public static function heartbeat(&$opcSender, $plcVal)
{
   $_SESSION['PLC_HB_TIME'] = time();		
   $tagHeartbeatAck = $_SESSION['serviceConfig']['opcDevicePath'] . '.Status.HB02';
   return self::writeOpcItem($opcSender, $tagHeartbeatAck, $plcVal);
}

public static function writeOpcItem(&$opcSender, $tag, $val)
{
 
   try {
	$opcSender->WriteItemValue($_SESSION['config']['opc']['machine'], $_SESSION['config']['opc']['server'], $tag, $val);
   } catch (Exception $e) {
	$tmp = str_replace(array("\n","\t"," "), ' ', $e);
	LogHandler::error(__METHOD__, __LINE__, "Fault to write '{$val}' to opc tag '{$tag}': {$e}");
	return false;
   }
 
   return true;
}

class DEasyDAClientEvents {
 
	public $tagHeartbeat; //heartbeat
	public $tagInFloatSeq1; //collect from the plc
	public $tagCollectorFault; // fault bit written by the collector
	public $MsSql;
	public $Collector;
 
	public function __construct()
	{
		$this->tagHeartbeat = $_SESSION['serviceConfig']['opcDevicePath'] . '.Status.HB01';
		$this->tagCollectorFault = $_SESSION['serviceConfig']['opcDevicePath'] . '.Status.HB06';
		$this->tagInFloatSeq1 = $_SESSION['serviceConfig']['opcDevicePath'] . '.In.FloatSeq1';
 
 
		$this->MsSql = new MsSql();
		$this->MsSql->openConnection();
 
		return;
	}
 
	public function __destruct()
	{	
		if (is_object($this->MsSql)) {
			$this->MsSql->closeConnection();
			unset($this->MsSql);
		}
	}
 
	function ItemChanged($varSender, $varE)
	{
 
		try {
			$itemId = $varE->ItemDescriptor->ItemId;
		} catch (Exception $e) {
			$tmp = str_replace(array("\n","\t"," "), ' ', $e);
			LogHandler::error($_SESSION['serviceName'], __LINE__, "Failed to read subscribed item tag: {$tmp}");
			return false;
		}
 
		try {
			$itemVal = $varE->Vtq->value;
		} catch (Exception $e) {
			$tmp = str_replace(array("\n","\t"," "), ' ', $e);
			LogHandler::error($_SESSION['serviceName'], __LINE__, "Failed to read subscribed item val: {$tmp}");
			return false;
		}
 
		switch ($itemId) {
			case $this->tagHeartbeat:
				Collector::heartbeat($varSender, $itemVal);
		   		break;
	   		case $this->tagInFloatSeq1:
	   			Collector::handshake($varSender, $this->MsSql, $itemVal);
	   			break;
	   		case $this->tagCollectorFault:
	   			Collector::collectorFaultReset($varSender, $this->MsSql, $itemVal);
	   			break;
			default:
				LogHandler::warning($_SESSION['serviceName'], __LINE__, "Unknown subscribed item '{$itemId}' changed to '$itemVal'");
		   		break;
		}
 
	}
}

exception 'com_exception' with message 'Source: OPCLabs.EasyDAClient.5.2 Description: Write not completed. This error indicates that it could not be verified that the requested write operation was completed during the timeout period. It is possible that the write operation will actually succeed or fail, but later. Increase the timeout period if you want to obtain positive or negative indication of the operation outcome. Other reason for this error may be that under heavy loads, topic request or response queue is overflowing. Check the event log for queue overflow errors (if event logging is supported by the product and enabled). 

exception 'com_exception' with message 'Source: OPCLabs.EasyDAClient.5.2 Description: Cannot connect topic (timeout).

$opcCom = new COM($_SESSION['config']['opc']['comObjName']);
	$opcEvents = new DEasyDAClientEvents();
 
	if (!com_event_sink($opcCom, $opcEvents, "DEasyDAClientEvents")) {
		LogHandler::error($_SESSION['serviceName'], __LINE__, "com_event_sink failed");
	}
 
// 	$opcCom->SubscribeItem($_SESSION['config']['opc']['machine'], $_SESSION['config']['opc']['server'], $opcEvents->tagHeartbeat, 10);
	$tmp = array($opcEvents->tagHeartbeat, $opcEvents->tagInFloatSeq1, $opcEvents->tagCollectorFault);
	$opcCom->SubscribeMultipleItems($_SESSION['config']['opc']['machine'], $_SESSION['config']['opc']['server'], $tmp, 100);
 
	$_SESSION['PLC_HB_TIME'] = time(); // setting the inital time to start checking the PLC heartbeat to trigger a fault
 
	while (WIN32_SERVICE_CONTROL_STOP != win32_get_last_control_message()) {
		//User Loop
		usleep(10000); //10000 micro seconds = .01 seconds
		com_message_pump(1000);
 
		if (time() - $_SESSION['PLC_HB_TIME'] > $_SESSION['serviceConfig']['plcHbFaultTimeout'] + 5) { // 5 is the hb cycling time
// 			GknDataCollector::writeOpcItem($opcCom, $opcEvents->tagCollectorFault, 1);
			GknDataCollector::setCollectorFault($opcCom, 1);
			$_SESSION['PLC_HB_TIME'] = time() + 60;
		}
	}
 
	$opcCom->UnsubscribeAllItems();
	LogHandler::trace($_SESSION['serviceName'], __LINE__, "Service now unsubscribed to all change events");
 
	unset($opcCom);
	unset($opcEvents);