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Analog meters output more current to measure resistance at low currents? Vacuum Tube

Discussion in 'General Electronics Chat' started by Billy Mayo, Dec 6, 2013.

  1. MrAl

    MrAl Well-Known Member Most Helpful Member

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    Hi Billy,

    I think i can tell from your responses that you need to sit down and try this yourself first hand. Sometimes just reading about something isnt enough, that's what we have "labs" for in college courses. This allows you to get hands on experience with the subject matter and it makes a lot more sense when you do this. The text sometimes sounds vague and complex but a few minutes with the test equipment and a few simple test procedures and you understand it 1000 times better all of a sudden.

    So what kind of meter do you have available for your personal testing needs or that you can get hold of for this hands on testing? Also, do you have any diodes around or can get one or two?
    You will need to specify the meter and perhaps take a picture of the meter face as others have done in this thread. we can take a look at your meter and figure out how you can do the test on the diode. You will quickly see how easy and fast this is. You probably also have to be able to open up the meter battery compartment to see exactly what size and voltage the battery is (or if there are two batteries then get both specs), or maybe measure the open circuit voltage across the two leads with a high impedance DC voltmeter when the analog meter is in the x1 resistance range and also in other resistance ranges.
     
  2. Billy Mayo

    Billy Mayo Member

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    i have a simpson 260 at work , I just need to know

    This was not made clear on how to do this

    And how did the Simpson 260 , give you those specific forward voltages and the forward currents?

    What range and settings did u use?

    If I knew what range and settings u used and how you got the specific forward voltages and forward currents , I can try this at work
     
  3. MrAl

    MrAl Well-Known Member Most Helpful Member

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    Hi,

    Verify that your meter looks like this pic...or if different then how so.
     

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  4. dave

    Dave New Member

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  5. ChrisP58

    ChrisP58 Well-Known Member

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    You set it to "Volts" to measure voltage, and you set it to "Amps" or "milliAmps" to measure current.
    You choose the range dynamically to get the best measurement. If the measurements peg the meter, you increase the range.
    If the measurements are all at the low end of the scale, you decrease the range to get better resolution.
     
  6. Billy Mayo

    Billy Mayo Member

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    .

    I know that, but how do you measure the forward voltages and forward currents? are you using an external power supply , cause the Simpson meter can't output different voltages and different currents can it?

    At work they measure a diode using a Simpson 260

    They measure the OHMS of the forward bias and the Reverse Bias, but the diode is in parallel with the gyro or synco motor

    I'm guessing you measure the Diodes resistances because it's in parallel with another component?

    The Simpsons 260 at work, does not have a Diode or semijunction reading on the meter it has only DC, AC, AC Clamp, DB , that's it

    Maybe you guys have a different Simpson 260
     
  7. MrAl

    MrAl Well-Known Member Most Helpful Member

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    Hello Billy,

    You're not reading all the replies. This was described already.

    You use the Ohms x1 scale first, then read off the ohms and the voltage at the same time, using a DC voltage scale as well as the Ohms scale. Then knowing the internal battery voltage you can estimate the voltage of the diode and the current of the diode and that gives you the first data point. You then switch the Ohms range and do it again and that gives you another data point.
     
  8. ghostman11

    ghostman11 Well-Known Member

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    The main difference between there Simpson 260 and yours at work, is the OPERATOR!
     
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  9. MrAl

    MrAl Well-Known Member Most Helpful Member

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    Hi,

    I asked him to verify that his meter was as the picture i posted, but he didnt do that. We need that info to know what the series resistance is, and he also has to check the battery voltage so we know what that is too.
     
  10. ghostman11

    ghostman11 Well-Known Member

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    LG is following on his (i think 1952) AVO meter! it has inspired him to try and fix a couple of the broken ones.
     
  11. MrAl

    MrAl Well-Known Member Most Helpful Member

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    Hi,

    Oh that's a good idea, nice to have a couple working meters around. I kept my one analog meter even though i got several other digitals over the years. I have a couple analog panel meters too that come in handy sometimes.
     
  12. Billy Mayo

    Billy Mayo Member

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    Yes I thought this is what your guys were talking about but it was so confusing with all that math so i wasn't clear

    So you put the ohms on X1 and you're reading ohms SCALE and the DC voltage SCALE? write that down and calculate the current and the internal battery voltage?
     
  13. MrAl

    MrAl Well-Known Member Most Helpful Member

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    Hi,

    Well for the voltage if you dont have a reverse scale (probably dont) then you have to subtract the voltage reading from the max voltage to form a percentage. Then multiply that by the battery voltage.
    So if you use the 10v DC scale and you read 8 Ohms and 6 volts, then 10 volts minus 6 volts equals 4 volts, but that means 40 percent of the battery voltage, so if the battery voltage is 1.5v then multiply 0.4 times 1.5 and that gives you the voltage of the diode (which would be 0.6 volts for these readings). You could then take that voltage and divide by the resistance (8 ohms) and that gives you the current. So now you have one voltage and one current, and that makes up one data point for the diode curve. You then change resistance scale to the next one up i guess and do it again, but this time you'll get different readings.
    You do have to check your battery voltage first however, and since there could be battery loading the low ohms reading will be just a rough estimate of sorts.

    If this still isnt clear, then bring a diode to work with you and use the meter to measure it on the x1 Ohms scale, and take readings for the Ohms and the volts using the 10v DC voltage scale, then come back here and report those values and we'll go through the numbers. You also should get the battery voltage used on the x1 resistance scale so we know what it is.
     
