How to find non printable characters in a column using regexp

I am trying to find the records where there are non printable characters, i am not having success with it

select * from njcrc.tblprogram where REGEXP_INSTR(description,'[[:cntrl:]]')
>0;

Above sql pulls records where there are no "non printable" characters.

Can any point me to an alternate way achieving this or let me know what am i doing wrong.

Thanks

Deen

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