Create a Tag Table

Once you've gathered the list of system processes, you essentially have all the information you require to plan for the tags you will need. For example, we know whether each process is an input or output process, we know the type of data read from or written to the I/O device, we know the I/O device addresses, and so forth. The only planning requirement left towards the configuration of the actual tags is to decide on a meaningful and consistent naming convention for the tags.

In the tutorial, we will follow a naming convention as follows:

Abbreviation of the tag type, followed by the equipment number (as labeled in the P&ID), followed by a sequential number to keep multiple processes for the same equipment separate.

 

For example, review the following entry from our process information table:

 

Based on this information, we know that we will require a digital input tag to read the status of the booster pump (as the status is an incoming value from the booster pump). The name of this first tag will therefore be "DI10_1", where "DI" is an abbreviation for the tag type (digital input), "10" is the number labeling the booster pump in the P&ID, and "_1" is used to separate this tag from other digital input tags related to the booster pump.

 

On its own, this name will be useful for you as the developer, but may not be meaningful for the operators of your system. This is where tag descriptions become important. In addition to the name we will provide for each tag, we will include a clear description of the process the tag represents. For example, based on our knowledge of the process that this tag will be monitoring, we might choose to describe the tag as "Booster Pump Status".

 

The next step in planning your application is to add the name and description for each tag to the table.

VTS provides you with a number of standard tag types, each of which has a different purpose. Basic I/O tags (analog input, digital input, analog output, and digital output) are used to read and write data to equipment. In order to do so, these tags require a chain of communications. They must have an I/O device driver tag to translate data and communicate it to the I/O device, and they must have a serial or ethernet port tag to facilitate communications between the I/O device and the I/O device driver tag. It is important to note these communications-related tags in your tag table.

 

Finally, there are two important attribute tag types: logger tags, and alarm tags. Logger tags are capable of recording the values of another tag to a data file on disk, while alarm tags are designed to monitor the value of other tags and signal an alarm in VTS's built-in alarm system if the tag being monitored reaches a user-defined value. In order to meet the special requirements outlined by the client, we will need 2 logger tags and 2 alarm tags. These tags have also been added to the table below.