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The MultiWrite tag will write predefined values to a list of selected tags upon triggering. This can be used to place a plant into a state of operation or to quickly shut a plant down in one step.
Trihedral technical support frequently receives requests for help with scripting when people want to send a control signal in response to a trigger. The response is almost always to use a Multi-Write tag in place of a script.
Reference Notes:
Up to 100 output and memory tags can be controlled by a single MultiWrite tag, with a defined value set to be written to each. The trigger for the write may be any of a manual button press, a tag that changes state from false to true, or an expression that evaluates to true.
Each value to be written will be checked to ensure that it is valid before it is written. Invalid writes will be ignored. All valid values will be written, regardless of whether they have changed since the last write.
Should 100 tags not be enough, it is possible for one MultiWrite tag to trigger another upon finishing its write sequence.
An event will be recorded in the event history whenever a MultiWrite is triggered.
If triggering a Digital Control or Digital Output with a pulse duration, use care that you do not attempt to send a pulsed zero.
Set Value Buttons and Multi-Write tags.
This tag will work with the Set Value Button Widget but support is limited:
- Value to Write must be set to 1 in the widget for use with a Multi-Write tag. No other value will work.
- Multi-write tags cannot act as feedback tags. To use Select Before Operate in the Set Value, a separate I/O tag must be configured as the feedback tag and used as the linked tag in the Execute / Cancel buttons.
MultiWrite properties ID tab
The ID tab of every tag includes the same common elements: Name, Area, Description, and Help ID.
Name:
Uniquely identifies each tag in the application. If the tag is a child of another, the parent names will be displayed in a separate area before the name field.
You may right-click on the tag's name to add or remove a conditional start expression.
Area
The area field is used to group similar tags together. By defining an area, you make it possible to:
- Filter for particular tag groups when searching in the tag browser
- Link dial-out alarm rosters to Alarm tags having a particular area
- Limit the number of tags loaded upon startup.
- Filter the alarm display to show only certain areas.
- Filter tag selection by area when building reports
When working with Parent-Child tag structures, the area property of all child tags will automatically match the configured area of a parent. Naturally, you can change any tag's area as required. In the case of a child tag, the field background will turn yellow to indicate that you have applied an override. (Orange in the case of user-defined types. Refer to Configuration Field Colors)
To use the area field effectively, you might consider setting the same Area for each I/O driver and its related I/O tags to group all the tags representing the equipment processes installed at each I/O device. You might also consider naming the Area property for the physical location of the tag (i.e. a station or name of a landmark near the location of the I/O device). For serial port or Roster tags, you might configure the Area property according to the purpose of each tag, such as System or Communications.
You may define as many areas as you wish and you may leave the area blank for some tags (note that for Modem tags that are to be used with the Alarm Notification System, it is actually required that the area field be left blank).
To define a new area, type the name in the field. It will immediately be added. To use an existing area, use the drop-down list feature. Re-typing an existing area name is not recommended since a typo or misspelling will result in a second area being created.
There is no tool to remove an area name from VTScada since such a tool is unnecessary. An area definition will exist as long as any tag uses it and will stop existing when no tag uses it (following the next re-start).
Description
Tag names tend to be brief. The description field provides a way to give each tag a human-friendly note describing its purpose. While not mandatory, the description is highly recommended.
Tag descriptions are displayed in the tag browser, in the list of tags to be selected for a report and also on-screen when the operator holds the pointer over the tag’s widget. For installations that use the Alarm Notification System, the description will be spoken when identifying the tag that caused the alarm.
The description field will store up to 65,500 characters, but this will exceed the practical limits of what can be displayed on-screen.
This note is relevant only to those with a multilingual user interface:
When editing any textual parameter (description, area, engineering units...) always work in the phrase editor. Any changes made directly to the textual parameter will result in a new phrase being created rather than the existing phrase being changed.
In a unilingual application this makes no difference, but in a multilingual application it is regarded as poor practice.
Help Search Key
Used only by those who have created their own CHM-format context sensitive help files to accompany their application.
MultiWrite properties Write List tab
The Write List displays the output or memory tags that will be written to, and controls what value will be written to each. The outputs will be written in the order in which they are displayed.
You can add or edit any tag in the list by clicking on a row. You must select a tag before configuring the value to be written to it.
The Tag and Value input fields will be activated when a row is selected, except that rows must be filled in sequence from #1. You cannot add a tag to row three before row two has been completed.
The grid displays the name and description of each tag selected to be written to. The Value column shows what will be written to each tag when the MultiWrite is triggered. The value may be any of a constant, an expression or another tag’s value. In the case where another tag’s value is to be written, that tag’s name will be display in the Value column.
Note that, the display may show a tag's Unique ID rather than its name when the tag is not selected. The description will always be shown for every tag, to help avoid confusion.
To add a tag to the list, select the next available row, then click on the Tag Browser button. Select or create an output tag. After you have specified the tag to write to, you can provide a value to write using the Value field.
To remove a tag from the list, select its row, then click on the X button in the lower-right corner of the window.
The arrow buttons below the grid may be used to move a selected row up or down in the list, thus controlling the order in which output tags are written to.
MultiWrite properties Activation tab
The Activation tab provides a way for MultiWrite tags to be controlled automatically.
Activation Trigger
Any tag or expression that will change from a false (0) to a true (1 or any non-zero number) can be used to trigger the write.
Privilege
Select a custom security privilege
Log an event on automatic multi-write
Selected by default. You can choose to not log events when multi-writes occur in response to the activation trigger. Choose this if you have a multi-write operation that triggers frequently.
An operator pressing the Multi-Write Button or Hotbox will always cause in a new event to be logged.
MultiWrite Tag Widgets
