Data Acquisition Idea Exchange

I bought a NI USB-6251 BNC but the support explained me that it would have no Linux support out of the box. I will have to find out how to use it on Linux systems myself now (perhaps with help of the forum). It would be a nice feature, if it would ship with Linux support.

Hello,

How often you have build Labview applications using simulated DaqMx boards ...

And how often you were limited by the default behaviour of simulated boards ... ( Sinewave for analogic inputs, Counter square signal for digital inputs ... )

It would be nice to integrate in DaqMx simulated boards, the abilty to modify the default behaviour of simulated inputs ... thru dedicated popups

It would be nice, for each task linked to a simulated daqMx board, to launch a popup window ...

• For digital input, give the abilty to modify for each configured channel , the current binary value.
• For analog input, give the ability to choose between a fixed value, a sine wave, a square signal ... white noise ...
• For digital output, give the ability to view the current setted values
• For analog output, give the ability to view the current simulated output value on a waveform chart ...

A more powerfull tool could also integrate a simulated channels switching mechanism ... A simulated output could be linked to a simulated input 

This feature could be a good way to create an application which could simulate a complete process ... this application could be used to validate a complete system

(such a kind of SIL architecture)

Other idea .... A complete daqMx simulation API ...

• Creation of an API which could instanciate a simulated daqMx board (Wich could be seen via MAX)
  • Takes place of the actual limited daqMx simulated board
• This device could then be accessed by other application thru daqMx
• This API could have access to all channels of this simulated device.
• This API could force, programmatically, the value of the simulated input channels according to a realistic process model

Something like this ...

Currently when streaming analog or digital samples to DAQ board, output stays at the level of last sample received when buffer underflow occurs. This behavior can be observed on USB X Series Multifunction DAQ boards. I have USB-6363 model. The exact mode is hardware-timed, buffered, continuous, and non-regenerating. The buffer underflow error code is -200290 “The generation has stopped to prevent the regeneration of old samples. Your application was unable to write samples to the background buffer fast enough to prevent old samples from being regenerated.”

I would like to have an option to configure DAQ hardware to immediately set voltage on analog and digital outputs to a predefined state if the buffer underrun occurs. Also, I would like to have an option to immediately set one of PFI pins on buffer underrun.  

I believe this could be accomplished by modifying X series firmware and providing configuration of this feature in the DAQmx API. If no more samples are available in the buffer the DAQ board should immediately write predefined digital states / analog levels to outputs and indicate buffer underrun state on PFI line. Then it should report error to PC.

Doing this in firmware has certain advantages:

1. It can be done quickly (possibly within the time of the next missing sample – at 2Ms/s that’s 0.5us).
2. Handles all situations (software lockups, excessive CPU loading by other processes, loss of communication do to bus traffic, interface disconnection…)
3. It does not require any additional hardware (to turn off outputs externally).
4. Buffer underrun indication on PFI line could provide additional safety measure (it could be used for example to immediately disable external power amplifier connected to DAQ AO). 

Doing this using other methods is just too slow, does not handle all situations, or requires additional external circuitry.

Setting outputs from software, once error occurs, is slow (~25ms / time of 50000 samples at 2MS/s) and does not handle physical disconnection of the interface. Analog output does eventually go to 0 V on USB-6363 when USB cable is disconnected, but it takes about half a second.  

Using watchdog timer would also be too slow. The timer can be set to quite a short time, but form the software, I would not be able to reset it faster than every 10ms. It also would require switching off analog channels externally with additional circuitry, because watchdog timer is not available for analog channels.

The only viable solution right now is to route task sample clock to PFI and detect when it stops toggling. It actually does stop after last sample is programmed. Once that occurs, outputs can be switched off externally. This requires a whole lot of external circuitry and major development time. If you need reaction time to be within time of one or two samples, pulse detector needs to be customized for every possible sampling rate you might what to use. To make this work right for analog output, it would take RISC microcontroller and analog electronic switches. If you wanted to use external trigger to start the waveform, microcontroller would have to turn on the analog switch, look for beginning of waveform sample clock, record initial clock interval as reference, and finally turn off the switch if no pulse is received within reference time.

I’m actually quite impressed how well USB-6363 handles streaming to outputs. This allows me to output waveforms with complexity that regular arbitrary generators with fixed memory and sequencing simply cannot handle. The buffer underflow even at the highest sampling rate is quite rare. However, to make my system robust and safe, I need fast, simple, and reliable method of quickly shutting down the outputs that only hardware/firmware solution can provide.

Thanks,

Sebastian

Based on this question, I would like to add a new category of events to LabVIEW: Max-events.

