17
The algorithms described in items
b
and
c
comprise the following steps:
- delay of output switch-on (approx. 15 s); - time for switching on the power supply of the operating element
(heating/cooling power, fan, etc.);
- determination of the object's characteristics;
- calculation and saving in the controller's permanent memory parameters 38:
Pb
, 39:
ti
, 40:
td
and 41:
tc
- switching on the regulation with new PID settings;
Programmed interruption of the auto-tuning
b
or
c
(with the message
Errt
) may take place, if the conditions for
proper operation of the algorithm are not met, such as:
- the initial value is higher than the set value for heating or lower than the set value for cooling;
- the maximum tuning time (4 hours) has been exceeded;
- the process value is changing too fast or too slowly.
It is recommended to restart the automatic tuning
b
or
c
after a significant change in the
SEt1
threshold or the
controlled object's parameters (e.g. the heating/cooling power, the batch weight, the initial temperature, etc.).
12.6. PID PARAMETER CORRECTION
The automatic tuning function correctly selects the PID regulation parameters for most processes; however,
sometimes it may be necessary to correct them. Due to the strong correlation between those parameters, only
one parameter should be changed and the impact of the change on the process should be observed:
a) oscillations about the threshold - increase the range of proportionality 38:
Pb
, increase the integration time 39:
ti
,
reduce the differentiation time 40:
td
, (or change by a half the impulse period of output 1, parameter 41:
tc
)
b) slow response - decrease the range of proportionality
Pb
, differentiation times
td
and integration times
ti
c) over-regulation - increase the range of proportionality
Pb
, differentiation times
td
and integration times
ti
d) instability - increase the integration time
ti
.
12.7. PROGRAMMED OPERATING CHARACTERISTICS (RAMPING)
Setting of parameter 43:
rAMP
(see chapter 10, Table 10) to value
MAnv
or
Auto
makes it possible to program the
device as a 4-step process controller, implemented through output 1, acting in accordance with the diagram
shown here (Fig. 12.7). This type of operation can be started both manually at any time (when parameter 43:
rAMp
=
MAnv
or
Avto
) and automatically (
rAMp
=
Avto
) at the time when the control is started (after power supply is
switched on and by using the
[F]
function button when parameter 50:
Func
=
StSP
, chapter 9.1). In order to
manually switch on (
on
) or switch off (
oFF
) the process controller, use the
P-St
function available in the quick
menu (chapter 11).
Fig. 12.7. Diagram showing the operation of the 4-step process controller
