System.Timers.Timer Usage

Question

For the purposes of this question I'm including a class of mine in its entirety:

public class SerialPortConnection
{
    private SerialPort serialPort;
    private string ping;
    double failOut;
    bool isReceiving;

    public SerialPortConnection(string comPort = "Com1", int baud = 9600, System.IO.Ports.Parity parity = System.IO.Ports.Parity.None, int dataBits = 8, System.IO.Ports.StopBits stopBits = System.IO.Ports.StopBits.One, string ping = "*IDN?", double failOut = 2)
    {
        this.ping = ping;
        this.failOut = failOut * 1000;

        try
        {
            serialPort = new SerialPort(comPort, baud, parity, dataBits, stopBits);
        }
        catch (Exception e)
        {
            throw e;
        }
    }

    //Open Serial Connection. Returns False If Unable To Open.
    public bool OpenSerialConnection()
    {
        //Opens Initial Connection:
        try
        {
            serialPort.Open();
            serialPort.Write("REMOTE\r");
        }
        catch (Exception e)
        {
            throw e;
        }

        serialPort.Write(ping + "\r");
        var testReceived = "";
        isReceiving = true;

        Timer StopWatch = new Timer(failOut);
        StopWatch.Elapsed += new ElapsedEventHandler(OnTimedEvent);
        StopWatch.Interval = failOut;
        StopWatch.Enabled = true;

        while (isReceiving == true)
        {
            try
            {
                testReceived += serialPort.ReadExisting();
            }
            catch (Exception e)
            {
                throw e;
            }
        }

        StopWatch.Dispose();

        if (testReceived.Contains('>'))
        {
            return true;
        }
        else
        {
            return false;
        }
    }

    public string WriteSerialConnection(string SerialCommand)
    {
        try
        {
            serialPort.Write(String.Format(SerialCommand + "\r"));
            var received = "";
            bool isReceiving = true;

            Timer StopWatch = new Timer(failOut);
            StopWatch.Elapsed += new ElapsedEventHandler(OnTimedEvent);
            StopWatch.Interval = failOut;
            StopWatch.Enabled = true;

            while (isReceiving == true)
            {
                try
                {
                    received += serialPort.ReadExisting();
                }
                catch (Exception e)
                {
                    throw e;
                }
            }

            if (received.Contains('>'))
            {
                return received;
            }
            else
            {
                received = "Error: No Data Received From Device";
                return received;
            }

            StopWatch.Dispose();
        }
        catch (Exception e)
        {
            throw e;
        }        
    }

    //Closes Serial Connection. Returns False If Unable To Close.
    public bool CloseSerialConnection()
    {
        try
        {
            serialPort.Write("LOCAL\r");
            serialPort.Close();
            return true;
        }
        catch (Exception e)
        {
            throw e;
        }
    }

    private void OnTimedEvent(object source, ElapsedEventArgs e)
    {
        isReceiving = false;
    }
}

What I'm attempting to do here is keep a loop running for a set amount of time (two seconds in this case) because the device connected to the serial port I'm working with is unpredictable. I don't know what data I will receive from it and I don't know how long it will take. That can't be fixed and is something I have to work with. My best option, currently, is to wait a set amount of time and check the data I've received for an end token (">"). I've tried wiring up a timer even in the class like so:

Timer StopWatch = new Timer(failOut * 1000);
StopWatch.Elapsed += new ElapsedEventHandler(OnTimedEvent);
StopWatch.Interval = failOut;
StopWatch.Enabled = true;

But it doesn't appear to work. The event itself looks like so:

private void OnTimedEvent(object source, ElapsedEventArgs e)
{
    isReceiving = false;
}

My objective is to cut the loop isReceiving is tied to:

(while isReceiving == true)
{
    //Do Something
}

But it doesn't appear to work. I assume I've completely misunderstood the function of the timer but I've had suggestions before to implement it. What am I doing wrong? If I'm just completely misusing it, what can I use instead of a timer? As I've said, I've no choice but to wait a set amount of time and check what I've received. That can't be avoided or handled in any way other than waiting and hoping I get something.

EDIT:

Maybe it's best I clarify this. The OnTimedEvent event is firing and the variable is set to false but it doesn't cut the loop as isReceiving isn't getting set to false.

EDIT 2:

Mr. Passant's answer works beautifully barring a strange error I'm encountering. As I don't believe it's a problem within his answer, it's more likely that it's a hardware flaw, or something else strange and obscure along those lines, I'm leaving his answer marked as accepted. I recommend anyone that chooses to implement his answer also view the question I have submitted here:

Apparent IO.Ports.SerialPort Flaw in C# or Possible Hardware Flaw

Answer 1

You are making it too difficult on yourself. Simply change the SerialPort.NewLine property to ">". And use SerialPort.ReadLine() to read the response. You can still use a timeout if you need it, assign the SerialPort.ReadTimeout property and be prepared to catch the TimeoutException.