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how to get signal from the body


on Sun 23 of May, 2010 13:47 CEST, by HaiderIftikhar
hello

iam facing a problem that i ve designed a an Ecg preamplifier using an instrumentation amplifier say AD620 or INA121 and coupling its out put to a 150 hz lowpass 12th order filter. The differential inputs of the Instrumentation amplifiers have leftleg at the +ve input pin and rigth arm at the -ve input pin and the refrence of the Instrumentatin amplifier is grounded so is the right leg. With this configuration i get a ver good and clear Ecg view of lead II using an ECG simulator but when i directly connect the electrodes to the body i don get an ECG waveform but everything other than that.

the gain of the instrumentation anmplifier is set for 1000V/V by a rehostat

any help and suggestions are welcomed and greatly needed!
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Re: Re: how to get signal from the body

on Wed 11 of Aug., 2010 07:21 CEST, by HaiderIftikhar
Hi, tjh51
Thank you very very much you were right in order to attain maximum CMRR of my instrumentation amplifier i was taking my gain as 100V/V which was also amplifying the DC offset between the electrodes and the skin interface. i recently studied this in a book of Bio Instrumentation by Joseph Carr Brown but i m glad that you confirmed it too. for this i m great full and please do share further knowledge in any regard we all are enthusiastic learners and are eager of knowledge from any dimension and source
Thank You!
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Re: how to get signal from the body

on Tue 10 of Aug., 2010 12:08 CEST, by tjh51
Hi,

> the gain of the instrumentation anmplifier is set for 1000V/V by a rehostat

Are you saying that the gain of your instrumentation amp is 1000x? If so then the problem is that you're not allowing for the DC offset that is formed between your body and the electrodes. I can explain further if required.
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Re: Re: how to get signal from the body

on Wed 04 of Aug., 2010 07:13 CEST, by HaiderIftikhar
> i am having sticker type ecg electrodes how should i get data from it?

definitely u can use them they in fact yield lesser noise
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Re: how to get signal from the body

on Sun 01 of Aug., 2010 10:02 CEST, by r.vignesh
i am having sticker type ecg electrodes how should i get data from it?
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Re: how to get signal from the body

on Thu 03 of June, 2010 21:10 CEST, by mshieh
1)If the noise that you are seeing is composed of frequencies higher than the components in a typical ECG waveform then pass the signal through a variable low pass filter and start decreasing the cut-off. You should start seeing your expected signal appear.

2)Since you are grounding the right leg anyway, try feeding the common mode noise (inverted) back into the body to further suppress it.
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