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Registered Member #258
Joined: Sun Feb 26 2006, 03:58PM
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Posts: 21
Nice website there "..."
I have an old PAL color pattern generator which is capable of 25kHz square wave and a home brew PWM up to around 700Khz(ok) to 1Mhz(kinda erratic at this Freq). Any of them usable ?
Trying to find out a few salvaged toroidal and rod inductors which I believe is in the range of mH to uH.
Registered Member #2463
Joined: Wed Nov 11 2009, 03:49AM
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Posts: 1546
Try a square wave from a source with a low internal resistance driving the inductor and look at the slope of the triangle when you sample the current. amps/second = Hy.
With a iron core coil the slope up could be compared with the slope down. If you changed the drive to a constant voltage the slope could measure Farads. Dielectric absorption is a concern for capacitors. Ii you havent got a generator, you can use batteries and a push button to furnish the current;works well for very big values; get the button to trigger a single sweep.
Registered Member #2463
Joined: Wed Nov 11 2009, 03:49AM
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Posts: 1546
If you have a function generator that can sweep, the inductor can be connected parallel to a capacitor and the network driven through a resistor. The Y axis voltage across the network will peak at resonance, and if the X axis is driven at the sweep rate of the generator you will get a display that can tell you what the inductance is by calculation. Once you know there is a peak, just manually sweep to find the frequency. This has an advantage because you may see more than one peak due to added capacity in the coil. You could sweep your coil without the external capacitor as well.
You mentioned you had some TV test gear, and perhaps you have an old sweep generator which would be fine for measuring uHy range coils.
With big values of L and C sometimes the value obtained is somewhat defined by the method used to measure it. This is pointed out by Sencore in their manuals on their patented Z meters.
(the phrase constant voltage should be constsnt current in my previous reply in this thread)
Registered Member #258
Joined: Sun Feb 26 2006, 03:58PM
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Posts: 21
radiotech: Thanks for the feedback, It sure took me a while to digest all that! I realized DSO I'm using can in fact generates 5v square wave for probes calibration purpose. Still figuring out how to program the DSO to include the inductance formulae computation.
Below is the video of the inductor I'm trying to measure. The signals looks kinda odd to me, as the oscillation on the left happens during switch on and when switch is off it started to shift to the right with increasing amplitude. What kinda wave form is this ? ]movie.wmv[/file]
Registered Member #258
Joined: Sun Feb 26 2006, 03:58PM
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Posts: 21
Steve: Hahahaha.. noted. But that’s is why I’m here asking, Two or more “Spongy Thingy†are better than one. The scope I mentioned is not the handheld shown in the video. It is an older LeCroy LC564A which I got off cheap from a closed out business. This scope is basically a computer, RISC based with built-in macros and have arithmetic capabilities. Support from manufacture was discontinued a while ago, and their existing document does not seem to be helpful at all with most of their macros had very cryptic names. I was hoping to be able accurately compute the inductance or at least part of it using their built-in software package. Interesting website you got there, What is your take on the wave form ?
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Inductance measurement using true DSO
