'Acknowledge'

Hi all.
This question is some sort of survey and my question is:

When you program your PLC/SCADA system does your PLC know if operator has acknowledge an alarm on SCADA or doesn't?
In other words - does acknowledge an alarm have any impact on control?

I just like to know your opinion and habits
Thanks!

Generally, no, acknowledging an alarm has no impact on control. I only use it in order to make sure that the operators have seen the alarm message and I only use alarms that need acknowledging for important stuff. If its just general 'running' messages such as 'buildback from filler' or something then I don't use an acknowledge as the message will then disappear when the condition disappears.

;-)

I generally use acknowledge to clear ther list. An operator has to acknowledge an alarm to remove it from the list. I will have a seperate button for actually clearing the alrm.

I prefer to have the unacked-bit in the PLC. Then I can decide if it should be acked from the SCADA, a local HMI (touch panel), a mobile phone or a local button by the equipment or...or... The SCADA and HMIs are all acked via the PLC.

With some equipment combinations this require to much work though...

***
Control influence example:
After a feedback (timeout) error, the error is latched (unacked). A command (edge, of course) is rejected while the error is unacked.


Kalle

Thanks a lot guys!

I generally divide alarms into two categories.

1 - Severe alarm. These are latched alarms that don't clear until acknowledged and indicate personell safety hazard or potential equipment damage. If the alarm shuts down a piece of equipment, I don't allow it to start until the alarm is acknowledged.

2 - Informational alarm. These are generally used to indicate an imminent severe alarm or a process occurrence that is of concern but not a hazard. These often don't latch, but they can if you want to log an operator's awareness of them. If latched they require an acknowledge to clear them.

I separate "Silence" from "Acknowledge". If possible I use a separate key to clear the alarm log - most HMIs allow this from the alarm log page only if you set them up that way.

And, I usually put a breaker or secret disconnect on the alarm horn to maintain sainity and hearing during start-up.

Tom Jenkins said:

I generally divide alarms into two categories.

1 - Severe alarm. These are latched alarms that don't clear until acknowledged and indicate personell safety hazard or potential equipment damage. If the alarm shuts down a piece of equipment, I don't allow it to start until the alarm is acknowledged.

Click to expand...

Acknowledged by means of clicking the typical acknowledge button on SCADA alarm bar? Or you have separate, symbol specific button to click and reset equipment?

I generally want the operator to see the equipment before clearing the severe alarm, so I generally have the acknowledge be a button on the HMI and/or a physical acknowledge pushbutton on the panel. If they want to acknowledge the alarm remotely from the SCADA I'll give tehm the bit address used by the acknowledge on HMI but warn them they are on their own after that. If they want to use SCADA to clear warning alarms only it is a simple thing to have a separate bit for that in parallel in the logic for just these alarms.