Continuous output voltage at DAQ board delivers undesired discrete signal

I am attempting to output a continous decaying signal as seen below.
(For the time being, assume that I must leave the sampling rate at Fs: 1000 and #s: 1000.)
In the loop where the signal is generated, I inserted a 'Wait (ms)' block so that the iterations would maintain the correct timing. If not, the speed of the iterations would be too fast. Although, when I measure the output at the BNC connector, the actual output is in discrete steps, which depends on the speed of the iteration. (e.g. for the above signal with freq = 1/4 Hz, the output would remain 1V for two seconds, 0.5V for one second and 0V for one second, then repeat)
Is there any way to fix this?
Before I attempted this method, I had used the DAQ assistant output, which did not require me having to insert the 'Wait (ms)'. But, the problem with this method was that there was a delay between the time the program sent out the signal and when the BNC output connector received the signal.
I assume the second method did not output in discrete steps because of the buffer which is maintained in the assistant. I attempted to have some sort of buffer for the first method, but was unable for lack of experience I assume. If I was able too, it seems that I might introduce a delay once again, which is undesireable.
Any help on this topic would be appreciated. I will attach a copy of the section that is giving me trouble.
Thanks.
Mike
Solved!
Go to Solution.
Attachments:
Voltage Generation.vi ‏122 KB

Mike310 wrote:
Thanks for the advise Mike.
At the moment, I went back to using the DAQ express, since the signal, while using the same sampling rate, appears nearly continuous on an oscilloscope. Although, as I mentioned previously, this introduced a problem with the signal output at the board being delayed by a few seconds. To compensate, I wired the generated signal to a delay before entering the 'write file to spreadsheet.vi', so that the input signal, which was a result of the generated signal, and the generated signal, would be synchronized on the saved file.
The fact that the DAQ express is taking a few seconds must mean it is doing something to condition the voltage. Without really wanting to know what goes on inside the express VI, I would guess that it actually samples at a much higher rate than you specified to give it a smooth ramp, but keeps the external clock at what you did specify.
Bill
(Mid-Level minion.)
My support system ensures that I don't look totally incompetent.
Proud to say that I've progressed beyond knowing just enough to be dangerous. I now know enough to know that I have no clue about anything at all.

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Hi All,
I am calling a simple subvi that creates a user-defined number of pulses with "Square Waveform.vi." This square wave (with the given total number of pulses) is then used as an input to a DAQ Assistant controlling an analog output signal on a NI USB-6259 DAQ board. I am using Labview 8.5 right now.
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Hi John,
I am running your code over here and seeing
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nonetheless more than once). Sometimes it is difficult to troubleshoot
the DAQ Assistant in cases like this--it is trying to be "smart" and
seems to be avoiding re-configuring its parameters inside the loop.
This is intended to improve loop speed for when customers are
performing continuous operations. In this case, it is performing a
finite generation, and the number of samples generated appears to carry
over from one loop iteration to the other.
It sounds
like you have discovered one workaround for this already: putting a DAQ
Assistant in each frame of the main VI. Two other options that come to mind are:
Use the lower-level DAQmx functions inside
the sub VI. Here you will have explicit control over when the task is
created and cleared, and when parameters are set. You can find
examples of how to use the DAQmx API in the Example Finder at:
Help >> Find Examples... >> Hardware Input and Output >> DAQmx
Write
a consistent amount of samples to the DAQ assistant by "zero-padding"
your signal. For example, instead of writing [10, 1010], try writing
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of samples to generate.
One lesson to take away here is
that the DAQ Assistant is good for basic functionality, but for more
advanced control over the execution and configuration of your task you
should learn to use the lower-level DAQmx functions. In this case it
sounds like the problem is actually a bug. I'll file a bug report, since the DAQ
Assistant is not checking for waveform timing changes even though your
timing is set to Use
Waveform Timing.
Thank you for pointing out this odd
behavior--out of curiosity which version of DAQmx are you using?
-John
John Passiak

