Gossen MetraWatt R2700, Operating Instructions Manual, Page: 40 / 56

GMC-I Messtechnik GmbH R2700–40
Performing the Oscillation Test
If a start-up test is not possible, for example if neighboring control loops influence the actual value too greatly, if the switching output for cooling 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 parame-
ters 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 if applicable start the recorder. Record several oscillations until they become uniform in size.
– Measure oscillation amplitude x
ss
.
– Record on-time T
I
and off-time T
II
for the oscillations at the switching output for heating or the continuous output.
Evaluating the Oscillation Test
1
If either T
I
or T
II
is significantly greater than the other, value tu is too large.
Parameter Value
tu
1
0.3  (T
I
+ T
II
) 0.2  (T
I
+ T
II
– 2 tY )
tc tu / 12 tY / 100
Pb I x
ss
x
ss
 T
II
(T
I
+ T
II
)
2  x
ss
2  x
ss
 T
II
(T
I
+ T
II
)
x
ss
/ 2
Pb II – Pb I  (T
I
/ T
II
) – Pb I  (T
I
/ T
II
) –
Parameters 2-step controller 3-step controller Cont.-action controller Split range controller Step-action controller
T
I
T
II
x
ss