Remote Control of cDAQ controller

[obsessed]

I have an application I would like to develop using National Instruments gear but I am not 100% sure of what I can and cannot do, or what would be the easiest most efficient way.

These are the requirements right now:

1. Must have a remote panel.  The chassis will be located somewhere in the neighborhood of 250' away from where the operator will be.  The cDAQ must accept commands from some sort of VI.  Whether the remote panel is just a touchscreen or something like a rugged tablet always running an OS, I don't care.

-and-

2. The controller must be able to perform some actions in the case that the remote panel gets disconnected. For example some sort of controlled shutdown.  For this reason the cDAQ must be able to house some level of code.

3. Environment may have some noise over the communication run between chassis and operator.  For this reason I was thinking Ethernet for the connection in between.  I can easily convert to fiber if necessary.

4.  I am decent with LabVIEW and due to time constraints was trying to stick with that.  For this reason NI suggested staying away from the FPGA stuff.

The actual application is control of a remotely located electrical load box for the purpose of generator testing.  What do you think? Right now I think a 9134 can handle this but I have not seen  much discussion that I can relate to. I tried to not get too far into the weeds with details but if you need more information by all means please ask.

Thanks

Trent

[Cavarval]

Hello,

The 9134 is definitely a good option, but there may be a more cost effective solution using a TPC-2230 with one of the new cDAQ-9185 or cDAQ-9189, depending on how complex the shutdown operation needs to be.

If you just need to ensure all the digital or analog outputs go to a specified value if a communication error occurs, the TPC/Ethernet CompactDAQ combination may be more cost effective, but if the shutdown procedure must be an actual code sequence, you need an embedded controller like the cDAQ-9134, which could actually be running a Real-Time Operating System instead of Windows for increased reliability.

Notice that if you chose to use the TPC / Ethernet CompactDAQ combo, the actual code would be executed in the TPC. The cDAQ-9185/9 can implement a watchdog timer that allows defining safe states that will be executed on all outputs if the hardware loses communication with the host computer (in this case, the TPC).

http://www.ni.com/product-documentation/14616/en/

Hope it helps. Let us know if you have more questions.

Regards,

[obsessed]

Camilo

Thanks for the response.  I read the documentation and had a few questions regarding the watchdog timer and the cDAQ series of controllers.

1.  The paper implies that one of the options for the watchdog timer is to hold its current state.  Is this accurate?

2.  It also looks like the fail safe state can be programmed via property nodes.  Does this mean the fail safe state could change throughout the code depending on which part of the code you are on?  Just as a simple example a state machine with different fail safe's depending on which state you are in.

3. What is Tristate?

Thanks

Trent

[Cavarval]

Hello Trent,

1. C Series Analog Output modules be default maintain the last generated value (except the NI 9260, which returns to 0 V) when the task is stopped. One of the watchdog timer configuration options is "No change" which means the module will use its default behavior when the timer expires, meaning it will continue generating the "current value". The other option is to specify a voltage or current level depending on the channel capabilities.

2. The fail safe can be programmed using property nodes, but cannot be changed at run-time. You would need to stop the watchdog timer task, change the value and start it again, which would kind of ruin the watchdog timer idea; if there is a network error in the middle of that sequence, the watchdog timer would not be executed. Furthermore, doing that would slow down the code execution and maybe even delay or conflict with other hardware operations (haven't tested this, just thinking of how reservations work).

3. Tristate sets the digital port to high-impedance. It only works in bidirectional ports and it has to be the whole port, you cannot set it to individual lines as you could with High, Low or No Change.

Hope it helps! 

[obsessed]

Cavarval

Final clarification (I think)

You describe the options for the Analog output module.  Are the digital modules such as the 9476 capable of the No Change?  Meaning if they are set to true when communications are lost they will stay true?

I think the answer lies in #3 but just wanted to clarify.

Thanks again.  This is very helpful.

[Cavarval]

Hello Trent,

I am glad you find the information to be useful!

Yes, the 9476 use the No Change option. In the link below you will find the different ways to configure the Analog Output, Digital Output and Counter Output channels configuration states.

http://zone.ni.com/reference/en-XX/help/370469AD-01/lvdaqmx/mxconfigurewatchdogexpstates/

Also, I attached an old example I made for a cDAQ-9188XT. I simulated a cDAQ-9185 with an NI 9263, an NI 9401 and a NI 9476 and it runs with no error. It should work as a starting point for you if you decide to go for the cDAQ-9185. It is saved for LabVIEW 2015, but if you need it for an older version I can convert it for you.

If you want to try the same and simulate a cDAQ-9185 you will need to install NI-DAQmx 17.1.

Hope it helps!