Re: How to measure inductance indirectly?

> I have several inductors I'd like to know the values of. I have no way to 
> measure L directly, ie, with a meter. 
>
> I've got a scope and signal generator. Is it as simple as hooking a known 
> value of C in series with the L and sweeping the frequency range looking for 
> a peak in V (accross the inductor) and a drop in I?

Not really- it depends on what the application is. If for example the 
inductors are for a switching power supply application, then you would 
want to measure the current response to a step voltage at various levels 
of DC bias- inductance is inferred from rise time L/R. If the inductors 
are to be used for RF or some other linear application where Q might be 
of interest then a simple technique is to use the Hay bridge at the 
application frequency:

        Please view in a fixed-width font such as Courier.

                           Hay Bridge


           +-----------+-----------------------------------+
           |           |                                   |
           |           \ _                                 \
           |       R1  / /|                             R3 /
           |           \                                   \
           |          //                                   /
           |           | _                                 |
           |           | /|                                |
           |       C1 ===   +------------------------------+
          ---         /|    | +-----+                      |
         /   \         |    )|(     |                      |
         | ~ | sig     |    )|(     |                      |
         \   / gen     |    )|(    ===                     |
          ---          |    | |     |                      |
           |           +----+ | sd  |                      +------+
           |           |      +-|>|-+-/\/\-+-> VOM         |      |
           |           \      |            |               )      \
           |       R2  /      |           ===           Lx )   Rx /
           |           \      | detector   |               )      \
           |           /      |            |               )      /
           |           |      |            |               |      |
           |           |      |            |               |      |
           +-----------+------+------------+---------------+------+
           |
           |
          ---
         ///


          Adjust R1 C1 for null at operating  w=2pif where:


          (R1-j/(wC1))(Rx*jwLx)=R2R3(Rx+jwLx)


                  Lx
          =>  Rx* -- = R2R3Rx  or Lx=C1*R2*R3
                  C1


               and

                                    R2*R3
         => R1RxwLx=R2R3wLx  or Rx= -----
                                     R1

            Rx
         Q= ---
            wLx