Normalizing circuits for a DVM meter

Discussion in 'General Electronics Chat' started by DexterMccoy, Feb 19, 2014.

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  1. DexterMccoy

    Thread Starter New Member

    Feb 19, 2014
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    At work we use these 1 Meg ohm Normalizing Black box with banana plugs that goes to the DVM meters inputs RED and BLACK probes

    What are these Normalizing boxes do for DVM meters? it puts a 1 meg ohm resistor across the DVM meter probes for measuring voltage

    It's to make a normalizing circuit , which is a voltage divider it looks like

    But when do you use these normalizing circuits to do voltage measurements?

    a resistor decade box in series to get a 10volts dc reference

    We use the 1 meg ohm Normalizing plug which goes across in parallel in the DVM meter input jacks, then we use a resistor decade box in series , we rotate the resistors decade box until the DVM meter reads 10 volts DC. This is called a Normalizing circuit

    I'm not sure what this normalizing circuit is or why it is used to take certain measurements

    I don't understand the theory or why would want to "normalize the meter readings?

    What circuits or tests would you want to normalize the meter readings?


    Do you now understand the concept of "normalizing?"
    No I don't, please explain to me what it is and what it is used for please?

    When have you used to "normalize" the DVM meter readings?

    What circuits or tests would you want to normalize the DVM meter readings?

    Without normalizing the DVM meter readings what would happen? the readings would be to hard to make sense?
     
  2. ericgibbs

    Senior Member

    Jan 29, 2010
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    hi,
    Whenever you connect a DVM or analog meter across a source that you wish to measure, the impedance of the meter will 'load' the source.

    If the impedance of the source is high and its required that a very precise voltage be measured in the circuit, the voltage being measured while the meter is attached will change when the meter is removed.!

    To allow for the meter loading, which may vary from meter to meter, a fixed accurate load is used across the DVM, ie: in your case 1Megohm at 10.000v.

    So when a measurement is taken the DVM loading of the measured is normalised and the measured voltage is also normalised.

    OK.?
    E
     
  3. DexterMccoy

    Thread Starter New Member

    Feb 19, 2014
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    What do u mean by how the loading is normalized and the measured voltage is normalized?

    What's the difference between meter loaded normalized and Not normalized?
    What's the difference between measured voltage normalized and not normalized?
     
  4. dubbod

    New Member

    Oct 25, 2011
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    Not sure where the term "normalised" comes from but I would expect it has to do with the fact that a modern DVM has a very high input impedance and measuring a voltage with no load may result in errors due to electromagnetic pickup. Try setting your DVM on AC volts and hold the probes in your hands and you will measure a voltage from EM radiation.
    Setting it to low range DC by holding probes to different metals can also measure a small DC voltage due to the Seebeck effect.
    We use a 20K ohm shunt across the DVM input on AC when measuring for line to earth faults on isolated supplies to prevent spurious voltages. The 20K ohm shunt provides a load across the meter so spurious volt pickup is eliminated. I see the system you use as being similar.
     
  5. DexterMccoy

    Thread Starter New Member

    Feb 19, 2014
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    So when normalizing the DVM meters input, you're setting up a max peak voltage

    The 1 meg ohm resistor is in parallel with the meters input, this sets up a max peak voltage? or a peak limiter
     
  6. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    What this set up does is convert measurements down to a range of 10.000 volts nominal.

    That is useful if you want to get readings directly in percentage of changes from that 12 volt reference:

    If your meter reads 11.000 volts you know by inspection your point is 10% higher then nominal, which may not be so obvious if you were to directly read a voltage of 13.2V without doing the math.
     
  7. DexterMccoy

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    Feb 19, 2014
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    Thanks Ernie for the information

    What's the point of doing this converting measurements like this? what would be the difference if you didn't normalize the measurements? yes they would be at a different range or higher voltages, but it's a different percentage than VS a normalized measurement because it's percentage and range is different than a non-normalized measurement?

    The Difference between a Non-Normalized measurement VS a Normalized measurement is?
    1.) The percentage is different?
    2.) The range is different?
    3.) What else?
     
  8. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    When I set up tests for production I assume my mother is doing the test and make things as simple as possible, and try to guide the tech's hand as much as possible.

    Say you have 100 units to test and they require 5% accuracy, and the percent accuracy must be recorded. By normalizing the measurements once at set-up you avoid the time and mistakes from performing 100 division calculations.
     
  9. DexterMccoy

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    Feb 19, 2014
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    So normalizing the meter changes the percentage accuracy? so you don't have to do multiple math calculations?
     
  10. ErnieM

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    Normalizing the meter changes nothing.

    Normalizing the meter allows a direct reading of the percentage accuracy.

    WHY your company does this is just a guess to me, my answer is based on why I would so such a thing.
     
  11. Billy Mayo

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    Mar 24, 2013
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    what do u mean please by percentage accuracy? So normalizing changes the percentage? Percentage range?
     
  12. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    Accuracy = [Vnominal - Vactual] / Vnominal * 100 %

    No.
    No.

    I can do no more to explain this to you.
     
  13. DexterMccoy

    Thread Starter New Member

    Feb 19, 2014
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    So Normalizing the DVM meter changes the Accuracy? or sets an Accuracy range?
     
  14. DexterMccoy

    Thread Starter New Member

    Feb 19, 2014
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    Mr. Chips can you please make this into a thread for me

    How does CR17 thyrsitor work with the RC network? R29 and C25 is a RC delay for the thyristor?
     
  15. DexterMccoy

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    Feb 19, 2014
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    sorry here is the real schematic for it
     
  16. Georacer

    Moderator

    Nov 25, 2009
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    You'll need to provide a title and a subforum if you want this split into a new thread.
     
  17. DexterMccoy

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    Feb 19, 2014
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    It won't let me create a new thread , what is going on?
     
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