As mentioned in the previous section, your VTS application is made up of many different tag types; however, it is unnecessary for you to become familiar with all the tag types. This section is intended to provide you with a brief overview of the standard tag types that you might encounter in your VTS application.
Note: It is typically the role of the VTS developer to work with tags and use them to effectively develop your VTS application; operators do not commonly work with tags.
Some of the most common standard tag types are:
• Analog input or analog status tags
• Analog output or analog control tags
• Digital input or digital status tags
• Digital output or digital control tags
• Alarm tags
• Logger tags
• Driver tags
• Serial port tags
Analog Input or Analog Status Tags
Analog input tags or analog status tags transfer analog (continuous) data from the equipment to your VTS application. An example of analog input values might a well level, water pressure, or temperature that is read from the equipment.
Analog Output or Analog Control Tags
Analog output tags and analog control tags transfer analog (continuous) output data from your VTS application to equipment. An example of analog output values might be a well level, water pressure or temperature to which you want the equipment set.
Digital Input or Digital Status Tags
Digital input tags and digital status transfer digital (discrete) data from equipment to your VTS application. An example of digital input values might be "0" or "1", "running or stopped", or "off or on".
Digital Output or Digital Control Tags
Digital output tags and digital control tags transfer digital (discrete) data from your VTS application to equipment. An example of digital output values might be "0" or "1"; or "Start", "Stop", or "Off", "On" commands.
Alarm Tags
Alarm tags are designed to monitor the value of other tags and compare their value with a condition. If the value of the associated analog or digital tag meets the condition, an alarm is triggered. For example, an alarm tag could be configured to monitor an analog input tag that is representing a tank level. If the level of the tank drops below 20 inches, an alarm must sound; therefore, if the value of the analog input tag is less than 20, the alarm tag triggers an alarm.
Logger Tags
Like alarm tags, logger tags are designed to monitor an analog or digital input or output tag to read its value. A logger tag then records the value of the associated analog or digital tag so that it can be graphed on the Historical Data Viewer page. Logger tags are used to record historical data about the associated analog or digital tag.
Driver Tags
Driver tags allow VTS to provide an interface to physical I/O devices such as PLCs, RTUs, or IO boards.
Serial Port Tags
Finally, serial port tags open a serial port for use by the driver tag.
Within your VTS application, there could be hundreds or even thousands of tags, some of which belong to the above tag types. Again, this section is intended to make you aware of the possible tag types you might encounter.
Regardless of the type of tag, each has a name, a unique ID, and other characteristics that distinguish it from the other tags in the system. These characteristics are called tag properties. The data the tag reads from or sends to the equipment to your application is referred to as tag data, while the representation of this tag data on the screen is called the tag's graphic object.