| Input ACT |
REAL (value measured by the way) |
| SET |
REAL (default) |
| SUP |
REAL (noise reduction) |
| SFO |
REAL (offset for the output) |
| M_I |
REAL (input value for manual operation) |
| MAN |
BOOL (switch to manual mode, MANUAL = TRUE) |
| RST |
BOOL (asynchronous reset input) |
| KP |
REAL (proportional part of the controller) |
| KI |
REAL (integral part of the controller) |
| LL |
REAL (lower output limit) |
| LH |
REAL (upper output limit) |
| Output Y |
REAL (output of the controller) |
| DIFF |
Real (deviation) |
| LIM |
BOOL (TRUE if the output has reached a limit) |
| CTRL_PI is a PI controller with dynamic anti-wind-up and manual control input. The PI controller operates according to the formula |
|
|
Y = KP * DIFF + KI * INTEG(DIFF) + OFFSET |
|
where DIFF = SET_POINT - ACTUAL |
| In manual mode (manual = TRUE) is |
Y = MANUAL_IN+ OFFSET |
| ACT is the measured value for the controlled system and set the setpoint for the controller. The input values of LH and LL limit Output value Y. With RST the internal integrator may be set to 0 any time. The output LIM signals that the controller has reached the limit of LL or LH. The PI controller is free running and uses the trapezoidal rule to calculate the integrator for the highest accuracy and optimal speed. The Default Values of the input parameters are predefined as follows |
KP = 1, KI = 1, LIMIT_L = -1000 and LIMIT_H = +1000. With the input SUP a noise reduction is set, the value on input SUP determines at which control difference the controller turns on. With SUP is avoided that the output of the controller varies continously. The value at the input SUP should be in dimension that it suppresses the noise of the controlled system and the sensors. If the input to SUP is set to 0.1, the controller is only at deviations greater than 0.1 active. At the output DIFF the measured and through a Noise Filter (DEAD_BAND) filtered control deviation is available. DIFF is normally not required in a controlled system but can be used to influence the control parameters. The input OFS is added as the last value to output, and is used to compensate mainly of noise, whose effect can be estimated on the loop. |
|
The controller works with a dynamic air- Up that prevents that the integrator, when reaching a output limit and further deviation, continues to run unlimited and affects the properties usually negative. In the introduction chapter of the control technology, more details can be found on anti-wind-up. |
| The following graph illustrates the internal structure of the controller |
|
