Monitor the operator stations (dead man's button)

The term dead man's handle or button originated in the railway industry. It is a control device to cut off power supply if the engineer is not physically able to continue controlling the speed of the train. A similar function can be set up in IGSS and it too is called a dead man's button. It's an object set up to monitor the presence and activity of an operator station in a multi-user system. Lack of operator activity activates the "dead man's button" object, which sends an alarm to the Alarm list.

By defining this object, it’s possible to trigger two alarms indicating the state of the given operator station. These could be…

“No activity on operator station” which is triggered when the specified period of inactivity has expired, and
“Operator station disconnected” which is triggered when the connection to the IGSS server is lost.
Our recommendation is to create an overview diagram with your complete system setup (server, operator stations and PLCs). You could then at a glance see whether all operator stations are up and running.

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In this example we use a rectangular field as the graphical representation of the object. Other choices for graphical representation are possible.

Choose the menu Objects – Rectangular Field…in the Definition program.
In the Object Browser dialog, do the following:

Click on Analog in the tree view and then give the object the exact same name (remember it’s case sensitive) as it appears in the System Configuration program.
In the Description field, type “Dead man’s button”; this is optional.
Check the Name box, to bring up the object’s properties, and then click Create.

On the Analog tab, do the following:

Set the Max. value to the number of minutes the operator station is allowed to be idle; in the example 20 is used.
Set the Min. value to -1.
Check mark the Low Limit box and set it’s value to 1.
Set the Low Alarm value to 0.

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Looking at the illustration above, you must remove the check mark from High Alarm and add a check mark on Low Limit.

When the value of the object falls from the Low Limit value of 1 to the Low Alarm value of 0, the “No activity” alarm is triggered.
When the operator station logs off or the server connection is lost, the Actual Value atom is set to the Min. value, -1, which triggers the “Operator station disconnected” alarm.

Go to the Edit Mapping tab and do the following:

Remove the check marks from all atoms except Actual Value, Low Limit, and Low Alarm.
Select the atoms one at a time and set the I/O mode to local.
If you wish to see the time remaining displayed on the object before the No Activity alarm is activated, go to the Display tab and under State/Value, check the box Enable and select Actual Value in the Atom drop down box.
Create the alarm texts and attach them to the atoms as follows: “No activity on operator station” for Low Limit and “Operator station disconnected” for Low Alarm. Enable the Auto acknowledge option for both alarms.

Click OK to save the object and then run Install Configuration from the File menu.

The analog OP1 object is set to the Max. value every time activity is registered by the IGSS Server as coming from the operator station. “Activity” must either be alarm related, for instance acknowledgment, or object control, for instance changing of set point, sending a digital command, etc. If no “activity” is registered from the operator station, the object value is decremented every minute until it reaches zero and triggers a No Activity alarm.
At operator logout or lost connection to the server, the Actual Value is set to the value defined for Min., i.e. -1. This triggers the second alarm, Operator station disconnected.

Copy and paste for each operator station needing to be monitored. Rename after pasting to the correct operator station name.