Lesson 8: Working with Digital Output Tags

Objectives:

•      Learn about digital output tags and their configuration.

Lesson 8 Overview

According to our system plan, there are still several tags required for your Booster Station application page. These tags are all related to the booster pump.

 

The system plan specifies that the booster pump can run either in auto mode or in manual mode. When it runs in auto mode, it automatically maintains the level of water in the booster tank between 60 and 80 inches. When it runs in manual mode, the operator must monitor the level of water in the booster tank, starting and stopping the pump accordingly. To provide the choice of mode, and to provide a means of starting and stopping the pump will require 4 tags as follows:

 

A digital input tag will read the mode of the pump. As per the Tag Table (see: Create a Tag Table), this tag will be "DI10_2 Booster Pump Mode". A value of "0" will indicate that the booster pump is in auto mode, while a value of "1" will indicate that the pump is in manual mode.

 

Enabling operators to start and stop the booster pump manually will require two digital output tags, along with appropriate drawing methods for sending control signals to the PLC.  For this application, you will create one digital output tag to send a start signal to the booster pump ("DO10_1 Booster Pump Start"), and another digital output tag to send a stop signal to the booster pump ("DO10_2 Booster Pump Stop").  As soon as either the "stop" tag or the "start" tag changes value from "0" to "1", the booster pump will be placed into manual mode.

 

To provide a way to put the pump back into auto mode you will create a third digital output tag "DO10_3 Booster Pump Auto". This will send a value of "0" out to signal the pump to enter auto mode.

 

Both the digital input, "DI10_2 Booster Pump Mode", and the digital output, "DO10_3 Booster Pump Auto", refer to the same PLC address. One reports the mode of the pump, while the other (the digital output tag) changes its mode.

 

If given an appropriate drawing method for "DO10_3 Booster Pump Auto", an operator can cause the output tag to write a "0" signal to the PLC (and out to the booster pump). The booster pump reads this signal and changes mode accordingly. The PLC then reads the change of signal from the booster pump and reports it to "DI10_2". The value of "DI10_2" then changes to "0" and its drawing methods display the value accordingly.

Estimated Time

It is estimated that Lesson 8 will take approximately 15 minutes to complete.