Re: [foxboro] Health Connectivity
- From: "Ray J Chouinard" <rjc2@xxxxxxxxxxxxxxxx>
- To: foxboro@xxxxxxxxxxxxx
- Date: Tue, 10 Jun 2003 13:05:13 -0400
A digital on/off pulse is not a good "heartbeat" to use for health
connectivity since it is too easy to "sink" to either the "on" pulse or
the "off" pulse. The best health indicator we have found to use is a
stepped integer. Starts at zero, every second advances 1, counts to
32,000 and resets. The system monitoring the health only needs to verify
that this value has changed. The "seconds since midnight" in a calc block
could be used for this.
Ray Chouinard
Process Control
MeadWestvaco
Escanaba, MI
"Jerry Hidahl" <Jerry_Hidahl@xxxxxxxxxxxx>
Sent by: foxboro-bounce@xxxxxxxxxxxxx
06/10/2003 10:01 AM
Please respond to foxboro
To: foxboro@xxxxxxxxxxxxx
cc:
Subject: Re: [foxboro] Health Connectivity
Have you considered using a "Watchdog" timer? It's an accumulator block
that adds one count per second. A discrete signal from the third party
system is connected to the "CLEAR" parameter and periodically resets the
accumulator to zero. The presets or targets (high and high-high alarm
parameters) provide an alarm if there is no signal from the third party in
the configured time limit. We use one that is cleared every 20 seconds and
alarms after 60 seconds, but shorter times are certainly feasible.
For just an indication for a display, I'd use a "one shot pulse" operation
(OSP) set for a time long enough for the display to update and the
operator
to perceive it. The advantage is that it will stay on after the input
turns
off, and it'll turn off by itself if the input stays on. It's available in
the LOGIC block as well as the CALC block, and for a function as simple as
this, the LOGIC block uses less processing resources (memory, time).
Jerry Hidahl
"Darren Edwards"
<darrenedwards626@h To: foxboro@xxxxxxxxxxxxx
otmail.com> cc:
Sent by: Subject: [foxboro]
Health Connectivity
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06/09/03 03:53 PM
Please respond to
foxboro
Hello:
I am trying to create a "health" tag in the Foxboro DCS that would change
its state every second or few seconds. It seems simple enough but I am
having difficulty doing this with CALC. I would like to provide a bit
that
changes state once per second for the purposes of indicating the health of
a
connection to a third party system. Can anyone share a sample of block
code
that would accomplish this?
Darren Edwards
Delta Central States Power Systems
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