Logging data fast in AB-L36ERM

Dear all,

Im using Allen Bradley Compact Logix L36ERM as a PLC.
and facing a problem where I need to create a FIFO buffer that fills an ARRAY[200] that are REALs.

Background: Running Fast Frequency Response (FFR) as a service by our energy management system requires rapid logging for Transmission Line Operator (Electric).

Task:
If action A is triggered, the Variable X needs to be pushed into an ARRAY that is later collected in an IPC and out as a response in an API query. The API response is the ARRAY[200]


Logging interval of each REAL shall be 100mS. I just see that i might will run into scan time and timer issues with this method. Do you agree that an external logger of type PLX51-DL-232 would be better fitted for this purpose or has anyone succeeded with the task above.


Some example code that does it purpose for now, however greatly affected by ScanTime/Task/Timers



FFR_CTD_Array.PRE:=199;
FFR_Timer_Log.TimerEnable:= FFR_Triggered;

TONR (FFR_Timer_Log);
CTUD(FFR_CTD_Array);

IF FFR_Timer_Log.DN AND FFR_Triggered AND NOT FFR_CTD_Array.DN THEN
FFR_Data_Buffer_Frequency[FFR_CTD_Array.ACC] := IV_HZ.Value;
FFR_Timer_Log.Reset:=1;
FFR_CTD_Array.CUEnable:=1;
FFR_BR:=1;

else

FFR_Timer_Log.Reset:=0;
FFR_CTD_Array.CUEnable:=0;
FFR_BR:=2;

END_IF;


IF NOT FFR_Triggered THEN
FFR_CTD_Array.Reset:=1;
FFR_Timer_Log.EnableIn:=0;
FFR_BR:=3;
else

END_IF;

I have completed several FFR projects, using Janitza UMG 512 Pro, at 10mS granularity (spec calls for 20mS, but the default in the 512 is 10).

I could not find a Power Meter I could poll externally (e.g. into a PLC), faster than 200mS.

How often does that Hz value get updated ? What kind of instrument is it coming from ?

What is the event that triggers the 100 ms log ?

ControlLogix has pretty decent physical event task triggers (for general purpose industrial stuff; it's not purpose-built for electrical distribution), and the Periodic Task operating system interrupt will be much more precise than a TON timer in the main Continuous Task.

We are using an ACCUVIM II Powermeter. Responsetimes better than 100mS. We collect data from MB-TCP at a scanrat of 80mS from the unit. @Ken_Roach

Have you verified, i.e. using an Omicron 356 etc, that the Accuvim is able to publish a change of frequency at the rate you desire?

In my early testing, whilst I was able to poll a Schneider power meter on Modbus TCP and get a response every 1 mS, the values were not changing.

Also, in the two TSO jurisdictions I have implemented FFR, there is a requirement for T-5 event data. This means you must record all the time, to have the ability to get the T-5 data once the event occurs.