[TCML] Terry Filter Resistors

[piranha]

Hi,

It's a 1000 ohm resistor in series with an inductor.  Feed it a sine 
wave at various frequencies and measure the current and maybe even the 
phase.  With two points you should know the inductance.  They don't make 
multilayer wire wound resistors ;)  One would have to drop on on the 
concrete to see about how it is wound but probably about 50mH.

To really see the inductive part you would have to run the frequency 
high enough to stand out against the 1000 Ohms.

Xl = 2 x pi x F x L

2000 = 2 x pi x F x 50mH  so a frequency of 6 MHz should do.  But that 
is high enough that the Medhurst capacitance could mess things up...  
That is probably what all this is about :D

I hope you get it figured out :D

But remember, those caps too that swamp out the stray capacitance.  At 
say 300kHz, the odd effects would be nil.  It's a second order low-pass 
filter.  Not much should get through it all unless I messed it up =:o

Terry


bartb wrote:
> Hi Ed, Gary,
>
> WOW! I think your right. That sure puts a damper on my multi-layer 
> technique! Would work in multilayer mode, but if a  1K 1/2W carbon is 
> measuring 184mH, then yes, all bets are off and a good lesson learned 
> with the 27XT (and maybe any LCR).
>
> Excellent test Gary!
> Take care,
> Bart
>
> Ed Phillips wrote:
>> I also have a 27XT multimeter.  If I take a 1.0K Ohm, 1/2W carbon 
>> comp resistor (i.e. NO significant inductance) and try to measure its 
>> inductance with this meter, it reads 184mH.  I don't think so!
>>
>> Bottom line - don't try to measure inductance of resistors with this 
>> meter!
>>
>> Regards, Gary Lau
>> MA, USA"
>>
>>     Measuring any kind of coil with this type of meter is sort of a 
>> gamble unless you know what you're doing - the measurement technique 
>> is quite an indirect one.  Works OK with reasonable coil Q but not at 
>> all suitable for measuring the inductance of a WW resistor.  To do 
>> that I'd break one and try to figure out the number of turns and then 
>> calculate it.  I don't think even a good impedance bridge would give 
>> useful results.
>>
>> Ed
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