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I am trying to make a circuit to implement a Galvanic skin response sensor to measure the skin resistance and then use it to find the skin conductance. Then, I wish to calibrate these readings with some standard data so that the actual body hydration level can be calculated. In order to do so, I used one of the reference designs of Texas Instruments (Link). (The discussion related to this project is running on another TI forum with the link HERE.) The final circuit has been pasted below. enter image description here The circuit has been implemented using hardware and I am getting voltage values from the op amp output terminal. The problem arises when I cannot compare these values with some standard data that is used in the Clinical labs for measuring body hydration level. So, the voltage values that I get cannot help in finding whether the person's body hydration level is high/low/some xyz value.

I need to calibrate these readings with some standard data so that the actual body hydration level can be calculated. Where can I get the standard data that I use for the calibration? OR is there some alternative approach to calibrate my readings? Thanks in advance.

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  • Where can I get the standard data that I use for the calibration? -- What "standard data" are you asking for? Your question is entirely unclear. – Carey Gregory Feb 7 '19 at 3:21
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    He is looking for standard data against which to compare his readings, voltage levels. I thought it was clear, I just don't know the answer, or whether there is an answer. – De Novo Feb 7 '19 at 5:56
  • @De Novo, thanks for restating my query better... As you already mentioned, to calibrate my readings against standard voltage values is one approach that I have taken up ...but I am open to any other approach. – Pe Dro Feb 7 '19 at 12:44
  • This might be worth posting on the electrical engineering Stack Exchange, but I don't think it's off topic here either. – Chris Feb 8 '19 at 10:17
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    @Chris, you might be surprised to know that I have copied this exact question from there ( it was posted by me) here as it was listed as off topic and I was rewarded with -2 points. – Pe Dro Feb 8 '19 at 11:40
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Skin becomes a better conductor of electricity in response to physiologically arousing stimuli which can be external or internal. Increased sweat increases skin conductivity. This is known as the Skin Conductance Response (SCR) - also known as the Galvanic Skin Response (GSR). (See this Massachusetts Institute of Technology faq page).

Another name for GSR is Electrodermal Activity (EDA) and EDA measurement is one component of modern polygraph devices, which are often used as lie detectors (Source: BIOPAC Systems, Inc.).

Bearing this in mind, even though Microsoft submitted a patent application for such a device in 2015 (full technical details here), galvanic skin response sensors cannot be deemed reliable to determine body hydration levels. There can be no standard voltage levels because different people sweat at different rates. Look at hyperhidrosis sufferers for example.

Estimations of hydration levels can be made however, if other data is combined with galvanic skin response results — body mass index, heart rate and skin temperature (Suryadevara et al., 2015).

References

Suryadevara, N. K., Mukhopadhyay, S. C., & Barrack, L. (2015). Towards a smart non-invasive fluid loss measurement system. Journal of medical systems, 39(4), 38. doi: 10.1007/s10916-015-0206-6

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  • This is interesting, and perhaps useful information for the OP, but it doesn't seem to directly address his question, which is "where can I find/are there standard voltage levels" – De Novo Feb 7 '19 at 5:58
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    @DeNovo - There can be no standard voltage levels. Edited to reflect that and thanks for highlighting that. – Chris Rogers Feb 7 '19 at 6:04
  • @Chris Roger, thank you for this informative answer. Although this might not suffice this question, it is as good as the answer. I have concluded that as the exact Hydration level of body cannot be determined using this, I can surely get the variation in that, which will be almost as helpful in my case. Thank you once again. – Pe Dro Feb 8 '19 at 12:00

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