[GreenKeys] Measuring Electromagnet Saturation?

[WA5CAB at cs.com]

You did.  Although you apparently don't realize it.  The original question 
was how to determine the saturation current of a DC solenoid.  There are quite a 
few ways in which to do this, none really having anything to do with 
saturable reactors or mag-amps, unless you just want to try to baffle people with 
bullshit.  But no engineer who just wanted a quick and relatively accurate answer 
would use most of them.  

As I said earlier, if you know the core material, dimensions and the number 
of turns in the coil, you could simply use the B-H curve for the material and 
arrive at a pretty accurate answer in a few minutes without ever getting up 
from you desk.  If you want to actually measure it, there are two practical 
methods.  The Gaussmeter and the Integrator.  The former has mostly replaced the 
latter, although the ready availability of simple reliable op amps has made the 
latter much easier to implement.  And there are some cases (flux density in 
pipeline pipe, for example) where winding a coil may be more practical than 
milling a slot for a Gaussmeter probe, and doesn't introduce any secondary 
calculation.

Anyway, who cares what the AC impedance of the solenoid coil is.  Or how you 
design a magnetic amplifier (not much done since the 50's anyway - pretty much 
a dead technology).  If you want to drain a swamp, use a pump.  If you want 
to measure flux density, use a Gaussmeter.

In a message dated 7/30/2007 10:54:43 PM Central Daylight Time, 
comcents at bellsouth.net writes: 
> Who said anything about measuring inductance with a DC source? The 
> question was how to determine the amount of DC current to saturate a 
> coil inductor with a iron (steel) core.  Since the AC impedance (not 
> inductance - impedance) of such a coil drops like a rock when the core 
> saturates - that is one way to determine the DC current required.
> 
> >And the solenoid coil impedance is just the DC coil 
> >resistance.
> 
> Which is why you use AC riding on the DC "offset".
> 
> Again - look up Magamps and Saturable reactors to learn about this.
> 
> Here is one place to start:
> 
> http://en.wikipedia.org/wiki/Saturable_reactor
> 

Robert & Susan Downs - Houston
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