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Calibration Of Electronic Equipment In The Home Workshop

Discussion in 'Electronic Repair' started by Too_Many_Tools, Mar 1, 2007.

  1. 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.

    Thanks

    TMT
     
  2. chuck

    chuck Guest

    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
     
  3. MassiveProng

    MassiveProng Guest

    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!
     
  4. James Sweet

    James Sweet Guest


    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.
     
  5. Guest

    As alone as you on a Friday night?
     
  6. Jim Yanik

    Jim Yanik Guest

    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.
     
  7. Ken Smith

    Ken Smith Guest

    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.
     
  8. Phil Allison

    Phil Allison Guest

    ** 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
     
  9. 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 :)
     
  10. 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
     
  11. 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
     
  12. Robert Baer

    Robert Baer Guest

    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.
     
  13. Robert Baer

    Robert Baer Guest

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

    --
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    --
     
  15. 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.

    The only time I altered a Fluke 8060 was an eBay purchase. When
    testing some new boards, I was reading 4.998 on the 5 volt ref. Never
    saw any boards that far off and then tried the other Fluke which was
    as expected. The eBay meter got a little 'tweak' but that was very
    unusual. BTW, the 5V ref on the boards was an ADI AD588 which is
    almost good enough for the 8060. I would use it to cal a 3.5 digit
    meter with no qualms.

    GG
     
  16. 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 :)
     
  17. <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).
     
  18. doug

    doug Guest

    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.
     
  19. JW

    JW Guest

    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&Site=US&Cat=34342147
     
  20. JW

    JW Guest

    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.
     
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