Tag Reference

The flexible nature of VTScada is due to the custom building blocks upon which it is based. These building blocks are called "tags".

Points? A tag is a point and a point is a tag. VTScada uses the word "tag" more often (that's what the T in VTScada is for, after all) but "point" was used first, and you'll still see it from time to time.

A tag is a software component that can communicate with objects in the physical world. For flexibility, each tag type is a specialized component that can be combined with other tag types to build diverse systems. For example:

  • Port tags handle communication between the VTScada server and the outside world, whether through a serial port or a TCP/IP port.
  • A specialized driver tag is available for nearly any brand of PLC hardware. Driver tags rely on port tags to communicate with the hardware.
  • Input and output tag types, both analog and digital, monitor and communicate with individual addresses on the remote PLC. I/O tags rely on driver tags to ensure that communications are properly formatted for the remote hardware.
  • Alarm tags and Logger tags can be linked to any I/O tag to monitor and record values.
  • Memory tags. A memory tag is an I/O and Calculations Tag, configured without an address. The data type can be Analog, Discrete, Digital, or String. 2-bit Digital, and all Calculation options of the I/O tag do not count as Memory Tags.
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The term, "communications chain" describes the linkage of VTScada with remote hardware through the I/O tag, to the driver tag, to the port tag. By choosing appropriate tags for each link in the chain, you can build VTScada applications for nearly any situation.

It is typical to begin each application you create by configuring a port tag to accept the data that is flowing through your PC, and a device driver tag to provide an interface to physical I/O devices such as programmable logic controllers (PLC), remote terminal units (RTU), I/O boards, or to Windows system features such as Dynamic Data Exchange (DDE). After you have these essential tags in place, you can create analog, digital and other tag other types to make your application communicate with the outside world.

Standard versus Custom Types.

All of the various types of tags that come with VTScada are described in this chapter. These are known as the standard types.

VTScada also gives you the ability to define your own types of tag. This can be done by creating groups that include a port, a driver, I/O, alarm and other tags that fully describe a type of equipment, such as a pumping station, motor, well, etc. You are also able to use the VTScada programming language to build completely new types of tag, designed specifically for your needs. Custom-programmed tags do count towards your license limit.

Tips:

  • During a development session, each new tag of the same type will start out identical to the last of that type, save only the name. This can save time when making several similar tags since you won't have to set the same values over and over. But, if the majority of the fields in each new tag differ from the last, this feature may not be so useful. You can disable it by setting the application property, RememberNewTagParameters to 0.
  • Even with RememberNewTagParameters set, it's often easier to create new tags by copying and pasting existing tags, then changing a few properties to suit the new one.
  • You can export the tag database for editing in a spreadsheet and then import the modified database back into VTScada. This can save time when creating a lot of tags. It's especially helpful when you need to change one property in a long list of tags since the spreadsheet will allow you to do a search and replace on that property.
  • Advanced developers can obtain a list of tag areas in an application via a public variable. Refer to VTScada Constants and Public Variables