Experimental Physics and
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If you use the EtherIP driver, see http://ics-web1.sns.ornl.gov/~kasemir/etherip/index.html you'll notice that it's much more efficient for it to access array tags. I just noticed that Bob beat me in stating this ;-) So the situation is typically like this: You might have records with great looking names like ThingyXY1_Voltage and ThingyXY1_Current which both read data from PLC tags. Those PLC tags, however, are meaningless array tags like ANA_XFER_RD[10] and ANA_XFER_RD[11] Well, the only meaning is: ANA_XFER_RD=analog data transfer array, meant to be read by IOC. To beautify your PLC code, you can create aliases in RSLogix: ThingyXY1_Voltage = alias for ANA_XFER_RD[10] ThingyXY1_Current = alias for ANA_XFER_RD[11]. That way, you have somewhat readable ladder logic, while the data still resides in the array elements, and can be transferred in a single array 'read' request. Now one could rephrase your question as: How well do your alias tags and the EPICS record names match? In the systems that I've been somewhat involved with, they didn't because a) There were several instances of the same PLC code, duplicated on different PLCs. So on each PLC, you'll find the same tag names, but of course their associated EPICS record names needed to be unique. b) The PLC programmer was free to pick any names. The only interface with him were the transfer array names, which of course don't carry any signal meaning. -Kay On May 12, 2006, at 12:04 , John Dobbins wrote: ControlLogix Users,
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ANJ, 02 Sep 2010 |
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