Data Type Conversion does not convert to boolean when attached to transfer function block
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Timo Dietz on 9 Jun 2020
Commented: Timo Dietz on 10 Jun 2020
I attached a "Data Type Conversion" block to a PT1 low pass filter (transfer function) trying to convert the ouptut signal from double to boolean. Unfortunately this did not work as expected - the output was constantly '1' or '0'.
The same issue appears when a logic block is used after the transfer function. (I assume the same type of conversion is made internally.)
I have to convert the double value to an integer first, and than to boolean. This does the trick but in principle it should not matter in which block a double value is created. Converting e.g. a pulse source double output directly to boolean works certainly.
This strange behavior has been encountered in 2018a and 2019a and with all possible conversion settings.
Here comes some additional information:
Simulation result at Conv1_out: directly converted to boolean
The direct conversion delivers a constant signal, only.
Simulation result at Conv2_out with first conversion block set to 'int8':
Now, the output looks as expected.
Your filter coefficient 50e-6 makes it respond faster but the output will "creep" for a long time.
The boolean conversion or the boolean(a) or logical(a) function basically is to check if value a is equal to zero. For double precision data, "true zero" is hard to get. see "help realmin".
You "Filter_out" value never reaches "zero" for double precision data. Log the data to workspce and check a value that seems to be 0 but the real value is around 2e-22 (depending on your solver and time step).
The rest makes sence if you add a "convert to integer" in the middle. To do it directly, use a Comparator block and see "help eps".
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