CFCFilter (FPScript)
Filters a data set using a CFC filter. CFC is short for Channel Frequency Class.
Syntax
CFCFilter(Signal, CFC [ , Algorithm = CFCFILTER_ISO6487 ])
The syntax of the CFCFilter function consists of the following parts:
Part |
Description |
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|---|---|---|---|---|---|---|---|
Signal |
The signal to be filtered. Permitted data structures are signal und signal series. All numeric data types are permitted. For the X component additional restrictions do apply.The values must have a constant positive spacing. If the argument is a list, then the function is executed for each element of the list and the result is also a list. |
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CFC |
Specifies the filter type. Typical values are 60 (CFC60), 180 (CFC180), 600 (CFC600) and 1000 (CFC1000). Permitted data structures are scalar value. All integral data types are permitted. The value must be greater than 0. If the argument is a list, then the first element in the list is taken. If this is also a list, then the process is repeated. |
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Algorithm |
Specifies the algorithm for the CFCFilter calculation. The argument is optional. The argument Algorithm can have the following values:
If the argument is a list, then the first element in the list is taken. If this is also a list, then the process is repeated. If this argument is omitted, it will be set to the default value CFCFILTER_ISO6487. |
Remarks
The result has the same structure and unit as the argument Signal.
The data type of the result is always a real or complex 64-bit floating point value.
The CFC argument influences the filter coefficients. The signal's sampling frequency (X component) must be greater than six times the 3dB cut-off frequency.
As a digital filter, a 4-pole Butterworth low pass filter is used with a linear phase and specific starting conditions. To achieve the filtering, the data must pass through the two-pole filter twice, once forward and once backward, in order to prevent phase shifts.
The following filter types are available:
Filter type |
3dB cut-off frequency |
Stop-band attenuation |
Sampling frequency |
|---|---|---|---|
CFC60 |
100 Hz |
-30 dB |
≥600 Hz |
CFC180 |
300 Hz |
-30 dB |
≥1,800 Hz |
CFC600 |
1,000 Hz |
-40 dB |
≥6 kHz |
CFC1000 |
1,650 Hz |
-40 dB |
≥10 kHz |
Standard |
Description |
|---|---|
ISO 6487:2000 |
Road vehicles - Measurement techniques in impact tests - Instrumentation |
SAE J211/1 MAR95 |
Instrumentation for Impact Test—Part 1—Electronic Instrumentation |
The two standards use slightly different equations for calculating the filter coefficients.
Available in
Option Digital Filters
Examples
CFCFilter(Signal, 60) |
Filters the signal using a CFC60 filter. |