BSL PRO 4 Manual - Biopac

Part C — Analysis Functions 259ExpressionSee the tables starting on page131 for descriptions of sources,operators and functions for theEquation Generator/Expressiondialog.The post-acquisition Expression transformation is available for performing computations more complex thanavailable with the Math and Function calculations. The post-acquisition version Expression transformationincludes all the same features as the online version described on page 131. The Expression transformation willsymbolically evaluate complex equations involving multiple channels and multiple operations. Unlike theMath and Function calculations, which can only operate on one or two channels at a time, the Expressiontransformation can combine data from multiple analog channels, or specify other calculation channels as inputchannels. Also, computations performed by the Expression transformation eliminate the need for “chaining”multiple channels together to produce a single output channel.To have BSL PRO solve an equation/expression and save the result to a new channel, choose Transform >Expression. A dialog will be generated. For each equation/expression, specify a source channel (or channels),the function(s) to be performed, any operators to be used, and a destination for the result. The differentcomponents of each equation/expression can be entered either by double-clicking items from the pop-upmenus (sources, functions, and operators) in the setup dialog, or by typing commands directly into the boxusing standard mathematical notation.You can divide a complex equation into several steps and perform each part of the equation with a separatechannel. With up to 60 channels, almost any calculation can be performed.The Expression transformation can reference past and future points.DelayThe Delay transformation allows the addition of time delays in post-processing (similar to the Delaycalculation channel that can be used to add time delays to signals). The time delay can be added byintroducing zero-valued samples at the start of the area to be delayed. The length of the waveform will remainthe same; an amount of data at the end of the wave prior to the delay will be lost, with the length equal to thedelay. The delay can be applied by using the Transform > Delay menu item.When inputting the delay amount, the units can be changed between seconds and samples. Delay by samples is applied according to the acquisition sampling rate, not the channel samplingrate. Delay specifies the units of acquisition and graph sampling rate for samples. For Delaycalculation channels, the units of “samples” need to be kept constant under changes to the channelsampling rate as there is no opportunity to adjust them. As a result, acquisition sampling rate is usedto determine “samples” for calculation channels. This same logic is applied to the transformation.The Automator action allows Delay to be used in Automator workflows. See page 21.BSL PRO Manual