5.1 Adding a Digital Input Tag to Represent the Status of the Booster Pump

In this exercise, you will create a digital input tag to represent the status of the booster pump. As planned in your Tag Table (see Create a Tag Table), the name and description of the booster pump will be "DI10_1" and "Booster Pump Status".

 

Once again, you will be working with the Tag Browser to create the tag.

 

1.  Click the Tag Browser button in the Configuration Toolbox to open the browser dialog.

2.  Select Digital Input from the Type drop-down list.

3.  Click the New button.

A new digital input tag properties folder opens and displays the identification properties of its ID tab.

Figure 49

At first glance, the digital input's config folder appears quite similar to that of an analog input tag. As stated earlier, all tag properties folders (regardless of tag type) have the same ID tab and identification-related properties (Name, Area, Description, and Help Search Key). The difference between the analog and digital input tag types will be seen as you work through the properties of the I/O tab.

 

Note that "Tank" has automatically been entered in the Area field, as it is the last known area entered.

4.  Enter "DI10_1" in the Name field and press the Enter key.

5.  Enter "Booster Pump Status" in the Description field and press the Enter key.

The ID tab should look similar to Figure 49

6.  Click the I/O tab. The I/O tab opens and displays its properties.

7.  Click the tag browser button.

 

The Tag Browser opens and displays the available I/O device driver tags.

8.  Select the "Modbus1 Virtual Modicon PLC" driver tag.

9.  Click the Select button.

The "Modbus1" tag is now selected in the I/O Device field.

Examine the I/O tab for the digital input tag. Unlike the analog input tag's I/O tab, the digital input tag has two address fields (Bit 0 Address and Bit 1 Address). A digital input tag can be single bit or double bit. For single bit digital inputs, there are two possible states (corresponding to the Bit 0 Address field), and for digital inputs that use two address bits, there are four possible states (corresponding to the Bit 0 Address and Bit 1 Address fields).

 

10. Enter "4" in the Bit 0 Address field and press the Enter key to input the value.

This digital input tag is a single bit tag, and requires no further configuration. The I/O tab should appear like the example below when complete.

Figure 50

Note that the Scan Interval is set to 1 by default; all the tags configured in our application will have the same scan interval in order to reduce the number of separate data polls, and to improve overall data update performance.

 

It should be noted (although it is not required at this time) that there is an Invert Input checkbox available on the I/O tab. The typical use for this field is to employ a convention in a project where a signal of "0" from equipment indicates an "on" state, rather than the typical "1 = on" arrangement.

 

As with our analog input tag, the remaining tabs and their associated properties are not required at this time.

 

11. Click the OK button. The new digital input tag ("DI10_1 Booster Pump Status") is added to the Tag Browser's list of tags.

 

In the next step of the exercise, you will use the Image Change drawing method to draw this tag.