measuring ECG signals


by samaaa
Tags: measuring, signals
samaaa
samaaa is offline
#1
Nov6-12, 01:56 PM
P: 48
Hi guys:I have a project to design ECG

i want to calculate the six leads(I,II,III,aVR,aVL and aVF) by this method:


i will measure the voltage of three probe or electrode(RA,LA and LL) RL as a reference
by using DAC(digital to analog converter) the DAC connected to PC computer,
and then calculate(I,II,III,aVR,aVL and aVF) mathematically(by using matlab) according to these equations:
I=LA-RA,II=LL-RA,III=LL-LA,aVR=-((I+II)/2),aVL=I-(II/2) and aVF=II-(I/2)

so,what's your opinion about this method versus classical method(other methods)???
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berkeman
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#2
Nov6-12, 04:37 PM
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Quote Quote by samaaa View Post
Hi guys:I have a project to design ECG

i want to calculate the six leads(I,II,III,aVR,aVL and aVF) by this method:


i will measure the voltage of three probe or electrode(RA,LA and LL) RL as a reference
by using DAC(digital to analog converter) the DAC connected to PC computer,
and then calculate(I,II,III,aVR,aVL and aVF) mathematically(by using matlab) according to these equations:
I=LA-RA,II=LL-RA,III=LL-LA,aVR=-((I+II)/2),aVL=I-(II/2) and aVF=II-(I/2)

so,what's your opinion about this method versus classical method(other methods)???
I believe you mean "ADC". A DAC is an output device, and an ADC is an input device.

You will need to do some preamplification between the ECG pads and the ADC inputs. Instrumentation amplifiers are traditionally used for this function...

You also need to consider patient safety in such a design. UL544 is the applicable standard in the US, for example:

http://ulstandardsinfonet.ul.com/toc...sp?fn=0544.toc

You have to be very careful not to let any bias voltages show up between pads on a patient -- they have very low impedance access to the patient's body.
Enthalpy
Enthalpy is offline
#3
Nov6-12, 04:49 PM
P: 660
I hope I didn't understand...

You have already realized that only potential differences can be measured, have you?

For instance, you can measure I, II and III. These voltages are tiny and must be shielded properly before careful preamplification.

samaaa
samaaa is offline
#4
Nov7-12, 08:34 AM
P: 48

measuring ECG signals


Quote Quote by berkeman View Post
I believe you mean "ADC". A DAC is an output device, and an ADC is an input device.
yes i mean ADC


Quote Quote by berkeman View Post
You will need to do some preamplification between the ECG pads and the ADC inputs. Instrumentation amplifiers are traditionally used for this function...
i will use AD620a for preamplification .
samaaa
samaaa is offline
#5
Nov7-12, 08:37 AM
P: 48
Quote Quote by Enthalpy View Post
I hope I didn't understand...
why

Quote Quote by Enthalpy View Post
You have already realized that only potential differences can be measured, have you?
i don't understand what you mean,can you explain more?
Carl Pugh
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#6
Nov7-12, 12:57 PM
P: 383
Quote Quote by Enthalpy View Post
I hope I didn't understand...
You have already realized that only potential differences can be measured, have you?

samaaa, this was a trick question and you flunked.
trini
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#7
Nov7-12, 01:32 PM
P: 208
he can just reference each to ground guys don't give him a hard time
marcusl
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#8
Nov7-12, 01:47 PM
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Listen to Berkeman's advice. To protect the body against all faults, no matter how unlikely, it is common and prudent practice to run the instrumentation amplifier from a battery and couple it to the rest of the system through an opto-isolator. Then if your PC power supply shorts, or a meteor hits your computer and it melts down putting 110V onto your ECG amplifier, the human subject cannot be shocked. This is particularly important since ECG gel electrodes are designed to provide a low resistance connection to the body, thus vastly lowering the electrocution threshold.
samaaa
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#9
Nov7-12, 02:52 PM
P: 48
Carl Pugh , my english is not strong enough to understand trick question

trini and marcusl thank you for your advice
Windadct
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#10
Nov7-12, 05:22 PM
P: 532
As I read this RL is the Reference - A Relatively neutral point on the Body - regarding Heart function.
The calculation of I, II and III are highly dependent on these points being linear, between RA and LA for example. So this - while technically valid, is probably not very consistent patient to patient - which is important. In the US this is EKG - I have seen have 6 to 8 electrodes - MANY very smart people have tried to simplify this but the subject is too variable - Humans vary too much to make more assumptions).


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