cRIO scan mode PWM frequency --- more options possible??

[MarkCG]

Hi all, 

I notice that if you want to use a digital out module for PWM in scan mode, you can only select a few frequencies: 1 Hz, 50 Hz, 250 Hz, 500 Hz, 1 KHz, 5 KHz and so on. 

I need to control a device that only accepts a PWM signal in the range 60-100 Hz. Is there any way to do a scan mode PWM frequency OTHER than those option? Is there something I can tweak? 

[Aldo_A]

Hi MarkCG,

Since you are working with Scan Mode, you can change the period of the Scan Engine from the Project Explorer >> right-click your cRIO Target >> Properties >> from the left-hand menu, select Scan Engine. You can define the Scan Period from here but keep in mind that the Scan Engine will be able to do only 1kHz max frequency. I hope this helps!

[MarkCG]

Sorry Aldo, I may not undestand correctly. I understand the scan engine update rate. But what does that have to do with the PWM frequency you select? Could you not have a 5 kHz PWM signal being generated on one channel of a DO card, while the scan engine runs at a rate of say, 1 Hz? Doesn't the scan engine rate just affect the rate at which said PWM output's duty cycle (pecent time on /off) can be updated cia your LV code running on RT?

[Aldo_A]

Hi Mark,

I apologize for the mixup. To be able to set the frequency of the PWM to a user defined frequency, you will have to use the cRIO in FPGA Mode instead of Scan Mode. Using the cRIO in Scan Mode limits the frequencies we can select. In addition keep in mind that there will be a hardware limitation depending on which module you are using for output.

[MarkCG]

Thank you for the answer Aldo. I guess I might have to do that then!