i am look to build some sort of AUTO balancing of a room that needs to be a negative pressure by using 2 fans, 1 input fan and 1 extract fan - these are controlled by drives(vsd's) the input fan will be a fixed speed and the extract fan needs to be controlled by PI on the LOGO via 0-10v 

i will be using a 0-10v pressure sensor within the room to read -50Pa to 50Pa and the setpoint needs to be -10Pa but the extract fan will only move within some limits of say 30hz to 40hz but this i can scale on the drive its self.

i have tried using the PI controller but it does not seem to move the output.

any help thanks

p.s

the input fan is not controlled by the LOGO

yup your correct:

:)

ixo65

I do not know where to start ...
I do not want to spoil your attempts.

My question:
What should the two ramps do? You must have thought something about using them.

You do not scale the sensor value. So the actual value can never reach the value of -10.
In addition, you still scale the analog amplifier with other values.

All in all, the program is unfortunately not to be understood ...

And based on your program, I can not offer you help for your program because I do not understand it.

I can only offer you help for a new program. But first I have to know what you thought.

 the first ramp is because of the sensor fluctuations and this smooths it a lot and the second ramp is to ramp the output to the drive because i need to control the drive speed in small steps because i have already set the acceleration & deceleration speed on startup of the fan.

because of the nature of the pressurised cabin the pressure will vary very much to reach -10Pa and will move around constantly to try and achieve this set point so a ramp is very important.

also can i ask why you scaled the sendos at -500 to 500 ? 

Hi, I had recently worked with LOGO. Maybe I can help. But I couldn't download this file program. It says it's empty. I am happy to help if you can share more details.

Thanks,

Jay