System.Threading.Timer interval in Windows Service

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C#

.NET

threads

I have developed the windows service & in widows service used the system.threading.timer .in this the timers works fine but sometimes it will shifting the timing of the execution e.g. I have set the timer to the 10 sec then it executed at every 10 sec but sometimes it will started at 11 sec . I have got this output

18-08-2011 10:00:10
18-08-2011 10:00:10  
18-08-2011 10:00:20
18-08-2011 10:00:30
18-08-2011 10:00:40
18-08-2011 10:00:11
18-08-2011 10:00:22
18-08-2011 10:00:33
18-08-2011 10:00:44

but i want the output as

18-08-2011 10:00:10  
18-08-2011 10:00:20
18-08-2011 10:00:30
18-08-2011 10:00:40
18-08-2011 10:00:50
18-08-2011 10:00:00
18-08-2011 10:00:10
18-08-2011 10:00:20

//code

  public void SetTimers(int timer, DataRow row)
        {
            TimeSpan dueTime;
            TimeSpan interval;
            SetTimeIntervals(row, out dueTime, out interval);         

            timer1[timer] = new System.Threading.Timer(databaseTrensfer, row, dueTime, interval);         

        }



private void SetTimeIntervals(DataRow row, out TimeSpan tsDueTime, out TimeSpan tsPeriod)
        {

            string alarmType = Convert.ToString(row["EBase"]);
            string EType = Convert.ToString(row["EType"]);
            string EFrequency = Convert.ToString(row["EFrequncy"]);
            if (alarmType == "Milisecond")
            {
                int frquency1 = Convert.ToInt32(row["Tfrquency"]);
                tsDueTime = new TimeSpan(0, 0, 0, 0, frquency1);//frquency1=interval
                tsPeriod = new TimeSpan(0, 0, 0, 0, frquency1);
            }
            else if (alarmType == "Second")
            {
                int frquency1 = Convert.ToInt32(row["Tfrquency"]);
                tsDueTime = new TimeSpan(0, 0, 0, frquency1);
                tsPeriod = new TimeSpan(0, 0, 0, frquency1);
            }
            else if (alarmType == "Once")
            {
                tsDueTime = new TimeSpan(0, 0, 0);
                tsPeriod = new TimeSpan(0, 0, 0);
            }
            else if (alarmType == "Minute")
            {

                int frquency1 = Convert.ToInt32(row["Tfrquency"]);
                tsDueTime = new TimeSpan(0, frquency1, 0);
                tsPeriod = new TimeSpan(0, frquency1, 0);
            }
            else if (alarmType == "Hour")
            {

                int minute = 0;
                int frquency1 = 1;
                if (Convert.ToString(row["RelativeFactor"]) != "")
                    minute = Convert.ToInt32(row["RelativeFactor"]);
                if (Convert.ToString(row["Tfrquency"]) != "")
                    frquency1 = Convert.ToInt32(row["Tfrquency"]);

                tsDueTime = new TimeSpan(frquency1, minute, 0);
                tsPeriod = new TimeSpan(frquency1, 0, 0);
            }
            else
            {
                tsDueTime = new TimeSpan();
                tsPeriod = new TimeSpan();
            }

            if (EType == "Start" && EFrequency == "Event" || EType == "Stop" && EFrequency == "Event" || EType == "Event" && EFrequency == "Event")
            {
                int freq = 500;
                tsDueTime = new TimeSpan(0, 0, 0, 0, freq);
                tsPeriod = new TimeSpan(0, 0, 0, 0, freq);
            }

        }

thanks in advance