square wave

[pbr_forum]

Hello,

Does anyone have any tips on how to generate a square wave on RSLogix 5000?
Thank You!

 

[Bob O]

Turn the output on and off?

 

[bernie_carlton]

A 'square wave' is a digital output with equal ON and OFF times. Set up a a self re-triggering timer. Set the preset to the total ON plus OFF time. Turn the output on when the accumulated value is less than half of the total time.

 

[Ron Beaufort]

I'll assume (gosh, I hate that word) that you might be asking about an analog square wave ... if so, the attached screen shot might be helpful ...

.

 

[jimbo3123]

If you are concerned with accuracy, you should look at putting your logic in a periodic task (vs. a continuous one).

 

[nwboson]

If you are concerned with accuracy, you should look at putting your logic in a periodic task (vs. a continuous one).

Or use a dedicated high speed output so your square wave (digital) is dead on....

 

[jimbo3123]

Or use a dedicated high speed output so your square wave (digital) is dead on....

That would be even better. Perhaps necessary depending on the accuracy or frequency requirements.

 

[pbr_forum]

Wow thanks everybody for the helpfull tips.
I'll be a bit more clear on what I have to do:
I have to generate a square wave to modulate the pH of a system. The pH must varie from 7.4 to 8, and the periode is 6hrs. I would like to generate a square wave in a Function Bloc Diagram by only using Elements (no LADDER). So is there a block that would generate a TRUE(for 3hrs) or FALSE(for 3hrs) automatically (because it has to run for a week, so I can't turn it on or off manually)...?

 

[pbr_forum]

A 'square wave' is a digital output with equal ON and OFF times. Set up a a self re-triggering timer. Set the preset to the total ON plus OFF time. Turn the output on when the accumulated value is less than half of the total time.

So it's like you said sir. Except that I need to find a way to set the output on and off automatically...

 

[Karsten]

Wow thanks everybody for the helpfull tips.
I'll be a bit more clear on what I have to do:
I have to generate a square wave to modulate the pH of a system. The pH must varie from 7.4 to 8, and the periode is 6hrs. I would like to generate a square wave in a Function Bloc Diagram by only using Elements (no LADDER). So is there a block that would generate a TRUE(for 3hrs) or FALSE(for 3hrs) automatically (because it has to run for a week, so I can't turn it on or off manually)...?

Wait now, Is really the square wave your biggest problem here? What makes the pH change?

 

[pbr_forum]

I have a control loop that regulates the pH by introducing/cutting CO2.

 

[TConnolly]

Look at using the TONR instruction to trigger a flip flop every three hours.

Something like this: