Starting a trigger measurement

[minghuo77]

Hello,

I'm new to LabView and I want to measure 6 channel of analog signals using NI 9220 16-channel analogue input module (DAQmx Acquire Analog input). However in the pull down menu "Trigger Type" I cannot select any trigger except "software" (please seeattachment). My question is: how can I activate the trigger function?

I thank you in advance for your help...

Ming Huo

P.S: the configuration of the system is:

- LabView 2011

- NI cDAQ-9174 chassis

- Ni 9220 16-channel analogue input module

[Zach J]

Hello minghuo77,

It appears that Measurement and Automation Explorer does not allow you to configure a triggered input with the NI-9220 module.  However, in LabVIEW itself, this is possible.  I have provided a link to a document below that I believe may be useful for you to understand how to set up a triggered input in LabVIEW.  When you have time, please review the document and let us know if you have any questions!

 Tips and Techniques in Data Acquisition Triggering - NI-DAQmx

[minghuo77]

Hello BluesKnight,

Thank you vera much for your useful information.

I also tried to trigger a measurement with NI 9237 (4-Channel, ±25 mV/V, 24-Bit Simultaneous Bridge Module). the configuration of the system is (I only used one channel of NI 9237):

• LabView 2011
• NI cDAQ-9174 chassis
• NI 9237, 4-Channel, ±25 mV/V, 24-Bit Simultaneous Bridge Module

However I have the same problem: in the pull down menu "Trigger Type" I cannot select any trigger except "software".

Last Thursday I fund  In LabWIEW SignalExpress that beside the menu "Step Setup" there is a pull down menu called Recording Options in which I can select "Start Condition" to configurate a trigger measurement. I clicked "Start Condition" and then "Signal trigger". I selected "Rising slope" with a Trigger value of 30 mv. It did not work. However as I read the description of "Trigger type" (please read the sentences marked with red color below) I got confused. Why does the trigger in "Start Condition" stops logging when the signal crosses the value? Or it should stat logging! Am I right?

Thank you for your conformation in advance.

Regards,

MingHuo77

Trigger type—[Condition type: Signal trigger] Specifies the behavior of the Signal that triggers LabVIEW SignalExpress to stop logging. You can select from the following options:

       Rising slope—(Default) Stops logging when the signal crosses the value you specify in the Trigger value field with a positive slope.

       Falling slope—Stops logging when the signal crosses the value you specify in the Trigger value field with a negative slope.

       Entering window—Stops logging when the signal enters the window between the values you specify in the Higher value and Lower value fields.

       Leaving window—Stops logging when the signal leaves the window between the values you specify in the Higher value and Lower value fields.

[Zach J]

Hi minghuo77,

It appears that the documentation you have found does not reflect the latest documentation on Step Setup in SignalExpress.  For your reference, please refer to Page 4-4 of the following document, which mentions that the Trigger Type for a Start Condition is a condition to start logging.  I will submit a Corrective Action Request concerning this documentation to get it fixed in the future.

Getting Started with LabVIEW SignalExpress

In SignalExpress, the triggering options are very limited when compared to LabVIEW itself.  I would recommend that you perform your triggering functions within LabVIEW instead of SignalExpress if you can.  You can refer to the documentation provided in my previous post to accomplish this task.  

[minghuo77]

Hi BluesKnight,

Thank you for your confirmation and advice.

Actually I succeeded yesterday in using SignalExpress to make a trigger measurement. However your right that the function for data acquisition in SignalExpress is very limited. I will start today to use LabVIEW to accomplish my task.

Have a nice day.

MingHuo77

[minghuo77]

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@BluesKnight wrote:

Hi minghuo77,

It appears that the documentation you have found does not reflect the latest documentation on Step Setup in SignalExpress.  For your reference, please refer to Page 4-4 of the following document, which mentions that the Trigger Type for a Start Condition is a condition to start logging.  I will submit a Corrective Action Request concerning this documentation to get it fixed in the future.

Getting Started with LabVIEW SignalExpress

In SignalExpress, the triggering options are very limited when compared to LabVIEW itself.  I would recommend that you perform your triggering functions within LabVIEW instead of SignalExpress if you can.  You can refer to the documentation provided in my previous post to accomplish this task.  

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Hello BluesKnight,

As you suggested I am trying now to create triggering measurement with LabView block diagram. I generated at first a code of 6-channel analog measurement with help of DAQ Assistant, then I added the Trigger VI of Start Analog Edge (falling slope) to the block diagram (please see fig. 1 in attachment). After running the program I got the error message shown in fig. 3 (invalid analog trigger source). I changed the Source Wiring shown in fig. 2. Here my question is: what should I put in the "Trigger source"? If I put DAQ Assistant_0 in it, or cDAQ1Mod3/ ai0, I got the same error massage shown in fig. 4. Then I established a new NI-DAQmx Task with the name of Force Measurement-2 and 6 global VI-Channels  (please see fig. 5 and 6 ). Running this program I got again same error (invalid analog trigger source). Without trigger all programs run well.

Could help me to solve the problem? Thank you in advance.

Regards,

Ming

[Zach J]

Hi minghuo77,

It appears that only two modules on the cDAQ support analog triggering like you would prefer.  These are the NI-9205 and NI-9206.  

Does NI CompactDAQ Support Analog Triggering?

Since this is the case, do you need to perform the triggering or can you continue sampling and record the data that you need without a trigger, then post-process the data to obtain the necessary signals?  Another option is to gather samples and test to see if the samples cross a threshold.  If they cross that threshold, they can be then logged to a file.  It would require a bit more logic and decision making but it is an alternative to triggering.  

[minghuo77]

Hello BluesKnight,

Thank you for your advice.

Using a triggered data acquisition is the best solution for my case. Is it allowed me to use a digital trigger?

The configuration of my system is:

- LabView 2011

- NI cDAQ-9174 chassis

- Ni 9220 16-channel analogue input module  

If the digital trigger is allowed, which way is simple, digital trigger or the way you suggested to me (Another option is to gather samples and test to see if the samples cross a threshold.  If they cross that threshold, they can be then logged to a file.)? Thank for your help.

Regards,

Ming

[Zach J]

Hi minghuo77,

The NI-9220 has no triggering capabilities at all.  It would be best, if you want to use this card for your purposes, to perform a continuous acquisition and check to see when the samples cross a threshold.  When they cross this threshold, you can log the data to a file for post-processing.  This test could essentially be a comparison between a numeric value and the signal.  If the signal crosses this numeric boundary, a case structure could have logic within to write to a file.  When the signal is within the boundary, the case structure would sit on an idle state.