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Trevor Wilson
Guest
Wed Jun 22, 2011 11:49 pm
StrandElectric wrote:
Quote:
"Trevor Wilson" <trevor_at_rageaudio.com.au> wrote in message
news:96cg0fFur4U3_at_mid.individual.net...
StrandElectric wrote:
Can anybody with a good inductance meter, please measure a 10 watt
wirewound resistor of 820oms and tell me the inductance. I am
getting wildly different figures from various sources.
**That's because there is no one, correct answer. Some wirewound
resistors are bifilar wound, which exhibits far lower inductance
figures than regular wound resistors. You need specify which
resistor you are using. Better still, you should contact the
manufacturer, as he/she will be able to provide all the data you
require. Even betterer, would be for you to measure the inductive
reactance of the resistor, as this data is likely to be far more
useful to you. --
Trevor Wilson
www.rageaudio.com.au
Agreed Trevor, but my crude instrument is very poor at measuring L. I
was hoping that someone who uses Jaycar 10% R would also have a
decent measuring instrument.
**I did not suggest that you try to measure inductance. I said you should
measure INDUCTIVE REACTANCE. BIG difference.
All you need to do is:
Measure the resistance.
Measure the total reactance at (say) 100kHz).
Subtract the resistance and you are left with inductive reactance.
With the inductive reactance figure, you will be able to calculate the
inductance.
--
Trevor Wilson
www.rageaudio.com.au
Trevor Wilson
Guest
Wed Jun 22, 2011 11:54 pm
Phil Allison wrote:
Quote:
"Trevor Wilson"
StrandElectric wrote:
Can anybody with a good inductance meter, please measure a 10 watt
wirewound resistor of 820oms and tell me the inductance. I am
getting wildly different figures from various sources.
**That's because there is no one, correct answer. Some wirewound
resistors are bifilar wound,
** Invariably labelled "non inductive" and cost way more.
You need specify which resistor you are using.
** 10W, WW = standard rectangular cement coated resistor.
Better still, you should contact the manufacturer, as he/she will be
able to provide all the data you require.
** If you speak Chinese.
Even betterer, would be for you to measure the inductive reactance
of the resistor,
** OK - you go get a 10W, 820 or 1000ohm cement resistor and YOU
measure its inductance.
**I said: INDUCTIVE REACTANCE.
Quote:
Go on - try !!
**I've done so on many occasions. Though, I hasten to add, not 820 Ohm
resistors. Usually, much lower value resistors. The principle is the same
however. I don't see the point in trying to measure inductance directly. As
you have already stated, the resistance value will completely swap the
inductive reactance value. With rudimentary test equipment, it is simple
enough to measure the total reactance and perform the appropriate maths to
calculate inductance.
--
Trevor Wilson
www.rageaudio.com.au
StrandElectric
Guest
Thu Jun 23, 2011 1:58 am
"Phil Allison" <phil_a_at_tpg.com.au> wrote in message
news:96e1tcFparU1_at_mid.individual.net...
Quote:
"StrandElectric"
"Phil Allison"
Can anybody with a good inductance meter, please measure a 10 watt
wirewound resistor of 820ohms and tell me the inductance.
** The inductance is so small it is totally irrelevant compared to the
820 ohms of resistance.
Phil. That depends entirely on the frequency in use, in this case up to
30 Megs!
** The change in impedance is not going to be more than 2 ohms - and
might be up or down.
I still neeed that measurement.
** Try using this.
http://www.daycounter.com/Calculators/Air-Core-Inductor-Calculator.phtml
You should get about 0.3 uH
At 30 MHz, this has a Z of 56 ohms
The new impedance of your 820 ohm resistor is then 822 ohms - in theory.
You are wasting your time.
That's a bit hasty Phil,
** No it is not.
as you don't know what I'm trying to do
** Not knowing what you are doing IS your problem !!
You know nothing twit.
.... Phil
Oh dear, back to type. That was a very mild comment from me hardly requiring
such an extreme put down! The last few posts from you have been really
helpful. Now you have degenerated into the same person I remember from long
ago. No, there's much I don't know but I know that, and don't mind asking
for opinions, including yours, one of which hopefully won't be how to
speak/type in a civilised manner to your correspondents, beacuse you have a
bit to learn about that.
Quote:
StrandElectric
Guest
Thu Jun 23, 2011 1:59 am
"Trevor Wilson" <trevor_at_rageaudio.com.au> wrote in message
news:96fdmmFailU3_at_mid.individual.net...
