hi all

i am trying to control the speed of a motor using a inverter on a motor using a 0-10v output form the logo and i am struggling to get it to do want i want.

Here is the project:

2 x motors and 1 is of a fixed speed and the other in controlled by the logo,i have a a 0-10v pressure sensor with a range of -50Pa to +50Pa 

The set point i am trying to achieve is -10Pa 

now i can do this by using the PI control but if the PV is above the setpoint i.e 5Pa then the output of the PI control is 0 and if is 0 then the drive/motor is not running, so i need to have a constant output to the motor relevant to what the pressure is i,e the motor constantly moves speed up and down .

i hope that makes sense?

yes that is correct and also the one i cant seem to understand if its me being stupid or a i am doing something wrong. i can not have the output at zero.

the PV value will never be at the setpoint due to the nature of the system but i am trying to maintain a pressure of -10Pa so if say the PV goes to 5Pa the output is zero when in reality i need the motor to increase speed and if the PV is -15 then i need to decrease the speed of the motor.

maybe i am looking at this the incorrect way