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If I understand correctly, you want to retrieve the actual gain value (and, therefore, usable input range) used by your DAQ card for a particular measurement.
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http://digital.ni.com/public.nsf/3efedde4322fef19862567740067f3cc/c93d3954ec02393c86256afe00057bb0?OpenDocument
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Attachments:
pj_pushbutton.zip ‏692 KB

Hi,
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Regards,
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applications Engineer
National Instruments
Attachments:
MostRecentAcquiredData.vi ‏97 KB

7830R digital output voltage

Hi,
I am using a 7830R DAQ card to work with MOSFETs as switches.
We have a 25-MOSFET array. Each MOSFET is controlled by a DIO line of the 7830R card.
When the DIO line is at 0V, the MOSFET is off, and when the DIO line is at 5V, the MOSFET is on.
However, the output voltage automatically drifts to 5V and gradually
turns on the MOSFET if I do not keep updating the voltage of the line.
Can I set the default output voltage at 0V once for all?
Thanks.
Guang

Gaung-
I believe some clearification is in order. Are your DIO lines floating to 5V while your FPGA VI is running or are they floating after the FPGA is reset (usually the cloase FPGA reference resets teh device)? The DIO lines are expected to float when not being explicitly written to. You have a few options:
1) Set the default power up states via the instruction in this post:
http://forums.ni.com/ni/board/message?board.id=170&message.id=221423#M221423
2) Dont reset your FPGA VI when you close it. This will continue to drive the digital lines in thier last state.
3) Use pull down resistors on the DIO lines in question to force lines to 0V when not being driven
Xaq
Applications Engineer
National Instruments

Interfacing LabView compatible DAQ board w/ third party DAQ boards

Dear NI-team and board-members,
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To sum that up, are there physical limitations (e.g. ground loops, damage equipment, shorting) connecting an analog output of one board, to the analog input of another board?
Also, which DAQ of NI might be best suited for my intended purpose, using a NI DAQ board for "simulating" temperature values (etc.) onto the analog inputs of another third party board.
Thank you,
Sandro

Hi Sandro,
If both boards are in the same computer I wouldn't be too worried about ground loops or damaging equipment. The ground reference to the AO board will be the same ground reference as the computer and AI board. You would have to check with the specs for your third party AI board to see what overvoltage protection it has and whether or not our AO board could give a voltage high enough to damage it.
I would suggest one of our AO boards to do the job. Depending on what kind of control and precision you want, we have static update boards available in PCI form. The static board will be cheaper but you are limited to software timed voltage updates (instead of clocked buffered waveform output).
http://sine.ni.com/apps/we/nioc.vp?cid=12550〈=US
I would suggest the AO board (PCI-67xx) instead of our M series multifunction boards because the AO boards have 8 or more output channels. The multifunction boards only have two output channels.
-Sal

Not receiving any signal input with LabVIEW SE, USB DAQ board

Hello all, good afternoon.
I am having a little trouble with my DAQ device, I hope that someone will be able to help me.
I'm plugging a BNC pH sensor to a NI USB 6251 M-series board, to try and obtain the electrical response of that particular sensor, measuring the voltage output for each buffer solution (pH 4 and 7). Have 9.2.3 mx (lastest) drivers.
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I'm measuring in differential mode, as I said both wires of the sensor are going through a voltage follower each, and into the DAQ board. The Op-amps are being powered by +-15v as seen, again, in http://zone.ni.com/devzone/cda/tut/p/id/4494
I did take the time to read the manuals and tutorials I found, did quite a bit of investigation over the last few days, and wired the system carefully.
In labview signal express, I choose to take an analog voltage read, and select input range from -500mv to 500mv, because the sensor should output at most -400mv to 400 mv
Now, much to my dismay labview registers in that channel absolutely nothing, only a little noise (~1 mV). I unplug the sensor and realise that whether the sensor is connected or not, it doesn't make a difference in the presented output - it's as if it the sensor wasn't there at all. And yes, I am measuring the correct channel. I tried connecting the wires to different AI channel pairs as well, could be a faulty one, but no success either.
If I plug a voltimeter to the wires that are going into the analog inputs (after conditioning), it measures about 50 mV, which is a lot more than the 1 mV the board is measuring, but a lot less than the ~180 mV I should be measuring with a pH 4 buffer solution.
I know for a fact the problem is not the sensor, and the DAQ board seems to be fully operational.
I think it might have to do with the signal conditioning I'm doing, or some sort of configuration with the hardware of the DAQ board.
So, any idea what I might be missing?
I'm a week behind schedule because of this, hopefully I will find my answer here.
Thank you very much in advance!

