Tempco tec-220, Instruction Manual, Page: 20 / 36

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3–11 Auto-tuning
For best results the auto-tuning process should be
performed near the set point. The process will oscil-
late 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. Do not set a zero value for PB and TI, or the auto-tuning pro-
gram will be disabled. The LOCK parameter should also be
set at NONE.
2. 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.
3. Press several times until appears on the display
(for TEC-220), or an AT indicator on lower-right of screen is
lit (for TEC-920).
4. Press and hold for at least 5 seconds. The AT indicator (for
TEC-920) or the display (for TEC-220) will begin to flash
indicating the auto-tuning procedure has begun.
NOTE: The ramping function, if used, will be disabled while
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 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 again.
2. Don't change the set point value during the auto-tuning proce-
dure.
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 unsatisfac-
tory, the following rules can be applied for further adjustment
of PID values:
Figure 3.9 shows the effects of PID
adjustment on process response.