  14. Billy Mayo

    Billy Mayo Member

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    the tech next to me uses the simpson 260 to test for OPEN components or if vcc and ground is open. he said that it takes a lot of current to drive the simspon needle to read an open compared to a digital meter will not read overload when there is an open circuit or component. is this true? that a digital meter will measure random when there an open
     
  15. Reloadron

    Reloadron Well-Known Member Most Helpful Member

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    You totally lost me with that statement. When a circuit is open it is open. When a circuit is open there is Zero current flow. Now if there is zero current flow in an open circuit how can there be any current? Reading zero ohms (a dead short) on a Simpson 260 as in zero ohms (as far from open as we can get) and where we see maximum current from the source. The further we get from zero ohms towards open circuit the less current we draw. Open circuit as I have a lead in each hand going nowhere, no path for current flow, how can it take a lot of current? Think about it.

    A digital meter under open conditions measuring resistance will measure OL (Over Load) and if you look close at a Simpson 260 scale to the extreme left for resistance I see an infinity symbol, what do you see? A digital meter does not read random it reads OL which makes sense. My analog meter reads infinity which also makes sense.

    Back in post #65 I clearly demonstrated this with an image. Did you miss that? Obviously you did or you never would have posted what you just did.

    Ron
     
    Last edited: Dec 17, 2013
  16. Reloadron

    Reloadron Well-Known Member Most Helpful Member

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    My Bad, please be so kind as to ignore this post.

    Ron
     
  17. ghostman11

    ghostman11 Well-Known Member

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    I am just trying to follow all this, as i am sure you will appreciate it is all somewhat complicated. So let me see if i have things correct so far, lets call this a recap.

    In your company when you have a dead/dud board, it goes to a as yet unnamed department.
    On its arrival to said unnamed department, the board is given to the ' MANAGER ', who obviously being the manager, and in charge is allowed to play with use the oscilloscope.
    He presumably is the slightly more technical one, as he is the one that answer's some of your questions, and on occasion has a good idea. So he.... randomly pokes about probes the board.
    Now this bit i am unsure of due to recent information you have given, but here goes, lets see if this is right. After his random poking about probing of the board, he declares the fault as either a short, in which case he passes it to you, presumably because he know's you have no chance of finding the short, seeing as you ask him so many basics, such as how to switch the meter on. Then after a unknown and again presumably random time frame, declares that you desolder a large amount of unknown IC's, in the hope that will scare the short away.

    or he declares the fault as open, and obviously as this is a different type of fault, to the one you are designated to find, he passes it to a recently discovered other, who is designated the open fault finder?
    do i have this correct so far?
     
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  18. Billy Mayo

    Billy Mayo Member

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    I agree with you and this is what I thought also about an open circuit has zero current flow

    But the tech next to me said that the simpons 260 takes a lot of current to drive the needle to make it an open circuit, it's not easy for the simpson 260 to measure an open circuit unless it's really an open circuit the tech said.

    The tech said that with a DVM meter it picks up false open circuits and false open components, VS a simpson will really tell you if the circuit , path or component is OPEN because of how much current you drive the simpson , the needle of the simpson needs a lot of current

    But I was like an open circuit has no current flow, but I think i know what he is trying to say , do u?
     
  19. ghostman11

    ghostman11 Well-Known Member

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    So that only makes any sense if he is trying to open a short by using high current, never used or seen a simpson, but i doubt very much is has that much power ;), if he is trying to blow open short's, be nice to him and point out a PSU with a good amount of Amps (say 20 -40), is probably a better choice.

    Erm if the simpson is a multi meter and not a cartoon, then it can measure a non open circuit, while on the correct range just fine. If its a open circuit, then it wont read anything, the odd thing about a open circuit is there isnt anything to measure.

    So his meter gives a reading when the circuit or component is actually open? In this case send it out to be repaired. or do you mean the components isnt really open (false)? and the meter tells you this?
    Hate to say it, but if a circuit isnt really open (false) and your meter takes a reading that shows it isnt open.........then it's doing what they paid for.


    This would imply that, it takes alot of current to measure nothing?

    2 things
    1) i thought YOU were the tech?
    2) please stop calling him that, he isnt.

    Then TAKE you FINGER off the needle! and you should find it draw's a little less!

    so he sits next to you, i bet i can guess what they call that corner ;)
     
  20. Billy Mayo

    Billy Mayo Member

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    When you use a DVM meter VS an analog meter, what is better when measuring an OPEN circuit, path, component?

    The tech next to me claims a DVM meter is the wrong choice for this because it doesn't measuring Open circuits, paths, components well? maybe cause of the test current and test voltage, but he claims you will get false or random readings VS a simpson analog it will be a for sure thing it's an open circuit, path, component never a false reading from it
     
  21. ghostman11

    ghostman11 Well-Known Member

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    I have never measured an open circuit, ive tried a few times but couldn't find anything to measure, so they are both crap at taking readings from open circuits.

    please i asked you nicely to stop calling him that!

    Well i wouldn't say the wrong choice, but i would agree all meters are rubbish at taking readings from open circuit's.

    Or maybe because there isnt anything to measure.

    If its under warranty send it back, if it isn't BIN IT , because it's broken, or ask your technical department to get a tech to look at it. Try and stay away from the ones they allow to play with use an Oscilloscope, there is a very small chance,that one of those types might fix it.
     

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