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Old 22nd August 2005, 11:31 AM   #11
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All very amusing.

Ever considered that metal is magnetic, carbon is not.
The body of a metalfilm sticks to a magnet, the leads generally do not as most leads are tinned copper.
Even MOX metaloxide bodies stick to a magnet.
None of the Vitrohm, Amroh, or Allan Bradley's carbon composites i have do
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Old 22nd August 2005, 11:56 AM   #12
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Jacco,

You are the smartes man I have the pleasure to know!

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Old 22nd August 2005, 12:11 PM   #13
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I don't want to be the skunk at the picnic, but...

Nichrome is not ferromagnetic.

If it were, the film is too thin to have any significant attraction to a magnet.

What the magnet is attracting is the ferromagnetic end caps which make contact with the resistive film/ceramic substrate.
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Old 22nd August 2005, 12:15 PM   #14
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SY,

do some or all carbon composites have ferro-magnetic end caps ?
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Old 22nd August 2005, 12:26 PM   #15
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Composition resistors, no, but carbon film resistors, yes. And to further confuse things, some metal film and some carbon film resistors use nonmagnetic end caps.
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Old 22nd August 2005, 12:26 PM   #16
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.... so what exacltly does the magnetism do? Nobody have to answer because this is only a fashion, no?
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Old 22nd August 2005, 02:20 PM   #17
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True, nickel-chrome is not ferromagnetic.

Neither is a metaloxide layer, nor a carbon resistance track, a ceramic body, tinned copper or alloy leads.
The carbon composition resistors do not have end caps.
All of the carbon film resistors i have do not seem to have nickel-ferro end caps.
I know Beyschlag(Vishay BC / Philips BC) makes/made 2% accurate carbon films that look almost identical to the metal films they produce.

One way of finding out could be to check the TK value.
Regular low power metal films have a TK of 50, carbon films are in the order of TK = 200.
Yageo MF series have a TK of 25.
A reason for not using carbon films.

Any one of you have an idea how to check the power rating of a resistor, 1/4W, 0.4W, 1/2W, 0.6W, without having to destroy it ?
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Old 22nd August 2005, 04:44 PM   #18
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JV, a resistor costs maybe a nickel. It's cheap to destroy two or three in the interests of understanding construction and testing of limits.
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Old 22nd August 2005, 05:47 PM   #19
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power rating of a resistor is a function of it size, the abillity to disapate the heat created when acurrent flows. So the smaller they are the less power they can handle.....this is only good for descretes not smt's
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Old 22nd August 2005, 07:10 PM   #20
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SY-master,

you are right that it is far easier to just open up a couple.
i was merely wondering if there is a neat way of measuring the temperature of a resistor under load.
(i only buy resistors with a datasheet)

0.4 watt Yageo's are half the size of a 0.4 watt Beyschlag Components metal film resistor.
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