Analog comparison/start trigger

Is it possible to use the analog comparison (typ under start trigger) with a continous task that I want to start immediately? I want to take samples from the get go, but then generate the analogcomparisonevent pulse when the values leave an analog window. The way it seems so far is that it will only work if I use that as the start trigger, but then I don't recieve samples until that trigger is reached.
Any help is appreciated.

Hi again Michael,
Here's what I'd do in your case:
1. Set up the analog input task to be continuous.
2. Set up the quadrature position encoder to be hardware timed as well, but use the AI Sample Clock for the clock source. This way, you will still have one counter left and your AI and CI tasks will be synchronized.
3. Set up a "dummy" Counter Output task to generate a single pulse that will be retriggerable. You should be able to use the analog trigger from the AI channel or you can route the signal externally to the APFI line and use that to do the triggering. You can use either the analog comparison event or the pulse generated on the Ctr1InternalOutput terminal as you are generating a retriggerable pulse anyway. Either one should work.
Let me know if you have questions about this.
Regards,
John Bongaarts
AE Specialist - Test Products

Similar Messages

Data acquisition from analog start trigger to analog stop trigger

Hi,
I'm trying to start and to stop a data aquisition by using an analog input trigger. I'm using NI-USB-6251. At input channel ai0 is a sin-signal connected. At input channel apfi0 is an analog trigger signal connected. I can start the trigger signal by pushing a button on my frequency generator. Here's a part of my code:
Hi,
ich versuche eine Messung mit einem analogen Eingangssignal zu starten und zu beenden. Ich benutze die Messkarte NI-USB-6251. An Eingang ai0 ist ein Sinus-Signal angeschlossen. An Eingang apfi0 ist der Triggereingang angeschlossen. Das Triggersignal löse ich immer per Tastendruck auf dem Funktionsgenerator aus. Hier ist ein Teil des Quellcodes:
TaskHandle taskHandle = 0;
int32 read;
float64 *data;
float64 sampleRate = 1000; //Samples per Channel per Second
uInt64 sampsPerChan = 4000; //Samples per Channel to read
int sumOfChan = 1;
double triggerLevel = 2.0;
double min = -0.2;
double max = 0.2;
double timeOutReadAnalog = 10.0;
void calculate()
DAQmxCreateTask("", &taskHandle);
DAQmxCreateAIVoltageChan(taskHandle, "/dev1/ai0", "", DAQmx_Val_Cfg_Default, min, max, DAQmx_Val_Volts, NULL);
DAQmxCfgSampClkTiming(taskHandle, "", sampleRate, DAQmx_Val_Rising, DAQmx_Val_FiniteSamps, sampsPerChan);
DAQmxCfgAnlgEdgeStartTrig (taskHandle, "/dev1/apfi0", DAQmx_Val_RisingSlope, triggerLevel);
DAQmxCfgAnlgEdgeRefTrig (taskHandle, "/dev1/apfi0", DAQmx_Val_RisingSlope, triggerLevel, 3000);
DAQmxStartTask(taskHandle);
if( (data=malloc(sampsPerChan*sumOfChan*sizeof(float64)))==NULL )
MessagePopup("Error","Not enough memory");
//set start and stop trigger
//set breakpoint here
DAQmxReadAnalogF64 (taskHandle, -1, timeOutReadAnalog, DAQmx_Val_GroupByChannel, data, (sampsPerChan * sumOfChan), &read, NULL);
I've choosen the sample rate (1000/s) and the samples per channel (4000), that the aquisition needs 4 seconds to be complete. I can start the aquisition by Start-Trigger, but I think I have a problem with the function DAQmxCfgAnlgEdgeRefTrig. Actually the array will always be filled with 4000 values. I thought I can start the aquisition by triggering once and e.g. after two seconds triggering again for stopping aquisition with result of 2000 values in the array. I hope you can help me with this problem.
Ich habe die Sample Rate (1000/s) und die Samples pro Kanal (4000) so gewählt, dass die Aufzeichnung 4 Sekunden dauert. Ich schaffe es auch die Aufzeichnung über den Trigger zu starten, jedoch funktioniert das Stoppen mit der Funktion DAQmxCfgAnlgEdgeRefTrig nicht. Aktuell ist es so, dass das Array immer mit 4000 Werten gefüllt wird.
Ich hatte mir erhofft, dass ich durch einmalige Triggerung die Messung starten kann und beispielsweise nach zwei Sekunden erneut triggere und die Messung damit stoppe und dann nur 2000 Werte eingelesen habe.
Ich hoffe, ihr könnt mir dabei helfen.

