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PWM Update Rate using PXI 7334 & 6602 cards

I have a NI 8176 controller and a PXI 7334 (FlexMotion) Motion Controller Card. I am using the PWM output to control an actuator and I would like to update the duty-cycle as frequently as possible.

I have the card PWM frequency set to 32 kHz, but can only achieve 1.5 kHz update rate.

The attached VI shows the code I'm using to write to the card.

I also have a PXI 6602 card, I can achieve an update rate of 6.5 kHz with that, but I bought the 7334 card with the expectation of achieving a faster update rate.

Any advice on how to improve the update rate of either card would be appreciated. Likewise, does anyone know another hardware set-up that would be a viable alternative?

Many thanks,

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You may want to try this firm ware update which will let you use the PWM output of the 7344 as if it were a servo axis. I believe this may give you the faster control you are looking for.

NI Application Engineer
Message 2 of 5
Thanks Amaury,

I went to:

Support > Product Reference > Drivers and Updates > Current Versions - Motion Control > NIMotion/Flexmotion Version 5.2 for windows 2000/95/98/ME/NT/XP

I have successfully upgraded my firmware. I now need example code to show how the PWM output can be updated as if it were a servo axis.

At the moment, using the code posted above, updating just 1 channel, I can only manage an update rate of just 3.6 kHz.


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Sorry to take so long Brain, I was just looking through some old posts and noticed that I had never given you the firmware you actually needed!

Try this!
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Hi Amaury, thanks for the fp2 file, I’ve just moved site, got my lab back yesterday. (please watch the numbers 7344 and 7334 in the text below!)

The FPGA2 firmware I had was Version 5.20.0001, MAX would not allow me to select the file 7344pwm.fp2, I got the message “This file is not valid for the Flexmotion board selected”.

However, I went to C:\Program Files\National Instruments\Motion\FlexMotion\bin and deleted 7344.fp2
I then renamed 7344pwm.fp2 to 7344.fp2 and copied it to the “bin” folder, then in MAX I selected new file to download, pointed to 7344.fp2 and successfully download the new firmware to my 7334 motion controller. Now in MAX the FPGA2 firmware version is 5.20.000f.

Unfortunately I c
an still only update the PWM duty-cycle on my 7334 at 3.6 kHz!

Is this correct? do I need to update the file 7334.fp2 instead? or does the file 7344pwm.fp2 also work for the 7334 card?

Also, is it possible to generate a PWM using the stepper motor output in open-loop mode? If so, do you have example code on how this is done?

Thanks again for your help,

Ray Farmer
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