Good afternoon.
Yes I have tried all of that. The board responds very well when a flat 5V DC voltage is fed into a channel.
However after much investigation I believe to have found the problem yesterday, it probably has to do with the operational amplifiers I was using. The input bias current was in the magnitude of nanoAmps, while for pH measurements an IBC of picoAmps or less is necessary due to the high impedance of the sensor. This was causing a drift of over 100 mV on my output which is about 2 pH and thus unnacceptable (even though I had the Bias resistors at the input to ground, like suggested in the NI tutorials, but apparently they were not enough to compensate for the high IBC).
In the lab all available op-amps suffer from this, even Instrumentation op-amps like AMP04 from Analog Devices. I still haven't had a chance to acquire new op-amps with the necessary IBC but hopefully it will do the trick. Makes sense since I checked the datasheets for every op-amp in the lab, and they all had IBC around 400 nanoAmps (and none of them worked), while every single op-amp for every pH meter circuit I found have IBC's of pico/femtoAmps.
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How can I acquire data in a PCI DAQ board using a SCXI rack?

Hello.
I have an acquisition system that consists in:
· 3 PCI DAQ boards:
- PCI-MIO-16-E-1
- PCI-6052-E
- PCI-6034-E
· 3 cables to connect PCI boards and SCXI modules
· 1 SCXI chassis:
- SCXI-1001
· SCXI modules + terminal blocks:
- 4x SCXI_1121 + SCXI_1320 (for voltage analog inputs)
- 1x SCXI_1520 + SCXI_1314 (for strain gauges)
- 1x SCXI_1530 (for accelerometers)
I have been trying to acquire different signals (specially voltage signals that are easier to reproduce) but I haven't been able to do it. I can't read anything from MAX or LabView. I have tested the PCI boards with a SCB68 terminal block (without any SCXI component) and they work properly. Problems appear when I use the SCXI chassis and the SCXI modules. I don't know if there is a problem with the hardware or it is a wrong configuration.
I guess channels in the SCXI modules correspond to analog input channels in the PCI board they are connected to, but I don't know if I have to read data from analog input channels of the PCI boards or from SCXI channels that appear in MAX (I have tried both posibilities, but they don't seem to work).
I don't know if I have to use Differential, RSE or NRSE configuration. I have tried all of them. Sometimes I only read noise, sometimes signal is fixed in a limit value (maximum or minimum, it depends), sometimes it's fixed in a value near zero,... I have changed connections and configuration options so many times I can't exactly say when one thing or another happens.
I have tested only one PCI board with only a SCXI module in order to avoid interaction and confusion. Nothing.
I think I have tried changing almost every option in MAX, but it doesn't work.
I'm sure I'm missing something and solution is quite simple, but I can't find it.
Can anybody explain to me how to connect and configure my system to read any signal? I only need a few steps or highlights. Maybe some clues about what the problem can be.
Thanks!

