修复 ModbusMapper_Client 实际采样周期统计，第1次读取时时间太短。

Project.FLY.ModbusMapper/FLY.ModbusMapper/WithThread/ModbusMapper_Client.cs

@@ -104,6 +104,7 @@ namespace FLY.Modbus.WithThread
         void OnPoll_update()
         {
             Stopwatch stopwatch = new Stopwatch();
+            Stopwatch stopwatch_act = new Stopwatch();
             bool isTimeForRead = true;
         _connect:
             while (true)
@@ -152,10 +153,17 @@ namespace FLY.Modbus.WithThread
                 if (isTimeForRead)
                 {
                     isTimeForRead = false;
-                    TimeSpan elapsed = stopwatch.Elapsed;
-                    ActUpdateInterval = elapsed;
                     stopwatch.Restart();
-                    
+
+
+                    if (!stopwatch_act.IsRunning)
+                    {
+                        stopwatch_act.Restart();
+                    }
+                    else {
+                        ActUpdateInterval = stopwatch_act.Elapsed;
+                        stopwatch_act.Restart();
+                    }
                     if (!UpdateReadData())
                     {
                         if (cts.IsCancellationRequested)//可能是外部强制关闭