Hi Martin,
I looked over your code and noticed that you called the function without checking the returnvalue.
Try to change the line to the following:
First: define a new int32 value and call it for example: errorcode
Second: The function returns a status code, wich if it fails, includes an error code so save this code in the new generated value
errorcode = DAQmxCfgAnlgEdgeRefTrig (taskHandle, "/dev1/apfi0", DAQmx_Val_RisingSlope, triggerLevel, 3000);
and try to run the programm and read out this value.
If you got this value, please post it here and I will try to help you if I can.
Regards
Philipp

Analog start trigger for x series card gives an error?

Hi everyone,
I am having some trouble setting up an analog start trigger for DAQ using an x series PCIe card (6351)... Attached is my configuration... After reading the manual (http://digital.ni.com/manuals.nsf/websearch/08B4B2E1B5373B94862579BA006E6BAB), my understanding is that AFPI0 is a compatable analog trigger for the device; however, the vi will not run and I get an error... Although if I change the soruce to "Force" (which is ai0) it works..
Also, the device document says (pg 11-8):
"To improve trigger accuracy, do the following:
• Use an AI channel (with a small input range) instead of APFI <0,1> as your trigger source. The DAQ device does not amplify the APFI <0, 1> signals. When using an AI channel, the NI-PGIA amplifies the AI channel signal before driving the analog trigger circuitry. If you configure the AI channel to have a small input range,"
To me, this implies that I probably should use "Force" as the trigger soruce anyway (note that the instrunment is used to acquire data load cell data generated from human muscle contractions; so slew rates are relatively low compared to signals acquired from industrial tests).
Could someone please comment on these issues for me?
Regards,
Jack
LV2010
Attachments:
Untitled 1.vi ‏22 KB

Ok... I think I have answered by own question... APFI0 needs a low impedence signal to drive the terminal... I mistakenly thought this was an internal terminal or trigger...
So I should stick with using the first analog signal acquired in my DAQ device (e.g. ai0) as the trigger source?
Regards,
Jack
LV2010

PXI question: four analog ouput cards to start-trigger simultaneously

Hi all,
Here's the situation:
We have built a system that ouputs 24 analog signals using a PXIE-1073 chassis. It has 5 slots:
Slot 1:          Internal
Slot 2:          Empty
Slot 3:          Empty
Slot 4 (Hybrid): PXI-6733
Slot 5 (Hybrid): PXI-6733
Slot 6 (Hybrid): PXI-6733
As you can see, it has three analog output cards, which occupy all three of the hybrid slots. And we have two empty slots.
Our LabVIEW code is designed to output analog signals on all three cards (at the same rate) using three DAQmx tasks which start-trigger simultaneously. To do the triggering, we setup two of the tasks to start-trigger off of the first task (master-slaves style). In this manner, we can get all outputs to start at the same time. Its actually quite simple.
My question: I want to add another output card. But I am fairly I can only use hybrid slots for my application. I remember working with NI and they told me I had to use the hybrid slots to be able to get the triggers routed automatically along the backplane. Our code actually failed (error) when we used the non-hybrid slots (I forgot the error code).
Is there any way to add another PXI-6733 and have it trigger with the other cards?

I can't speak to the chassis, but I'd warn you that if you want your tasks sync'ed, you'd better share a sample clock too and not just a start trigger.  The onboard clocks will have a tolerance (often ~50 ppm, dunno for your 6733's) and their sampling instants will drift apart from one another over time. In fact, I rarely both with triggers at all for syncing tasks & boards. I'll usually *only* share a sample clock, and then make sure I start all the slave tasks before the master whose sample clock is being shared.
Good luck on your real question though...
-Kevin P

