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Jonathan_hodgkins's avatar

Resistivity of saline at various frequencies?

Asked by Jonathan_hodgkins (397 points ) April 3rd, 2014

I am running an experiment were I am testing the resistance of saline under different conditions. I’ve noticed that if I change the frequency of the LCR meter, the resistance reading varies wildly. Why is this happening?

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2 Answers

ARE_you_kidding_me's avatar

Because you are dealing with more than simple dc theory. Resistance (impedance to be more correct) of an rlc circuit changes with frequency. You will need to correct the impedance for the frequency You are using. That’ll take some work with complex numbers. So why are you doing this? If I am thinking about your set up correctly. You could replace the saline with a known resistance then run some tests at various frequencies to draw a curve you can use to correct for freq. It won’t be perfect but it should give you an idea. That’s a quick and dirty way.

LuckyGuy's avatar

I am not sure of the frequencies you are using. At radio frequency ranges ~10MHz and above, components change. Wires can act like inductors and capacitors.
Measure a capacitor at DC, 10kHz, 1MHz, 100MHz, 10GHz and you will see its impedance change all over the map.
Stay in the audio region (<40kHz )and your life will be simpler.

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