Tag Naming-Name changes-Tracking

I am in need of some input on tag referencing and changes to tags and tracking the changes.

Whether it be a P&ID, PLC System, or SCADA System(my current concern), it seems this can become a very confusing area if the system is changed in any way.

Lets say originally you have a pump, and it controls the pressure in the discharge line.

So you have, for example:

PIT1000CV = Pump Speed
PIT1000PV = Discharge Line Pressure
PIT1000SP = Pressure Setpoint
PIT1000AM = Pressure Loop Auto/ Manual

Is this clear enough so, when someone wants to find the pump speed, they know to look for PIT100CV? Or should there be a separate tag, for example PMP1000SR for the pump specific Speed Reference?

Now, what if you add a flow meter and control valve on the discharge line? Then, the pump speed is now controlling the flow, for example, and the control valve is controlling the line pressure.

So, you now have:

PIT1000CV = Valve Output
PIT1000PV = Discharge Line Pressure (input from transmitter)
PIT1000SP = Pressure Setpoint
PIT1000AM = Pressure Loop Auto/ Manual

and...

FIT1000CV = Pump Speed
FIT1000PV = Discharge Line Flow (input from transmitter)
FIT1000SP = Flow Setpoint
FIT1000AM = Flow Loop Auto/ Manual

Now, how is it clear to the folks browsing historical data what controls the pump speed?

Is it more sensible to have a unique tag for each field device, even if it is showing duplicate data? And this tag never changes?

For example:

PMP1000SR = Pump Speed Reference (whether it be controlled by pressure or flow?

And also have:

PIC1000CV = Pump Speed
PIC1000PV = Discharge Line Pressure
PIC1000SP = Pressure Setpoint
PIC1000AM = Pressure Loop Auto/ Manual

I think the input values are fairly self explanatory, for example, the transmitter in the field will always be PIT1000 and any loop associated with controlling it will be referenced as PIC1000, but how about handling the final control elements?

So would the best way to handle this be:

PCV1000CV = Valve Position

PIT1000CV = Valve Output
PIT1000PV = Discharge Line Pressure (input from transmitter)
PIT1000SP = Pressure Setpoint
PIT1000AM = Pressure Loop Auto/ Manual

Where PCV1000CV and PIT1000CV are essentially the same except maybe PCV is a raw scaled output and the CV is the loop output?

and...

PMP1000SR

FIT1000CV = Pump Speed
FIT1000PV = Discharge Line Flow (input from transmitter)
FIT1000SP = Flow Setpoint
FIT1000AM = Flow Loop Auto/ Manual

Just looking for suggestions some may be using to keep this straight. We have recently changed around several control schemes, and added some cascade control for more confusion and some in production are wondering how this can be made more clear to them what each loop controls etc....

Thanks for any suggestions

If you have a pump with a plant code of DCWP-A-B its is fairly simple and logical to start all symbols that are associated with that pump with DCWPAB or DCWP_A_B and continue on.
I do not work in plants and someone else will probably have a better scheme fro you.
I do work in buildings a lot and usually use L20T1 for Level 20 Tenant 1 for example. If it is a network bit it would be NL20T1.

cntrlfrk said:

PIT1000CV = Pump Speed
PIT1000PV = Discharge Line Pressure
PIT1000SP = Pressure Setpoint
PIT1000AM = Pressure Loop Auto/ Manual

Is this clear enough so, when someone wants to find the pump speed, they know to look for PIT100CV? Or should there be a separate tag, for example PMP1000SR for the pump specific Speed Reference?

Click to expand...

PIT as a tag prefix denotes a Pressure Indicating Transmitter. The proper tag prefix for the PID loop is PIC (Pressure Indicating Controller). You do it this way once, but most of the examples use PIT.

The PIC1000 can have PV, SP, and CV (or OUT) parameters. It actually has a lot more parameters, depends which ones you make accessable from the control system.

It is OK to have a PIT1000 tag and a PIC1000PV tag, but in this case I usually do not create the redundant PIT tag. I will use PIT1050 for a pressure transmitter that is not part of a PID loop. (I'd probably use PI1050 for the tag actually, the transmitter is out in the field, not on the screen.)

When I have a VFD as the output of a PID loop, I generally have tags for the VFD as well as the PID loop. i.e. PIC1000CV may have the same value as SC1000SP. However, depending on how you do your control, it may not always match. The VFD may also have a SC1000PV to show actual speed which won't match the PID loop output. You can think of any PID loop with a VFD as final element as a cascade loop.

You may have a PCV1000 tag to represent the control valve. If you have no position feedback on the valve, I'd consider it redundant. If you're using a smart positioner and you're bringing back actual position and PM data, you pretty much have to have a tag for the control valve.

Using a tag of PMP1000SR is really messing up your tag name conventions. I know you mean Pump, but it's not an ISA instrument tag, that's an equipment name, apples and oranges. Stick to one convention. SC = Speed Control (it could be SIC) and the SP or PV suffix means the same thing it did in the pressure loop. A setpoint on a VFD is still just a setpoint, no need to make up a special suffix for it.

In current and even many older systems where structures are used, you generally have one tag for a PID loop, with all the parameters included in the structure. i.e. PIC1000.PV, PIC1000.SP, etc.

In general, there is no value to having duplicate tags. It is more confusing than helpful. However, you have to determine if they really are duplicate. In the example of the VFD setpoint, if you can put the VFD in local control and input a setpoint directly, then they aren't duplicate tags. If you are reading one value from the PID output and one value from the VFD setpoint, they aren't the same thing, even if 99% of the time they have the same value. If you have a structure for a PID loop, and a structure for a VFD, you pretty much have to live with 2 tags even if your code has an unconditional "SC1000.SP = PIC1000.CV" in it.