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?
Links to recommended circuits, pictures and sources would be appreciated.
Since this is a need for anyone who has test equipment, I hope to see a good discussion on this subject.
"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.
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.
** 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.
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)
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.
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.
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?
On 28 Feb 2007 21:47:49 -0800, "Too_Many_Tools" Gave us:
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 f*ck 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.
On Thu, 1 Mar 2007 06:05:56 -0600, "Anthony Fremont" Gave us:
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.
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.
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!
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