Why is my integral channel calculation drifting continuously in one direction?

Depending on the characteristics of the signal being used to calculate the integral and the type of integral being used, the additive nature of an integral calculation can cause the integral to drift continuously in the positive or negative direction over time.  To counteract this behavior, there are a variety of integral reset types available in the Integral Channel Calculation's Settings Window.  These reset types are as follows:

  • No Reset: integral is not reset, and the integrated signal is summed indefinitely. 
  • Timed Reset: integral is reset periodically, at intervals specified in the text box to the right of the reset type menu. 
  • Reset Each Cycle: integral is reset each time the source signal passes through zero to a positive value.
  • Time Constant Decay: In this mode, input samples are summed to generate the output, as for the standard integral mode. However, each time a new sample is added the sum is multiplied by a positive constant that is a little less than 1. For a constant input voltage Vmax, the resulting sum – namely, the integral output – approaches a maximum (Vmax.?) with the time constant (tau, ?) that is entered by the user. In electronic terms, this mode approximates the behavior of a 'leaky' analog integrator, or 'RC' low pass filter. Unlike a filter, the integral multiplies the output values by the sample period in seconds and correspondingly changes the units to V.s.  

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                         The Integral function in Time Constant Decay mode with a Time Constant of 0.6 seconds

  • Reset By Event: uses a specific event to trigger the reset. This reset option uses the settings defined in the Event Options dialog pictured below, which can be accessed by left mouse clicking the Event Options... button in the Integral Channel Calculation's Settings Window.

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