SRS Labs SIM960, Руководство по эксплуатации и обслуживанию

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2 – 2 Advanced Topics
2.1 PID Tuning Basics
PID control provides a simple way to minimize the e
ff
ect of dis-
turbances to a system. The system consists of a closed feedback
loop between two elements, the SIM960
controller
and the user
pro-
cess . The controller has two inputs,
Setpoint
and
Measure
, and an
Output
. The process consists of a power source that can be directly
changed by the controller, in conjunction with a sensor to monitor the
process behavior. The sensor signal, after any necessary condition-
ing, is the process output. This should be connected to the
Measure
input of the SIM960, and the SIM960
Output
should be connected to
the process input, forming a feedback loop.
The di
ff
erence between the
Setpoint
and
Measure
inputs is the error
signal,
ε ≡ Setpoint − Measure
(Eqn 1.1). In the SIM960 the error
signal is amplified by the proportional gain. The controller uses the
amplified error,
P × ε
, to generate three control signals:
1. Proportional, the
P
amplified error with no changes.
2. Integral, the time integral of the amplified error signal multi-
plied by a gain coe
ffi
cient
I
.
3. Derivative, the time derivative of the amplified error signal
multiplied by a gain coe
ffi
cient
D
.
These signals, as well as an
O ff set
, are combined at a summing
junction to produce the controller output (see Eqn 1.2). Figure 2.1
shows a schematic representation of the SIM960 controller topology.
Note the proportional gain coe
ffi
cient is common to all three terms, so
the net integral and derivative gains are
P × I
and
P × D
, respectively,
whether or not proportional control is enabled.
The controller monitors the process output and makes small adjust-
ments to the process in order to minimize deviations of
Measure
from
Setpoint
due to external disturbances. To accomplish this, the
controller must be properly tuned, meaning that the gains for each
of the three control signals—proportional, integral, and derivative—
must be chosen appropriately to match the behavior of the process.
A well-tuned controller should be able to maintain a stable process
output.
The control loop feedback should be negative. However, because
the polarity of the process response to the controller output is an
arbitrary function of the design of the system, it is vital that the
controller polarity be chosen properly. Based on the topology of the
SIM960 design, feedback polarity can be changed simply by changing
the polarity of the proportional gain parameter
P
. The user must
first determine which polarity will provide negative feedback. If the
SIM960 Analog PID Controller