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 24th October 2009, 03:51 AM #21 star882   diyAudio Member     Join Date: Mar 2007 If you only need to measure a few inductors, you can use a dual channel oscilloscope and signal generator to measure the phase shift. (Use a known resistor as a load.) Then calculate the inductance. It works but is time consuming. In ECEN 325 class, one practical quiz I had to do was identify unknown components using the tools available on the workbench (a signal generator, dual channel oscilloscope, multimeter, and power supply) and a few known reference resistors. The "unknown" components are encased in plastic with two terminals and could contain a resistor, capacitor, or inductor inside. My approach was to connect it into a voltage divider with a reference resistor and then vary the frequency while observing amplitude to narrow down the type of component. Then I do the phase shift trick (or just use the multimeter if it's a resistor) and calculate the value. I was able to obtain some pretty accurate results but I wouldn't want to deal with that every day. __________________ "Fully on MOSFET = closed switch, Fully off MOSFET = open switch, Half on MOSFET = poor imitation of Tiffany Yep." - also applies to IGBTs!
 24th October 2009, 04:27 AM #22 Pano   diyAudio Moderator     Join Date: Oct 2004 Location: SW Florida That's a good class!
 24th October 2009, 09:42 AM #23 Karsten Sømand   diyAudio Member   Join Date: Mar 2006 Location: Outside Copenhagen Since I haven´t got my house full of technical equipment I am normally going for equipment with more functions ie. DMM´s with LCR function etc. In this way you are not "locked" to only doing one thing with the meter. A lot of measuring has to be done when making electronic circuits, loudspeaker cross-overs etc. so an extra DMM can easily be used. Therefore, my suggestion would be to go for a DMM with the L-function (at least). I have found a link which might be useable for you. The prices are not dirt cheap but also not too expensive, I think: Digital Multimeters, DMM, Multimeter Otherwise, try googling "LCR Meter" og make a search on eBay. You might be lucky finding some equipment that is exactly what you want / need. Karsten
anatech
diyAudio Moderator

Join Date: Jun 2004
Location: Georgetown, On
Hi Karsten,
Quote:
 Since I haven´t got my house full of technical equipment I am normally going for equipment with more functions ie. DMM´s with LCR function etc. In this way you are not "locked" to only doing one thing with the meter.
I can see your point there, however a signal generator and an oscilloscope are basic tools you need on the bench. Of course, you can do many things with them, including measure reactive components. A frequency counter is another item that should be on your bench as well.

Now, if you look at the pricing on Eeekbay, an LCR meter is one thing you probably will not be buying. An impedance bridge can be much less expensive, and far more accurate than a function on a DMM. Speaking of these extra functions on a DMM, the only brand that was accurate, and held the accuracy was Fluke. The 87 was pretty accurate for capacitance, but you didn't get any other information about it. A bridge is far more useful and certainly expected in the room of a hobbyist that works on loudspeakers.

The other really big problem when people use a DMM is that they assume an accuracy far greater than what the reality is. At least a needle moving back and forth can remind the user that these readings are approximate. Even the more expensive Agilent / HP LCR meters have limited accuracy. In fact, the accuracy depends greatly on how the test is carried out and whether the leads and / or jig have been compensated for.

-Chris
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