Question about difference in Q readings

Discussion in 'General Electronics Chat' started by EdGs, Oct 30, 2012.

  1. EdGs

    Thread Starter New Member

    Mar 10, 2011
    17
    2
    I work for a company that manufactures custom voice and specialty coils.

    We have a custom job wound with litz wire and gets checked at 40KHz.

    We are using a Protek Z9218 LCR meter and get readings of 703uH inductance and 220 Q at the 40KHz test frequency.

    We sent some samples to our customer and they got very similar inductance readings, but their meter read only 130 Q.

    I don't know what brand of meter they use, but it also is a lower end model similar to ours (I was shocked at the price of some of the higher end meters). I called Protek to see if they could shed some light on the reason for the difference in Q reading, but they could not explain it. In the time since I last spoke with them, they are no longer in business.

    Any thoughts as to the reason for the different Q readings? This is pure curiousity on my part as our customer is very pleased with the coils we make for them, and there are no problems with functionality, etc.

    Thanks very much.
     
  2. panic mode

    Senior Member

    Oct 10, 2011
    1,318
    304
    Protek is still in business but your LCR meter is obsolete
    http://www.protektest.com/ProdInfo.asp?prodId=Z9218
    Given that you also have no info about the other meter, it is not surprising that they didn't bother to dig deeper. This is high precision unit, when was the last time it was calibrated?
     
  3. Papabravo

    Expert

    Feb 24, 2006
    10,135
    1,786
    We might want to start with what the Q of a coil represents and how it might be measured. Start with the process and the equipment you are familiar with. Then we have a basis for hypothesizing about differences in setup and measurement that might explain the differences. Sound like a plan?
     
  4. EdGs

    Thread Starter New Member

    Mar 10, 2011
    17
    2
    I emailed Protek about replacement parts/and accessories about 2 weeks ago and was told they were no longer in business.

    The protek meter is in calibration according to our standard coils that we use for reference. This difference was noticed on this litz wire coil. We also have another LCR meter here, but it does not have the available test frequency required for these. I am in the process of comparing the two meters at frequencies that they both cover to compare the results.

    I am not at liberty to discuss the process used for this job. I am aware that these meters are very sensitive to outside influences and such. I just wanted to aske here since Protek couldn't give me an answer on the meter that they built.
     
  5. Papabravo

    Expert

    Feb 24, 2006
    10,135
    1,786
    So here is the thing. There are several different methods of making the measurement. Each of them depends on the values and tolerances of other components to determine what the coil will do in a resonant circuit. I would expect a given coil to show a range of Q values over time. Depending on the application this may be OK or it may not. Without more details it is hard to be more helpful.

    If I were you I'd bone up on measurement techniques with other instruments you have at hand to see if you can form some kind of a consistent picture.

    For example:
    http://www.wetterlin.org/sam/SA/Operation/Measurement_Inductor_Q.pdf
     
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