Hi
First of all I would recommend using 3 electrode system and a low frequency AC voltage say 100-200 Hz. The exitation voltage should be around 100mV amplitude. Could you tell us more about how you plan to use your measurement system
Hi every one,
I found an article about explaining "Skin Conductance" below.
But I don't know the definition clearly and how to construct it to measure.....
especially what is the purpose of 1 megOhm feedback resistor?
Dose this circuit use OPAmp?
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Conductance (G), as expressed in units
known as Siemens, is the inverse of
Resistance (R):
G = 1 / R
The device presents a voltage of 200mV
across the resistance being measured, so
that the Current (I) flowing across the load
from one electrode to the other is equal to
applied voltage divided by the resistance:
I = 200mv / R = 200mV × G
In the device, the Current (I) flows through a 1megOhm feedback resistor to produce
the Output Voltage (Vout), so that:
Vout = 1 / Rfeedback = I × 1 megOhm = 200mV × G × 1megOhm
Solving for Conductance (G):
G = Vout / 0.200V × 1megOhm
Since 1 megOhm is the reciprocal of 1 μSiemens, the Conductance (G), in μSiemens, is equal to 5 times the Output Voltage:
G (μSiemens) = 5 . Vout
Therefore, for the device, 1 Volt of output equals 5 μSiemens. This relationship along withthe calibration function of the recording device can be used to convert the voltages recorded from the subject to μSiemens of conductance.
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Conductance is the reciprocal of resistance - C = 1/R
So what you can do, although it isn't very accurate, is hold the probes of a multimeter in each hand and set it to Ohms, you will get a resistance and you can apply this formula to find the conductance. The problem is that if you pinch the metal on the probes harder, you'll get lower resistance. So it isn't very accurate. Just for a general Idea though.
Let me add to your idea. Put some coins on the skin. This will give you a better idea about the skin conductance. But the skin is NOT a pure resistor. The very simplified model is a a capacitor in parallel with resistor. So the most correct thing is to apply a constant AC voltage and measure the current
Indeed, the skin is not a pure resistor, you may eat something one day and have a varying resistance and devour something another day and have a completely different resistance.
But it is still DC based and measure the skin conductance of two electrodes in series. With this system you a unable to isolate the conductance under a single electrode