I have several comments and suggestions:
A) Have you "added a device" in MAX and actually added the SCXI chassis? This step is necessary to get the chassis to work. Click on "add a device" and choose the 1001 chassis . Do this for one DAQ card and one module only initially. The Set Up wizard should walk you through the configuration. If you are unable to add a chassis within MAX, I suspect the chassis is not working correctly.
B) Once configured, you can examine the SCXI channels in MAX as follows:
1) Open the DAQ card in MAX and Open the Test Panels
2) For the SCXI channel to view, use the following convention OB0!sc(n)!md(m)!ch where the letter (n) corresponds to the chassis number in MAX (usually = 1), the letter (m) corresponds to the module number (slot) where the module is located in the chassis, and (ch) represents the channel(or channels) you wish to view. So presuming chassis ID=1, and a module in slot 1, and you wish to view channel 3, you would type the following in the channel field for the DAQ card channel to view:
OB0!sc1!md1!3 (note OB0!sc1!md1!3:6 will display channels 3 through 6)
All of the SCXI channels for a given DAQ card are multiplexed through channel 0 of the DAQ card, Channels 1 and up are not used, hence the initial three characters in the SCXI call refer to "On-Board Channel 0 (OB0)"
C) For the subsequent set up, it will be necessary to first add the additional modules to the chassis (when powered off). Then open MAX and update the chassis. (If you get an error then simply delete the chassis reference in MAX and add a new chassis). You will then be required to set the interface mode of each module as either parallel or multiplexed. In parallel mode, you associate a distinct module with a distinct DAQ card in the host PC. For those DAQ cards that will address multiple modules, you must first configure the modules to be in adjacent slots in the chassis and then assign the first module to the cabled DAQ card - then all of the modules assigned to that DAQ card should be configured in "multiplexed" mode.
D) Once the chassis has been properly configured, you can click on each module and set the gains, filters, and terminal block types.
I hope that this helps to get you started.

DAQmx: Digital - Continuous Output.vi example with PCI-6519 (error -200077)

Bonjour everyone,
Main goal :
I want to use 1 digital output of the PCI-6519 harware to make a staked light indicator blink when user is needed to operate the test station.
What I am trying:
I open the labview 2013 wxample "DAQmx: Digital - Continuous Output.vi" to learn how I could use a DAQmx task to perform this blink instead of using a dynamic call of a VI changing the output in 'while loop'.
The example states that my hardware should be able to run it but I always get an error -200077 right at the beginning with the DAQmx Timing.vi mentionning that my PORT2, line 0 does not support the 'Sample Clock' property which is hard coded in the example. I can't find a different property that this example will accept to try to change the status of my digital output on a time basis. Does the PCI-6519 device support timing for a digital output or not?
If anyone has a better or simplier idea to achieve such a simple goal, feel free to suggest. I am using DAQmx for the first time and I don't know much about what my options are.
Thanks

Hi Nienscecco,
Unfortunately PCI-6519 doesn't support HW timing, I've just tried with a simulate PCI-6519 device and I confirm you that you must specify an external clock in order to use this example.
Do you have some kind of frequency generator to provide it ? Or maybe another NI board with embedded counters in order to build it ?
Thanks in advance for your answers.
Mathieu_T
Certified LabVIEW Developer
Certified TestStand Developer
National Instruments France
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How to generate a pulse of 5 V -ve polarity in synchronisation with a 10 v input using PCI 6251 DAQ board

HI
I want to generate a 5V -ve polarity pulse to trigger my IEEE 1394 camera using an PCI 6251 (scb68 pin E) device, furthermore I am reading a standard Vsync signal from a SVGA port which is 10 v.
Now I want to synchronise the image capture of an IEEE 1394 camera with the Vsync signal so that camera is triggered to capture at every 4th Vsync signal (which is 50HZ.). Presently I am able to read the Vsync signal and also generate the -5 v signal But the Daq board generates a continues -5v signal while I want a 1 ms pulse (for every 4th Vsync).
Also this 5 v signal is generated even if the vi is stopped running.
Can anybody guide me so this problem can be solved.
Thanks a lot in advance
Shri

You can use the Write function, that is you can use the 10 volt signal as a trigger for the task, and when you get this trigger, the task starts and generate (writes) a waveform you defined in an array ("data", in the example).
Something like this..
DAQmxCreateTask("",&taskHandle);
DAQmxCreateAOVoltageChan (taskHandle, clokSource, your_sampling_freq, -10.0, 10.0,
DAQmx_Val_Volts, "");
DAQmxCfgSampClkTiming (taskHandle, clockSource, SAMPLING_RATE,
DAQmx_Val_Rising, DAQmx_Val_FiniteSamps,
samp_to_read);
DAQmxCfgAnlgEdgeStartTrig (taskHandle, input_channel, DAQmx_Val_RisingSlope, 9.0);
DAQmxWriteAnalogF64 (taskHandle, 1000, 0, 10.0,
DAQmx_Val_GroupByChannel, data, //data contain a pulse
&samp_per_channel, 0);
DAQmxStartTask(taskHandle);
// and then you create a loop....
For example you can specify data to be like this:
data[0] = -5;
for(i=1;i<1000; i++){
data[i] = 0;
Tell me if you need more help.....
bye

