What are the differences between CompactRIO and PXI-RT?

[Daniel_Chile]

Hi. We want to perform distributed data acquisition, specifically with (let's say) eigth IEPE accelerometers, wich are about (let's say) 80 meters away from the host PC. We think a good solution is to acquire locally (with PXI-RT or cRIO), maybe do some temporary storage, and then transmit the acquired data through ethernet to the host. This way, we can mantain a desktop PC on a safe place to perform centralized data processing and storage and avoid long accelerometer cable runs, subject to signal degradation.
As I mentioned, we thought on a basic PXI-RT system or a cRIO system, since little or no processing and storage is needed, while providing signal conditioning to the accelerometers. We thought about the next configurations:

1. PXI-RT: PXI-1002 chassis, PXI-8145 RT controller, PXI-4472 8 channel DSA. Total: $ 6585
2. cRIO: cRIO-9101 chassis, cRIO-9002 real-time controller, 2x cRIO-9233 4ch IEPE AI. Total: $ 5260

Prices are relatively close and none is absolutely cheaper than the other if we add accesories, change the number of channels or other characteristics.

We are new to PXI-RT and cRIO, so I would like to know what could be the main effective differences for my application and what do you think would be the best solution.

Thank you,

Daniel R.
Universidad de Concepcion

[John Rich]

There are several advantages which I see in the CompactRIO system over the PXI system for most applications. First of all, the CompactRIO system is exactly what its name implies, compact. While I believe that the PXI system is a good, rugged computer, it will not stand up next to the CompactRIO system in ruggedness.

The CompactRIO system also has the advantage of hot swappable modules. You don't have to shut down the entire power if an interface module goes bad.

One disadvantage to the CompactRIO is the additional development system required. For the PXI system you will need LabVIEW plus the LabVIEW RT module. For the CompactRIO system you will need both of these plus the FPGA module. Unless you're expecting to have applications in the future for which you could use the CompactRIO or you already have these modules then the extra cost may not be justified for this one-off application.

In order to take full advantage of the power of either of these systems I recommend that you do at least a portion of the processing on the CompactRIO or RT system. There's no need to burden down your PC when you have computing power readily available and unutilized.

[A.S.]

Hi Daniel,
I agree with John's comments on the difference between PXI-RT and cRIO. To add to this discussion, Compact RIO is an FPGA platform. So you can compile a VI and download it onto the cRIO's FPGA. The cRIO also has an RT portion, meaning that you can have a VI running on the FPGA and a VI running on the RT part and they can communicate with each other. I would recommend cRIO only if you need to take advantage of its FPGA functionality, which gives you extremely fast program execution with amazing loop cycle times. The ruggedness is also a plus. However, programming for LabVIEW FPGA is a bit different than programming for LabVIEW (or LV RT). FPGA programming is very low level and will require additional development time. This is why the direct comparison between PXI-RT and cRIO brings up more than just the price as a differentiator.
If you are looking for a compact platform like cRIO, I would recommend Compact FieldPoint. In ruggedness, it is quite close to the cRIO platform. Development-wise, its exactly like programming for the PXI-RT. This means that basically, any regular LabVIEW VI can be downloaded and run on it. So as you can see, its not a lateral step between PXI/Fieldpoing RT and cRIO. I would recommend that you read more about these platforms before proceeding. If you call us at NI, we can also help you decide a suitable platform for you.
cRIO: http://www.ni.com/compactrio/
FPGA: http://www.ni.com/fpga/
RT: http://www.ni.com/realtime/

Hope this information is helpful.