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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. Rich Grise

    Rich Grise Guest

    And cover everything in the lab with aluminum foil, so your body
    capacitance doesn't zap your meter first time out. ;-)

    Cheers!
    Rich
     
  2. Jim Yanik

    Jim Yanik Guest

    After reading all this,I checked the $3 DMM I bought at a Harbor Freight
    sidewalk sale,and it turns out the *input Z is only ONE megohm*. YUK!

    I only bought it as a 2nd DMM,for monitoring PS outputs and the like.
    The manual did not list that particular spec,either....
     
  3. Robert Baer

    Robert Baer Guest

    Why?
    I made that shunt box and use it on occasions where i need to measure
    low currents, and have seen no problems whether i use it with my 3.5
    digit DMM or my 4.5 digit DMM.
     
  4. Robert Baer

    Robert Baer Guest

    I bet it also does not state the input Z onthe current scales, or the
    current(s) to be expected on the resistance scales.
    OTH, most meter manuals leave out most of those (significant, at
    times) details.
     
  5. According to the specs, the accuracy is a percentage of the reading that is
    being observed. I take that to mean that at small readings, you have an
    equivalently small error since it's a percentage (well...+ uncertainty
    digits which never changes and is certainly a large part of the reading when
    trying to measure 50nA). Hence the 30-70nA expected reading. Now that I've
    read the manual, I see that their marketing material was a little optimistic
    on the number of digits in current mode. Turns out to be 20 and not 2 like
    the marketing slick says, hmmm..... is there no truth in advertising
    anymore? At least there is a delta button to erase away the noise reading
    of about 10nA after it settles down.

    I would hope that the days of needing to keep things in the upper third of
    the scale went out with the analog meters. But aparently they haven't. I
    was looking at the manual and they mention that true RMS readings are
    specified over 5% - 100% range. Tell me what this means: "Maximum Crest
    Factor <5:1 at full scale, <10:1 at half scale" and then they add some extra
    that makes it sound like they are only referring to AC signals that are
    non-sinusoidal with that.

    And you're right, it is inaccurate when you look at it like that.
    Fortunately by using the delta button or just a little quick math to
    subtract the idle reading, I can obtain what I need. Sort of.... ;-)
    Sorry about that, here you go:
    http://www.extech.com/instrument/products/alpha/MM560_570.html

    Not that I can see.
    Got it today, I like it so far. :) See the new thread on the Extech vs.
    Micronta shootout.
     
  6. MassiveProng

    MassiveProng Guest

    Your dumb shit is as old as grandma's hills and just as weak.

    Your doc needs to up the Lithium dose, dipshit.
     
  7. MassiveProng

    MassiveProng Guest


    Simple Ohms's law also states that when you series that mess with
    your circuit under test, all the voltage will drop on your precious
    resistor/meter set-up , and there won't be any in the circuit you wish
    to examine.

    In other words, dumbass, the reason that shunts are of low ohmic
    value is so they do not modify the circuit you are attempting to
    examine.

    Your stupid shit certainly would do just that. Your lack of
    understanding that a current meter needs to be of low resistance is
    quite a tell as well. You must be a digital guy, and seemingly not a
    very good one to miss this basic.
     
  8. MassiveProng

    MassiveProng Guest


    Idiot! The GriseTard is declaring that HE is a trollbaiter.

    Go play in traffic. Oh... that's right... you are.
     
  9. MassiveProng

    MassiveProng Guest


    This is why when I use a meter to measure current, I use very short,
    huge gauge 14Ga SPC leads. When I measure low voltages, I twist the
    meter leads together to cancel any local "injection" sources.

    Trust me, both methods have a positive effect. Typical meter leads
    are very small ga, and are a poor choice for current measure as there
    is an error introduced by the lead resistances. Twisted meter leads
    most certainly do cancel out local disturbances that could render your
    readings in error. Both practices work well.
     
  10. MassiveProng

    MassiveProng Guest

    You're an idiot, and this is not a useful, relevant, or practical
    post.
     
  11. MassiveProng

    MassiveProng Guest

    You are truly clueless.

    Typically two groups of scaling, and two shunt resistors, one for
    each group.

    BOTH VERY LOW resistance.
     
