Adding Delay to 9225 module for signal to match 9215

[cwildmann]

I am working on a VI to acquire voltage signals for performing tests on a generator set.  We are using cDAQ-9172 and 9178 chassis.  For monitoring the voltage of the generator we are using NI9225 modules and for monitoring the current, we have current transformers sending a 5V signal to a NI9215 module. We have set everything up so that the two modules are in the same chassis for synchronous readings.  But we are having a problem with the signals between the two chassis not being synchronized due to the Delta Sigma ADC being different between the 9225 and the 9215.

To confirm the delay between the two modules, we jumpered the same 5V sinusoid waveform to the 9225 and 9215.  The delay between the 9225 and the 9215 was confirmed to be 0.0039s as described in the 9225 manual (fs = 10000; input delay = 38.4/fs + 3us).  Also see attached for "Sync VI Waveform" to show the delay between the two modules.  The red waveform is from the 9215 and the white waveform is from the 9225.

So my question is how do I implement a delay to the 9215 waveform so the two are synchronized?  I have attached a screenshot of my VI ("Sync VI") - just a very simple VI to acquire the signals from the two modules and to display and record the waveforms.  I have already read the knowledgebases on "Why is my data delayed when using DSA devices?" and "How to compensate for different group delays with C series modules in LabVIEW FPGA." but am still very confused as to how the delay should be implemented to the one channel.  I cannot delete data to try to synchronize them as the waveforms will be used for RMS votlage and current calculations later on.

Your help is greatly appreciated.

Chris

[Brian_P]

Hi cwildmann,

Thank you for posting to the forums.  The best way to accomplish this is to add the delay that is mentioned in the "Why is my data delayed when using DSA devices?".  You will first need to do a manual synchronization of the DSA device and the multifunction device.  You can then perform an extra read of the DSA device that is equivalent to the delay.  Once you perform that extra read you DSA and 9215 will be synchronized.  You can even keep the data from that extra data if you don't want to lose any data.  This would be the same as adding a delay to the 9215, instead we are just starting the DSA device earlier which in a sense is just delaying the 9215.  I hope that I explained this well enough, please let me know if you have any questions.

Regards,

Brian P. 

[manel549]

Good afternoon

I have the same problem synchronising modules 9215 with 9225, but in my case i'm using a Crio 9074. I've read in NI forum, that i have to apply a filter to delay the acquisition of the module 9215. My doubt is which filter apply and where apply it. In appendix i make available my fpga code and a screenshot of my waveforms, where the yellow one is acquired with the module 9215, and the red one is acquired with the module 9225. if someone could help me or have a alternative way of synchronizing the two modules, please let me know. Thanks in advance.

Best Regards

[Ficare]

Hi,

Is the extra reading described in "Why my data Delayed ..." still works if we read data in waveform ? I seems not... I think the best way is to measure the delay (with a jumper between signals) and then change t0 (substract the offset) of the DSA waveform.

Any comment ?

[Branch_Support-NIC]

Hello Ficare,

You can create waveform data from array data by specifying a t0 and dt. Since this is the case you can get waveform data from both channels, pull the Y-array out of the waveform cluster and take a subarray of it (removing the samples that are not needed) then replacing that array back into the waveform cluster. The jumper idea you have is viable but this can be done programmatically since we know how many samples make up the delay difference between the two waveforms.

Regards,

-Travis E