PV550 Alarm Setup?

The system I am working on has a SLC5/03 with a PV550 communicating via DH485. And I like to know what the function of 'Ack. Hold Time' and 'Snapshot Timeout' boxes under Alarms - Setup are? The reason I am asking is that I have the following problem: Sometimes an alarm is acknowledged on the PanelView but the SLC misses the acknowledgement. This only happens occasionally and it is hard to re-produce. What is happening?
Adrian

From the PV on-line help:

Ack Hold Time: the length of time (milliseconds) the terminal holds the trigger value at the address defined by the acknoledge tag. The hold time should exceed the scan time of the controller to ensure that it is used at least once. The default hold time is 500 milliseconds.

Snapshot Timeout: the length of time (seconds) the terminal waits for the controller to complete I/O scans when an alarm is triggered. If the message contains embedded variables, the controller may have to complete several scans. The default is 2 seconds.

Variables appear in the alarm message as ???? until the data is read. If data is not read before the timeout occurs, the variable appears as ****.

Hope that helps,

Marc

I've seen exactly the same problem. Happens with other manufacturer's hmi's too.
As I understand it, the alarm bit clears after Acknowledgement, but the alarm condition comes back on i.e. the plc is fast enough to re-latch the alarm but the comms to the hmi has never seen the alarm drop off i.e. it thinks it's already ACKed the alarm. Increasing the hold time above the default (500ms?) won't really help this.

I think it's the price you pay for handling alarms in this way - 1 alarm, 1 acknowledge bit. I do it this way on my machines rather than 1 big reset button.

Cure? Tuck away an ACK ALL button on the alarm viewer screen. I'd be interested to see if there's another way round it.

pp

Not sure if this is what we're talking about, but the way i set the PV alarms up is to use the 'Remote Fields' option in the Alarm setup page. I then create my own ACK button for every screen i have using the same Tag address but unique Tag names and place it at the bottom of every screen. You also need to make sure you don't disable the whole screen when the banner pops up, just the covered objects. Then you can use the handshaking from the remote field in your logic to hold the ACK on as long as you need it.........


Just an option.



Rob.