LABVIEW-RT Extension

[Matthew G. Feemster]

We are currently in the process of transforming LABVIEW from a basic data
acquisition tool into a possible closed-loop control environment. Though
standard Windows NT 4.0 does provide a limited ability for scheduling, we
are considering the upgrade to LABVIEW-RT to ensure a deterministic
response. However, I am seeking advice/suggestions/recommendations as to the
performance of this real-time extension. What are the possible control
frequencies? Reliability? We are currently are using the PXI-8156B
controller in the PXI-1000B chasis with the MIO-6070# I/O card. What
hardware modifications are required (I was informed that the PXI-8156B could
be used as our RT engine and that any PXI compatible I/O card could be used
in lieu of the RT
series I/O boards). Any suggestions/comments are
appreciated.

Matthew Feemster

[Jimmie_A.]

Hello Matthew,

RT is reliable but as always there are things to consider when programming in order to get the highest performance and reliability possible so things like starvation are avoided.

8156b might be on the lower side of things when it comes to CPU processing power but it all depends on what kind of performance you are aiming to achieve. Worth mentioning is that the version of LabVIEW RT used will affect performance just like the version of the PID toolkit used (later versions greatly improved performance). Data acquisition driver version will also affect performance, especially when using the DAQmx driver that has greatly improved single-point I/O performance compared to traditional NI-DAQ.

Down below you will find some figures on PID loop performance on different controllers.

PID on 8156 running on LV RT 5.1.2 and NI-DAQ 6.7:

http://digital.ni.com/public.nsf/allkb/FAC66608B1AF9EA586256A320052D47F?OpenDocument

PID on 8170 running on LV RT 6.1 and NI-DAQ 6.9.2:

http://digital.ni.com/public.nsf/websearch/B7BC0A08C95D505286256A32005488CE?OpenDocument

PID on 8176 running on LV RT 6.1 and NI-DAQ 6.9.2:

http://digital.ni.com/public.nsf/websearch/b06d5e50f04f280b86256b3e0070ba2d?OpenDocument

Comparison table of PXI controllers:

http://digital.ni.com/public.nsf/allkb/3003B0E10C3C71E286256CAD0070FCAA?OpenDocument

Latest RT controller can achieve rates up to 94 kHz.