Hi When measuring resistors should it be exactly what it is rated at ? EG I have a 47k resisor measuring at 51k - is this faulty ? And I also have a 680k that takes ages to adjust on the meter and doesn't measure out at 680k - again faulty ? And if I'm told to check for open circuit what am I looking for ? Many thanks
it all depends on the tollerance of resistor. If the 47k resistor has a tollerance of 10% then it isnt faulty however if it is 5% then it is outside the stated tollerance. There should be a band which says what the tollerance is. You should always check resistances with no power applied and preferably with the component isolated from everything else i.e. by it self out side teh circuit. hope this helps
If the 47k's tolerance is 5%, then it's running a bit high. It should be within 2.35K for 5%, double that for 10%.
in most cases that first resistor should be fine... the second resistor sounds like is is in the same circuit as a capacitor... try desoldering one if its legs and measure...
Most carbon or carbon film resistors are have either a 5 or 10 percent tolerance in value as others have stated. They usually indicate the tolerance by using the fourth band in the color code. A silver band means 10% and a gold band means 5% tolerance. By adding or subtracting the tolerance you can find the range the resistor value is supposed to be within. Most electronic circuits can get by using 10% resistors since they are not real critical. When real precision is required then you will find more expensive 1% or even better resistors used. When someone says to "check for an open" they mean for you to see if the resistance in the circuit or device you are measuring indicates there is no connection. The resistance then will be infinitly high. Like measuring the resistance of a blown fuse. This is the opposite of a short, which has zero ohms of resistance.
or you could just use a universal / wheatstone bridge! to .00 ohm accuracy! (never yet found a resistor dead on what is should be!
