Re: End of Line Resistor - Are they a standard design?

["Robertm" <Respond@xxxxxxxxxxxxx>]

"Robert L Bass" <robertlbass@xxxxxxxxxxx> wrote in message
news:wcqdnQeuD-0RLKDenZ2dnUVZ_sqdnZ2d@xxxxxxxxxxxxxx
>> I don't think so. If you're looking for a 2K
>> resistor and you find a 2.5K - 20%, it could
>> be anywhere from 2K to 3K.  If it's more
>> than 2.3K, you'd be out of spec for many
>> systems...
>
> Robertm is right.  However, resistor sizes are standardized and the
> various values are easily had.  If you can't get exactly what you need you
> can also run two or three resistors in parallel, series or a combination
> to obtain virtually any value you need.
>
>> You'd have to actually measure the resistor to see what it's value is...
>
> Agreed again, but that's easy enough.  It looks like he's being "blagged".
>
> (R1xR2) / (R1 + R2).
>
> Hmm.  That works for two resistors in parallel.  For multiple resistors
> I've always used:
>
> Rn = 1/((1/R1) + (1/R2) + (1/R3) + ...))
>
> Thus two 8-Ohm and one 4-Ohm resistors would give you 1/(.125 + .25) =
> 1/.375) = 2.67 Ohms.  [common speaker system problem].
>
> Or 1000-Ohm and 1000-Ohm and 2200-Ohm = 407.4-Ohms.
>
> --
>
> Regards,
> Robert L Bass
>
Yes, the reciprocal resistance formula can be used for more than two
parallel resistors. Or you can combine two, measure the resultant resistance
and then treat the pair as one, combining it with yet another and another.
And then the whole mess can be added to series resistors. We used to have a
machine that would sort 10%  and 5% resistors so we wouldn't have to pay for
1% resistors. The fallout from most 5% and 10% lots resembled a bell curve
with most values within 2% of the middle. In reality, component manufacture
is not always a precise science. Therefore, they sort them and charge you
more to get a higher percentage close to what you want. You want me to buy
all your rejects? OK, cheaper price, you have 10% resistors instead of 5%
which means the manufacturer has just cut his scrap rate. I worked for a
company one time that had contracts that specified the number of parts out
of spec that the customer would agree to receive for the negotiated price.
If we had a super day with no rejects, we'd go to the warehouse and get bad
parts and add just enough rejects to the shipment to give the customer the
agreed upon percentage. The business world can be harsh at times.

Bob