help required to connect to the digital weighing machin

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VB

Hi
I am writing an application to read weighing scale reading of a milk dairy.

The instrument has got RS232 Port and I have purchased a USB converted to connect this to my laptop.

weighing machine is of class 3.
I am using Serial Port option in vb.net 2010

"COM13", 9600, Parity.None, 8, StopBits.One

I am unable to open the connection but unable to read the data.. I am using following code to read the data

Private Sub port_DataReceived(ByVal sender As Object, ByVal e As System.IO.Ports.SerialDataReceivedEventArgs) Handles port.DataReceived
        Try
            If port.IsOpen = False Then port.Open 
            ReceivedText(port.ReadExisting())
        Catch ex As Exception
            MsgBox(ex.Message)
            Exit Sub
        End Try
    End Sub()

 Private Sub ReceivedText(ByVal [text] As String)
        If Me.rtbReceived.InvokeRequired Then
            Dim x As New SetTextCallback(AddressOf ReceivedText)
            Me.Invoke(x, New Object() {(text)})
        Else
            Me.rtbReceived.Text &= [text]
        End If
    End Sub

 'rtbReceived is a Rich text box

I am getting some garbage data which needs to be purified... and unable to get data all the time.

don't no how to connect and how to get data.

have tried port.write("P") and port.write("T") and port.write("P").... but without any result ... message received as operation timed out.

Please help me to get the result

Thanks and regards
Santosh Sharma