PXI , advice for a total newb

[Dan Bookwalter N8DCJ]

Ok , i am looking for someone with extensive real world  PXI experience , who doesn't work for one of the suppliers etc... where I work none of us have any PXI experience.

Here is a big picture overview of what we would be replacing for now.

We have test stands that need upgraded, they currently use discrete instruments, Function Generator (4 Ch) , 4 channel oscilloscope , a Keithley 2750 , with 40 channels of DAQ , multiplexer card and relay cards ... all slots are full on the Keithley.

So, for PXI I was thinking DMM card , multiplexer(s) , relay cards , Oscilloscope and Function Generator ...

Ideally I would like to talk to someone for say 30 minutes on phone or Teams or whatever to get a better real world application feel etc..

From what I have read , we would not need a controller as the PC would be in control of everything and not offloaded to the controller.

One of the aspects of PXI I like is the ability for expansion in the future.

if you have any inclination to talk to us , message me on here and we will figure it out ...

TIA Regards

Dan

 

[Lior Bilia]

Skip the PXI DMM, FG and scope cards, they are expensive and usually do not perform as well as standard instruments. Instead pick whatever instrument fits your requirement with a modern interface (LXI, USB) and a rack kit.

Example Keysight 33465A vs NI PXI DMM. The NI card is ~4000USD, with slightly worse performance. 

Definitely use the PXI for massive multiplexers, DAQs, Digital interfaces (CAN, I2C etc) and GPIO. Also, take into account that PXI is being phased out in favor of PXIe. Some of NI PXI muxes are EOL, without an alternative.

[Dan Bookwalter N8DCJ]

Lior

Perfect , that is the kind of insight I was looking for ....

 

thank you 

Dan

[mcduff]

I don't have extensive experience with PXIe systems, but have made some systems in the past and present. A current system collects data continuously at 20-30MSa/s for 32 channels. At that rate the 15TB RAID array is filled up in a few hours.

Advantages:

1. Throughput. Unless your modular instruments are attached via thunderbolt, hard to beat PXIe throughput. However, it might not be needed in your case.
2. Triggering. Simple to implement triggering or advanced triggering through the backplane. Can be done with modular instruments also, but more wires and more hassles. If you need a synchronized start, the PXI backplane is your friend.
3. Synchronization. Can share reference/sample clocks through the backplane. Can be done with modular instruments also, but more wires and more hassles.
4. Compact. Somewhat more compact than modular instruments.

Disadvantages.

1. Expensive. Noted in previous message.
2. Support. If you have instruments from different vendors and there is a problem, each vendor may blame the other. I had a chassis, a controller, and digitizers from three different companies. When there was an issue with the cards and the slots they could occupy, everyone at first blamed the other, Eventually, it was found that the chassis had an issue with the interrupts. PXI is supposed to be standardized but ...
3. Future proof. The embedded PXIe controllers seem to always be a generation or two behind current CPU offerings. In addition, their components are difficult to upgrade or have limited upgrade capabilities. You may want to also purchase an external TB controller card. This allows to you to attach the chassis to a computer via the TB port and control from that computer instead of using an embedded controller.

[Lior Bilia]

One more thing: Vendor lock in, software subscriptions and proprietary drivers - Some high end vector signal generators by NI require subscription, in addition to their high initial cost. These instruments do not have standard SCPI (or IVI) drivers. Similarly, their new PXIe DMM, the 4080 has proprietary drivers, vs standard IVI drivers for previous models. If NI decides to drop support for this instrument, you are out of luck.

[codcoder]

On 8/27/2024 at 1:03 AM, Dan Bookwalter N8DCJ said:

From what I have read , we would not need a controller as the PC would be in control of everything and not offloaded to the controller.

 

If you have a controller in the PXI chassis it can either run LabVIEW RT (used to be a PharLaps derivate but they are now switching over to something built on Linux) or Windows.

If you want the PXI system to run as an embedded system, and if you need any real-time capabilities, then LabVIEW RT is the way to go. If you don't need that I do not suggest running Windows on the controller. We have a system where we do that and unless you really don't have space for a rack computer or some other external PC I don't see any advantages. What you get is basically a more expensive computer with worse performance.

Just connecting to the PXI system with an MXI link is much better (which we do in all our other systems) and if I understand you correctly that's already your idea.