Carbon Composition Resistor ID

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Stuntman

Joined Mar 28, 2011
222
Alright, this one seems like a gimme, but look closer (yes, at my super crappy picture). These do not seem to obey normal band nomenclature.

The top resistor colors from L-R

Red - Black - Brown - Gold - Orange.

Normal 5-band decoding would say this is a 20.1Ω resistor with tolerance orange. Nope, this came marked as a 200Ω, and measures out accordingly. Second, orange is not a tolerance marking according to my charts or those I found during a web search. So this one seems like perhaps the first three colors give the resistance (as in a 4 band), the gold is tolerance (5%) and orange is temperature coefficient.

The bottom resistor reads (L-R)
Brown - Grey - Black - Gold - Orange

This can be particularly confusing as if you use standard decoding, you come up with 18Ω (which measures correctly) and again, orange tolerance. However, if you use the scheme from the first resistor, you also get 18Ω but with an orange temperature rating.

This is the first I've run into this discrepancy. Is this a carbon comp thing?
 

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dl324

Joined Mar 30, 2015
18,326
Five band carbon comp resistors are military grade. The fifth band indicates reliability. Reliability is defined as the failure rate at 50% rated power after 1000 hours.

Orange is 0.01% failure rate after 1000 hours.

This is from an Allen Bradley guide.
upload_2017-6-6_7-39-16.png
If you have more part number information, RCR and RC conform to military specs MIL-R-39008 and MIL-R-11, respectively.
 
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