trim custom field text value and show (…)

Question

I am using this code here:

<?php
$trim_length = 25;  //desired length of text to display
$custom_field = 'my-custom-field-name';
$value = get_post_meta($post->ID, $custom_field, true);
if ($value) {
 echo rtrim(substr($value,0,$trim_length));
}
?>

It works - but I would like to have a "(...)" at the end of the trimmed text. And only if the value really was trimmed.

I used if ($value) { echo rtrim(substr($value,0,$trim_length)) . '(...)'; } ?> But this makes the "(...)" at the end of every text from custom field..

Thank you!

AD