Analog output digital start trigger c api

Hi, I am attempting to start analog output based off a digital trigger (either PFIO, or a PXI line) I can do this easy in LabVIEW. However with the C API (through Python wrappers), the problem isthat when I call DAQmxBaseWriteAnalogF64, the write will always timeout as the acquisition has not been triggered. However, I cannot call this after the trigger occurs, as obviously that will be too late.
I cannot find any C API examples where analog output is triggered off a digital trigger. I can find them for analog input, but that is fundamentally different as you can performan read anytime after the trigger occurs.
Python code as follows (the functions are equivalent ot C API, though you do not need ot pass the task handle as it maintained as part of the Task object)
# create analog output task
analog_output = Task()
analog_output.CreateAOVoltageChan("Dev1/ao0","",-10.0,10.0, DAQmx_Val_Volts, None)
analog_output.CfgSampClkTiming("",outputRate, DAQmx_Val_Rising, DAQmx_Val_FiniteSamps, numSamples)
analog_output.CfgDigEdgeStartTrig("/Dev1/PFI0", DAQmx_Val_Rising)
analog_output.StartTask()
analog_output.WriteAnalogF64(numSampsPerChan=numSamples, autoStart=False,timeout=1.0, dataLayout=DAQmx_Val_GroupByChannel, writeArray=data, reserved=None, sampsPerChanWritten=byref(samplesWritten))
print("Analog output: Wrote %d samples" % samplesWritten.value)
# create digital trigger
dig_out = Task()
dig_out.CreateDOChan("Dev1/port0", "", DAQmx_Val_ChanForAllLines)
# create digital trigger function
highSamples = 1000
numpts = 3 * highSamples
doData = np.zeros((numpts,), dtype=np.uint32)
doData[highSamples:2*highSamples] = 2**32 - 1
# send digital trigger
doSamplesWritten = c_int32()
dig_out.WriteDigitalU32(numSampsPerChan=numpts, autoStart=True, timeout=1.0, dataLayout=DAQmx_Val_GroupByChannel, writeArray=doData, reserved=None, sampsPerChanWritten=byref(doSamplesWritten))
print("Digital output: Wrote %d samples" % doSamplesWritten.value)

Hi PatrickR,
You can review some of the text based NI DAQmx (ANSI C) code examples on generating an analog output using a digital start trigger. If you included/checked text-based support dusing your NI DAQmx driver installation, you can navigate to Windows Start>All Programs>National Instruments>NI DAQ>Teaxt-Based Code Support>ANSI C Examples>Analog Out>Generate Voltage>Mult Volt Updates-Int Clk-Dig Start. If you have any questions/concerns regarding the NI hardware.

Using a Counter as a start trigger to one or more tasks

I am using the NI USB-6251. I want to configure a counter (e.g. Dev1/ctr0) at a user-specified frequency and the rising edge on this counter should act as a start trigger for an analog input task and a digital output task.
I've tried to do this by creating a task for the counter:
integStartTriggerTask.COChannels.CreatePulseChannelFrequency(
"Dev1/ctr0",
"Integration Start Trigger",
COPulseFrequencyUnits.Hertz,
COPulseIdleState.Low,
0,
integFreqHz,
0.5);
and then connecting this to the StartTrigger for the analog input task:
analogReadTask.Triggers.StartTrigger.ConfigureDigitalEdgeTrigger("Dev1/ctr0", DigitalEdgeStartTriggerEdge.Rising);
However running this gives the error:
Source terminal to be routed could not be found on the device.
Make sure the terminal name is valid for the specified device. Refer to Measurement & Automation Explorer for valid terminal names.
Property: NationalInstruments.DAQmx.DigitalEdgeStartTrigger.Source
Property: NationalInstruments.DAQmx.DigitalEdgeStartTrigger.Edge
Source Device: Dev1
Source Terminal: Dev1/ctr0
Task Name: analogReadTask
I have also tried "Dev1/ctr0/StartTrigger" instead of "Dev1/ctr0". What am I doing incorrectly? Thanks.

