function  valor(){
    <?php
        $con_string = "host='ip' port=numero dbname='banco' user='usuario' password='***'";
        $conn = pg_connect($con_string);
        $query="SELECT tubeteira from velocidadereal";
        $output=pg_query($conn,$query);
        $retorna =  pg_fetch_array($output);
        $valor = $retorna["tubeteira"];
    ?>
     return <?php echo $valor ?>;
}

setInterval(valor,1000);