LP('Expression','Omega*','Reset=0')
Arguments
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'Expression' |
Measured value |
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'Omega*' |
Specification of the angular frequency of the filter, which results in the frequency of the LP function to frequency = 'Omega'/(2*PI) |
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'Reset' |
Optional digital parameter that can be used to deactivate the function. ‘Reset’ can be an expression as well. |
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'Reset' > 0 |
Filter is deactivated, input signal is displayed unfiltered |
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'Reset' = 0 |
Filter is applied |
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Parameters ending with * are only evaluated once at the start of the acquisition.
Description
The function is a low-pass filter with frequency = 'Omega'/(2*PI) applied to 'Expression'. The filter is a single-pole filter with a roll-off rate of 20 dB/decade. If the optional 'Reset' parameter is TRUE then the filter is deactivated and the result is the unfiltered 'Expression' input signal. 'Reset' can also be formulated as an expression.
Examples:
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LP([0:0],10) |
Filter is active ('Reset' omitted). |
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LP([0:0],10,If([0:0]<0,1,0)) |
The filter function is only used for positive values. |
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LP([0:0],10,[3.1]) |
e.g. with [3.1] = If([0:0]>10, 1, 0) The filter is deactivated as soon as the expression [3.1] returns TRUE, i.e. if the expression [0:0] exceeds the limit value 10. |
Example
Applying the filter function to a sine wave with 10 Hz, which is overlaid by a further wave with 50 Hz.
Task description
The filter function should be applied with the values 5, 10 and 40 for 'Omega'.
Solution
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Blue |
Original signal of a superimposed sine wave |
Red |
Filtered signal with 'Omega' = 5 |
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Green |
Filtered signal with 'Omega' = 10 |
Yellow |
Filtered signal with 'Omega' = 40 |
The lower the value selected for 'Omega', the more the signal is attenuated.