Hi zkhan.cimtec,
To use a digital trigger for your start task you need to use a PFI line to read a signal that is coming in. You are setting up a task that outputs a start trigger on your counter line, but you can't read off that same line to start the task since that line is already configured for output. An example of how to setup a start trigger coming into a PFI line can be found in the examples here:
<National Instruments Public>\NI-DAQ\Examples\DAQmx ANSI C\Analog In\Measure Voltage\Cont Acq-Ext Clk-Dig Start
Hope this helps,
Kevin

Working of start trigger

i want to know how a start trigger starts the acquisition of data.please give me any example

Hello Christian,
Thank you and Best Regards,
I implemented a advance Measurement and Control system using cRIO-9074
with c-Series I/O cards( NI 9217, 9411, 9264)
I have some questions about it,
(1)- Data rate from FPGA targate to host vi is too low. how can I increase
it, when I run my host VI, sometimes all temperature sensor update at
same time and sometimes one by one, can you please give me some hint, how
can I correct it, I used two FIFOs for NI-9411 digital pulses, I put all
Digital input and all analog output and input in a seperate while loop in
FPGA targate VI.
(2)- I have to write that data to analyse for further result. I tried all
possible way to write data including wite to spreadsheet.vi, write to
text.vi, Data storage.vi, Write to measurement.vi. All this VI work
efficientlywhen it run individualy, But when I connect this VI to
writedata from FPGA host VI. than it always give empty file.
I saw your post in NI discussion forum about how to write data from
Host.vi, But still I am confuse that how can I creat a protocol between
host VI and Fpga target vi. to write the data in a file. I have nearabout
38 channel to write data.
(3)- I have to measure time difference between two digital pulses, to find
a flow rate. I am using counter for it with risisng edge shot.vi, but when
i get a timestemp when there is risisng edge for the second rising edge
how can I get timestemp. Its like i have to measure time between two
pulses, I triend waveform measurement.vi to find cycle period. but it not
worked. any other was to measure it.
I am stuck in this question since from last one month. I already followed
NI-discussion forum solution but it doesnt work. I think the way I applied
is may be wrong.
Looking forward to hear from you soon.
Plese send an additional email copy to [email protected]

Determine analog input task trigger status

I am writing a basic analog input function, which will be triggered via a start trigger sent by another instrument. Is there a way to programmatically deteremine if the Analog Input task has been triggered? I would like to have a Boolean indicator that shows "True" after the Analog Input task is triggered, but I couldn't find out how. Does anyone have a suggestion? Thanks!

Is this a continuous acquisition?
I am not aware of a function querying the trigger state of a task. Nevertheless, i don't think this is necessary as you usually start reading right after starting the input task.
So in case a trigger is late, you will/should run in a time out error. Otherwise, you will get some data which is a clear indication that the task is running....
Norbert
CEO: What exactly is stopping us from doing this?
Expert: Geometry
Marketing Manager: Just ignore it.

DAQ Assistant, Analog Signal to Analog Comparison Event for sample clock

I am using a PCI-6071E and DAQmx. I would like to use an analog signal on PFI0 to trigger Analog Comparison Event to be used as the sample clock in DAQ Assistant. Is this possible and if so, how?

Hi Ben,
You can use your analog signal on a PFI0 line as you are intending. A few pitfalls of doing so are listed in this article. Additionally, this Developer Zone article explains what you are trying to do, and gives and example that you may find helpful. Have a good one!
aNItaB
Applications Engineer
National Instruments
Digital Multimeters

Start trigger 6608

Program works in CVI 8.0
I use several 6225 for analog acquisition and one 6608 for time metering.
For simultaneous start of all devices start trigger must be set up.
DAQmxCfgDigEdgeStartTrig function allows me to connect ai\StatrTrigger of "master" 6225 with PXI_Trig0 and to connect ai\StartTrigger of other 6225 with DevN\PXI_Trig0.
So, one of 6225 defines strarting others devices 6225. For complete syncronization I must tune up start of 6608. This mean, that I shall connect PXI_Trig0 with DevN\Ctr0StartArmTrigger, where DevN - name of device 6608 in system.
What function must be applied for it? Maybe I need fundamentally other method of syncronization?
Best regards, Alexander

Hi Alexander,
To define the source terminal of the Arm Start Trigger in LabVIEW, use the DAQmx Trigger Property Node (see attached image). The C function for the same operation would be DAQmxSetDigEdgeArmStartTrigSrc(). Is this what you're trying to configure?
Regards,
Andrew W
National Instruments
Attachments:
trigpropnode.JPG ‏25 KB

