Why is the WMI connection, established to a remote PC, closed after a while on my PHP page? (I want that it stays open as long page is open)

I am reading some values like Operating system version, CPU Load, Memory Size... with WMI from a remote PC. At top of my PHP script I am building a connection to the remote PC and then query informations. When I open my page the first time it takes 15-20 seconds for the first WMI connection and after that i get the required values. When I reload the page after 3-5 seconds the values are updated immediatly (after 1-2 seconds). But when I keep the page open for a while and reload after 1 Minute, I see that the connection is lost and connecting once more, so it takes again 20 seconds that i get the updated values. It seems so that the WMI connection is closed after a while. How can I keep the WMI connection open, as long as the php page is open, or perhaps define a session time like 5 Minutes ?

<?php    
// Connection to WMI ****************   
$strComputer = "10.92.114.85";
$objSWbemLocator = new COM ("WbemScripting.SWbemLocator");
$objSWbemServices = $objSWbemLocator->ConnectServer($strComputer, "root\cimv2", "user",  "password");
$objSWbemServices->Security_->ImpersonationLevel = 3;
$obj = $objSWbemServices;

$Processor             =    $obj->ExecQuery("Select * from Win32_Processor");
$PhysicalMemory        =    $obj->ExecQuery("Select * from Win32_PhysicalMemory");

// WMI Processor Informations
foreach ( $Processor as $wmi_Processor )
{               
    $CPUName = $wmi_Processor->Name;
    $CPU3264bit = $wmi_Processor->AddressWidth;
    $CPUSpeed = $wmi_Processor->MaxClockSpeed;
    $CPUCores = $wmi_Processor->NumberOfCores;      
}

// showing values on screen
?>