Hardware timed Dataacquisition with cRIO

hi,
i am trying to develop a code for dataacquisition using cRIO. my application specifications are:
Digital Input: 1 (trigger for acquisition, i have a cRIO-9401 DIO module
Analog Inputs-2 (i have cRIO-9215 and also cRIO-9221 AI modules for this)
i need to develop a code in which the acquisition is triggered by a pulse signal of Period=20 ms and On-time=1 ms on a falling edge
the two analog inputs are: a current waveform which is on when ever there is a trigger and shuts-off on the falling edge

Hello,
By running the VI for a second time, you mean, stop the whole Host VI and the re run it? Or just trigger it for the second time? When you say that it reduced, you mean in Amplitude or the number of samples? I ask this because you have "Data read" that once you write a True to it, it will always be true. You never set it back to False, so the FPGA keeps running all the time, overwriting the "AI Data",
Ricardo S.
National Instruments

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Hello,
I am trying to measure frequency using NI 9402 in NI cDAQ9178 chassis. I am setting the clock for my counter channel to be my chassis ai Sample Clock.
I am able to measure frequency above 20 Hz. For frequencies less than 20Hz, I get the following error:
DAQmx Error: Multiple Sample Clock pulses were detected within one period of the input signal. Use a Sample Clock rate that is slower than the input signal. Ifyou are using an external Sample Clock, ensure that clock signal is within the jitter and voltage level specifications and without glitches.Task Name: _unnamedTask<0>
Status Code: -201314
Setting the Rate to 1 also not does resolve the issue.
OTHER DETAILS:
* Running on 64 bit, Win7 platform.
* NIDAQmx Driver Version: 14.5
I had posted regarding this earlier and I was told that this might be because the counter is armed immediately before the first sample is taken. The recommendation was to add a hardware-timed delay using the DAQmxSetStartTrigDelay method to the AI task. I have added this delay but I still receive the same error message. The previous post I had mentioned can be found below:
http://forums.ni.com/t5/Multifunction-DAQ/Cannot-measure-frequency-below-20-Hz-on-a-NIDAQ-9178-chassis/td-p/1537274
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Regards,
Varun Hariharan
The MathWorks

Alright so I got everything working correctly in both C and LabVIEW code.
The problems is in fact with the first sample, as John_P1 suggested. You simply need to delay that first sample from being requested. It is simple to do this in software instead of hardware.
If you are using CVI, just add #include <utility.h> to the top of your .c file and then add a delay before your DAQmxErrChk (DAQmxStartTask(AItaskHandle)); line.
Comment out / remove the DAQmxSetStartTrigDelay(AItaskHandle,10); line, as it wasn't doing what we thought it would. (Hardware delay).
I added Delay (.05); to delay long enough for the full period of the input signal at 20 Hz.
Depending on your frequency, this value may need to be adjusted. 100ms wouldn't be a bad idea.
This is expected behavior, and I don't think we need a CAR.
Let me know what you think!
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Hi everyone,
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hi, thanks for responding.
with using example of dynamic generation with script, I can manage to generate the ramp with controllable delay (generate the whole waveform, including delay with script command, then write to the card).
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How can I use a USB camera with cRIO 9022. Please see my strange problem.

Hi,
I would like to use a USB camera with NI cRIO 9022. I used the same USB camera with NI USB 6216 DAQ device and developed a VI(within a PROJECT and outside it). So, It is working fine with NI USB 6216 device when I use the Vision Assistant Express VI and gets detected in its Initialization Window. Please see JPEG File 3 where I get NO ERROR.
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Attachments:
NI Vision Acquisition Express Error for NI cRIO 9022.JPG ‏39 KB
IMAQ and dx Modules Installed on my NI cRIO 9022 hardware(No NI Vision Acquisition 2010 SP1).JPG ‏82 KB
NI Vision Acquisition Express NO Error for NI cRIO 9022.JPG ‏48 KB

Only GigE comms are supported on the cRIO Real Time OS. Have a look at the following:
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Hi all,
As part of a complex project, I must implement an acquisition hardware interface for a linear motion sensor using the Synchronous Serial Interface (SSI) output common in industrial motion control. (I have a fair bit of experience in digital electronics, but I'm new to hardware timer-synchronized digital I/O in LabVIEW.)
To do this, I need to create a hardware-timed bursted pulse train TTL clock signal. Each burst consists of 25 high-low transitions with a full-cycle period of 2.67 microseconds (375kHz). The output must then be held high until the next burst, which occur at 1ms intervals.
Using cDAQ timers and a NI 9401 (based on the example at http://www.ni.com/example/30256/en/), I've been able to create the pulse train burst as described (see attached VI image). Next I need to configure another timer to trigger this burst to repeat at 1ms intervals.
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Go to Solution.
Attachments:
Hardware Timed Pulse Train Clock.jpg ‏102 KB

Hey Ryan,
A picture of the behavior you are seeing would be helpful. The NI 9411 should only be reading 50 bits every 1 ms.
It may not be possible to read 25 bits (do you mean 50 bits? 25 high 25 low) and push it to a queue without encountering an overflow error. If you take a look at the above code the digital input will receive 50 sample clocks every 1 ms. This is equivalent to acquiring 50 points every 1 ms which is an acquisition speed of 50 samples/1 ms=50 kHz. The read loop must keep up with the 50 kHz rate otherwise the buffer will overflow. In the above example I’ve set the read to pull 5000 samples (x) with the assumption that the loop will take less than or equal to .1 seconds (y). This yields a software acquisition speed of 50 kHz (5000 samples/100 ms). If the loop speed is faster than 100ms then the 10 seconds timeout on the DAQmx read will allow for the read to block so the FIFO may be filled.
The options available for question 2 are below. They may be used separately or in conjunction.
Move the DAQmx Read for the NI 9411 to its own independent while loop, set the DAQmx Read to acquire 50 samples, do not graph the data, and pass the data to a Queue for processing in a consumer loop. This will increase the loop speed which may allow you to keep up with the 50 kHz acquisition speed. This may not work because the loop speed will need to be 1 ms or less.
Increase the value of the Samples per Channel control that goes into the DAQmx Timing VI. This will increase the DAQmx Software Buffer size. This buys time until you receive an overflow error because the DAQmx Software Buffer is being filled faster than samples are removed.
Read in 5000 sample chunks (producer loop), push this to the queue, and perform the analysis in 50 bit chunks (consumer loop). The additional queue created should allow for the acquisition loop to keep up.
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PXIe-4141 hardware timed 4- channel sweep

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•Once the sequence runs Sequence Loop Count times, the operation is complete, and NI-DCPower generates the Sequence Engine Done event, as shown in the following figures.
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The figure could you find in the screenshot.　
You can find a screecshot in the attachment.
Regards,
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Attachments:
Help PXIe-4141.png ‏250 KB

Starting out with cRIO

Hello,
What's the most inexpensive way to start programming for FPGA cRIO based applications? I'm interested in learning to develop for an FPGA and cRIO but can't afford the cRIO, is there an inexpensive way to simulate for these (I think even the realtime drivers may be expensive)
I found this RIO eval kit, but I'm not sure if it's what I need to start learning cRIO/FPGA LabVIEW development?
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Go to Solution.

Yes - I agree with GerdW that the myRIO is a great way to get started with cRIO & RT/FPGA programming. It's very easy to set up and use.
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Certified LabVIEW Architect, Certified TestStand Developer
NI Days (and A&DF): 2010, 2011, 2013, 2014
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