Rise Time Measurement with NI PXI-4070

[GM.PTH]

I want to do a rise time measurment with the ni pxi-4070 to get the switching time of a relay!!!

thx

gm.pth

[Brent_R]

The PXI-4070 is capable of operating as a flexible resolution, high speed digitizer up to 1.8MS/s. If this speed is fast enough and you can provide a suitable digital trigger, then the PXI-4070 would be a suitable device. If you need a higher sampling rate or more triggering options, then you should consider one of the PXI-51xx high speed digitizers.

The DMM provides high voltage capability, isolation, and very good accuracy. The PXI-51xx provides much higher sampling rates, higher analog bandwidth, and more triggering options. Depending on the type of relay you are measuring, you may see voltage events less than 1us, in which case the higher speed of the PXI-51xx would be a great asset. The PXI-5122 represents the ultimate in speed, precision, and fle
xibility, however the 5102 or 5112 may be more than adequate for this measurement.

Please take a look at the specifications for the following products and let me know if you have any questions.

http://sine.ni.com/apps/we/nioc.vp?cid=12602〈=US

Regards,

Brent R
Applications Engineer
National Instruments

[GM.PTH]

thanks for your comment!
i know this features! i tried a combination of to example programms, but it does not work properly!
i combined cont. acquisition & chart multiple samples. vi (under dmm in the examples) and pulse and transition measurements.vi (under transition in the examples). so maybe you can help me!

thanks!

mfg

GM.PTH

[Claudia]

Hello,

It seems you are trying to run DAQ examples programs with the NI 4070.

The NI 4070 FlexDMM has its own API, NI-DMM. Please follow this link to download NI-DMM 2.2, currently the latest version of the driver.

NI-DMM 2.2 will install example programs for different programming languages in your computer. Please refer to Start»Programs»National Instruments»NI-DMM»Examples for waveform acquisition examples in LabVIEW and LabWindows/CVI (C based programming language).

NI-DMM will also install the "NI Digital Multimeter Help" file, accessible from the Start menu as well. This help file contains information about the har
dware architecture and features of your NI 4070, description of the programming flow, and full documentation of the API function calls.

Hope this helps,

Claudia Lorente
National Instruments
http://www.ni.com/ask

[Claudia]

GM.PTH,

Reading with more attention your previous comment, I realized that you were already looking at some of the DMM example programs in LabVIEW.

When using the NI 4070 as an isolated digitizer, you need to use the waveform functions. I recommend you to look at the example programs "Read & Graph Waveform.vi" and "Triggered Waveform.vi". You can use the LabVIEW 7.0 Example Finder and browse for these examples in the folder "Hardware Input and Output >> Modular Instruments >> NI-DMM (Digital Multimeters) >> Acquiring Waveforms". You can also look for these example programs from the start menu.

You also mentioned in your comment above that you are using the example program "Pulse and Transition Measurements.vi". That example is exactly the
one I wanted to show you.

I would recommend you to start the waveform acquisition before you switch your relay, so you have enough data that characterizes the shape of your switch pulse. The functions "niDMM Fetch Waveform.vi" and the "niDMM Read Waveform.vi" return the sample data in a waveform data type. You can connect this directly to the "Transition Measurement.vi" (used in one of the cases of the "Pulse and Transition Measurements" example) to measure the switch time of your relay.

As Brent R. pointed out before, keep in mind that the NI 4070 maximum sampling rate is 1.8 MSamples per second, so samples will be acquired aproximately every 0.6us. If this sampling rate is not big enough to characterize the shape of the switch pulse, please consider using the NI 5122 or NI 5112 high-speed digitizers instead.

Hope this helps,

Claudia Lorente
National Instruments
http://www.ni.com/ask

[GM.PTH]

Hallo Claudia!!!

Thanks for your input! I have tried your suggestions before, but they do not work properly, because of timing problems. There is my test.vi attached, maybe you can have a look at it. the problem is that the relay is switched before the dmm is measuring, that is why I cannot "catch" the rise area of my signal. but when I use a sequence structure I have the probelm that the nidmm fetch waveform.vi does its measurement depending on fetch time- out.... and then the relay( respectively bit of my dio card) is switched afterwards. .... I am a beginner with labview, and so i am looking forward to an answer and maybe some help!
thx!

GM.PTH

[Sonya W.]

Hello,

I noticed your post and took a look at your VI. I have a couple suggestions for you, in case you are still working on it.

You are on the right path using the sequence structure. Currently in your program, the DMM enters the Wait-for-Trigger state after you call the niDMM Initiate VI. Next, the sequence structure is executed: (0) a delay in frame zero (1) followed by a software-initiated trigger in frame one using niDMM Send Software Trigger.vi. I assume that this is the only trigger option which you are using.

As soon as the software trigger is initiated, the DMM will begin acquiring the number of samples specified by the "Number of samples" parameter on the front panel.

You need to ensure that your software trigger initiates sampling before your relay is switched. Currently your application does not guarantee this due to two reasons. First, your switch subVI is in the same frame of the sequence structure as the trigger subVI. Second, within that frame, there is no structure or wiring to guarantee that the trigger subVI will be executed before the switch subVI.

LabVIEW uses dataflow programming to determine the order of execution. For additional information regarding this concept, please see the "Block Diagram Data Flow" section of the LabVIEW User Manual (LabVIEW Help menu >> Search the LabVIEW Bookshelf >> LabVIEW User Manual).

To ensure that your software trigger initiates sampling before your relay is switched, I recommend adding one more frame to the end of your sequence structure and moving your switch subVI to this last frame.

When you do this, you may need to increase the "Fetch time-out (ms)" and "Number of samples" parameters on your front panel. If you do not increase these values, you may receive a timeout error or you may not collect enough samples of data to actually capture the relay switching. I would recommend beginning by selecting large values for both of these parameters to ensure that there is plenty of time for the relay to be switched before sampling would stop or a timeout would occur. Then you could gradually reduce these numbers to more closely match the amount of time required to switch the relay.

Please reply back if you have questions regarding this post.

Best Regards,

Sonya W.
National Instruments

[Claudia]

For those out there interested in this application, there is now an example program recently posted by one of NI's Applications Engineers that performs pulse and transition measurements.

Follow the link below:
Making Pulse and Transition Measurements with the NI-4070