4
\$\begingroup\$

For my science fair project, I am measuring the resistance of a 100 foot piece of 32 gauge Nichrome wire. Using a Innova 3300 digital multimeter, I get the following results for each resistance range value:

  • 200 ohms: 1 (to far left, indicating over range)
  • 2000 ohms: 1025-1030
  • 20k ohms: 1.02-1.03
  • 200k ohms: 01.0
  • 20M ohms: 0.00

I understand that precision varies based on the range value, so the right-most digits makes sense to me. However, I don't understand the scale of the left-most digits? Why aren't they all in the 1000 range if actual resistance doesn't change.

I have read the manual several times but it just says:

  1. Plug the RED test lead into the "Ω" jack of the multimeter; plug the BLACK test lead into the "COM" jack.
  2. Set the meter’s Function/Range Selector Switch to the OHM "Ω" range function.
  3. Place the RED test lead onto one side of the item being tested and the BLACK test lead onto the other side of the item. (Polarity does not matter when checking resistance).
  4. Read the results on the display

There is no mention of what the results mean. After thinking about this with my dad and searching the internet, I think I have an answer: The units of the display value are in the units of the range. For example, 200 and 2000 are in ohms, 20k and 200k are in kilo-ohms, and 20M is in mega-ohms.

Is my hypothesis correct? And what about the leading zero in the 200k range?

\$\endgroup\$
  • \$\begingroup\$ There should be a leading zero in the 20k range too. There should be two leading zeros in the 200k range. Maybe your meter is different but your assumption about what they mean is correct. \$\endgroup\$ – Andy aka Jan 1 '14 at 23:16
  • \$\begingroup\$ If your wire is in a coil, reverse the winding of 1/2 the turns to cancel out any currents from magnetic fields. You might stabilize the readings this way on the 2000 ohm scale. \$\endgroup\$ – C. Towne Springer Jan 2 '14 at 2:06
  • \$\begingroup\$ @Andyaka the "half digit" on a multimeter can't display a zero, it can only display a 1 or nothing at all. \$\endgroup\$ – Peter Green Feb 14 '17 at 5:11
7
\$\begingroup\$

The relevant part in the manual is enter image description here

200 Ohm range can show 000.0 - 199.9 Ohms
2K Ohm range can show 0000 - 1999 Ohms
20K Ohm range can show 00.00 - 19.99K Ohms
200K Ohm range can show 000.0 - 199.9K Ohms
20M Ohm range can show 00.00 - 19.99M Ohms

Regarding your results, they should be interpreted as:

2000 ohms: 1025-1030 Ohm
20k ohms: 01.02K - 01.03K Ohm
200k ohms: 001.0K Ohm
20M ohms: 00.00M Ohm

| improve this answer | |
\$\endgroup\$
3
\$\begingroup\$

Your meter has a 3 1/2 digit display, which means that the maximum reading it can display is 1999 (with a decimal inserted as needed). The range switch sets where the decimal place is located on the display. On the 200 ohm range, full scale will be 199.9 ohms. On the 2K scale, it is 1999 ohms. For 20K, 19.99 K, and 20 Meg, 19.99 meg.

It appears that the actual resistance of your wire is 1025 - 1030 ohms (perhaps poor contact on your probes accounts for the variation). This will display most accurately on the 2K range. On the 20 K range, the last digit falls off the end of the display, so you see 1.02 or 1.03 K. On the 200K range, two digits fall off the end, so you only see 1.0 K, and on the 20 Meg range, four digits fall off the end, so you see 0.

| improve this answer | |
\$\endgroup\$
0
\$\begingroup\$

Is my hypothesis correct?

Yes, it is normal for the units to change on a multimeter as you move up through the ranges. The reason for this is simply practical. On a 3½ digit display you can't cover the range and precision needed without changing units.

Some multi-meters have little letters on the display to indicate the current units.

And what about the leading zero in the 200k range?

It is easier to display a digit in that position for all valid measurements than to suppress it in cases where it is not needed.

| improve this answer | |
\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.