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Old 31st May 2006, 07:48 AM   #1
ostie01 is offline ostie01  Canada
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Default Non inductive resistor

Hi, How can I know if a resistor is non inductive if I want to use it in crossover set up. is there a way to measure it, Thanks
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Old 31st May 2006, 08:03 AM   #2
Jennice is offline Jennice  Denmark
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What kind of measurement equipment do you have?
Do you have an oscilloscope or a True RMS voltmeter with sufficient frequency range (see its datasheet)?
Do you have a signal generator of some sort?

Jennice
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Old 31st May 2006, 08:15 AM   #3
ostie01 is offline ostie01  Canada
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HI, yes I have everything you have listed
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Old 31st May 2006, 08:26 AM   #4
matjans is offline matjans  Netherlands
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check the resistor's datasheet. Most of the time the data given in there is within 10-20% of measured data.

that is, if you know the resistor's make or brand
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Old 31st May 2006, 09:28 AM   #5
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I think that inductance measurement in range below 1uH will be very difficult at home. You can measure inductance of wirewound resistors(without non inductive windings), which is high above 5-10uH.
Better way is looking in datasheets.
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Old 31st May 2006, 12:35 PM   #6
Jennice is offline Jennice  Denmark
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Agreed. Data sheets are clearly the number one choice, but my guess is the brand/type is unknown.

My suggestion would be to make a voltage divider with the unknown resistor and a well known, non-inductive type in series.
Using a sine generator, a sweep should show a change in the divider ratio between the known and unknown type.
The needed sweep range will depend on the inductance.
If the sweep goes way beyone audio frequencies before it reveals any change, the resistor should be fine for a XO-design.

Jennice
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Old 31st May 2006, 12:54 PM   #7
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Default Re: Non inductive resistor

Quote:
Originally posted by ostie01
Hi, How can I know if a resistor is non inductive if I want to use it in crossover set up. is there a way to measure it, Thanks
Check how wirewounded resistors usually look like, compare datasheets, ask us!

In most cases you can see if a resistor is wirewounded or not.
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Old 1st June 2006, 08:06 AM   #8
AndrewT is offline AndrewT  Scotland
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Hi,
let's assume my resistor (0r1 or 0r22) is wirewound (I know it is).

I also have a high value metal film resistor (1r0) that may have a spiral track ground into it.

Now wire the metal film and wirewound in series and measure the inductance of the wirewound.
HOW?

Can we assume the inductance of the metal film is zero?

Some can of worms!
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Old 1st June 2006, 08:51 AM   #9
Jennice is offline Jennice  Denmark
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AndrewT,

You seem to have too many worms in your scot'ch drinks.

One thing is that you don't agree, but there are many ways to disagree. Maybe your location on an island isolated from the european mainland was God's way of saying you don't behave too well?

I took the liberty to assume some knowledge on Ostie01's behalf, which you have clearly demonstrated to lack yourself, or hide behind equal portions of arrogance and ignorance.

Anyway...

Quote:
My suggestion would be to make a voltage divider with the unknown resistor and a well known, non-inductive type in series.
As I pointed out, the reference resistor should be well known, i.e. by a datasheet which would also indicate any inductance, if applicable.

I did not say I wanted to MEASURE the inductance of the wirewound resistor.

As the frequency changes, so does the complex impedance of the unknown resistor, if it is inductive.
If Z_unknown is sqrt(R*R + Inductive_part*inductive_part), and the inductive_part is zero at DC, then the changing ratio (over frequency) of the voltage divider (compared with the ratio at DC) should make it possible to calculate the complex part, and hence the inductance of the unknown resistor.

Jennice
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Old 1st June 2006, 11:28 AM   #10
AndrewT is offline AndrewT  Scotland
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Hi Jennice,
nice of you to come back and illuminate.

Could you take the time to turn your description into a formula?

i.e. I measure the volts drop across the metal film and wirewound at DC and again at an AC frequency. How do I convert that into useful answers?

Do I need to parallel the high value metal film to approach the resistance of the wirewound?
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