c#使用WMI查询Win32_Fan类和风扇转速返回null

这是我用来查询风扇速度的代码，但风扇速度总是返回null。有人知道为什么吗?

Win32_Fan()｛SelectQuery =新SelectQuery("Win32_Fan");

        // Initialize an object searcher with this query
        ManagementObjectSearcher searcher =
           new ManagementObjectSearcher(query);
        // Get the resulting collection and loop through it
        foreach (ManagementObject fan in searcher.Get())
        {
            Console.WriteLine("{0} = ActiveCooling {1}",fan["Name"], fan["ActiveCooling"]);
            Console.WriteLine("DesiredSpeed = {0}", fan["DesiredSpeed"]);
        }
    }