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What Instrumentation Amplifier would you recommend for Electrocardiography ?

Posted on 2011-09-22
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Last Modified: 2012-06-22
Hello Guys,

I'm building a system such as shown in this link:
http://www.cisl.columbia.edu/kinget_group/student_projects/ECG%20Report/E6001%20ECG%20final%20report.htm#1

What Instrumentation Amplifier would you recommend for this application ?

Thanks


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Question by:adkry
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by:☠ MASQ ☠
☠ MASQ ☠ earned 150 total points
ID: 36581523
Whatever you use you need to make sure it has a high CMRR and you'll need to filter the signal post-amp to remove movement artefacts.
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d-glitch earned 250 total points
ID: 36581604
The website in your post suggests the AD624 which is a fine choice but a little pricy at $32.

The INA126 would probably work fine too.  They are in stock at Digikey for $2.80

     http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=INA126PA-ND

The best thing to do is start prototyping.  You can even start with the 4-resistor op amp version
of a differential amplifier.  You may have to trim the resistor values to optimize CMMR, but there
is no reason you can't start making measurements today.
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by:adkry
ID: 36581871
Thanks, so you believe the AD624 is all I need ? Not sure if I can get INA126 ?
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by:adkry
ID: 36581874
MASQUERAID, how can I filter the signal post-amp to remove movement artefacts ? any hints please ?
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by:adkry
ID: 36581898
so what's the difference between AD620 and AD624 ? and which is better for ECG ?
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by:Dave Baldwin
Dave Baldwin earned 100 total points
ID: 36582049
You should take their safety note seriously.  Actual approved ECG interfaces for hospital use are electrically isolated with both transformers and optoisolators.  Although that page 'says' they are using the opto for isolation, it's not really isolated because they have the same battery connections on both sides of the opto.
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by:adkry
ID: 36582235
Thanks for the heads up Dave!
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by:d-glitch
ID: 36582301
The AD620 is also a fine choice at $6.50.

http://www.jameco.com/webapp/wcs/stores/servlet/StoreCatalogDrillDownView?langId=-1&storeId=10001&catalogId=10001&freeText=ad620&search_type=jamecoall

Where are you located?  If you are in the US, you can mail order IC's from Digikey, Mouser, Jameco, and lots of other places.

Are you trying to develop a medical product?  Is this a school project?  Are you just trying to see what you can do with electronics?

Electronic (and every other kind of) Design should start with Requirements.
Are you trying to build an EKG machine, or a heart rate monitor.  
Do you want to see your EKG on a scope or a computer screen.
Or do you want to see how much your heart rate increases when you exercise.
The requirements for the amplifier and filter are very different.
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Author Comment

by:adkry
ID: 36582407
Hello D-glitch and thanks for your response,

I'm located in the UK. It's fine I'm not exactly worried about cost for the IC. This is my university degree final year project. I wish to send this signal wirelessly, get it received by a computer, then apply digital signal processing on the computer and display it on the computer, also, I wish to apply some logic to it, i.e. I wish the computer to be able to reason if the heart signal has got any abnormalities.

Why are you mentioning a EKG ? is it the same as ECG ?
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by:d-glitch
d-glitch earned 250 total points
ID: 36582419
>> how can I filter the signal post-amp to remove movement artifacts ? any hints please ?

How much electronics background do you have?
Do you know how to make a passive RC filter?
Do you know how to make and active op amp filter?
Do you have an oscilloscope and a soldering iron?

You can get filter design calculators on line:   http://www.daycounter.com/Filters/Sallen-Key-LP-Calculator.phtml

There is a high-pass one too.
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by:☠ MASQ ☠
☠ MASQ ☠ earned 150 total points
ID: 36582517
Not sure we should be doing your project for you.
You'll need info like this on interpreting the signal
http://www.clinitec.be/downloads/whitepaper_rhythmx.pdf

Beware of wireless use and RF interference particularly mobiles - that's one of the reasons there isn't mainstream AED wireless monitoring.

(EKG = ECG  US - UK)
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Author Comment

by:adkry
ID: 36582529
MASQUERAID, I didn't ask you about the project, I only asked for advise on the instrumentation amplifier. I'm gonna use bluetooth for wireless, I'm yet to research if it's gonna affect the heart or not, if wireless was a big deal, I'll make it wired.
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Author Comment

by:adkry
ID: 36582547
I was good at micro-electronic circuits some 2 years ago, I'm yet to refresh my memory
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LVL 82

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by:Dave Baldwin
Dave Baldwin earned 100 total points
ID: 36582561
Wireless might be interesting for a project but it would be a No Sale in a hospital.  Too many possibilities for problems including generating and being interfered with.  EKG/ECG interfaces are connected to alarms that bring nurses running.  The second time you got a false alarm, your wireless unit would be trashed and replaced by a wired unit.
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Author Comment

by:adkry
ID: 36582564
thanks for the link d-glitch, very useful
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Author Comment

by:adkry
ID: 36582583
Thanks Dave, that's why engineers have to solve those many problems, I've got a year for this, so I'm gonna try to make the product as robust and accurate as I can.
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Expert Comment

by:d-glitch
ID: 36582624
I made an EKG monitor for my school work in the 1970's.  
I have never heard it called ECG.
I don't know if that's because I am in the US or because I haven't been paying attention.

The analog front end is reasonably straightforward.  
Do you have a candidate for wireless transmission of analog data?
Do you understand the signal resolution and bandwidth requirements?

I have purchased parts from Newark Electronics in the US and had them delivered
from Farnell/Element14 in the UK.

It seems to be early in the year to be starting a senior project.  That is a good sign.
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LVL 82

Expert Comment

by:Dave Baldwin
ID: 36582630
You're welcome.  If you Google ECG EKG interfaces, you will find a number of projects including at least one complete one with a circuit board.  There might be some applications outside of hospitals where wireless might be a good idea.  Hospitals just have too much 'stuff' in them.
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LVL 62

Expert Comment

by:☠ MASQ ☠
ID: 36582631
Use the filter to remove unexpected frequencies and a third "earth" lead to eliminate movement artifacts.
The issue with wireless interference is all about the signal interpretation.
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