4 ~ 17 February 2013 (week 4 )

Title Of Activity

-Project Progress

 Using filtering to filter the signal .

 

Objectives

-The filter Express VI processes signals through filters and window. We use the filtering signal to remove the noise from a signal .

-Get to know what type of filter that am i going to use in the project , and what is the type of filters ?

-Compare and absorb the differences in both signal ( filtered , unfiltered ) . 

Content /Procedure 

-The types of filters are many such as Specifies the following types of filters to use: lowpass, highpass, bandpass, bandstop, or smoothing. The default is Lowpass.

-Filtering specification : Contains the following options:

• Cutoff Frequency (Hz)—Specifies the cutoff frequency of the filter. This option is available only when you select Lowpass or Highpass from the Filtering Type pull-down menu. The default is 100.
• Low cutoff frequency (Hz)—Specifies the low cutoff frequency of the filter. Low cutoff frequency (Hz) must be less than High cutoff frequency (Hz) and observe the Nyquist criterion. The default is 100. This option is available only when you select Bandpass or Bandstop from the Filtering Type pull-down menu.
• High cutoff frequency (Hz)—Specifies the high cutoff frequency of the filter. High cutoff frequency (Hz) must be greater than Low cutoff frequency (Hz) and observe the Nyquist criterion. The default is 400. This option is available only when you select Bandpass or Bandstop from the Filtering Type pull-down menu.
• Finite impulse response (FIR) filter—Creates an FIR filter, which depends only on the current and past inputs. Because the filter does not depend on past outputs, the impulse response decays to zero in a finite amount of time. Because FIR filters return a linear phase response, use FIR filters for applications that require linear phase responses.
• Taps—Specifies the total number of FIR coefficients, which must be greater than zero. The default is 29. This option is available only when you select the Finite impulse response (FIR) filter option. Increasing the value of Taps causes the transition between the passband and the stopband to become steeper. However, as the value of Taps increases, the processing speed becomes slower.
• Infinite impulse response (IIR) filter—Creates an IIR filter that is a digital filter with impulse responses that can theoretically be infinite in length or duration.
• Topology—Determines the design type of the filter. You can create either a Butterworth, Chebyshev, Inverse Chebyshev, Elliptic, or Bessel filter design. This option is available only when you select the Infinite impulse response (IIR) filter option. The default is Butterworth.
• Order—Order of the IIR filter, which must be greater than zero. This option is available only when you select the Infinite impulse response (IIR) filter option. The default is 3. Increasing the value of Order causes the transition between the passband and the stopband to become steeper. However, as the value of Order increases, the processing speed becomes slower, and the number of distorted points at the start of the signal increases.
• Moving average—Yields forward-only (FIR) coefficients. This option is available only when you select Smoothing from the Filtering Type pull-down menu.
• Rectangular—Specifies that all samples in the moving-average window are weighted equally in computing each smoothed output sample. This option is available only when you select Smoothing from the Filtering Type pull-down menu and the Moving average option.
• Triangular—Specifies that the moving weighting window applied to the samples is triangular with the peak centered in the middle of the window, ramping down symmetrically on both sides of the center sample. This option is available only when you select Smoothing from the Filtering Type pull-down menu and the Moving average option.
• Half-width of moving average—Specifies the half-width of the moving-average window in samples. The default is 1. For a half-width of moving average of M, the full width of the moving-average window is N = 1 + 2M samples. Therefore, the full width N is always an odd number of samples. This option is available only when you select Smoothing from the Filtering Type pull-down menu and the Moving average option.
• Exponential—Yields first-order IIR coefficients. This option is available only when you select Smoothing from the Filtering Type pull-down menu.
• Time constant of exponential average—Specifies the time constant of the exponential-weighting filter in seconds. The default is 0.001. This option is available only when you select Smoothing from the Filtering Type pull-down menu and the Exponential option.

                            Figure 1 : context help of filter .

                            Figure 2 : block diagram of filtering .

                              

                            Figure 3 : front panel of filtering .

 Result & Analysis 

-From the filtered signal  we can remove the noise from the signal .-Get to know the types of  filtered that i'm going to use which is low pass filter , Infinite impulse response (IIR) filter—Creates an IIR filter that is a digital filter with impulse responses that can theoretically be infinite in length or duration .