All About Circuits Forum How to measure Skin Conductance?
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#1
05-11-2009, 02:33 AM
 PSIR Junior Member Join Date: Apr 2008 Location: Taiwan Posts: 29
How to measure Skin Conductance?

Hello every one:

What is Skin Conductance? How to measure it?
Why connected to the fingers when measuring?

For example the sensor below:
http://www.bio-medical.com/product_info.cfm?inventory__imodel=SA9309M

Best Regards
#2
05-11-2009, 02:43 PM
 t06afre Senior Member Join Date: May 2009 Posts: 5,939

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
#3
05-11-2009, 03:51 PM
 beenthere Senior Member Join Date: Apr 2004 Location: Missouri, USA (GMT -6) Posts: 15,815 Blog Entries: 10

The Wikipedia article - http://en.wikipedia.org/wiki/Galvanic_skin_response
__________________
First comes the hardware, then the software.
#4
05-13-2009, 03:54 AM
 PSIR Junior Member Join Date: Apr 2008 Location: Taiwan Posts: 29

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?

//---------------------------------------------------------------------
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.
//---------------------------------------------------------------------
#5
05-13-2009, 09:14 PM
 t06afre Senior Member Join Date: May 2009 Posts: 5,939

I think you forgot to post a link or a picture
But no harm done
#6
05-26-2009, 02:15 AM
 PSIR Junior Member Join Date: Apr 2008 Location: Taiwan Posts: 29

Excuse me.
How many Ohms while 1 μSiemens?
In other word, 1 μSiemens is equal to the number of resistance?

Thank you very much.
#7
06-30-2009, 02:33 PM
 StayatHomeElectronics Senior Member Join Date: Sep 2008 Location: NE Ohio, USA (GMT - 5) Posts: 787

Siemens are the inverse of Ohms. Siemens = 1 / Ohms. Ohms = 1 / Siemens.
#8
06-30-2009, 02:51 PM
 t06afre Senior Member Join Date: May 2009 Posts: 5,939
skin conductance using soundcard and Labview

If you are interested in skin conductance and have access to Labview 8.0 or newer this is mayby something

Last edited by t06afre; 06-30-2009 at 02:54 PM. Reason: Missing link
#9
06-30-2009, 03:36 PM
 ELECTRONERD Senior Member Join Date: May 2009 Location: Outer Space Posts: 1,145

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.
#10
06-30-2009, 04:07 PM
 t06afre Senior Member Join Date: May 2009 Posts: 5,939

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

 Tags conductance, measure, skin

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