# Resistance Measurement

1. Feb 6, 2006

### Agent

Hey, I'm just starting out Electrical Engineering but I need some help. (edit) My Lab prof didn't explain to well. A lot of us feel confused by the way he teaches. I would switch lab prof but it is too late. Anyways, if someone can help me out, show me how its done, I would really appreciate it. Heres it is:

http://img441.imageshack.us/img441/3839/untitled1cd.jpg

Edit: sorry, fixed.

Last edited: Feb 6, 2006
2. Feb 6, 2006

### Staff: Mentor

Looks straighforward enough. What are you going to use to connect the resistors? Will you twist the leads and solder them, or do you have a wireless breadboard that you can plug them into? Once they are connected, turn on your DVM and put it on a resistance measurement setting. It may have an Autorange setting for resistance, where it figures out the right order of magnitude to use in the test, and then it displays the resistance in kOhms or MegOhms or Ohms, etc. If it's an older DVM it may not have Autoranging capability. In that case, you have to guess the total resistance (resistances add in series, right?), and set the DVM resistance range to a range that is >= that total value.

When using the DVM, just connect the leads to the two points you want to test (in this case the indicated points between the resistors).

BTW, you might want to tone down the badmouthing of profs here on PF. Probably a lot of the folks who stop by to help out are profs and TAs....

3. Feb 6, 2006

4. Feb 6, 2006

### Cliff_J

Agent - since the setting determines the highest reading the meter can read (limited by the 1 digit on the display) you should be able to figure this out: Does 199 ohms or less cover the readings you should see?

5. Feb 6, 2006

### Agent

I get .463 for the first one. Is that correct? I will just ask my prof (another one) on Thursday if I can't figure it out.

6. Feb 7, 2006

### Staff: Mentor

That would be 0.463kOhm, which is within 1.5% of the 470 Ohm resistor for the first measurement. 470 Ohms is a 5% tolerance resistor, so your measurement is reasonable.

All of the resistor values in your sketch are 5% values, except 10 Ohms, which is in both the 5% and 1% tolerance resistor series. Usually you would write it as 10.0 Ohms if it were a 1% tolerance resistor though, so my guess is that all of your test resistors are 5%.

Quiz question -- how can you tell whether a resistor is 1% or 5% tolerance by looking at the color code?

Quiz question -- what are the value sequences for 1% and 5% resistors? It's handy to keep a list of both series in your notes, BTW. If you are calculating resistor values for a bias network or something, after you calculate the ideal values, you can refer to your notes to see what a real resistor value is that is close to your ideal value.