“12K3” has one advantage. Whoever drew the schematic finds the contactor straight away on page 12, path 3. What it does in the plant, the designation does not reveal. Supply air or exhaust air, heating or cooling, which unit, which function? “12K3” answers none of these questions. And these are exactly the questions the maintenance engineer asks when the plant has stopped.
Page and path are handy in the drawing, useless in the plant
In building automation, designation by page and path is still widespread. In an industrial plant it becomes a problem at the latest with the first larger change. If the schematic is restructured and a device moves to another page, two bad options remain. Either it is renamed, and labels, PLC program, visualisation and all further documents have to follow. Or the old designation stays and points to a place in the drawing where the device can no longer be found.
The difference fits into two sentences. The page number says where to find something in the drawing. The functional designation says what it does in the plant.
Three signs, three questions
A function-oriented designation to IEC 81346 separates three pieces of information, each with its own prefix. Here is a deliberately simplified example.
=HTC1 +LR1.UFH -QM01
| Sign | Question | In the example |
|---|---|---|
= |
Which higher-level function does it belong to? | =HTC1, heating circuit 1 |
+ |
Where is it located? | +LR1.UFH, underfloor heating in room 1 |
- |
What kind of device is it? | -QM01, a switching valve |
The function designation does not describe what the individual device does, but
the function it belongs to. A fuse -FC01 in the control cabinet is also clearly
part of heating circuit 1 as =HTC1-FC01.
Even the letter codes carry information. -QM stands for a device that switches
the flow of a medium, open or closed. If the valve has to regulate the flow, it
becomes -QN. A maintenance engineer who knows the system learns more from that
than from “valve 1”, before even opening the drawing.
“+EXT” is not a location designation
Inside the control cabinet, clean location designations by cabinet, section and
mounting plate are usually a matter of course. Out in the field, often only +EXT
remains. On a compact machine that may be enough. On a blast furnace, a large
conveyor system or a site where several hundred metres lie between cabinet and
field device, +EXT only says where the device is not.
A location designation has to answer one single question. Where do I have to go? How fine the structure needs to be depends on the plant. Building, level, room or plant area are usually enough. On an oil production site covering several square kilometres, by contrast, we laid a coordinate system over the site, measured from a fixed zero point in X and Y, plus Z for the height. The location designation led to a grid of nine by nine metres. Not every plant needs that. What matters is that someone on site finds the device without calling three colleagues first.
Structure is not the same as labelling
Not every piece of information has to be stuck on every component. If a control
cabinet is clearly marked +S01, everything in it is already in that area. There
is no need to print +S01 on every fuse again. Where needed, it is subdivided
further with +S01.F01, +S01.F02.
In the structure, on the other hand, the location has to be included. In EPLAN a
designation can be kept as “descriptive”, in which case EPLAN does not evaluate it
for identification. For the location that is the wrong way. If under the same
plant there is a -FC01 in the control cabinet and a second -FC01 in the
terminal box, EPLAN must not turn them into a single device. So the location
belongs in the structure, just not necessarily on every label.
Built properly, the structure pays off with repetitions. If a machining centre
+BZ1 is built a second time, it becomes +BZ2. The devices below keep their
names and are still unique. In the same way, =HTC1 becomes a second, identically
built heating circuit =HTC2 without renaming a single device. This is where
EPLAN shows its strength, because identical plant sections can be reused this way.
Fix it before the first page exists
A function-oriented designation takes more thought at the start than simply numbering through. That time comes back with extensions, at commissioning, in PLC and visualisation and above all in maintenance, often exactly when every minute counts. This applies in ELCAD and WSCAD just as in EPLAN. EPLAN simply evaluates the structure most consistently, for better and for worse.
How a designation to IEC 81346 is composed can be tried out with our reference designation calculator. Why we tend to continue an existing system in grown plants rather than convert it halfway is explained in IEC 81346 designations. And in our EPLAN design services the designation structure is the first step of every project.