Other Tag Types
VTS contains a variety of additional tag types, each of which serves a distinct purpose in your applications. These are:
|
Tag Type |
Description |
|
Alarm Tag |
Alarm tags enable you to monitor the value of other tags and trigger an alarm based on the value of the tag being monitored and a setpoint configured within the alarm tag. |
|
Alarm Priority Tag |
Alarm priority tag types contain the properties that determine the color, sound, and timing for the different priorities of alarms in your system. Every new VTS application you create contains a set of 5 default alarm priority tags, and you are welcome to add your own custom alarm priority tags. Note: You should never modify or delete the default alarm priority tags. |
|
Logger Tag |
Logger tags allow you to record the values of tags with numeric values to disk. This logged data can then be used to generate reports, or can be graphed on the Historical Data Viewer page. |
There are three links in the chain that allows a VTS application to communicate with physical equipment:
• Port tags open a serial or TCP/IP port to facilitate communications between the I/O device and the I/O device driver tag
• The device driver tags communicate with the actual I/O devices
• The input/output tags represent the individual processes for the equipment in the system.
The information provided in this section will help you to understand the relationships among tags and the means by which you configure them.
Consider the following example:
Figure 4
Figure 4 demonstrates the method of communication used to allow information to pass from equipment to the tag representing it within the VTS application. In this example, a pump and a tank are connected to an I/O device (such as an RTU or PLC). The I/O device regularly polls the tank for its water level and pressure (analog data), and the pump for its status (digital data). It will also accept data to control the pump (digital data).
The I/O device is also connected to the serial port of a PC running a VTS application that has been configured especially for this system.
Within the VTS application, a serial port tag opens the port to which the I/O device is connected. The device driver tag is able to communicate through that port with the I/O device using a specific communications protocol. It translates the data into a format that is understandable by the input/output tags in the application.
The I/O device driver tag then passes this information to the analog input (AI) tag representing the tank level, to the analog input tag representing the tank pressure, and to the digital input (DI) tag representing the pump status. This data is updated continuously as it occurs in real-time. The digital output (DO) tag representing the pump control enables operators to send a signal to the PLC or RTU to stop or start the pump.
Finally, each of the basic I/O tags has its own equipment graphic to display its value (and consequently the pump's status and the tank's water level and pressure) on the screen for the operator to view. The digital output (DO) tag is drawn as a button that can be clicked to send a value of 0 or 1 to the PLC or RTU to stop or start the pump.