How to handle hardware that spans multiple loops
How to handle hardware that spans multiple loops
(OP)
Hi Folks, two questions:
1. We have several cases where a single physical block of valves, with a single common DeviceNet interface, are connected to multiple loops. What is the recommended way to identify (TAG) the stack?
2. Similar to question 1 we have I/O blocks that connect to multiple loops. In some cases the individual modules connect to multiple loops. What is the recommended way to identify those?
Regards,
Greg
1. We have several cases where a single physical block of valves, with a single common DeviceNet interface, are connected to multiple loops. What is the recommended way to identify (TAG) the stack?
2. Similar to question 1 we have I/O blocks that connect to multiple loops. In some cases the individual modules connect to multiple loops. What is the recommended way to identify those?
Regards,
Greg





RE: How to handle hardware that spans multiple loops
Q2. Can you give an example of this?
xnuke
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RE: How to handle hardware that spans multiple loops
Tagging each valve is a bit problematic. One stack we are using is http://www.festo.com/cat/en_us/products_VI10_10 CPV10. It has 8 slots that each hold 2 3-way valves for a total of 16 control points. It is possible to trade out the contents of a slot but in practice the stack is treated a single unit.
The system consists of a PLC connected via DeviceNet to distributed blocks of I/O. In one case the first 3 channels of a digital input module are monitoring a 3 position level sensor and the fourth is monitoring a pressure switch for a different loop. In another case channels 1 & 2 monitor spill sensors, 3 the power good output from a power supply, and the fourth is connected to a smoke detector.
I'm new to using P&IDs, Loop Diagrams, etc... Reading ISA 5.1 and Instrumentation And Control Systems Documentation went a long way towards getting me up to speed but it still isn't clear to me how to document multi-channel I/O type stuff and stuff that is shared by multiple loops.
Thanks for the help!
Greg
RE: How to handle hardware that spans multiple loops
For your first DI module, you'd have tags of LS for your level switch inputs and a PS for your pressure switch. For the second, I'd probably tag the spill sensors as YS, the power supply ES or JS, and the smoke detector YS. (Y means event, state, or presence.) For the YS instrument bubbles, I'd add an amplifying label of SPILL or SMOKE outside the bubble to provide more information.
What brand of PLC are you using?
xnuke
"Live and act within the limit of your knowledge and keep expanding it to the limit of your life." Ayn Rand, Atlas Shrugged.
Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.
RE: How to handle hardware that spans multiple loops
The P&ID should show the Instruments and how they relate to the process equipment/piping/etc... and how they relate to each other in a control loop. ISA 5.1 does recommend line difference shown, such as:
Electrical: ---------------
Internal or software link: ---o---o---o---o---o--- (this is generally shown between two controllers e.i. A primary controller cascading to a secondary controller...both of which remain in the PLC/DCS controller...no physical wiring)
Pneumatic: ---//---//---//---
and there are others as you've seem if you have ISA5.1.
In typical systems, the connection between PLC and Instrument is a pair of wires, shown on the P&ID coming from a Shared Control (Box 4 of General Instrument symbols of ISA 5.1) going to an instrument bubble with --------- between them.
Using Profibus, you could use the ----o-----o----o---- line between them instead, to show that it is a 'soft' connection. The instrument bubble will indicate that it is a field instrument, so users should understand that it is a 'hard' device, but connected 'soft'ly...
Loop Diagrams can be a bit more troublesome: Do you put the distribution point/trunk with all its instruments on one loop drawing? Or each instrument on an individual drawing that references the Distribution point/trunk?
My preference is each instrument has its own loop drawing. The Distribution point/trunk would be referenced on each loop that connects to it. One would still show the ---o---o---o--- line between them on the loop drawing.
Hope that helps. If you have specific questions, PM me with drawings, or include a sketch on this site.
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This is normally the space where people post something insightful.
RE: How to handle hardware that spans multiple loops
Thanks for the help!
P.S. I have not been able to figure out how to PM on this site.