谷歌地理编码API错误:超过查询限制

我目前正在使用Google Geocoding API，并且使用得很少。限制是每天2500次查询，我可能最多在20-50之间。在过去的一周里，我每隔一段时间就会收到一个OVER_QUERY_LMIT错误。我一次只处理一个地址，没有循环或任何东西。它只进行一次地理编码，并将lat/lng发送到数据库，之后它将只从数据库中引用。有人能告诉我为什么会出现这个错误吗？

$request_url = "http://maps.googleapis.com/maps/api/geocode/xml?address=".$siteAddress."&sensor=true";

直到大约一周前，在一个多月的测试中，这一切都完美无瑕。

我有几个页面做着同样的事情，但只是在不同的时间被引用，用于不同的目的。以下是用于地理编码的所有代码。

  $request_url = "http://maps.googleapis.com/maps/api/geocode/xml?address=".$siteAddress."&sensor=true"; // the request URL you'll send to google to get back your XML feed
$xml = simplexml_load_file($request_url) or die("url not loading");// XML request
$status = $xml->status;// GET the request status as google's api can return several responses
if ($status=="OK") {
    //request returned completed time to get lat / lang for storage
    $lat = $xml->result->geometry->location->lat;
    $long = $xml->result->geometry->location->lng;
echo "latitude:$lat, longitude:$long <br>";
    echo "$lat, $long <br>";  //spit out results or you can store them in a DB if you wish
}
if ($status=="ZERO_RESULTS") {
    //indicates that the geocode was successful but returned no results. This may occur if the geocode was passed a non-existent address or a latlng in a remote location.
$errorcode = "ZERO RESULTS";
echo "ZERO RESULTS";
}
if ($status=="OVER_QUERY_LIMIT") {
    //indicates that you are over your quota of geocode requests against the google api
$errorcode = "Over Query Limit";
echo "Over Query Limit";
}
if ($status=="REQUEST_DENIED") {
    //indicates that your request was denied, generally because of lack of a sensor parameter.
$errorcode = "Request Denied";
echo "Request Denied";
}
if ($status=="INVALID_REQUEST") {
    //generally indicates that the query (address or latlng) is missing.
$errorcode = "Invalid Request";
echo "Invalid Request";
}