diff --git a/App/ACZero.cpp b/App/ACZero.cpp
index 0f7ec9a8..0222d168 100644
--- a/App/ACZero.cpp
+++ b/App/ACZero.cpp
@@ -10,7 +10,6 @@ ACZero::ACZero()
 	Period = 10000;
 	Width = 0;
 	Count = 0;
-	Last = 0;
 }
 
 ACZero::~ACZero()
@@ -65,16 +64,11 @@ void ACZero::OnHandler(InputPort& port, bool down)
 		return;
 	}
 
-	auto now = Sys.Ms();
-	Count++;
-
 	// 每256*10ms修正一次周期
-	if (Last > 0 && (Count & 0xFF) == 0)
-		//if (Last > 0 && (Count & 0xFF) == 0)
+	if (Count++ > 0 && (Count & 0xFF) == 0)
 	{
 		// 两次零点
-		int ms = now - Last;
-		int us = ms * 1000;
+		int us = Last.Elapsed();
 
 		// 零点信号可能有毛刺或者干扰，需要避开
 		//if (us <= Period / 2 || us >= Period * 2) return;
@@ -86,23 +80,22 @@ void ACZero::OnHandler(InputPort& port, bool down)
 		debug_printf("OnHandler us=%d Period=%d Width=%d _Delay=%d \r\n", us, Period, Width, _Delay);
 	}
 
-	Last = now;
+	Last.Reset();
 }
 
 // 等待下一次零点，需要考虑继电器动作延迟
 bool ACZero::Wait(int usDelay) const
 {
-	if (Count == 0 || Last == 0) return false;
+	if (Count == 0) return false;
 
 	// 计算上一次零点后过去的时间
-	UInt64 now = Sys.Ms();
-	int ms = now - Last;
-	if (ms < 0 && ms > 40) return false;
+	int us = Last.Elapsed();
+	if (us < 0 && us > 40000) return false;
 
 	Sys.Trace(4);
 
 	// 计算下一次零点什么时候到来
-	int us = Period - ms * 1000;
+	us = Period - us;
 	// 继电器动作延迟
 	us -= usDelay;
 
@@ -110,17 +103,17 @@ bool ACZero::Wait(int usDelay) const
 	while (us < 0) us += d;
 	while (us > d) us -= d;
 
-	Sys.Trace();
+	//Sys.Trace();
 	//debug_printf("ACZero::Wait 周期=%dus 等待=%dus Width=%dms Count=%d Last=%d Now=%d", Period, us, Width, Count, (int)Last, (int)now);
 	_Delay = us;
 
-	TimeCost tc;
+	//TimeCost tc;
 
-	Sys.Trace();
+	//Sys.Trace();
 	//Sys.Delay(us);
 	Time.Delay(us);
 
-	us = tc.Elapsed();
+	//us = tc.Elapsed();
 	Sys.Trace(4);
 	//debug_printf(" Now2=%d Cost=%d \r\n", (int)Sys.Ms(), us);
 
diff --git a/App/ACZero.h b/App/ACZero.h
index 4eb9f39c..6b83628c 100644
--- a/App/ACZero.h
+++ b/App/ACZero.h
@@ -1,6 +1,7 @@
 #ifndef __ACZero_H__
 #define __ACZero_H__
 
+#include "Kernel\TTime.h"
 #include "Device\Port.h"
 
 // 交流过零检测
@@ -11,7 +12,7 @@ public:
 	int		Period;		// 周期us
 	int		Width;		// 零点信号宽度ms
 	uint	Count;		// 累计次数
-	UInt64	Last;		// 最后一次零点
+	TimeCost	Last;		// 上一次零点
 
 	ACZero();
 	~ACZero();
diff --git a/Kernel/TTime.h b/Kernel/TTime.h
index 12e80cc8..413a4f95 100644
--- a/Kernel/TTime.h
+++ b/Kernel/TTime.h
@@ -69,8 +69,9 @@ public:
 
 	TimeCost();
 
-	int Elapsed();	// 逝去的时间，微秒
-	void Show(cstring format = nullptr);
+	void Reset();
+	int Elapsed() const;	// 逝去的时间，微秒
+	void Show(cstring format = nullptr) const;
 };
 
 /*
diff --git a/Kernel/Time.cpp b/Kernel/Time.cpp
index b9bd684a..b68218ca 100644
--- a/Kernel/Time.cpp
+++ b/Kernel/Time.cpp
@@ -177,13 +177,18 @@ bool TimeWheel::Expired()
 /************************************************ TimeCost ************************************************/
 
 TimeCost::TimeCost()
+{
+	Reset();
+}
+
+void TimeCost::Reset()
 {
 	Start = Time.Current();
 	StartTicks = Time.CurrentTicks();
 }
 
 // 逝去的时间，微秒
-int TimeCost::Elapsed()
+int TimeCost::Elapsed() const
 {
 	int ts = (int)(Time.CurrentTicks() - StartTicks);
 	int ms = (int)(Time.Current() - Start);
@@ -198,7 +203,7 @@ int TimeCost::Elapsed()
 	return ms * 1000 - Time.TicksToUs(-ts);
 }
 
-void TimeCost::Show(cstring format)
+void TimeCost::Show(cstring format) const
 {
 	if (!format) format = "执行 %dus\r\n";
 	debug_printf(format, Elapsed());