Streaming data from cRIO

Hi everybody,
This is quite a general question and I am looking for some pointers\opinions\suggestions.
I want to stream data from several channels at diffferent rates from my cRIO to the host PC. As far as I can see there are three options:
1) Use a network shared variable (NSV) for each channel and read them in a loop on the host PC.
2) Use one NSV which uses a cluster of an enum and variant. In this case the enum specifies which channel (and therefore data type) the packet contains and the variant contains the data.
3) Use STM to stream the data over the network using TCP/IP
These are my questions/thoughts:
1) not very scaleable as each NSV has to be read individually also just seems messy!
2) Seems nice and clean and scaleable, multiplexes the data into one channel. I am aware NSVs are not quite as efficient as directly using STM TCP/IP BUT... is there an additional (significant) overhead converting all the data to variant?
3) According to the documentation on NSVs using TCP/IP is the fastest way to stream the data. This method seems to offer the same avantages as (2) - clean, multiplexes the data. BUT it does add complexity in developing the cod. Also the data is still flattened to string, is this much different than converting to a variant?
THE QUESTION: is method (2) a reasonable compromise if the absolute highest data rates are not required?
Many thanks,
Steve.

Hi Steve,
I have been looking into this problem for you. It seems that each of the three options you highlighted could be used to achieve your goal though since you want to stream multiple channels method 1 would be highly inefficient and therefore should not be considered for this application. I would suggest that method 3 which uses TCP/IP to stream the data over the network is the optimal solution in this case though as you have alluded to, this does add a level of complexity. If you decide to pursue this option I have found a really useful link provides more details about this methodology and a LabVIEW example which should help you get started with the coding. I have also found this link to a forum which may be of interest to you (especially the final post by Kurt).
I would also like to add that I completely agree with Brian K, in that I believe method 2 is a very acceptable compromise, especially if high data rates are not necessary.
I hope this helps.
Best Regards,
Christian Hartshorne
Applications Engineering
National Instruments

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Dear All
I hope my message finds you all well
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Hi
I’m wondering if someone can help me. I’m trying to stream data from a sub vi to the main vi without opening and closing the sub vi continuously. The data also needs to be extracted from a while loop within the sub vi. background info: The sub vi controls a photomultipler tube, which once it is on it is best kept on. The PMT signal is generated in while loop of the sub vi. Attached are some basic vis showing what I’m trying to do.
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Attachments:
Main page.vi ‏11 KB
test2.vi ‏13 KB

If you are streaming measurements continously I would consider using a circular buffer instead of the queued producer/consumer approach.
Check out this implementataion of such a buffer, use only this if your DAQ device does not have an internal circular buffer.
https://decibel.ni.com/content/docs/DOC-20403
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Br,
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Stream data from a subvi to the main vi - path refnum

hello everyone
sorry my english
http://forums.ni.com/t5/LabVIEW/stream-data-from-a-subvi-to-the-main-vi/m-p/2205150/highlight/true#M...
- refnum boolean worked
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how to create a path refnum? stream data from a subvi to the main vi
where do I start?
thank
Solved!
Go to Solution.

Bom Dia Saille,
Eu acredito que o que você tenha hoje seja isso aqui (Desenho bem simplificado):
Hoje o que você tem é o Aplicativo do Medidor + USB Driver controlando o seu medidor. Basicamente, sua aplciação está dividida em três camadas:
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Device Driver - Intruções de SW de baixo nível para controlar um periférico através de um barramento.
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É possível acessar o Driver diretamente também, mas eu não recomendo. O resultado não compensa o esfroço!
Espero ter esclarecido suas dúvidas e espero que você tenha sucesso na sua aplicação!!
Atenciosamente.
Felipe Flores
Engenharia de Aplicações
National Instruments Brasil

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nook,
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Bom Dia Saille,
Eu acredito que o que você tenha hoje seja isso aqui (Desenho bem simplificado):
Hoje o que você tem é o Aplicativo do Medidor + USB Driver controlando o seu medidor. Basicamente, sua aplciação está dividida em três camadas:
Aplicação - Onde estão as funcionalidades principais do programa (interface com o usuário, apresentação de dados, geração de arquivos, etc.)
VISA - Uma arquitetura de Software para controle de instrumentos. Basicamente, ele se comunica com o Driver USB para poder enviar e receber pacotes de dados através do barramento USB.
Device Driver - Intruções de SW de baixo nível para controlar um periférico através de um barramento.
No desenho, eu aponto duas camadas onde você pode tentar atuar para automatizar suas medições:
Aplicação - Você pode usar o VI Server para controlar o Aplicativo do Medidor (Se este aplicativo tiver sido desenvolvido em LabVIEW, o que eu suponho ser verdade). No entanto é necessário saber se o desenvolvedor do produto permitiu isso (Veja Using VI Server to Pass Data Between a VI and a LabVIEW Executable). Outra alternativa é conversar com o fabricante para ver se ele desenvolveu alguma API (Application Programming Interface) para que você consiga controlar o instrumento diretamente.
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É possível acessar o Driver diretamente também, mas eu não recomendo. O resultado não compensa o esfroço!
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Atenciosamente.
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