The Function Approximation of the Signal Delay Time in the Anti-Alias Filter of the A/D Interface of the Instrumentation and Control System

Analytical expressions for the delay times of three types of the low-pass filters (Bessel, Butterworth, Chebyshev filters) as the functions of the filter order are obtained. These filters are a part of the input circuits of the analog-to-digital interface of the instrumentation and control systems (ICSs) and serve to reduce the value of the aliasing error (the anti-alias filters). The signal delay in the filters causes significant dynamic errors in the instrumentation and control systems that reduce the tolerance frequency of the sensor signal sampling. Using the Filter Solution application programs and the NI LabVIEW software environment the analytical expressions for the delay times of three types of filters at linear and polynomial approximation were obtained. The analysis of the obtained results enabled us to turn attention to the significant value of the dynamic errors due to the signal delay of the sensor in the anti-alias filter that makes their use in some instrumentation systems problematic.