Calibration Of Electronic Equipment In The Home Workshop

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

----== Posted via Newsfeeds.Com - Unlimited-Unrestricted-Secure Usenet News==----

The #1 Newsgroup Service in the World! 120,000+ Newsgroups

----= East and West-Coast Server Farms - Total Privacy via Encryption =----

What sort of equipment are you trying to calibrate? You can do a search online for various voltage reference sources. Accurate frequency reference can be picked up off the airwaves from transmitters such as WWV. What methods you use depend on what the equipment is and how accurate you need it to be.

"Too_Many_Tools" wrote in news: snipped-for-privacy@8g2000cwh.googlegroups.com:

Wavetek and Fluke both make nice all-in-one calibrators for voltmeters and scopes,they do V,I,R,timing and bandwidth checks.Not cheap,though. There's plenty of older,used cal standards on the market,too. Getting them certified may be a problem due to their age.

For F-counters,you need a WWV or GPS-based receiver.

high-end stuff,you send out to a lab. (consider them your "primary standards")

A warning;calibration procedures of some TEK gear may be written to use their recommended list of standards,and difficult or impossible to do fully with substitutes. Especially their video test gear.

--
Jim Yanik
jyanik
at
kua.net

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.

--
--
kensmith@rahul.net   forging knowledge

** Groper alert !

** A few 0.1% precision resistors does the first job for DMMs.

A Natsemi " LH0070 " 10.000 volt ( +/- 0.02% ) voltage reference IC with

0.1 % resistor divider chain giving 1.000 & 0.1000 volts for the DC volts ranges DMMs and scopes does the second.

For AC volts, a scope screen with internal graticule is used to establish the p-p amplitude of a sine wave - then it can be used to check then AC ranges DMMs etc - to a 1% accuracy.

A 12MHz crystal oscillator ( 11.99993 MHz @ 25C ) checks the DFM - calibrated using an off air standard frequency transmission picked up on a scanner.

....... Phil

If you've got that sort of gear at home then usually you have better (and calibrated) gear at work as well, in which case most of us would simply bring in our gear from home and spot check it against the good gear.

In the absense of this gear, you can simply use precision components. Voltage reference chips with 0.05% or better are cheap and readilly available.

0.01% resistors are available too.

If you have multiple meters for example, you can also keep an eye on them by comparison. Using any old component, if all three meters read the same then you can be pretty confident they haven't drifted.

Checking scope horizontal timebases is easy with a crystal oscillator and divider.

There are various methods for getting an accurate frequency standard, but one of the newst methods is using a GPS derived reference. Second hand Rubidium standards can also be had on eBay.

Generally though, good quality test gear does not drift out of spec, so the need for regular calibration is minimal.

Dave :)

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

You left many things unsaid: (a) Traceable to NBS/NTIS or not; (b) if not, how many reliable digits; (c) at what cost. You can make a 5V "standard" that any loading will not damage with error better than 0.5mV and runs for at least 6 months with no observable change - and the cost is only a few dollars (uses off-the-shelf parts). You can buy thru DigiKey, resistors rated at 0.05% and at 0.1% - rather decent as references. You can buy a Fluke bench meter rated at 6.5 digits and even pay a bit more for traceability.

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.

If it was me, I would start by reading Scroggie's Radio Laboratory Handbook.

--
.

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

Dave :)

In article , too_many snipped-for-privacy@yahoo.com (known to some as Too_Many_Tools) scribed...

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).

--
Dr. Anton T. Squeegee, Director, Dutch Surrealist Plumbing Institute
(Known to some as Bruce Lane, KC7GR)
http://www.bluefeathertech.com -- kyrrin a/t bluefeathertech d-o=t calm
"Salvadore Dali\'s computer has surreal ports..."

This works if you only need about 1 part in a million. The movement of the ionosphere makes wwv useless for real calibration. This was, of course, wonderful when we had nothing else. It is far better to get a gps standard (they are used on cell sites and show up on ebay) and 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.

[...]

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:

?Ref=3107&Site=US&Cat=34342147

For a cheap voltage reference, I would look into Analog device's AD780 series. The AD780BN has an initial error of +-1mV and is available in a plastic 8 pin DIP for easy assembly. Download the data sheet and you'll find sample circuit diagrams. Be sure to use a nice clean power supply and use good decoupling practices around the device.

For resistance, see my post with a link to Digikey.

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.

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.

[.....]

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

>

--
--
kensmith@rahul.net   forging knowledge

chuck wrote in news:1172759975 snipped-for-privacy@sp6iad.superfeed.net:

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.

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.

--
Jim Yanik
jyanik
at
kua.net

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).

--
  Keith