off-air standard, for example GPS or in many countries
there are low frequency standard transmissions (50kHz, 60kHz, 77.5kHz or
others, look up which ones are available in your country). It is quite
feasible to build your own receiver for these. These transmitters are
maintained to a higher accuracy than any piece of hardware that a hobbyist
could afford (e.g. 2 parts in 10^12).
http://www.npl.co.uk/time/msf/ctm001v05.pdf

Chris

 

[David L. Jones]

[...]

True, 0.01% resistors are available, *but* they are extremely
expensive (over $100 each) and they are made when and if the
manufacturer sees fit to do so.

Not so.
RS Components have 0.01% resistors for AU$34.50 (US$26)
Farnell have 0.02% for as little as AU$20

You guys are paying *way* too much. We use Riedon .01% precision resistors
in our A/D products, and pay about 5 bucks apiece. Their site is down at
the moment, but even Digikey has .01% resistors for around the same price:http://www.digikey.com/scripts/DkSearch/dksus.dll?Criteria?Ref=3107&S...

It's not too much when you only want a couple, and you can have it
within the hour.

If you want volume and price matters, sure, you shop around.

Dave