LXI as a control protocol

WTF is LXI?  Yet another protocol?  I have never heard of it.  Who
suppports it?  Who cares?  What makes it better than any other
protocol out of the hundreds that already exist?  Perhaps you will
answer this question by thinking about your reply.

Peter Nachtwey

Peter Nachtwey wrote:


LXI is an instrument protocol for gathering data from measurement
instrumentation. It can also issue triggers over the LAN which have a
certainty of synchronisation within about 40ns. This is not quite as good
as synchronising to a 10MHz distributed clock but it could help where the
data path lengths are extremely variant.

As for using it for control. It looks like it is probably certain enough but
there are other protocols that have  higher integrity that are probably
more suited to control than LXI would be. Searching on SafetyBusP and
SafetyNetP, for example, would find you
<http://www.safetybus.com/1_News/1.1_News_Front.htm>  which leads to quite a
bit more interesting information.

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Thanks Paul,

I work for a small tech company whose primary business is scientific
instrumentation but we do manufacture control equipment for use in high
energy physics labs.

The instrument side of the company is under market pressure to adopt LXI as
a protocol and the control products are due for a revamp in the near future
and, being a small company, it would be financially sensible to adopt one
protocol across the entire product range.

The systems we will be controlling are not critical but will require a
degree of determinism.

I'm not a control man but an instrument man (hell, if you can't measure it
you can't control it) and was debating with myself whether LXI would be
suitable for a control protocol and reading your reply your primary concern
is determinism about which you seem to be happy.

Personally I can't see much point for triggering over the LAN unless those
triggers are slaved from an external trigger.

Thanks again

Regards

Tim Fulcher

Tim Fulcher wrote:


In control of the high energy or just some auxiliary non-safety critical
equipment? If controlling the former then I would suggest a risk based
approach backed by HAZOP or other thorough safety analysis. If its the
latter, I would ensure that there is no safety implications and use
whatever is appropriate to the level of control required.


I understand the sentiment but take a look at the other links I provided as
it may be useful to incorporate the capability. It may be that the two
protocols could co-exists but I haven't looked that far into it myself yet.


LXI is good at determinism within its capabilities. There may be issues of
dependability though (from a safety point of view).
 

If you have a time window during which you wish to gather a mass of readings
which need to start a fixed time before a planned event, then the
triggering facility can be useful.

   Trigger 1 starts the data logging
   Trigger 2 initiates the event
   Trigger 3 stops the data logging.

We do similar things where I am working at present (which deals in high
energy physics as it happens). As the experiment operates in pulses under
the control of a team of operators we know when our important data is
likely to arrive. I am trying to introduce them to the notion of LXI there
too. However, we also have safety issues to consider and LXI would not be
part of the safety system.

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Forth based HIDECS Consultancy .....<http://www.amleth.demon.co.uk/>
Mob: +44 (0)7811-639972
Tel: +44 (0)1235-811095
Going Forth Safely ..... EBA. www.electric-boat-association.org.uk..
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Paul E. Bennett wrote:


You may also be interested in this article.

<http://www.embedded.com/showArticle.jhtml;jsessionid=JP0QII5FCR2REQSND>

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Forth based HIDECS Consultancy .....<http://www.amleth.demon.co.uk/>
Mob: +44 (0)7811-639972
Tel: +44 (0)1235-811095
Going Forth Safely ..... EBA. www.electric-boat-association.org.uk..
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<posted & mailed>

Paul E. Bennett wrote:


Tried the link myself after it was posted and Embedded Systems page
structure had changed. This one worked though.

<http://www.embedded.com/showArticle.jhtml?articleID 8500595>

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Forth based HIDECS Consultancy .....<http://www.amleth.demon.co.uk/>
Mob: +44 (0)7811-639972
Tel: +44 (0)1235-811095
Going Forth Safely ..... EBA. www.electric-boat-association.org.uk..
********************************************************************