niFGEN_InitiateGeneration() and relay is PCI5412 card

[Vasilich2004]

Hi,

I have 2 similar programs. One is written in VC and uses niFGEN_InitiateGeneration() function to start generation.

Another one is written in LabVIEW and uses niFGEN Initiate Generation.vi to start generation.

I hear a click when VC program run and niFGEN_InitiateGeneration() function generates the click. I don't hear any click when LabVIEW program works.

Definetely, PCI5412 card has a relay and it generates the click. Also definetely, relay on/off eats  so much time.

Please, any idea to avoid that?

[David S.]

Hi Vasili -

I'm not aware of any relays in the design of our AWG boards.  Are you certain that the clicking noise is coming from the 5412?  I'm also fairly sure that the C command is identical in function to the LV one, but I'll check with our development team to be sure.  In the meantime, could you post the test code you ran in LV and C to generate the discrepancy?  If there are any "unnecessary" sections to it, I recommend eliminating them.  In fact, you should try running a program in each language that does nothing more than the following:

1. niFgen Initialize
2. niFgen Initiate Generation
   
3. niFgen Close

And make sure no cabling is connected to the front of the device.  Does it still click and introduce a delay?

[Vasilich2004]

I can't do test right now. I am pretty sure that click comes from PCI 5412. We have another system that have PCI5411 (VBasic 6.0) and there is click too.

When I will have chance I will do test.

[kirsch]

The NI-FGEN LabVIEW VIs are basically nothing more than wrapper VIs that turn and call the corresponding C functions, so they behave the same way.
Check both your programs carefully, you must be configuring the board differently. All our AWGs have relays so they can achieve the desired gain by switching in and out a series of amplifiers and attenuators with the best possible analog performance.

Good luck
Marcos

Message Edited by kirsch on 02-19-2007 09:24 AM

[Vasilich2004]

Thank you - Marcos. You helped me second time.

>> All our AWGs have relays so they can achieve the desired gain by switching in and out a series of amplifiers and attenuators with the best possible analog performance.

I waited relay only in output of AWG channel.

Yes, C program changes gain. When generation stops AWG produces tha latest value. So I am not only stop generation I also play 0-value waveform with minimum points and set gain = 1 that is not equiled previous vaweform. (I think this is well done behavior.)

And last, time to time NI's hardware manuals haven't enough information.

[Vasilich2004]

Marcos hi

I thought a little ...

I suppose this card has just output relay. It is imposible that this type gain has relay. It can be if the card has set of gains. In this case when any gain can be setting it is implemented on DAC. 

So ... when I change gain driver switch off output relay, changes gain and switch on relay again. Can you ask NI developers?

Thanks, Andrei.

[kirsch]

Andrei

All NI 5412 cards use a set of relays for gain selection. This applies to the 5421, 5422, 5441, 5402, 5406 as well, since they all have a very similar analog front end, based on the same architecture.

This is what the analog path looks like, in a simplified manner, when it comes to gain control:

1. There is a fine gain control with a 0 to -3dB swing on the main DAC. No clicks will come out of changes in this.
   
2. 0, -3, -6, -9 dB pre Amplifier attenuators that are switched, any change on this attenuation will glitch the output but may not cause an audible click due to the type of relay used.
   
3. Another relay selects between the Low Gain Amplifier and the High Gain Amplifier. You will hear this one click.
   
4. 0, -12, -24 dB post Amplifier attenuators are selected with yet another relay. You will also hear this one click.
   

After all of this there is another relay for Output Enable. I guarantee that on the 5412 output is not disabled when you change the gain.

The driver selects the best combination of fine gain control, pre Amplifier attenuation, Low/High Gain amplifier and post Amplifier attenuation, combined with calibration constants for the specific device in order to give you the desired gain. So depending on how the gain changes, you may or may not hear a click from a relay.

I know all this first hand because I am part of the original R&D team for the devices listed above, including the NI 5412.

I hope this helps. If it still doesn't help you solve your issue, your best bet is to send test code to the Application Engineers to have them analyze and compare the VC and LabVIEW code.

If you determine that the relay switch is after all expected, and you must eliminate it, you should look into the Digital Gain property in the driver.

Marcos

[Vasilich2004]

Marcos hi,

Your answer really surprised me.

You wrote about the same approaach what I means, like DAC. I couldn't image this.

Thank you very much for your explanation.

I hope I will not have problem with system. When I will have chance (now system is used) I will set max gain in setup time and will tune waveform (less then -1 -> +1 V). Currently, I try to have max accuracity and I prepare waveform ( always == -1 -> +1 V) and tune gain.

Thank you again, Andrei.