Analog output to the DAQ that changes when controls on the front panel change

I'm using the PCI-6024E, and trying to output an analog waveform that can change when one of the two controls on the front panel change. It outputs fine setting it to continuous output and using a simple while loop around the "Is Task Done" VI, but if I put the "Write" VI in the while loop, it doesn't output steadily. I then tried to use an event structure, so that I'd only have to write every time something on the front panel changes, but for some reason it was writing finite samples, even though I set the Timing VI to continuous. I looked around the NI site, and found an article about this with an example. I tried to change it around to use my waveform, but whenever I run it, I get a memory underflow error. Has anyone needed to do this before? Thanks in advance.
-- Josh Matloff

Hi Josh-
It looks like you forgot to post the code still, but I'll take a stab at the problem anyway. It sounds like you're looking for a way to update a continuous waveform at runtime.
You will need to stop the task in order to replace the write buffer information, but this will only be a small gap in operation. I have attached a modified LabVIEW shipping example that shows how to use value change events for any of the pertinent waveform parameters to either programmatically stop the task, replace the buffer, set timing and restart or to just pass the task information straight through. This will lead to continuous operation with no breaks at the output.
Please let us know if this clears up your questions.
Thanks-
Tom W
National Instruments
Attachments:
Cont Gen Voltage Wfm-Int Clk with Runtime Update.vi ‏134 KB

How to play a wave file through the DAQ board?

Hi there,
we want to play a wave file that is saved on the harddrive via the DAQ board. Means we want to connect a amp to the analog output of the DAQ to amplify the sound and play it through a speaker.
We couldn't find any VI that does that. Can anybody tell us how to play a wave file, or perhaps even send us a VI that can do that?
Thanks a lot for your help
Martin - Physical Optics Corporation

Hi Martin,
The only example that I could find on how to do this was using our
older Traditional DAQ drivers version 6.9.3. If you're using Traditional
DAQ drivers, the vi can be found here.
The example reads a 8-bit mono .wav file (an example .wav file is included in the .zip file) and writes it to the analog out of your DAQ card. I've updated the
example to work with our newer DAQmx drivers and attached it here.
I hope this helps,
Paul C.
Message Edited by Paul C. on 08-14-2007 05:47 PM
Attachments:
daqmx_wav_file_to_ao_output.zip ‏27 KB

DAQ board for acquiring analog pulses

Hi. I'm using the USB-6251 DAQ board, and I'm trying to record analog Gaussian curve-ish pulses into LabVIEW. Except when there is a pulse, the analog input channel is at 0V. Right now, I've got the trigger working to start acquisition at the beginning of the pulse, but I can't figure out how to stop acquisition when the pulse is over. I've been using the DAQ Assistant, with an Analog Window start trigger, set at the range 10m to 10 V. Is that the right way to do it? I can't get any reference trigger to work to stop the acquisition however. It's set to acquire 5k inputs at 1 kHz and always goes for the full 5 seconds instead of stopping.
Thanks in advance for helping!

Not exactly. It's still picking up pulses separately, but it's including the empty space afterwards (as in, if the pulse lasts only 10 ms, it still acquires data for the full 1 second). Preferably, it would stop acquiring data when the voltage is outside the analog window.
I attached the VI as it is right now, with just a start trigger and no reference trigger. I'm unsure how to configure the reference trigger to have it stop the acquision once the voltage is outside the window again.
Thanks for your help!
Jeremy
Attachments:
DAQ integration.vi ‏90 KB

Continuous output voltage at DAQ board delivers undesired discrete signal

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