Quote:
Phil Allison wrote:
"Trevor Wilson"
StrandElectric wrote:
Can anybody with a good inductance meter, please measure a 10 watt
wirewound resistor of 820oms and tell me the inductance. I am
getting wildly different figures from various sources.
**That's because there is no one, correct answer. Some wirewound
resistors are bifilar wound,
** Invariably labelled "non inductive" and cost way more.
You need specify which resistor you are using.
** 10W, WW = standard rectangular cement coated resistor.
Better still, you should contact the manufacturer, as he/she will be
able to provide all the data you require.
** If you speak Chinese.
Even betterer, would be for you to measure the inductive reactance
of the resistor,
** OK - you go get a 10W, 820 or 1000ohm cement resistor and YOU
measure its inductance.
**I said: INDUCTIVE REACTANCE.
Go on - try !!
**I've done so on many occasions. Though, I hasten to add, not 820 Ohm
resistors. Usually, much lower value resistors. The principle is the same
however. I don't see the point in trying to measure inductance directly.
As you have already stated, the resistance value will completely swap the
inductive reactance value. With rudimentary test equipment, it is simple
enough to measure the total reactance and perform the appropriate maths to
calculate inductance.
--
Trevor Wilson
www.rageaudio.com.au
Hi Trevor, I presume you mean setting up a tuned circuit with known
capacitance and seeing what frequency it resonates at?
StrandElectric
Guest
Thu Jun 23, 2011 2:01 am
"Phil Allison" <phil_a_at_tpg.com.au> wrote in message
news:96e27mFs1oU1_at_mid.individual.net...
Quote:
"StrandElectric"
Agreed Trevor, but my crude instrument is very poor at measuring L. I was
hoping that someone who uses Jaycar 10% R would also have a decent
measuring instrument.
** Calculate the impedance of 20pF of stray capacitance at 30MHz.
I'll even give you the formula:
Xc = sq. rt ( 2 . pi . F .C )
Imbecile.
.... Phil
Thanks, apart from the completely unneceassry last word. I am loath to
killfile you because you often post good sense. Could you try not to be so
childish and nasty with it?
StrandElectric
Guest
Thu Jun 23, 2011 2:01 am
"Phil Allison" <phil_a_at_tpg.com.au> wrote in message
news:96e2baFsu4U1_at_mid.individual.net...
Quote:
"Phil Allison"
I'll even give you the formula:
Xc = 1 / ( 2 . pi . F .C )
.... Phil
Thanks very much.
Trevor Wilson
Guest
Thu Jun 23, 2011 2:21 am
StrandElectric wrote:
Quote:
"Trevor Wilson" <trevor_at_rageaudio.com.au> wrote in message
news:96fdmmFailU3_at_mid.individual.net...
Phil Allison wrote:
"Trevor Wilson"
StrandElectric wrote:
Can anybody with a good inductance meter, please measure a 10 watt
wirewound resistor of 820oms and tell me the inductance. I am
getting wildly different figures from various sources.
**That's because there is no one, correct answer. Some wirewound
resistors are bifilar wound,
** Invariably labelled "non inductive" and cost way more.
You need specify which resistor you are using.
** 10W, WW = standard rectangular cement coated resistor.
Better still, you should contact the manufacturer, as he/she will
be able to provide all the data you require.
** If you speak Chinese.
Even betterer, would be for you to measure the inductive reactance
of the resistor,
** OK - you go get a 10W, 820 or 1000ohm cement resistor and YOU
measure its inductance.
**I said: INDUCTIVE REACTANCE.
Go on - try !!
**I've done so on many occasions. Though, I hasten to add, not 820
Ohm resistors. Usually, much lower value resistors. The principle is
the same however. I don't see the point in trying to measure
inductance directly. As you have already stated, the resistance
value will completely swap the inductive reactance value. With
rudimentary test equipment, it is simple enough to measure the total
reactance and perform the appropriate maths to calculate inductance.
--
Trevor Wilson
www.rageaudio.com.au
Hi Trevor, I presume you mean setting up a tuned circuit with known
capacitance and seeing what frequency it resonates at?
**No. You are simply measuring the inductive reactance. All you require is a
signal source, a high freqency millivoltmeter, a known non-inductive
resistor (or resistors) and a pocket calculator.
You are over-thinking the whole thing. As Phil has already stated, trying to
measure inductance, with a resistor of such a value is fraught with
difficulty.
--
Trevor Wilson
www.rageaudio.com.au
Phil Allison
Guest
Thu Jun 23, 2011 2:38 am
"Trevor Wilson"
Quote:
Phil Allison wrote:
** OK - you go get a 10W, 820 or 1000ohm cement resistor and YOU
measure its inductance.
