Getting invalid output

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0020.0 0019.9 0010.0 0000.0 0100.0 0100.0 0000.0 0010.9 0000.0 0002.1 0000.0 0002.1 0000.0 0002.1 00000000000000000000000000000000

public override void DoJob()
        {
            try
            {
                mySerialPort.Open();

                mySerialPort.Write("$01I\r");

                
                //Console.WriteLine("{0} ", CurrentDate);
               // Console.WriteLine("Starting Time: {0}\n", CurrentDate);

                        if (mySerialPort.BytesToRead > 0) //if there is data in the buffer
                        {
                           string b = mySerialPort.ReadExisting(); //read a byte

                            //Console.Write(b);
                            string desktop = Environment.GetFolderPath(Environment.SpecialFolder.DesktopDirectory);
                            string image1 = System.IO.Path.Combine(desktop, "Temperature_LOG.txt");

                            using (FileStream fs = new FileStream(image1, FileMode.Append, FileAccess.Write))
                            {
                                using (BinaryWriter bw = new BinaryWriter(fs))
                                {


                                    bw.Write(b);
                                  

                                   
                                    //bw.Close();
                                }
                            }



                            //mySerialPort.Close();
                        }


                mySerialPort.Close();

            }
            catch (IOException ex)
            {

                Console.WriteLine(ex);
            }



        }