Using PID basic functions
7.3 TCONT_CP
PID control
Function Manual, 03/2017, A5E35300227-AC
221
Sampling time pulse generator
The sampling time pulse generator must agree with the time tact of the cyclic interrupt OB
being called. The duration of the created impulse is always a whole number factor of this
value. For an adequately precise manipulated value resolution, the following relationship
should apply:
CYCLE_P ≤ PER_TM/50
Minimum impulse/break duration
Through the minimum impulse/break duration, short on or off times on the actuator are
avoided. An impulse smaller than P_B_TM is suppressed.
Recommended are values P_B_TM ≤ 0.1 × PER_TM.
The period duration should not exceed 20% of the determined integration time of the
controller (TI):
PER_TM ≤ TI/5
Example for the effect of the parameter CYCLE_P, CYCLE and PER_TM:
Period duration PER_TM = 10 s
Sampling time PID-algorithm CYCLE = 1 s
Sampling time pulse generator CYCLE_P = 100 ms.
Every second, a new manipulated value, every 100 ms the comparison of the manipulated
value occurs with the previously emitted impulse length and break length.
● If an impulse is emitted, there are 2 possibilities:
– The calculated manipulated value is larger than the previous impulse length/PER_TM.
Then the impulse is extended.
– The calculated manipulated value is less than or equal to the previous impulse
length/PER_TM. Then no impulse signal will be emitted.
● If no impulse is emitted, there are also 2 possibilities:
– The value (100 % - calculated manipulated value) is greater than the previous break
length / PER_TM. Then the break is extended.
– The value (100 % - calculated manipulated value) is less than or equal to the previous
break length / PER_TM. Then an impulse signal will be emitted.
Mode of operation TCONT_CP (Page 472)
Operating principle of the pulse generator (Page 481)
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