Hi Markd77If they are not connected to anything it's fine. If they are in a circuit then other components around it are likely to give you inaccurate readings. Also note that if you are holding the leads of a loose resistor to the probes with your fingers then the resistance of your body will affect the reading, especially for high value resistors.
Hi BillBIt would be to your advantage to learn to use the color code, as well. That is very helpful in reverse engineering existing circuits.
Yes, but in many cases there will be other components and combinations of components that are in parallel with the resistor you are trying to measure. Thus, the reading you get is the combination of the resistance value of the resistor in question plus all the other circuitry that is in parallel with it. In such cases, you must isolate (i.e., unsolder and disconnect) at least one end of the resistor from the rest of the circuit in order to get an accuate measurementHi Markd77
If they are in a circuit then how would it affect the reading. In normal cases, isn't the resistance of a resistor measured this way by connecting the DMM (in resistance mode) parallel to the resistor?
It seems that you understand perfectly, but to give an example, suppose that your body resistance is 10 million ohms and the resistor you are measuring is also 10 million ohms. The resistance you will read on the DMM is 5 million ohms (two resistances in parallel.) But if the resistor you are measuring is a low value like 10 ohms, then the effect of the 10 million ohm body resistance in parallel with 10 ohms will be negligible. To avoid this issue, be sure not to touch both ends of the resistor with your body while you are measuring it.Hi Markd77
When I'm holding the leads of a resistors to the probes of DMM then I and the resistor is making a parallel connection to the DMM. Right? My body has a resistance of the mega-ohm level then zero (or extremely low) current would pass through my body. But both I and the resistor will have same voltage across because of parallel connection. Could you please clarify it a little?
For example, if you identify by color code a 1.2KΩ resistor in a circuit, you would expect to reak 1.2kΩ with your DMM, but instead you read 600Ω. This is because there is another 1.2KΩ resistor in parallel with it on the other side of the board that wasn't immediately obvious.Hi Markd77
If they are in a circuit then how would it affect the reading.
Ideally you would measure the resistance of the resistor alone, so that would be in series. There's no way to measure the resistance of a single resistor in parallel.In normal cases, isn't the resistance of a resistor measured this way by connecting the DMM (in resistance mode) parallel to the resistor? Please tell me.
yesWhen I'm holding the leads of a resistors to the probes of DMM then I and the resistor is making a parallel connection to the DMM. Right?
Mostly correct; The resistance of your body is not consistent across all parts. There are other factors like how moist your skin is. play around with it. For example, I just measured from my thumb to index finder and got 1.2MΩ; I then measured from left thumb to right thumb and got 550KΩ. If I were measuring a 500KΩ resistor in parallel with the 550KΩ resistance of my body, this would significantly affect my measurement, causing my to read roughly half of the true value. If I were measuring a 1.2KΩ resistor, this would cause me to read 1197Ω; not a huge difference.My body has a resistance of the mega-ohm level then zero (or extremely low) current would pass through my body.
That's correct, same voltage. It's common for a meter to put out 1 or 2 volts, so it's not dangerous.But both I and the resistor will have same voltage across because of parallel connection. Could you please clarify it a little? I'm beginner so please keep things simple. Thanks a lot.
Hi BillB
I understand your advice. With some effort I can decode the color coding of a resistor to know the resistance. But the real problem is resistor are so small and perhaps it would take a magnifying glass to see the color codings!
Regards
PG
Yes, I actually have to use a cheap jeweler's loupe to see the color codes on resistors and to read the designations on some capacitors, IC's, and other components.Thanks a lot, tracecom. Your reply was really helpful.
By the way, don't you need a magnifying glass to read the colors correctly?!
Best regards
PG
Thanks for confirming this!Yes, I actually have to use a cheap jeweler's loupe to see the color codes on resistors and to read the designations on some capacitors, IC's, and other components.
by Duane Benson
by Jake Hertz
by Jake Hertz
by Jake Hertz