**I said: INDUCTIVE REACTANCE.
Go on - try !!
**I've done so on many occasions. Though, I hasten to add, not 820 Ohm
resistors.
** Weeeeellllll - that is what I am asking you to try !!!
Quote:
Usually, much lower value resistors.
** That is the whole point.
The nature of the "coil" is much the same over a wide range of resistance
values.
As is the turn to turn capacitance.
Quote:
The principle is the same however.
** No it isn't.
Quote:
I don't see the point in trying to measure inductance directly. As you
have already stated, the resistance value will completely swap the
inductive reactance value. With rudimentary test equipment, it is simple
enough to measure the total reactance and perform the appropriate maths to
calculate inductance.
** You have not tried to do it and are still making silly assumptions.
Read my other posts in this thread.
..... Phil
Phil Allison
Guest
Thu Jun 23, 2011 2:47 am
"Trevor Wilson"
Quote:
All you need to do is:
Measure the resistance.
Measure the total reactance at (say) 100kHz).
** That second job is not possible.
The Z value will be exactly the same as the resistance.
Try 100MHz instead and then see how a few pF of strays ruins the outcome.
..... Phil
Phil Allison
Guest
Thu Jun 23, 2011 2:57 am
"StrandElectric"
Quote:
Oh dear, back to type. That was a very mild comment from me hardly
requiring such an extreme put down!
** Listen fuckhead.
**YOU** will not say what you are up to and the same time you BLAME me for
not knowing.
How fucking CRAZY is that ?????
Bet anything what you are doing with that 820 ohm resistor is 100% nuts.
---------------------------------------------------------------------------------
Quote:
No, there's much I don't know but I know that, and don't mind asking for
opinions,
** Then like most fuckwits on usenet - you PICK the one YOU like the best
and ignore the correct one or ones.
That is both extradinarily stupid and very bad mannered.
..... Phil
StrandElectric
Guest
Thu Jun 23, 2011 6:05 am
"Trevor Wilson" <trevor_at_rageaudio.com.au> wrote in message
news:96fm90F1k3U3_at_mid.individual.net...
Quote:
StrandElectric wrote:
"Trevor Wilson" <trevor_at_rageaudio.com.au> wrote in message
news:96fdmmFailU3_at_mid.individual.net...
Phil Allison wrote:
"Trevor Wilson"
StrandElectric wrote:
Can anybody with a good inductance meter, please measure a 10 watt
wirewound resistor of 820oms and tell me the inductance. I am
getting wildly different figures from various sources.
**That's because there is no one, correct answer. Some wirewound
resistors are bifilar wound,
** Invariably labelled "non inductive" and cost way more.
You need specify which resistor you are using.
** 10W, WW = standard rectangular cement coated resistor.
Better still, you should contact the manufacturer, as he/she will
be able to provide all the data you require.
** If you speak Chinese.
Even betterer, would be for you to measure the inductive reactance
of the resistor,
** OK - you go get a 10W, 820 or 1000ohm cement resistor and YOU
measure its inductance.
**I said: INDUCTIVE REACTANCE.
Go on - try !!
**I've done so on many occasions. Though, I hasten to add, not 820
Ohm resistors. Usually, much lower value resistors. The principle is
the same however. I don't see the point in trying to measure
inductance directly. As you have already stated, the resistance
value will completely swap the inductive reactance value. With
rudimentary test equipment, it is simple enough to measure the total
reactance and perform the appropriate maths to calculate inductance.
--
Trevor Wilson
www.rageaudio.com.au
Hi Trevor, I presume you mean setting up a tuned circuit with known
capacitance and seeing what frequency it resonates at?
**No. You are simply measuring the inductive reactance. All you require is
a signal source, a high freqency millivoltmeter, a known non-inductive
resistor (or resistors) and a pocket calculator.
You are over-thinking the whole thing. As Phil has already stated, trying
to measure inductance, with a resistor of such a value is fraught with
difficulty.
Yes, understood. Certainly this ancient brain now gets it that R swamps the
L and the C. Unfortunately (because I had much to learn from him) Phil's
nasty childish ways and foul language have now caused me to block him, so I
won't see any of his wisdom.
Quote:
glenbadd
Guest
Fri Jun 24, 2011 8:19 am
I took a hammer to a 820 Ohm 7 Watt wire wound resistor
http://www.flickr.com/photos/nowyouseeitall/5865323071/in/photostream
This damaged the wire in the process, but it allowed me
to measure the diameter to be about 0.04mm.
The end caps are like shorted turns which will
reduce the inductance, which is probably of the
order of 1 microHenry, and completely swamped
by the resistance.
HTH, G.
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