I am building my first PID controller.
My process variable and my actuator value are inversly related, meaning if actuator value increases process variable decreases, and vice versa.
So I have tried with a negative value of P and positive value of I.
It works fine for a while and then process variable keeps increasing with actuator becoming as 0.
Can some one help me with what might be the reason for this? Is it okay to have P as negative and I as postive?