Arrive time of start trigger

Dear all NI high speed digitizer experts:
I am asking how can I read the timestamp of the start trigger? In my measurement I configure my digitizer NI5154 to start a multirecord acquisition by sending a start trigger. Currently I use the timestamp of the first captured waveform as the trigger time. This is not a precise approximation since the time difference between the first waveform and the trigger varies in a few ms range.
Anyone know how to read the trigger timestamp?
thank you.
Lixin

Hello,
The timestamp that you're looking at is actually the software timestamp returned by the NI-Scope driver VI, so you're right that it will differ from when the start trigger on the digitizer hardware is received and when that first sample is returned in software, especially if you have a very long record length.
There are two properties that can help you determine a relative timestamp between records, but is actually a time value of a constantly running counter onboard the digitizer. The "Absolute Initial X" and "Relative Initial X" values that get returned as part of the "wfm Info" on the Fetch VI, will show you the timestamp of the first sample in each record of a particular acquisition and the time from the trigger to the first sample of the record, respectively. Take a look in the niScope Fetch (poly) detailed help and you can see this explanation.
These values are good for comparison between records, but not a good absolute timestamp, because this counter is constantly running and is only reset on rollover or when the board is reset. So, you can see that the values returned may look a little funny, but keep in mind they are values derived from the counter counting a certain rate. So, what you can do is take the first values returned for AbsoluteInitialX and RelativeInitialX and add/subtract them (depending on your trigger type) and make that value your "0" time, and then for each consecutive record, just extrapolate from there.
Hopefully this helps out.
Chris W

Analog input generating trigger on the counter gate to measure frequency

Hello,
I want to measure a frequency on the analog input but it doesn't seem to work.
I'm trying to get it working using DAQmx with the use of ansi c.
The
first step I made was acquiring the information on the analog input.
With the use of a simulated device this shows a sine wave on the input.
My next step was to generate a trigger signal for the counter, but this doesn't seem to work.
I don't see how it is possible to connect the trigger on the analog input to the counter.
For the creation of the analog input and trigger I use the following code:
    DAQmxErrChk (DAQmxCreateTask("",&taskHandle));
    DAQmxErrChk (DAQmxCreateAIVoltageChan(taskHandle,"Dev1/ai0","",DAQmx_Val_Cfg_Default,-3.0,3.0,DAQmx_Val_Volts,NULL));
    DAQmxErrChk (DAQmxCfgSampClkTiming(taskHandle,"",10000.0,DAQmx_Val_Rising,DAQmx_Val_FiniteSamps,1000));
    DAQmxErrChk (DAQmxCfgAnlgEdgeStartTrig(taskHandle,"Dev1/ai0",DAQmx_Val_RisingSlope, 0));
For the creation of the counter I am using the following code:
DAQmxErrChk(DAQmxCreateCIFreqChan(taskHandle1,"Dev1/ctr1",
"",1,2000,DAQmx_Val_Hz ,DAQmx_Val_Rising ,DAQmx_Val_LowFreq1Ctr ,1,4,"");
I hope some one could give me a hint.
I have also tried the examples that come with DAQmx but far as I know this are only counter examples using digital inputs.
Thanks in advance.
Solved!
Go to Solution.

Hi,
You have to use the comparison event output to the counter input. Change this property after the configure channel function.
DAQmxSetChanAttribute (taskHandle1, "", DAQmx_CI_Freq_Term, Dev1/AnalogComparisonEvent);
Regards,
Bas

With DAQmx, how to use AO start trigger for AO/AI synchronization with finite AI sampling

I am a new user to DAQmx and I am trying to synchronize AI (finite samples) with AO in LabVIEW 7.1 using a PCI 6229 card. I want to generate a finite waveform (AO) and, subsequently, collect a finite number of voltage samples (AI). I would like to repeat the AO-AI cycles in a while loop.
Alternatively, I could use an infinite AO generation and collect finite number of voltage samples on AI but always exactly at the same spot of the AO buffer.
Using traditional DAQ and a 6024E card, I used a counter triggered by AO start trigger signal (example attached). I have problems with translating this example into DAQmx.
Please help!
Ruber
Attachments:
AIAODelay_traditional_Eseries.vi ‏155 KB

