$re = '/(?<=^|\s)\b\d+([\/-]?\d)*(?<!\/|-)(с{1,2}|дсп)?\b(?=\s)/mu';
$str = '12/2с 12/2-2с 1-2/3дсп
аб12/2с 12/2-с 12/с 12/2-2ссс';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php