Up to 5 project-related user cycles can be defined. If the project name is selected in the left tree structure of the WinCC Explorer, clicking on the toolbar button displayed below will open the Project Properties dialog box.
In the Update Cycles tab of the Project Properties dialog box, the user-defined cycles 1 - 5 are offered for the project-related definition at the end of the default update cycles list. Only these user cycles can be parameterized.
These user cycles enable you to define time cycles other than the ones already available (e.g. 200 ms).
You can define user cycles for any length of time between 100 ms and 10 hours. You can give user cycles any name you wish.
These project-related units of time can be used for selected objects whose update cycle must be modified at a later time. Once reason for changing the time cycles could be to effect an optimization. The user-defined update cycles also make it possible for you to subsequently modify the set time cycle from a single central location. In this case, the individual objects of the pictures no longer have to be adjusted as well. This is why this method of defining user cycles should be preferred if you want your projects to be maintenance-friendly.
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3.3.1.3 Meaning of the Update Cycles
Before you begin putting the possible update cycles to use, we must first take a look at what the various update cycles mean.
For the update cycles, the following differentiations are made:
Type Meaning
Default Cycle Time Cycle
Time Cycle According to the time set, the property or action of the individual objects will be updated. This means that each of the tags is requested individually by the data manager.
Tag Trigger In accordance with the cycle time set and once the time interval has elapsed, the tags are determined by the system and checked for value changes.
If the value of at least one selected tag changes during the time frame set, this acts as a trigger for the properties or actions dependent on this.
All tag values are requested together by the data manager.
Picture Cycle Updating of the properties of the current picture object and all objects that are triggered by means of the Picture Cycle update cycle.
Window Cycle Updating of the properties of the window object and all objects that are triggered by means of the Window Cycle update cycle.
User-Defined Time Cycles Time units that can be defined specifically for a project.
C-Action for direct Reading from the PLC
Values can be read directly from the PLC by means of internal functions in the C-Actions. Further editing of the subsequent instructions in the C-Action is only continued after the process values have been read (synchronous reading).
Note:
Requesting of the current tag value by the data manager leads in each case to a change of task and to a data exchange between the individual tasks. In addition, the tag values must be requested by the data manager via the communication channel of the programmable controllers connected. Depending on the type of communication, this is done by means of request telegrams sent to the communication interface (FETCH) and data telegrams sent back from the programmable controller to WinCC.
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3.3.1.4 Information regarding the Application of Update Cycles
For the application of the update cycles, the following settings are recommended depending on the type of cycle selected:
Type Default
if tags are interdependent, you should at all events make use of tag triggering. This reduces the number of task changes and communication between the tasks.
Tag triggering Upon Change may only be used selectively, since it can lead to greater system loads! The tags are then checked constantly for changes. This polling mechanism always leads to a greater load on the system.
We recommend a cycle of 1 to 2 seconds for standard objects.
Time Cycle
2 seconds Make the time cycle dependent on the object type or the object property. The inertia of process components (tank fillings or temperatures in contrast to switching operations) should likewise be taken into account.
We recommend a cycle of 1 to 2 seconds for standard objects.
Tag Trigger
2 seconds (for Dynamic Dialog)
If this update option can be configured (depends on the dynamic type), preference should be given to using it! If tags are interdependent, always take into account all tags that are responsible for a change to the property or for the execution of the action. Only those tags contained in the list act as triggers for updating the property or action that has been made dynamic.
Tag triggering upon change should only be used selectively.
As soon as one of the selected tags has changed, the trigger for this property or action is triggered. This polling mechanism leads to a greater load on the system.
Picture Cycle
2 seconds This cycle should only be shortened if the dynamized
properties of the picture object themselves change in a shorter time interval and therefore have to be updated. Lengthening the picture cycle reduces the load on the system.
Window Cycle
Upon Change This setting makes sense if you are dealing with a picture window that is opened, for example, for adjusting process variables (process box).
If the picture window is displayed constantly for
informational purposes (e.g. screen layout), updating of the window and its contents should be set to tag triggering or a time cycle.
The internal functions (e.g. GetTagWordWait ) for
synchronous reading of process values (direct from the PLC) should only be used selectively. Application of these functions requires polling by the system (script control) and therefore leads to a greater communication load.
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