PHP database link class of PDO+Access instance sharing

PHP PDO Access links

class DbHelpClass
    {
        private $conn;
        private $qxId;
        private $ret;

        function __construct()
        {
            $path="../../App_Data/sd#f#45G_!.mdb";
            $constr="DRIVER={Microsoft Access Driver (*.mdb)}; DBQ=".realpath($path); 
            $this->conn= new PDO("odbc:$constr") or die ("PDO Connection faild.");
        }

        /* read */
        function Read($sql,$params=array())
        {
            $bind=$this->conn->prepare($sql);
            $arrKeys=array_keys($params);
            foreach($arrKeys as $row)
            {
                $bind->bindValue(":".$row,$params[$row]);
            }
            $bind->execute() or die('sql error:'.$sql);
            $result=$bind->fetchAll();

            return $result;
        }

        /* add , This method is called to modify */
        function Edit($sql,$params=array())
        {
            $bind=$this->conn->prepare($sql);
            $arrKeys=array_keys($params);
            foreach($arrKeys as $row)
            {
                $bind->bindValue(":".$row,$params[$row]);

            }

            $a=$bind->execute() or die('sql error');
            return $a;
        }
    }
    $dbh =new DbHelpClass();