Working with Parameters
A parameter is a named object whose value can be supplied by a different source each time it is used. Its purpose is to allow you to create re-usable components that can be adapted to a variety of situations.
For example, you might decide to create your own drawing method of equipment not found in the VTS graphic library – perhaps a windmill.
If you were to select one or more specific tags to use in that drawing method, then each time you added it to a page, you would always be monitoring and controlling the same windmill at the same I/O addresses.
However, if you create your windmill drawing method with parameters, then each time you add it to an application page, you can select a different set of tags and hence a different set of I/O addresses to monitor.
You can also create application pages with built-in page parameters. For example, each of the windmills will need its own control and monitoring page. Rather than build a separate page for each, you can build just one page, and define a parameter for every I/O tag that is to be displayed within the page. You could then add that same page to the menu three times, (or create three hotboxes linking to the page), and select the tag set for a different windmill for each instance. To an operator, it will look as though there are three distinct pages, but as a developer, you only needed to create a single page.
Note: Never define parameters in an application’s default page. The default page opens independently of the menu and the hotboxes, therefore there is no way to pre-define the tags to be used for its parameters.
Parameters can provide even greater efficiencies when used with Parent/Child tags. These are custom-programmed tags (Parents) that encapsulate an entire set of related tags (Children), such all the I/O for an entire device can be found within a single tag.
Child tags are easiest to use when the I/O addresses for each device vary by a regular amount. For example, if the I/O address for a sensor in Windmill 1 is 40141, in Windmill 2 it’s 40241, in Windmill 3 it’s 40341 … With the help of a bit of VTS programming code, you can create a drawing method or parameterized page where all of the components are linked to the child tags of a single parent, Windmill_X. Each time a new windmill is added to the system you need only provide its base number to the parent tag and all the child tags will automatically be created and drawn. This powerful feature requires knowledge of VTS programming and hence is beyond the scope of this Developer’s Guide.
Quick Links: Common tasks for
parameters