NI9476 and PWM

[Penzium]

Hi all,

for a project I have three NI-9476 module mounted on a Ethercat NI-9145. All the slot of the Ethercat module are occupied. In the third NI-9476 module I have some DO channel free.

My client wants to command 9 SCR lines with PWM using the DO free channels. Is it possible to uso only some DOs as PWM via FPGA? Is there some examples online?

Thank you very much.

[GerdW]

Hi Penzium,

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@Penzium wrote:

Is it possible to uso only some DOs as PWM via FPGA? Is there some examples online?

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In the FPGA you can control each single DO channel as you like…

(Keep in mind the NI9476 switches rather slow.)

[Penzium]

How slow? I have to generate a cycle time of 100Hz maximum

[GerdW]

Hi Penzium,

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@Penzium wrote:

How slow? I have to generate a cycle time of 100Hz maximum

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Do you mind to read the manual of the 9476 module? It contains all the information you need!

The spec of the module mentions a 500us switching time, so this module only allows up to 2kHz. This will not give very accurate PWM at 100Hz cycle rate...

[Penzium]

Sorry, you are right I could read the manual. 

Thank you for all the info that you provide me. Probably I have to choose another way to generate the PWM.

Thanks. 

[Penzium]

Small update. I tried yesterday and I was able to command 6 SCR line in PWM with the NI9476 module so it seems ok to use this module to generate 100Hz cycle rate PWM.

Thanks

[GerdW · Accepted solution]

Hi Penzium,

as I wrote before: it's ok, but not very accurate…

(At 100Hz cycle rate you can only output PWM values at steps of 5%.)

[Penzium]

Hi GerdW,

thanks for the response, I don't have alternative is an existing installation with no update possibility so I cannot change or install new module.

I think step of 5% should be ok for our purposes. I will have to control the duty cycle with a PID so I will have to take into account this limitation.

Thanks