Measurement file header and NI Biomedical Start Kit

by Forrest Sheng Bao http://fsbao.net

This semester, I am building an ECG sampling system (yes, like the one you can see in ER in Grey's Anatomy on TV) for my Medical Instrumentation class project. For the first time in my life, I amplified a signal by 5000 times! And, luckily, I had the chance to use a prototype NI myDAQ - yup, the one before released to the market.

This is my ECG of one beat! It doesn't look like textbook version though.

Then I decided to use NI Biomedical Startup Kit to check the quality of my ECG. But something unpleasant. The ECG Feature Extractor of NI Biomedical Start Kit could only load the first 1 second of my data. Clearly, I had 2-minute long ECG recordings. Then I notice, the problem is on the header. The header of LVM file showed Samples: 1000. In my LabVIEW program, I selected One header only in Segment headers option in Save to Measurement file express VI. So I guess this might be the problem.

Hence, I changed the Samples tag to 120000. Everything worked perfectly as expected!

So, a reminder. If you are using NI Biomedical Start Kit out there, do select One header per segment when saving measurement data. Or you can manually change the header as I did.

PS: I sampled many classmates' ECG. But many of them do not look like the ``standard ECG'' as shown on the textbook. I really don't know why. So on my software interface, I call the one made from NI ECG simulator ``human ECG'' and the one sampled from us ``alien ECG."

On the left: ECG from simulator; On the right: ECG from us (We are confused whether we are human babies any more.)