wincc定时器有问题

int gscAction( void )
{
double Valve_SteamPress_1;
double Valve_SteamPress;

Valve_SteamPress_1=GetTagDouble("Valve_SteamPress_1"); 
Valve_SteamPress  = 5   +Valve_SteamPress_1;
printf("\n"); 
printf("SetTag之前  Valve_SteamPress=  %1.2f ",Valve_SteamPress);  
SetTagDouble("Valve_SteamPress",Valve_SteamPress);
SetTagDouble("Valve_SteamPress_1",Valve_SteamPress);

printf("\n"); 
printf("SetTag之后  Valve_SteamPress=  %1.2f   Valve_SteamPress_1=  %1.2f  ",GetTagDouble("Valve_SteamPress"),GetTagDouble("Valve_SteamPress_1"));
printf("\n"); 
printf("\n");
return 0; 
}
在界面的应用程序窗口里看到的结果是：
SetTag之前  Valve_SteamPress=  55.00 
SetTag之后  Valve_SteamPress=  55.00   Valve_SteamPress_1=  55.00  

SetTag之前  Valve_SteamPress=  60.00 
SetTag之后  Valve_SteamPress=  60.00   Valve_SteamPress_1=  55.00  

SetTag之前  Valve_SteamPress=  65.00 
SetTag之后  Valve_SteamPress=  60.00   Valve_SteamPress_1=  60.00  

SetTag之前  Valve_SteamPress=  70.00 
SetTag之后  Valve_SteamPress=  65.00   Valve_SteamPress_1=  65.00  

SetTag之前  Valve_SteamPress=  75.00 
SetTag之后  Valve_SteamPress=  70.00   Valve_SteamPress_1=  70.00  
从结果可以看到，SetTag之前显示的是中间变量的值，然后中间变量Valve_SteamPress的值SetTag给“Valve_SteamPress”和“Valve_SteamPress_1”这两个内部变量之后，显示出来的却和中间变量值不同。
3、如果是在按钮的C 动作里加同样的程序，然后每2S手动按钮周期运行，则每次的SetTagDouble都可以起作用。结果如下：
SetTag之前  Valve_SteamPress=  55.00 
SetTag之后  Valve_SteamPress=  55.00   Valve_SteamPress_1=  55.00  

SetTag之前  Valve_SteamPress=  60.00 
SetTag之后  Valve_SteamPress=  60.00   Valve_SteamPress_1=  60.00  

SetTag之前  Valve_SteamPress=  65.00 
SetTag之后  Valve_SteamPress=  65.00   Valve_SteamPress_1=  65.00  

SetTag之前  Valve_SteamPress=  70.00 
SetTag之后  Valve_SteamPress=  70.00   Valve_SteamPress_1=  70.00  

SetTag之前  Valve_SteamPress=  75.00 
SetTag之后  Valve_SteamPress=  75.00   Valve_SteamPress_1=  75.00  

请专家再给我解答一次，谢谢！