Siemens MICROMASTER 411 - Manual (Page 125)

Issue 03/01 10 Engineering Information
MICROMASTER 411 & COMBIMASTER 411 Operating Instructions
6SE6400-5CA00-0BP0 125
Figure 10-6 Damped response: P2280 = 0.20; P2285 = 0.15 s
Values of P2280 and P2285 are determined by the relationship between motor
frequency and the PI control quantity (e.g. pressure).
When optimizing a control process an oscilloscope is recommended to monitor the
feedback signal to see the system response. Most commonly small PI setpoint step
changes (1- 10%) without the PI ramp times (P2257 = P2258 = 0.0 s) are used to
evaluate the system response. Once the desired response profile has been
achieved, the operational ramp times are then set.
It is recommended to start with a small P term (e.g. P2280 = 0.20) and adjust the I
term until stable operation constant is achieved. A small PI setpoint change should
then be given and depending on the system response the parameters adjusted
according to the tendencies shown in the figures above.
In general, the most stable control is achieved by using both proportional and
integral terms, and if the system is liable to experience sudden disturbances we
would not recommend setting the P term (P2280) greater than 0.50.
A block diagram showing the relationships and interaction between PI Setpoint and
PI Feedback is shown in Figure 10-10 on page 128.