Instruction manual

17
3–11 Auto-tuning
T
he auto-tuning process is performed near the set
point. The process will oscillate around the set point
during the tuning process. Set the set point at a lower value if
overshooting beyond the normal process value is likely to
cause damage.
Auto-tuning is applied in cases of:
• Initial setup for a new process
• The set point is changed substantially from the previous
auto-tuning value
• The control result is unsatisfactory
Operation:
1. The system has been installed normally.
2. Set the correct values for the setup menu of the unit, but
don’t set a zero value for PB and TI, or the auto-tuning pro-
gram will be disabled. The LOCK parameter should be set
at NONE.
3. Set the set point to a normal operating value, or a lower
value if overshooting beyond the normal process value is
likely to cause damage.
4. Press and hold until appears on the display.
5. Then press
again
for at least 5 seconds. The AT indica-
tor will begin to flash and the auto-tuning procedure begins.
NOTE: The ramping function, if used, will be disabled when
auto-tuning is taking place.
Auto-tuning mode is disabled as soon as either failure mode or
manual control mode is entered.
Procedures:
Auto-tuning can be applied either as the process is warming
up (cold start), or when the process has been in a steady state
(warm start). After the auto-tuning procedures are completed,
the AT indicator will cease to flash and the unit will revert
to PID control using its new PID values. The PID values
obtained are stored in the nonvolatile memory.
Auto-Tuning Error
If auto-tuning fails an ATER message will appear on the upper
display in the following cases:
• If PB exceeds 9000 (9000 PU, 900.0°F or 500.0°C),
• if TI exceeds 1000 seconds,
• if the set point is changed during the auto-tuning procedure.
Solutions to
1. Try auto-tuning once again.
2. Don’t change the set point value during the auto-tuning pro-
cedure.
3. Don’t set a zero value for PB and TI.
4. Use manual tuning instead of auto-tuning (see section 3-12).
5. Touch RESET key to reset message.
3–12 Manual Tuning
In certain applications auto-tuning may be inadequate for the
control requirements. You can try manual tuning for these
applications.
If the control performance using auto-tuning is still unsatis-
factory, the following rules can be applied for further adjust-
ment of PID values:
Figure 3.9 shows the effects of PID
adjustment on process response.
Figure 3.9 Effects of PID Adjustment
Table 3.2 PID Adjustment Guide