在PHP中将utf8转换为latin1. 255以上的所有字符都转换为char引用

示例：我想将文字转换为

hello é β 水

成

hello é β 水

我在PHP中做这一切.我尝试了内置函数,iconv,整洁和组合,仍然无法获得可靠的解决方案.

这是我到目前为止所拥有的

// convert any characters fount in the entity table into HTML entities
// do not double encode entities,do not mess with quotes
// use UTF-8 as character encoding because the page submits UTF-8
$str = htmlentities($str,ENT_NOQUOTES,'UTF-8',false);
//print $str."n";

// convert text from UTF-8 to ISO-8859-1,// characters that cannot be converted will be converted to ?
$str = utf8_decode($str);
//print $str."n";    

// make string XML valid.
// mainly it converts text entities into numeric entities.
$opts = array(  "output-xhtml"      => true,"output-xml"        => true,"show-body-only"    => true,"numeric-entities"  => true,"wrap"              => 0,"indent"            => false,"char-encoding" => 'latin1'
        );
$tidy = tidy_parse_string($str,$opts,'latin1');
tidy_clean_repair($tidy);
$str = tidy_get_output($tidy);      
//print $str."n";