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

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 which leads to quite a bit more interesting information.

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

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.

You may also be interested in this article.

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