You cannot add a variable that already exists in the table. In your case, you are trying to concatenate a table that contains the variable "x_CSVA_01_01" two times.
One option could be to rename the variable that is inside the table. You can access the name of the variable through the properties. In your case:
t_sec.Properties.VariableNames
It should return a 1x1 cell array {'x_CSVA_01_01'}, which maybe you can rename using a counter inside the while loop.
Another option is to convert the table to a array, and concatenate all the elements as a 2D array. You could use:
t_sec = table2array(t_sec)
This will convert your 1 column table to a 1 column array. Once you have all the columns concatenated, you can convert the array to a table again using the array2table function. You could finally rename the columns as I have mentioned before, accesing the properties of the table.
Hope it is helpful.
