Siemens A1 User Manual
Advanced Applications
International English
48
MICROMASTER Applications Handbook
Setpoint
P2260
KK
Setpoint Source
P2253
KK
Feedback Source
P2264
Kp
Tn
P Gain
P2280
I Gain
P2285
x
y
r2294
PID Output
PID in upper limit/lower limit
P53.10/P53.11
+
PID Output UpperLimit
P2291
PID Output Lower Limit
P2292
P2293
Accel/Decel time of PID limits
Ramp - up time for
Setpoint
P2257
Ramp down time for
Setpoint
P2258
+
-
Transducer
Type
P2271
Error
P2273
x
y
Maximum
feedback threshold
P2267
Minimum
feedback threshold
P2268
Figure 8-1
A Typical Closed Loop Controller
Figure 8-1 shows how the closed loop controller is implemented in the MM420.
Note..
That all setpoints are now expressed in percentage. When controlling a Setpoint,
the frequency is not the desired quantity.
That all setpoints are now expressed in percentage. When controlling a Setpoint,
the frequency is not the desired quantity.
The setpoint usually derived from a fixed frequency has adjustable ramp rate that
can be set before being compared with a feedback signal. The feedback signal,
which is usually a 0-10 V or 4-20 mA signal derived from a transducer connected to
the analog input, is also pre-processed with threshold limits. The difference
between the set point and the feedback signal (the error) is then amplified and
filtered using gain and integration constants. These are usually known as the P
and I terms. In this case a differential term (D) is not included as it is rarely
needed. Before the P and I processing the error signal is optionally corrected
(“transducer type”). This correction is to determine whether to speed up, or slow
down the motor to reduce the feedback signal. That is, increasing the speed of a
vacuum pump will decrease pressure; increasing the speed of a compressor will
increase pressure.
can be set before being compared with a feedback signal. The feedback signal,
which is usually a 0-10 V or 4-20 mA signal derived from a transducer connected to
the analog input, is also pre-processed with threshold limits. The difference
between the set point and the feedback signal (the error) is then amplified and
filtered using gain and integration constants. These are usually known as the P
and I terms. In this case a differential term (D) is not included as it is rarely
needed. Before the P and I processing the error signal is optionally corrected
(“transducer type”). This correction is to determine whether to speed up, or slow
down the motor to reduce the feedback signal. That is, increasing the speed of a
vacuum pump will decrease pressure; increasing the speed of a compressor will
increase pressure.
After processing with the P and I terms, the resulting signal is passed to the
inverter which increases or decreases the output frequency as required, subject to
certain limitations, such as acceleration and deceleration times.
inverter which increases or decreases the output frequency as required, subject to
certain limitations, such as acceleration and deceleration times.
8.1.3
Setting up a feedback control system
Some general points.
· Remember that once closed loop operation is enabled values such as the
setpoint are displayed in percent of full scale.
· If possible run the drive open loop first, to check, in particular, the sensor
feedback voltage or current.
· Check P2271 value for the correct ‘sense’ operation. Set P2271 according to
the sensor/actuator types. If the feedback signal reduces as the motor speed
increases, select P2271=1. Otherwise, use P2271=0.
increases, select P2271=1. Otherwise, use P2271=0.