This category could contain the following events:

-Hardware Added

-Hardware removed

-Configuration changed

    -Scales

    -Channels

    -Tasks

If you know other events, please post them.

It would be great if the full DAQmx library supported all NI data acquisition products on Windows, Mac OS X and Linux. The situation right now is too much of a hodge-podge of diverse drivers with too many limitations. There's an old, full DAQmx library that supports older devices on older Linux systems, but it doesn't look like it's been updated for years.  DAQmx Base is available for more current Linux and Mac OS systems, but doesn't support all NI devices (especially newer products).  DAQmx Base is also quite limited, and can't do a number of things the full DAQmx library can.  It's also fairly bloated and slow compared to DAQmx.  While I got my own application working under both Linux and Windows, there's a number of things about the Linux version that just aren't as nice as the Windows version right now.  I've seen complaints in the forums from others who have abandoned their efforts to port their applications from Windows to Mac OS or Linux because they don't see DAQmx Base as solid or "commercial-grade" enough.

I'd really like to be able to develop my application and be able to easily port it to any current Windows, Mac or Linux system, and have it support any current NI multi-function DAQ device, with a fast, capable and consistent C/C++ API.

Anyone else see this as a priority for NI R&D?

When using TDMS on cRIO systems, there are a couple of considerations that doesn't normally play in too much when storing data as TDMS files and they are:

* The current version of the file system used on cRIO controllers degrades significantly in performance if -any- folder on the cRIO contains more than ~100 files. (work-around> more elaborate folder structures, but a lot of this structuring would be only to work around this shortcoming of the (old) version of the file system 

* The drives are SSD with limited life-length and wear-leveling etc. Writing and re-writing these index files add un-necessary overhead and wear on the disks

* They use up space which is (very) limited on some cRIO's (even if not much). (people may be quick to point out that you can add a thumb-drive, but down-sides to that is the thumbdrives (as far as I know) needs to be FAT. Compared to storing on the cRIO file system which is atomic and fail-safe where you pretty much don't have to worry about sudden power outages and interruptions mid-write.. on a thumb drive you would have all these issues that could worst case corrupt your whole thumb drive.)

I propose to add a boolean (default to false) on the TDMS Open called "supress writing tdms index to disk" or some smart name along those lines. What this would do is still allow for the tmds index to be created, but it will remain in memory only and never be written to disk. When the TDMS Close is called, the memory is released and the tdms file is written to disk without the index file. If the same file is opened again, extra time would be needed since the index file would be re-created (again in memory only if boolean indicates this), but I think for the most part this overhead would be more than acceptable.

I'm not sure how "simple" modifying the TDMS open and close functions would be, but I do know that there are many cases where this flag would make sense. 

If you set up a change detection event as so:

There isn't anything in the event data node to tell you which line triggered the interrupt. I'm proposing we add something in the event data node for this event (like a bit field or a reference to the channel) so the programmer would know which line fired the event.

The workaround is you do a DAQmx read at this point and you mask the data vs previous data.. but I would prefer not to do this.

Measurement and Automation Explorer MAX's Test Panel's Analog Input provides a quick method to examine a signal and vary acquisition parameters.  It would be useful to be able to zoom the time axis and have a cursor display so that for example noise level or rise time could be looked at in more detail.  The time axis limits can currently be manually overwritten as a way to zoom but that is cumbersome.  Assuming the graph being used in this test panel is built from a standard NI graph, it should have zoom and cursor capability already part of it and thus easily added.

Steve

Absolute encoders have been around for some time, but NI's motion hardware still supports only incremental encoders.  I would like to see support for absolute encoders in NI Motion or NI Soft Motion.

Hi All,

In my post on the LabVIEW board I asked if it was possible to have control over the DIO of a simualted DAQ device. Unfortunately it seems this feature is not available. Once MAX is closed the DIOs run through their own sequences.

If there was a non-blocking way to control a simulated DAQ device through MAX it would permit much simpler prototyping of systems before they need to be deployed to hardware. For example if you want to see how a program responds to a value change simply enter it in the non-blocking MAX UI. Or as in my original case can make an executable useable even if you don't have all the necessary hardware.

I think this feature should only be available for simulated devices.

Thanks for reading - and hopefully voting,

Dave

We need a way to query an output task to determine its most recently output value.  Or alternately, a general ability to read back data from an output task's buffer.

This one's been discussed lots of times over the years in the forums but I didn't see a related Idea Exchange entry.  Most of the discussion I've seen has related to AO but I see no reason not to support this feature for DO as well.

