Q: resistor tolerance

[--|--]

If a circut calls for a 10k resistor and you have r1 10k on the lower end of
the tolerance scale 9.6 k should you add another resistor to bring it to 10k
or just leave it ??

Thanks

 

[John Fields]

If a circut calls for a 10k resistor and you have r1 10k on the lower end of
the tolerance scale 9.6 k should you add another resistor to bring it to 10k
or just leave it ??

---
Depends on what the circuit calls for.

TOL LOW NOM HIGH
±% OHMS OHMS OHMS
-----|------|-------|-------
1 9900 10000 10100
5 9500 10000 10500
10 9000 10000 11000

 

[Don Pearce]

If a circut calls for a 10k resistor and you have r1 10k on the lower end of
the tolerance scale 9.6 k should you add another resistor to bring it to 10k
or just leave it ??

Thanks

You should do a tolerance analysis as part of your circuit design.
That will tell you what tolerance you can permit on any given part.
You will probably find that for most components the absolute value is
unimportant, while for others it matters a great deal. Choose your
tolerances accordingly, then don't be concerned with the actual values
you end up with - they will be taken care of.

On the other hand, if this is a one-off project, and you want
everything to be just right, by all means add in whatever you need to
achieve exactly the right value. But only you can tell how significant
this accuracy may or may not be to the function of the circuit.

d

_____________________________

http://www.pearce.uk.com

 

[John Woodgate]

I read in sci.electronics.design that --|-- <[email protected]>

If a circut calls for a 10k resistor and you have r1 10k on the lower
end of the tolerance scale 9.6 k should you add another resistor to
bring it to 10k or just leave it ??

With the circuit there should be information on what tolerances are
allowed for the passive components. These days, general purpose low
power resistors with +/-1% tolerance are so cheap that there is no point
in using anything else.

For higher power resistors, it is unusual for a tolerance closer than
+/-5% to be required. Provided your resistor value is within the
permitted tolerance range you do not need to add anything to it to bring
it to the nominal value.

 

[Mac]

If a circut calls for a 10k resistor and you have r1 10k on the lower end of
the tolerance scale 9.6 k should you add another resistor to bring it to 10k
or just leave it ??

Thanks

Usually, the schematic or some associated material specifies the tolerance
somewhere, somehow. If you really have a design with an unspecified
tolerance, then you could just use a +/- 1% tolerance resistor for it. It
is very rare to need better than 1% tolerance.

I wouldn't put two resistors in where only one is called for. It is
confusing when the schematic doesn't match the board.

Mac

 

[Tim Dicus]

If a circut calls for a 10k resistor and you have r1 10k on the lower end of
the tolerance scale 9.6 k should you add another resistor to bring it to 10k
or just leave it ??

Thanks

Do you mean that you have a 10K resistor that ohms out to 9.6K? If it is a 5% resistor (9.5K to 10.5K), it is within tolerance. If
the circuit calls for less than 5%, then you should adjust the resistance to within the tolerance range specified, or to the
tolerance of the resistor it is replacing. Normally, 5% will be ok unless otherwise specified in the schematic.

To what does this resistor connect?

Tim

 

[Peter Bennett]

If a circut calls for a 10k resistor and you have r1 10k on the lower end of
the tolerance scale 9.6 k should you add another resistor to bring it to 10k
or just leave it ??

Thanks

In most cases, things will work fine as long as the resistor is within
10% of the required value (often even 20% will do).

Where greater precision is required, the schematic/parts list will
call for 1% resistors. In such cases, the absolute value is usually
not too critical, but the ratio between two resistors is - for
example, in setting the gain of an opamp, the ratio of resistor values
matter - if the design calls for 10K and 20K, 9K and 18K should have
the same effect.

Of course, you also have to consider the accuracy of your meter before
you worry too much - if you measure a bunch of 10K resistors and find
that they are all around 9.6K, your meter is probably reading low.



--
Peter Bennett, VE7CEI
peterbb (at) interchange.ubc.ca
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