SRS Labs CTC100, Руководство пользователя

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Operation 34
CTC100 Programmable Temperature Controller
A utom atic tuning algorithms
During automatic tuning, the CTC100 changes the heater power, measures how much and how
quickly the temperature changes in response, and then estimates the optimum values of the gain
factors P, I, and D. Two tuning algorithms are available: the relay tuner and the step response
tuner.
R elay tuner
Temperature (top) and heater power (bottom) during relay autotuning.
Step Y is 2 W, Lag is 30 s, feedback is initially on, and the system starts
with the temperature stabilized at the 50°setpoint. After the tuning has
finished, the feedback turns on and re-stabilizes the system at 50°C after
a few cycles of oscillation.
The relay tuner creates a temperature oscillation by switching the heater between two output
values:
Output
high
= Output
I
+ (Step Y)/2
Output
low
= Output
I
(Step Y)/2
where Output
I
is the initial
that the relay tuner cannot be started unless the output is greater than (Step Y)/2. For best results,
the output should be greater than Step Y.
The relay tuner begins by disabling the feedback (if the feedback was on) and measuring the drift
and noise of the feedback input signal in the absence of any changes to the feedback output. The
drift-and-noise measurement continues for one-
control; the resulting drift-and-noise value is the difference between the largest and smallest input
signal observed during this time.
After the drift and noise measurement, the relay tuner sets the heater output to Output
low
for the
Lag time to start the oscillation. If during this period the feedback input does not change by at least
ten times the drift-and-noise value, an error message is displayed in the Status window and tuning is
cancelled. If this occurs, either 1) ensure that the temperature is stable before starting the step
response; 2) increase step Y; or 3) if it looks like the temperature
respond, increase the Lag time.
The tuner then sets the output to the Output
high
value. Then, each time the temperature crosses
its initial value (50 °C in the figure above), the output is switched from high to low or low to high.