Output Tags

Output tags are used to write data to an I/O device, such as a programmable logic controller (PLC), remote terminal unit (RTU), or an I/O board. These tags permit the handling of either digital (discrete), or analog (continuous floating point) values.

Output tags will not write INVALID data. (INVALID is a specific VTScada data type, roughly meaning, "no valid value available"). Also, except for the MultiWrite tag, no output type will write an unchanged value twice unless directed by the driver performing a "re-write outputs" operation.

Record Operator-Entered Values

While the output tags are designed to write to a device, they can also be used to record purely operator-entered values. For example, an operator may be asked to read a value from a device that is not connected to the automation system and record that value in a place where it can be included in the SCADA system's reports.

 

To record operator-entered values:

  1. Create an Analog Control tag.
    The name and description should match the information that is to be recorded.
    Do not configure an I/O device or address.
    Ensure that the scaled minimum and maximum values allow the full range of expected numeric values. (The Operator Notes page exists to record text.)
  2. Add a Logger tag to the Analog Control.
    Select the option, Log on Change as well as Time.
    Set the Log Range Interval to a very large value (for example, 3153600000 == 100 years). This ensures that a value will be written to the Historian only upon operator entry.
  3. Draw the Analog Control tag on a page as a Numeric Entry widget, having a relevant label. Operators should note that it is necessary to press enter, or tab away from the data entry field before the value will be saved.

 

Each time the operator enters a new value, it will be written to the Historian, and may be used in trend graphs and reports. Note that a click on any widget linked to an output tag does not open the trend window.

The following output tags are included with VTScada:

I/O and Calculations Tag

Analog Control Tags Analog Output Tags
Deadband Control Tags Digital Control Tags
Digital Output Tags Multi-Write Tags
Selector Switch Tags Trigger Tag
String I/O Tags  

Related information:

Communication Driver Tags - Driver tag reference

The Tag Browser - Using the Tag Browser to create and edit tags.

Deadbands for Reading and Logging - Avoid problems with system noise.