Hello, I need to adjust a PID FB41 on S7-300 PLC. I have process G(s)=2/(4s+1) which is made in MATLAB and downloaded to dSpace platform, so practicaly process is simulated with Matlab+dSpace. For PID controller is used FB41. Simulation is done in matlab and I know what should I expect. PID parameters are: 0.6+0.075/s+1.2 s, so PID constants are: Kp=0.6 Ki=0.075 Kd=1.2
Now I need to implement that parameters in FB41. FB41 block work with time connstants, so I thought that Siemens use this version of PID algorithm: K(1+1/(Tis)+Tds) so when calculate I got this: K=0.6 Ti=8s Td=2s But when I set these parameter I get response that is similar to what I expect, but it has overshoot of 15 %. So basically I get different response comparing to what I've expected. Now, I suspect that time constants in FB 41 is not exactly what I thik they are. I don't know how Siemens calculates PID algorithm. In others words, if I want to setup PID controller 0.6(1+1/(s8)+s2) what parameters should I enter FB41 parameters GAIN, TI and TD?. If someone is interested I would send complete STEP 7 project by email
Thanks for help