WooCommerce hide fields on product_cat ids not working

Hey folks. i try to hide fields only on categories from Woocommerce custom post type category = product_cat - with the code below it is not working. i need to hide only fields not meta boxes.
The product id of the Woocommerce product_cat equals 18.

I think something is wrong here, but i can't figure out where. Can you please assist?

In Woocommerce i also have products assigned to different product_cats and i need to hide some of the fields on one but not the other category - is that possible?

array (
                'id' => 'lautstaerke_minimum',
                'type' => 'text',
                'name' => 'Lautstärke Minimum',
                'desc' => 'Beispiel 49 dB (A)',
                'std' => '49 dB (A)',
                'tab' => 'geraet',
                '' => '',
                'hidden' => 
                array (
                    'when' => 
                    array (
                        0 => 
                        array (
                            0 => 'product_cat',
                            1 => '=',
                            2 => 18,
                        ),
                    ),
                    'relation' => 'or',
                ),
            ),