30
GOSSEN METRAWATT GMBH
Performing the Oscillation Test
If an actuation test is not possible, for example if neighboring control loops influence the actual value too
greatly, if switching output II must be active in order to maintain the actual value (cooling operating point), or if
optimization is required directly to the setpoint for any given reason, control parameters can be determined by
means of sustained oscillation. However, calculated values for
tu
may be very inaccurate in this case under
certain circumstances.
–
Preparation as described above. The test can be performed without a recorder if the actual value is
observed at the display, and if times are measured with a stopwatch.
–
dbnd
=
0
Setting for 3-step, split range and step-action controllers
–
Activate the actuators with
automatic operation
, and start the recorder if applicable. Record several oscilla-
tions until they become uniform in size.
–
Measure
oscillation amplitude x
ss
.
–
Record
on-time T
I
and
off-time T
II
at switching output I or the continuous output for the oscillations.
Evaluating the Oscillation Test
1
) If either T
I
or T
II
is significantly greater than the other, value
tu
is too large.
2) When controlling contactors,
tc
should be adequately increased.
Correction with manipulating factor limiting
YH
positive:
Pb 1
multiply by 100%
/
YH
YH
negative:
Pb11
multiply by –100%
/
YH
Parameter Values
Parameter
2-step controller
3-step controller
Continuous-action
controller
Split range
controller
Step-action
controller
tu
1)
0.3
•
(T
I
+ T
II
)
0,2
•
(T
I
+ T
II
– 2
tY
)
tc
tu
/ 12
2)
tY
/ 100
Pb 1
x
ss
•
100 %
MR
x
ss
•
T
II
•
100 %
MR (T
I
+ T
II
)
x
ss
•
200 %
MR
x
ss
•
T
II
•
200 %
MR (T
I
+ T
II
)
x
ss
•
50 %
MR
Pb11
–
Pb 1
•
(T
I
/ T
II
)
–
Pb 1
•
(T
I
/ T
II
)
–
T
I
T
II
x
ss