System.Threading.Timer Doesn't Trigger my TimerCallBack Delegate

I am writing my first Windows Service using C# and I am having some trouble with my Timer class.

When the service is started, it runs as expected but the code will not execute again (I want it to run every minute)

Please take a qu开发者_JAVA百科ick look at the attached source and let me know if you see any obvious mistakes!

TIA

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Diagnostics;
using System.Linq;
using System.ServiceProcess;
using System.Text;
using System.Threading;
using System.IO;

namespace CXO001
{
    public partial class Service1 : ServiceBase
    {
        public Service1()
        {
            InitializeComponent();
        }

         /*
         * Aim: To calculate and update the Occupancy values for the different Sites
         * 
         * Method: Retrieve data every minute, updating a public value which can be polled
         */

        protected override void OnStart(string[] args)
        {
            Daemon();
        }

        public void Daemon()
        {
            TimerCallback tcb = new TimerCallback(On_Tick);
            TimeSpan duetime = new TimeSpan(0, 0, 1);
            TimeSpan interval = new TimeSpan(0, 1, 0);
            Timer querytimer = new Timer(tcb, null, duetime, interval);
        }

        protected override void OnStop()
        {

        }



        static int[] floorplanids = new int[] { 115, 114, 107, 108 };
        public static List<Record> Records = new List<Record>();
        static bool firstrun = true;

        public static void On_Tick(object timercallback)
        {
            //Update occupancy data for the last minute
            //Save a copy of the public values to HDD with a timestamp

            string starttime;

            if (Records.Count > 0)
            {
                starttime = Records.Last().TS;
                firstrun = false;
            }
            else
            {
                starttime = DateTime.Today.AddHours(7).ToString();
                firstrun = true;
            }

            DateTime endtime = DateTime.Now;
            GetData(starttime, endtime);
        }

        public static void GetData(string starttime, DateTime endtime)
        {
            string connstr = "Data Source = 192.168.1.123; Initial Catalog = Brickstream_OPS; User Id = Brickstream; Password = bstas;";
            DataSet resultds = new DataSet();

            //Get the occupancy for each Zone
            foreach (int zone in floorplanids)
            {
                SQL s = new SQL();
                string querystr = "SELECT SUM(DIRECTIONAL_METRIC.NUM_TO_ENTER - DIRECTIONAL_METRIC.NUM_TO_EXIT) AS 'Occupancy' FROM REPORT_OBJECT INNER JOIN REPORT_OBJ_METRIC ON REPORT_OBJECT.REPORT_OBJ_ID = REPORT_OBJ_METRIC.REPORT_OBJECT_ID INNER JOIN DIRECTIONAL_METRIC ON REPORT_OBJ_METRIC.REP_OBJ_METRIC_ID = DIRECTIONAL_METRIC.REP_OBJ_METRIC_ID WHERE (REPORT_OBJ_METRIC.M_START_TIME BETWEEN '" + starttime + "' AND '" + endtime.ToString() + "') AND (REPORT_OBJECT.FLOORPLAN_ID = '" + zone + "');";
                resultds = s.Go(querystr, connstr, zone.ToString(), resultds);
            }

            List<Record> result = new List<Record>();
            int c = 0;

            foreach (DataTable dt in resultds.Tables)
            {
                Record r = new Record();
                r.TS = DateTime.Now.ToString();
                r.Zone = dt.TableName;
                if (!firstrun)
                {
                    r.Occupancy = (dt.Rows[0].Field<int>("Occupancy")) + (Records[c].Occupancy);
                }
                else
                {
                    r.Occupancy = dt.Rows[0].Field<int>("Occupancy");
                }
                result.Add(r);
                c++;
            }

            Records = result;
            MrWriter();
        }

        public static void MrWriter()
        {
            StringBuilder output = new StringBuilder("Time,Zone,Occupancy\n");

            foreach (Record r in Records)
            {
                output.Append(r.TS);
                output.Append(",");
                output.Append(r.Zone);
                output.Append(",");
                output.Append(r.Occupancy.ToString());
                output.Append("\n");
            }

            output.Append(firstrun.ToString());
            output.Append(DateTime.Now.ToFileTime());

            string filePath = @"C:\temp\CXO.csv";
            File.WriteAllText(filePath, output.ToString());
        }

    }
}

The manual states:

As long as you are using a Timer, you must keep a reference to it. As with any managed object, a Timer is subject to garbage collection when there are no references to it. The fact that a Timer is still active does not prevent it from being collected.

Your Timer is probably being collected by the GC.