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ADS1298: Problems with aVL and aVF

user5360089
Prodigy 30 points
Part Number: ADS1298

Hello! I'm new to the ADS1298/8R EVM Evaluation Software,

I'm trying to make a few test signals, and when I create an input short to either Lead I or Lead II, aVL and aVF do not match with the definition provided by the manual (aVL = Lead I - (1/2)*Lead II, aVF = lead II - (1/2)*Lead I), because when Lead I = 0, aVF = 0; and when Lead II = 0, aVL = 0. 

I suppose it has something to do with the configurations of GPIO and OTHER Registers but I am not sure how to proceed. 

Any help is greatly appreciated. Thank you very much!

  • 0
    TI__Mastermind 48681 points
    Hello User,

    Thanks for your post and welcome to the forum!

    Indeed it looks like the math is being performed incorrectly. I'll have to investigate this in the lab and I'll get back to you!
  • 0
    TI__Guru 59256 points

    Hello,

    Please refer to the following table:

    Lead

    Electrode Formula

    Measured or Calculated

    Calculation Formula

    Primary Limb Leads

    I

    LA - RA

    Both

    Lead II - Lead III

    II

    LL - RA

    Both

    Lead I + Lead III

    III

    LL - LA

    Both

    Lead II - Lead I

    Augmented Leads

    aVR

    RA - (LL + LA)/2

    Both

    −(Lead I + Lead II)/2

    aVL

    LA - (LL + RA)/2

    Both

    (Lead I - Lead III)/2

    aVF

    LL - (LA + RA)/2

    Both

    (Lead II + Lead III)/2

    Chest Leads

    V1

    V1 - WCT

    Measured

    -

    V2

    V2 - WCT

    Measured

    -

    V3

    V3 - WCT

    Measured

    -

    V4

    V4 - WCT

    Measured

    -

    V5

    V5 - WCT

    Measured

    -

    V6

    V6 - WCT

    Measured

    -

    For more information, I recommend viewing our video training series on ECG applications: 

    Best Regards,

  • 0 in reply to Ryan Andrews
    Prodigy 30 points
    Thank you for your reply, but the definitions are equivalent, right? if Lead III = Lead II - Lead I,
    in the definition I used, aVL = Lead I - (1/2)*Lead II = Lead I - (1/2)*(Lead III + Lead I) = (1/2)*(Lead I - Lead III),
    same with aVF = Lead II - (1/2)*Lead I = Lead II - (1/2)*(Lead II-Lead III) = (1/2)*(Lead II + Lead III)...
  • 0 in reply to Alexander Smith
    Prodigy 30 points
    Thank you! looking forward for your next reply :)
  • 0 in reply to user5360089
    TI__Guru 59256 points

    Hello,

    You're right, my mistake. Those are equivalent expressions for the augmented leads. I've edited my post above.

    By that logic, I can see where the confusion lies. When Lead I = 0, aVF = Lead II and aVL = -Lead II / 2. And when Lead II = 0, aVF = -Lead I / 2 and aVL = Lead I. That is not the case in the LabVIEW GUI plots.

    I opened the source code for the GUI and it appears the incorrect formulas are used for the aVL and aVF (the sign in the parentheses are reversed):

    Sorry for the confusion. We will make a note to update this in the future.

    Best Regards.