| NU_NRG |
Recently came across a weird lil resistor. Limited by knowledge i couldent guess it's value and limited with devices could not mesure it (guess it's below 1ohm).
So if anyone out here could demistify this pls do so
colors on the ½W carbon resistor are:
Yellow
Purple
Gold
Gold
Yellow
thank you for your answers!
-Simon |
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| Damon Hill |
| .47 ohms, 5%, probably wirewound |
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| NU_NRG |
thnx for the prompt response Damon.
on the same trail of thought, anyone know some sort of circuit/technique to precisely mesure low-ohm resistors?
-Simon |
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| Damon Hill |
Well, I found some wirewounds that were supposedly .3 ohms
which I was going to use for my upgrades to my Leach amps.
They were better quality than the sandcast resistors I'd been
using, but I wanted to try and match them more closely. Alas,
the expensive HP bench DMM that my favorite surplus shop
uses wasn't working, so I had to improvise:
For that, I took a bench supply and a couple of my DMMs and
put a 1.00 amp current through the resistor. Used one DMM
to measure the current and the other to measure the voltage
drop across the resistor. Since it was 1.00 amp, Ohm's Law
means the voltage drop is the same as the resistor; in this
case they all turned out to be .27 ohms. Somewhat lower than
the design called for, but not enough to affect proper operation
of the amplifier or the protection circuit.
This is a Kelvin circuit, or four-wire circuit, meaning the resistance
of the test leads doesn't affect the measurement as a conventional ohmmeter would. I don't know of any handheld
DMMs that use this method, so their resolution is limited at
low resistances.
Here's a test instrument that might be suitable; it's used for
measure the ESR of electrolytics. I want one...
http://www.anatekcorp.com/testequipment/esr.htm |
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