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Help me understand OHM readings

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Uncle Ben

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Joined
Dec 16, 2010
Messages
319
I am trying to test a few sensors on my transmission, but I'm unclear on how to interpret the numbers I'm getting on my digital multimeter. Here is an example for a countershaft speed sensor that is expected to read between 400~600 ohms. Below are the readings that I am getting at each setting on the multimeter...

audible continuity setting: .551 (no beep)
200: 1 (infinite resistance)
2k: .460
20k: .44
200k: .3
2m: .00

Do I ignore the decimal and go by the 2k setting (based on the expected range for this sensor) and conclude that the ohm measurement is 460, which is within the correct range?

Thanks!
 
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Olafur

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Iceland
200: 1 (infinite resistance)
2k: .460
20k: .44
200k: .3
2m: .00

The number on the dial represents the max reading for each scale.
200: 1 (infinite resistance) -> this means the value is over 200 ohms

For 2k, 20k, 200k, the reading is in k-ohms the most accurate one in the 2k range .460k=460ohm. The others .44k=440ohm and .3k=300 ohm.

(The last one (2m) should theoretically read 0.000460m (million) if your meter would have enough digits do display the number and be accurate enough.)
 
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diesel research

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Sep 12, 2010
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gulf coast, TEXAS
Is this a 2 wire sensor?

Those other guys have already explained your readings.

If it is a 2 wire sensor, the pins you are testing will also produce AC voltage (small amounts) while spinning. No set spec as it varies with winding resistance and shaft rotation. Often a just a decimal of a volt at lower speeds.
 
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oldtools

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Sep 15, 2008
Messages
2,706
The ohm setting on the multimeter give you the maximum ohm it can measure up to. For example, 2k (0 to 2000 ohm), 20K (0 to 20,000 ohm), 200K (200,000 ohm), 2m (0 to .002 ohm). If the resistance is greater than the range setting, it will give zero. For better accuracy, you want the setting closet to the actual resistance.

Example:

2m setting = 0 (460 ohm is out of 2m setting range)
2K setting = 0.460K ohm = 460 ohm
20K setting = 0.44K ohm = 440 ohm (less accurage since setting range is too large)
200K setting = 0.3K ohm = 300 ohm (even less accurage since setting range is even larger)

If there is resistance in the wire (like 460 ohm), there should be continuity and there should be a beep if it is set on the continuity setting. Some multimeter has two functions on the continuity setting. Make sure you select continuity when testing for continuity.
 
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Danglerb

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Sep 6, 2007
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Location
SoCal
What they said, and in this case pretty sure pin to pin is correct way to measure, sometimes its pin to ground.
 
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