Deathshead

When i place a 1k ohm resistor on a breadboard and test it using a Digital Multimeter am i supposed to read exactly 1k? Do you get the same results using a breadboard as you would using a program like multisim?

dividedsky701

no, it'll read somewhere around 1k ohms. Resistor manufacturers make them within a certain tolerance (usually 5 or 10 percent) and so they won't actually read 1k ohms. There could also be leakage current in the breadboard. Try measuring it outside of the board to see if you get closer.

As for simulation programs like multisim, they'll give you ideal results obtained by performing theoretical calculations on perfect values. Unfortunately the world is not so ideal.

Nigel Goodwin

No, all components have tolerances - resistors are usually 5% (they have a gold band for 5%).

With a breadboard you will get correct results, a simulator is only a simulation, and might (or might not) give an accurate enough simulation. From the questions asked on here, it seems simulators are quite troublesome!.

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ChrisP

The measured resistance can vary considerably based on three basic factors:
-- the tolerance of the resistor
-- the accuracy of the test equipment
-- the integrity of the breadboard connections.

A normal 1000-ohm resistor with a tolerance of 5% (gold tolerance band) can be anywhere from 950 ohms to 1050 ohms.

Weak spring clips in the breadboard can add additional resistance to the circuit, depending upon where the measurement is taken. If you take the measurement right on the resistor leads, e.g. above the breadboard, this variance is taken out of consideration.

This leaves meter accuracy as the last stumbling block...

Deathshead

Also what does it mean if im being asked to find "upper" and "lower " limit of each resistor?

thnx in Advance

Nigel Goodwin

ChrisP just gave you the lower and upper limits for a 1K 5% resistor, it's simply how far it could be away from it's specified value.

__________________
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Deathshead

Would this be correct?
they all have 5% tolerance


Resistor - Upper Limit - Lower Limit

3300 ohm - 3135 - 3465
4700 ohm - 4465 - 4935
10000 ohm - 9500 - 10500

ChrisP

Yeh -- those are all right -- the nominal value plus the tolerance is upper limit; the nominal value less the tolerance is lower limit...

Deathshead

One more thing, what is the correct way to measure resistance power? i've already measured resistance voltage, current, and resistance, but im not sure how to measure power. im only using a power supply, DMM, breadboard, and 1k resistor

THanx Again

Styx

measure volts across the resistor then v^2/R to get the power disippated in the Res.

It is easier to measure the voltage across a res (in cct) then the current flowing through it.

Nigel Goodwin

I presume you are actually wanting to measure a resistor to find it's maximum power rating (to see if it's 1/4W, 1W or whatever).

I don't know how you would do this?, it obviously involves measuring the temperature rise of the resistor - but I've never seen any specs about it. Certainly I would suspect you are likely to be testing it to destruction!.

Generally you can tell by the physical size of the resistor, and it's wise to keep it well below it's maximum rating.

__________________
PIC programmer software, and PIC Tutorials at:
http://www.winpicprog.co.uk