Re : PLC Rate

[kabooom]

Hi all

I have  a question concerning the PLC Loop Rate.

I created a Timing and synchronisation custom device in order  synchronize other custom devices (which are performing Daq acquisition/ generation), and Veristand PCL together.

In my Timing and synchronisation custom device, i set the flag DrvRTSI0? to true, and generate a 1 kHz signal on the RTSI0 (PXI_Trig0).I checked the signal with a scope and i have the 1 kHz signal on the PXI_Trig0. I also routed the trigger line in order to dispatch the Trigger lines on all buses of the chassis.

In VeriStand System Explorer:

- I configured the  Timing source of the PCL to use Timing and Sync custom device.

- I configured the chassis to  use the Timing and Sync custom device.

Everything deploy correctly. When i display the VeriStand System Tag called Actual Loop Rate, i see that it varies between 900 and 1100 Hz. How is that possible ? How is measured the Actual Loop Rate in VeriStand ?

Thanks for your Help ...

[sabri.jatlaoui]

Hi Kaboom,

Could you please send me your hardware configuration?

You can use the decimation control to set the model rate to be a decimation of the main loop rate. For example, if your primary control loop is at 200Hz and the decimation of the model is 2, the model will run at 100Hz.

Make sure your not in Low Latency mode in he controls of the timing of the VeriStand Engine.

http://zone.ni.com/reference/en-XX/help/372846F-01/veristand/pcl_modes_models/

Best regards.

[kabooom]

Hi!

Thanks for the answer.... i felt a little bit alone last days....

So the hardware configuration is :

- NI RMC 8354

- PXIe-1065 chassis

- PXI-8360 MXI link

-4 PXI-6254

-4 PXIe-6358

-1 PXI-6682H

-1 PIORC-5565

Normally my PCL should run at 1 k HZ, i have no model runing in this configuration. The Execution mode is parrallel.

I only have severeal custom devices in order to synchronize the acquisition boards together, to do the acquisition of all channels and to register the data on the disk... Some other to perform RMS calculation, RFM and Arinc 429...

So this is a huge configuration, My PCL is loaded to 50-60 % and when i watched the Actual Loop rate, i see it always varies between 900 and 1100 Hz. It is not stable. This is done whenever my PCL is synchronized with an external clock (generated at 1 KHz).

- So that's why i wonder how is measured the actual loop rate in VeriStand

- In the same time i also have problem when i goes over 50% with my PCL, it seems the software clock generated in order to synchronized the Asynchronous custom device is not generated properly.

Any help is greatly appreciated.

[Eric.M]

Hi kabooom,

Which type of CD are you using : Timing & Sync Asynchronous or Inline ?

Also, have you checked the HP Count system channel ? We can use it to guarantee there's no issue with the Actual Loop Rate (if it increases often, according to the graph of the loop rate you posted).

Is the PCL still unstable when you only use this CD alone in a definition file (less system complexity, less CPU usage) ?

That might be a good starting point to figure out which components of VeriStand or you definition file are unconsistent 😉

Regards,

[kabooom]

Hi!

Well the Synchronisation custom device is Asynchronous (the inline timing and Sync template doesn't work).

The Acquisition Custom device is Asynchronous but is synchronized with the PCL (pseudo synchronous)

The others are Inline Custom devices which launch an asynchronous vi.

As suggested, i've done a test this morning using only one Acquisition custom device, one synchronisation custom device and one custom device to do the recording. This is the minimum configuration to reproduce the problem. Even in this configuration i have the same phenomena (see attached picture). As i said, it seems the minimal and maximal values are symetrical around 1000 Hz. The HP Count still to 0 and the PCL CPU is around 8 % ....