Lesley,
Thank you very much for your suggestion. Late last night I actually tried a to use AI start trigger instead of AO start trigger and it worked (since I tried the AI & AO to start simultaneously, it does not matter what triggers what), even in the loop. The devil is in details, as I had to carefully wire the number of data points and what to place inside/outside the loop.
The problem with shared clock is that I need to sample the AI and AO at different rates but using AO and AI clock separately did not seem to affect the performance.
I still want to try to use the AO start trigger (as you suggest) because I would like to delay the AI by a few ms from the AO. Is there a simple way to to that?
I suppose, switching from traditional DAQ to DAQmx requires your brain to be rewired - after playing with it for a couple of days and nights I developed a "feeling" for it. One of the differences was that, in order to use this example in the loop, one has to use 'stop task' inside and 'clear task' outside the loop.
Thanks again!
Radek Uberna

Producer Consumer Start Trigger

Short Explanation: I'm using a 3rd party device to send a TTL signal to use as my start trigger in my VI. My cDAQ and modules appear to have the ability to send a start trigger independantly but I have been unable to hunt down how to do this in a producer/consumer system. I do have an idea at the bottom of the long explanation.
Long Explanation:
I'm running a test system that monitors the pressure wave from a hydrogen/oxygen ignition. Components are a cDAQ-9188 with modules 9222 (x3 high speed AI), 9481 (x2 relay), 9402 (x1 I/O Module), 9221 ("Low" Speed AI).
Based upon recommendations in this forum I've placed my DAQ in a producer/consumer architecture.
At this point the system mostly works, I still have a few more things to add for all the information I want to collect. However, it records at high speed and the 9221 and the 9222 modules are synchronized. It has successfully collected good data as of this writing.
When the system starts it will monitor, but not record. I need to fill the test structure with gas to a specific concentration before I ignite/record. When I press the record button I send a TTL signal from the 9402 to my high speed camera and I close a relay on a 9481 which engages a spark system. The spark system takes a variable amount of time to charge and fire so I have a timer that leaves the TTL and the relay active for a half second.
My problem, and it's a small one, comes in with the monitoring system and the synchronization. In order to get the system to synchronize properly I had to generate an external pulse into PFI0 to use as a trigger. I attempted to assign the various clocks available as a start trigger but I ended up with unsynchronized data.
Is there a way to generate a pulse on my 9402 to use as a trigger? It feels silly to me to use an external device when I have something that can generate the signal I need.
In thinking about this post I might have solved my problem, at least in my head. I'm thinking I can move the TTL output VI (which I will eventually change to DAQmx) into the producer loop and move my true/false statements to the consumer loop as a 1D array within my queue to start the record. Probably more to it than that but I can only learn by experimentation right?
Thoughts? Recommendations?
VI attached.
Solved!
Go to Solution.
Attachments:
HUCTA Controls.vi ‏186 KB

You can't generate a pulse with the 9402 itself. The pulse would actually be generated by the 9188. You should create a Counter Output task to generate a pulse train. Try the attached example as a start point to experiment with the counter.
This Vi is for LabVIEW 2013, if you have an older version let me know and I will try to convert it.
Camilo V.
Applications Engineer
National Instruments
www.ni.com/support
Attachments:
Pulse Train Generator.vi ‏18 KB

Using DAQ occurrence to wait for start trigger

Hi,
I'm trying to use digital triggers to start and stop datalogging. Every time start trigger appears, new file is created and data is acquired to file until stop trigger occurs. Now I'm using set DAQ occurrence and wait for occurrence functions to wait for start trigger before creating a new file. The problem is that after first stop trigger this occurrence method doesn't work. I believe it's because AI is not cleared and configured before calling DAQ occurrence again. Number of scans acquired is not zero, if I don't clear and configure AI again? Am I right?
Do I have to clear and init AI everytime before occurrence config or is there a better way to make program wait for start trigger?
Thanks in advance,
Jakke

Hi Matt99eo,
Have you configured your device for triggering? Although you have not mentioned your device specifically, the M series user manual provides a great explanation of digital triggering. Using the DAQ Assistant, this can be configured from the triggering tab. Hopefully this helps!
Regards,
h_baker
National Instruments
Applications Engineer
Digital Multimeter Resources

Analog comparison/start trigger

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