BSL PRO 4 Manual - Biopac

148 BSL PRO Manual• Top waveform: data is sampled relatively slowly; difficult to make out the shape of the waveform.• Middle waveform: sampled at the faster rate; more samples are taken in the same period of time, whichresults in higher resolution for some components of the waveform.• Bottom waveform: sampled at a relatively high rate; increased resolution of the waveform. Waveformcomponents that were obscured at slow sampling rates are now well defined, and measurements taken onthis waveform would be able to better establish the maximum amplitude, time between different ECGcomplexes, etc.Representation of ECG waveform sampledwith relatively few samples per second“True” ECG wave is superimposed over dotsthat indicate sample points.Preceding waveform as it would look ifplotted in BSL PRO (with data pointssuperimposed).Representation of same ECG waveformsampled at a relatively higher sampling rate.As shown, under-sampling completely misses the QRS complex of this waveform, although it might detectcomponents of the QRS in subsequent beats. Although this is an extreme example of how under-sampling canaffect digitally processed data, it is important to note that the rate at which data is sampled has importantimplications for the interpretation and analysis of data.The disadvantage of acquiring data at high sampling rates is that each sample point takes up memory, whetherit is RAM , disk space or memory. Moreover, once the file is saved, it will require more disk space than a fileof similar duration sampled at a slower rate.Note for variable sample rate processing:The Expression and Waveform Math functions will constrain operations between waves of different rates asfollows:If an equation is operating on two or more waves of different sample rates, the result of the operation willalways be output at the lowest sampling rate from the waves (F low). If the destination channel for the resulthas an assigned rate other than (F low), the operation will not be permitted. If the destination channel is set toa new channel, the operation will always be permitted.VSR data padding—If the channels are of unequal length (as a result of variable sampling rate or waveformediting), they will be padded for Append acquisition. Digital and Analog channels are stored as short integersby default; a waveform paste into a digital or analog channel, however, will result in its underlying data beingconverted to floating point. This will generate the “Abort/Replace” warning for pastes to Digital or Analogchannels since the data format has changed since the last acquisition.Additionally, if an Analog or Digital channel is used as the source waveform for a Copy, it will also beconverted to floating point and will result in the “Abort/Replace” warning being generated.Since Calculation channels are already floating point, pasting into them or copying from them will not changetheir data format. The channels will be padded with their last value and the append will commence.Waveform Cut operations do not change the underlying data format for Analog, Calculation, or Digitalchannels. If only Waveform Cut is used, no data format conversion will occur and channels will be paddedwith their last value and subsequent appends are allowed.Visit the online support center at www.biopac.com