There are many apps where normal behavior is to generate an AO waveform for a long period of time.  Some apps can be interrupted unexpectedly by users or process limit monitoring or safety range checking, etc.  When this happens, the output task will be in a more-or-less random phase of its waveform.  The problem is: how do we *gently* guide that waveform back to a safe default value like 0.0 V?  A pure step function is often not desirable.  We'd like to know where the waveform left off so we can generate a rampdown to 0.  In some apps, the waveform shape isn't directly defined or known by the data acq code.  So how can we ramp down to 0 if we don't know where to start from?  This is just one example of the many cases where it'd be very valuable to be able to determine the most recently updated output value.

Approach 1:

  Create a DAQmx property that will report back the current output value(s).  I don't know if/how this fits the architecture of the driver and various hw boards.  If it can be done, I'd ideally want to take an instantaneous snapshot of whatever value(s) is currently held in the DAC.  It would be good to be able to polymorph this function to respond to either an active task or a channel list.

Approach 2 (active buffered tasks only):

   We can currently query the property TotalSampPerChanGenerated as long as the task is still active.  But we can't query the task to read back the values stored in the buffer in order to figure out where that last sample put us.  It could be handy to be able to query/read the *output* buffer in a way analogous to what we can specify for input buffers.  I could picture asking to DAQmx Read 1 sample from the output buffer after setting RelativeTo = MostRecentSample , Offset = 0 or -1 (haven't thought through which is the more appropriate choice).  In general, why *not* offer the ability to read back data from our task's output buffers?

-Kevin P

When it comes to documentation of an measurement, you need to report ALL settings of a device that effects that measurement.

From a core memory dump written as a hex string to a XML document.... anything that shows up a difference in the settings that affect the measurement would be fine for documentation.

Something like a big property node readout followed by a format into string .... but make sure not to miss a property.... and a bit more complicated when it comes to signal routing....

A measurement that isn't sufficiently documented is all for naught. 

or

Just think of a nasty auditor

It's so easy to make measurements with LabVIEW, please make it easy and consistent to document it.

Example:

A quick measurement setup with the DAQ-assistant/Express fills Gigabytes but after a certain time they are useless because nobody knows how they where taken. A simple checkbox could add all this information in the variant of the waveform. (or TDMS or ...) even if the operator don't have a clue of all the settings that affect his measurements.

I continually come to your site looking for the DAQmx base API manual and have yet to find it.  I eventually have to dig out an old CD to find my copy.

How 'bout posting these online so that we can help ourselves out of jams?

Thanks,

Jeff

It seems the only indication in MAX that a device is simulated is that under the Devices and Interfaces section, the tiny glyph to the left of the device name is colored yellow instead of being white/transparent.  I end up not remembering what color means what.  It would be useful to add text "Simulated" next to the device name.  It would also help to distinguish simulated devices by having the color of that glyph be green (instead of its current transparent/white) when the device is installed and detected.  Have the color change to red (and keep the existing red X) if had been detected and a device number assigned but is currently not installed/detected.  Then simulated devices being yellow may imply "warning/caution" or "not real".  Perhaps also have a help-hint popup ("Detected" or "Not Detected" or "Simulated") when the mouse hovers over device names.

The title pretty much says it all. I would like the ability to either configure a full hardware compliment as simulated devices then switch them over to real devices when the hardware arrives or go from real devices to simulated devices without the need to add new, discrete simulated devices to MAX.

This would make for much easier offline development and ultimate deployment to real hardware.

Hi all,

Any series card should have a feature listing different  parameters like voltage, temperature etc it supports(May be a property node should be used). so that user can configure the required parameter among the supported.

Ex: SCXI -1520 module can be configured as Strain, Pressure or voltage but this information will be known only by seeing its manual or when a task is created in MAX. But in LabVIEW               Software i cant get this information directly. Because it allows me to configure 1520 as temperature also and we will come to known that 1520 module doesn't support for temperature       parameters only when once tried to acquire.

So what you people think about you.Share your ideas on this please. 

Regards,

geeta 

I rarely have to set up hardware for a new analog measurement and always have to puzzle over the difference between RSE and NRSE modes. I think of the inverting input as the reference, so "Non-Referenced Single-Ended" doesn't make sense to me. And, if I run the AISense line to my remote sensor, isn't that a Referenced Single-Ended measurement?

Yesterday, I noticed that at least some on-line documentation now refers to GRSE (Ground Referenced Single-Ended); adding that single letter helps a lot. What about adding another single letter and referring to the other mode as RRSE (Remote Referenced Single-Ended)? One letter could save a lot of people a lot of time.