TITLE Active Filters Signal Conditioning INTRODUCTION Digital Filtersare used primarily when transfer-function requirements have no counterpart in the analog world, or when a Digital Signal Processing (DSP) already resides on the circuit board to perform other functions. The three most common types of filters are called Butterworth, Chebyshev, and Bessel. Each type has unique characteristics that make it more suitable for one application than another. All may be used for high-pass, low-pass, band-pass, and band-reject applications, but they have different response profiles. They may be used in passive or active filter networks. The Butterworth filter has a fairly flat response in the pass-band for which it is intended and a steep attenuation rate. It works quite well for a step function, but shows a non-linear phase response. Chebyshev filters have a steeper attenuation than Butterworth, but develop some ripple in the pass band and ring with a step response. The phase response is much more non-linear than the Butterworth. Finally, Bessel filters have the best step response and phase linearity. But to be most useful, Bessel filters need to have a high order(number of sections) to compensate for their slower rate of attenuation beyond the cut-offfrequency. Signal conditioning modules, SCMs, used for measuring process control variables such as temperature, pressure, strain, position, speed, level, etc. are always subject to externally induced noise signals. Electrically and magnetically induced noise voltages/currents are inevitable. Field sensors with output voltages in the millivolt range are certainly degraded by induced noise levels on the order of volts. Consequently, signal conditioning modules must provide filtering to eliminate induced noise components.
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1. Determine the cut off frequency from the graph and compare it to the theoretical value if
given that
From the graph the cut off frequency is 20 kHz and the theoretical value is 15.92kHz.
The value from experiment more higher compare the theoretical value. The error bar
regions of the theoretical and experimental result is close. Percentage error is between
experiment and theoretical value is 25.6%.
2. What is the pass band gain? Compare it to the theoretical gain, 20 log (1 + RF/R1)
The pass-band for a high-pass digital filter is limited to the maximum bandwidth,
sampling rate, and word length that the filter order allows. Pass band filters allow
transmission of a range of frequencies between a lower and upper cutoff limit. Pass band
filter transfer functions can be rearranged to function as ³notch´ filters, which eliminate
frequencies between a lower and upper cutoff limit. From the graph the pass band gain is
4.73 dB and the theoretical gain is 6.03 dB. The theoretical value more higher comparethe experiment value. Percentage error different between experiment and theoretical
value is 21.56%.
3. What is the roll-off rate (in dB/decade) in the stop band?
The roll of rate in the stop band is 10.5 dB/decade which is smaller than the roll of rate
for the low pass filter. Above the cutoff frequency , attenuation rapidly decrease to
After doing this experiment, we can summarize that we had achieved the objectives.
From this experiment, we can also determine the pass band and roll of rate in the stop band. We
learn about low pass and high pass filter. An electrical low pass filter and higher pass filter was
tested with input sinusoidal signals of different frequencies. At frequencies below the break
frequency the input and output signals had essentially by the same amplitude. As the input
frequency was increased above the break frequency, the output signal amplitude began to
decrease significantly and vise versa for high pass value. The theoretical formula that predicts the
magnitude response gave results very similar to the experimental ones. This experiment was
successful in demonstrating the validity of the theoretical formula for low pass filter and higher
pass filter constructed from a single resistor and capacitor. We learn the general principles of manual and automated tuning procedures for active filter controller and application of amplifier
in signal conditioning. Then we learn the circuits which capable of selectively filtering range of