is it possible to use it in PEAR2_Net_RouterOS without "once" ? for example continuous running loop/for and put an "if ($signal < 60 ) then ...."
Sure. Well... not in a "for/while" loop, but using the loop() method instead, after previously specifying a callback for each response.
Just... to avoid a serious performance degradation, make sure to also add some reasonable interval.
e.g.
$monitorRequest = new Request('/interface wireless monitor numbers=wlan1 interval=2', null, 'm');
$client->sendAsync($monitorRequest, function ($response) {
$signal = $response->getArgument('signal');
if ($signal < 60) {
//????
}
});
$client->loop();