EBME Forums Forums Free discussion Free discussion Convert bpm to Hz

See my previous post !
You need to interface via a differential amplifier
(You are trying to measure a three terminal waveform with a two terminal device) Thats why we use dedicated ECG monitors instead of oscilloscopes.

Yes, I would agree with that. I would look at things from the other perspective. That is, use a decent (but old fashioned) "traditional" (CRT) ECG monitor, convince yourself that it is accurate ... then use that to check your ECG simulator(s) against!

You're right, Sean. ECG monitors started off as "simply" oscilloscopes arranged to display ECG signals. Special input amplifiers and all the rest.

I think you will find an ECG lead is a 2 terminal thing, the third electrode is there for noise cancellation.
Lead I RA - LA
Lead II RA - LL
Lead III LA - LL
etc
So it is easy to measure on a scope.
But why all this tech talk and complication? To convert BPM to Hz divide by 60 as has been said above, or to covert Hz to BPM multiply by 60.
Set the function generator to a frequency in Hz multiply this by 60 and the reading should be that in BPM. Simples!

Why are you checking this out of interest? Are you suspecting an error in a timing circuit? The most likely cause of incorrect BPM reading is incorrect detection of the QRS spike.

Robert

Only easy to measure (eg, R-wave to R-wave) if the 'scope is able to display such a low frequency.

But yes, "R-wave detection" is a much more interesting topic. And easy enough to do electronically, if I remember rightly.

And yes (again) we are in an age where the kit itself is generally more accurate than the test equipment (modern monitors, infusion pumps - especially syringe pumps, etc.).

R-wave detection:
Differentiate and look for the big spike?
or just look for the largest signal as manual mode usually uses?

Having worked in a cardiac hospital and seen P-waves bigger than R-waves it is not that simple, especially if the electrodes are either side of a huge cut down the chest.

Digital storage scope set to a slow timebase and the trigger accurately set - not too hard to do.
But why all this high tech stuff? It is easier to multiply or divide a known frequency from a sig-gen by 60.

Robert

Because that's what we do, Robert!

"I think you will find an ECG lead is a 2 terminal thing, the third electrode is there for noise cancellation"

2 + 1 = 3 (terminals - one +ve, one -ve, one grounded)

No wonder mathematical confusion reigns when considering ECG,

Consider Lead 1 + Lead 3 = Lead 2 ??????

Forget digging out the wide bandwidth storage scope "it is easy to measure on a scope" - Rojo . (dream on). I agree with felipespace " I got nothing" when using a scope. Significant CMRR, filtering and amplification is required, before you get anything readable.

I would go with Geoff's pragmatic approach, (which works for the rest of us mere mortals) cross check any suspect simulator or ECG module with a tried and tested CRT based Cardio-Rater or similar (even easier to do).

Einthoven's Triangle should settle any arguments!

Here's some more (for those with a little time).

2 + 1 = 3 (terminals - one +ve, one -ve, one grounded)

The third one is not ground it is usually active (Right Leg Drive) to get rid of common mode noise. The actual signal is the difference of the other two electrodes.

If you look at Holter monitors they usually have two pairs of two leads, each pair giving a signal. No third electrode needed in this fully floating environment.

Robert

It's not easy to generalise when talking about ECG electrode positioning (number of leads, and all the rest). We need to be a bit more specific.

For a start, consider monitoring versus diagnostic examinations (eg, with an electrocardiograph).

Some folk get confused between ECG leads as per Dr.Einthoven, and ECG leads as in physical colour-coded leads! Whilst obviously related, as we know these are not actually the same things!

But (as has already been mentioned) all ECG equipment uses a differential amplifier.