  12. Really now. And I thought that Ohm's Law stated that the voltage would be
    split up in a predictable way.
    Stupid me, I thought they were for fire prevention.
    You really aren't getting it are you? This is about measuring very small
    currents, the large resistance doesn't have to drop any significant voltage.
    I can't believe you have such an inept understanding of Ohm's law that you
    keep harping about. The world is not all about 200A and 15kV there are
    people getting things done with nanowatts of power. Just think about it,
    how much voltage drop do you get with 50nA thru a .01Ohm resistor? How
    would you measure 500 femtovolts? You have no concept of scale.
     
  13. MassiveProng

    MassiveProng Guest


    It will, dumbass. Most of it will be on his 1 M Ohm SERIES "shunt"
    (Bwuahahahahah). That means there wont be much left for the circuit.
    Can you really be that fucking stupid?

    If you are at 5Volts and passing 2 amps in a circuit, and add a 1M
    resistor in series with it, what do YOU think happens to the voltage
    presented to that ten ohm loading?

    Oh and it wouldn't just drop voltage. The current that the circuit
    WAS used to seeing will be a lot less as well.

    Ohm's law INDEED!
     
  14. MassiveProng

    MassiveProng Guest

    Stupid you indeed. That's not what the INLINE fuse is for, dipshit.
    It is in the meter, but is there to limit the voltage presented to the
    meter mechanism or when current is being shunted through the resistor.

    The shunt has nothing to do with fire prevention. They are a
    precision shunt meant to provide a precision voltage to a high
    impedance volt meter such that it can provide the user with a reading
    of the current in the circuit that it was placed into WITHOUT
    modifying the operation of the circuit.

    Your 1 M setup would NOT qualify for a device that does NOT modify
    the circuity to a great degree. It would qualify as a device that so
    badly modifies the circuit being tested that it no longer represents
    the circuit that was originally given.
     
  15. Robert Baer

    Robert Baer Guest

    I gave p ersponding to him a while back as being a useless waste of time.
     
  16. Robert Baer

    Robert Baer Guest

    I gave up responding to him a while back as being a useless waste of
    time.
     
  17. ehsjr

    ehsjr Guest

    But that's the greatest "extra" meter since sliced bread.
    Seriously. It costs next to nothing, so you are not afraid
    of abusing it, which means you can toss it in your tool box
    or your glove box or the trunk. If you fry it, drop it, the
    dog eats it, aliens from the UFO beam it up and disect it,
    whatever, it is essentially no loss. You treat (or should
    treat) your "real" meter far more kindly, and use it when
    you need more confidence in your measurements. That Harbor
    Freight meter is surprizingly accurate, in the sense that
    you expect that a $3.00 meter just _has_ to be way out of
    whack. It's not. If you absolutely have to know the exact
    number, you wouldn't use it - you'd measure with your "real"
    meter. But for most of the measurements people make with a
    DMM, the $3.00 meter is fine. And that $3.00 includes the
    9v battery!
    Perfect use for that meter. :)

    Ed
     
  18. doug

    doug Guest

    That is 333 kohms per dollar. That is a lot cheaper than the 10 kohms
    per dollar my hp34401s cost. I have a bunch of these for 30th -40th
    meters. (You cannot be serious about second meter). It is necessary
    to have a meter within arm's reach anywhere you are in the house. Also
    a digital caliper. We used to have three optical monochromators on the
    end table in the living room. They were handy when you wanted to check
    the spectrum of a new fluorescent bulb.

    The cheap meters are accurate encough for a lot of work and you do not
    care if they get broken. It is always a shock to my system to see how
    cheaply things can be sold.
     
  19. Can you???? You just can't accept the facts of this can you?
    Do you know how to calculate it? WE ARE TALKING ABOUT 50nA YOU MORON. Now
    get with the program or just STFU.
    50nA you idiot. DO THE MATH!
     
  20. BTW, I'm surprised you didn't have anything to say about my Extech/Micronta
    Shootout thread? I did some resistance measurements and the Micronta is
    right on with way less than 1% difference. Drifted to another plane, ha ha
    ha >15 years old and still within 1% on most functions. HA HA HA HA Wrong
    again DM.
     
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