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I just purchased this cheap-o multimeter: https://www.amazon.com/AstroAI-Digital-Multimeter-Voltage-Tester/dp/B01ISAMUA6/ref=sr_1_1?keywords=astroai+am33d&qid=1551837071&s=gateway&sr=8-1

I'm trying to test the resistance of my tongue by touching both probes to it (I have the red plugged into the middle port and the black into common). I start on the highest number as instructed (200M) and it gives an output of 1.1M Ohms. At 20M it fluctuates between 10M and 20M Ohms. Below that it blanks out and just says 1.

I read online that this exact procedure should give an output of 70K Ohms, the approximate resistance of the human tongue. What's up with my multimeter? Or is my tongue just insanely resistant to electricity?

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  • \$\begingroup\$ "I read online that this exact procedure should give an output of 70K Ohms" Can you link to the source of that claim? It would be interesting to see the context. Thanks. \$\endgroup\$ – SamGibson Mar 6 at 2:12
  • \$\begingroup\$ Oh, it actually said 50K Ohms. Still nowhere near mine. learningaboutelectronics.com/Articles/… \$\endgroup\$ – Aidan Mar 6 at 2:37
  • \$\begingroup\$ Thanks. Reading that article, and with respect to its author, it's a very poor experimental setup e.g. as explained by Sunnyskyguy EE75 and me, there is no mention in the article of the expected variations in readings due to varying contact area and pressure etc. I think it was written as a light-hearted piece, and you're expecting it to be more serious (and treating it more seriously) than the writer was. The main focus of that article, seems to be the difference in resistance values between a dry tongue and a wet tongue. \$\endgroup\$ – SamGibson Mar 6 at 2:58
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Your body is a lossy dielectric. The ion content in the skin will reduce Resistance with skin pressure and probe metallic contact area. i.e. salt content in fluid promotes ion content.

The tip only is a very low surface area, so resistance will be >10x higher than the flat side of the probe. Pressing harder will reduce resistance.

Your body resistance is much lower than the electrode tips, which affects the results greatly.

The meter uses xxx uA to measure voltage and convert to resistance.

Dry skin 10M , 10pF hard pressure 1M 100pF
Moist skin with seat and pressure 50k ~1M 1000 pF
Tongue 10k to 1M
9V battery current: 9uA to 900uA ! ballpark.

Your mileage will vary

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I read online that this exact procedure should give an output of 70K Ohms

Wherever you read that, is simply wrong. There will be a wide range of possible readings, all valid, depending on how much saliva is present on that person's tongue at that moment.

And, of course, the readings will also be affected by the varying contact area and pressure of the probes on your tongue.

What's up with my multimeter?

Likely nothing. The varying readings you mention on different ranges, will be due to the different current used by each measurement range. My results are different to yours, but that doesn't mean your multimeter is faulty.

Or is my tongue just insanely resistant to electricity?

Try making your tongue wetter and repeat the test. You'll get a lower reading.

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  • \$\begingroup\$ But why am I getting completely different readings on the 200M reading compared to the 20M reading? \$\endgroup\$ – Aidan Mar 6 at 2:53
  • \$\begingroup\$ @Aidan - I suspect it's due to the different test currents being used by the DMM on those two ranges, and saliva behaving differently in those two conditions. To prove this: Get a normal fixed resistor with a value which is readable on both of those ranges e.g. 1MΩ to 10MΩ. Put it on an insulating surface (or wear gloves if you will hold it in your hands) and measure its value on both of those DMM ranges. I expect you will see a stable similar value on both ranges. That would leave the explanation as something to do with saliva (ask a biologist :-) ) or... \$\endgroup\$ – SamGibson Mar 6 at 3:24
  • \$\begingroup\$ ... it could be that you are affecting the result e.g. the way you hold the probes, will have more effect on the 200MΩ range than on the 20MΩ range (e.g. leakage through the skin on your hands). || The main point of my answer was to explain that the stated objective from that article of specifically a 70kΩ reading (later corrected to a 50kΩ reading), is unrealistic. \$\endgroup\$ – SamGibson Mar 6 at 3:36
  • \$\begingroup\$ Yep, the resistor test gives the same reads approximately. This makes much more sense now, thanks for the reply \$\endgroup\$ – Aidan Mar 7 at 12:19

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