Nor-Cal SDC15 Controller - Manual (Page 73)

5-23
• When the Heat/Cool control is not used, the MV becomes a value
limited by both ranges, one range is between the MV low limit at AT
(AT.oL) and MV high limit at AT (AT.oH), and the other is between the
MV low limit (oL-1) and MV high limit (oH-1) of the PID constant.
When there are no common portions in two ranges, the AT function is
stopped automatically.
• When the Heat/Cool control is used, the MV becomes a value limited
by the MV low limit at AT (At.oL)/MV high limit at AT (At.oH), the heat
MV becomes a value limited by the MV low limit (oL-1)/MV high limit
(oH-1) of the PID constant, and the cool MV becomes a value limited
by the output low limit (Cool) (oL1.C)/output high limit (Cool) (oH1.C)
of the PID constant.
• When the MV low limit at AT (AT.oL)/high limit (AT.oH), MV low limit
(oL-1)/high limit (oH-1), output low limit (cool) (oL1.C)/high limit (cool)
(oH1.C) of the PID constant are set unevenly, the PV may not be
changed up or down even though the MV is changed by the AT. In
this case, the AT is kept continued. If this occurs, the AT is stopped
manually, the high limit and low limit of the manipulated variable are
set again, and the AT is started again.
• The number of limit cycles and period of time from the AT start to AT
end may vary depending on the control subject.
• The MV ON and OFF are repeated several times during execution of
the AT function to perform the limit cycle. (The OFF operation
described here means MV limited by the MV low limit at AT ([At.oL])
or MV high limit at AT ([oL]). The default setting before shipment is
“0%”. Additionally, the ON operation described here means MV
limited by the MV high limit at AT ([At.oH]) or MV high limit at AT
([oH]). The default setting before shipment is “100%”. If this AT
operation does not function correctly, take any of the following
measures:
(1) Change the MV low limit at AT ([At.oL]) or MV high limit at AT
([At.oH]) to an appropriate value, and then start the AT function.
(2) Use the ST function.
(3) Set the PID constants manually without use of AT.
• The AT progress value can be seen in the operation display mode.
For details,
refer to ■ Operation display in section 6-1, List of Operation
Displays (on page 6-1).
When the Heat/Cool control is not used, the AT progress value
decrements from [4] during execution of the AT function and becomes
[0] at completion of the AT function.
When the Heat/Cool control is used, the AT progress value
decrements from [8] during execution of the AT function and becomes
[0] at completion of the AT function.
In both cases, the AT progress value may be “1” or “0” when the AT
process is in the transient status.
• Appropriate PID constants cannot be obtained depending on the
control subject. If this happens, set the PID constants manually.
• The MV ON/OFF change point determined when the AT function is
started does not change even though the SP is changed while the AT
is running.
For details about AT function,
refer to AT Stop/Start (on page 5-8) and AT (on page 5-18).
Chapter 5. DETAILED DESCRIPTION OF EACH FUNCTION