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Chapter 7, Auto-tuning (heat and/or cool) – Watlow Series 988LF User Manual

Page 47

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Tuning, Manual Operation, Alarms, and Error Codes, Chapter 7

WATLOW Series 988LF Users Manual

7.1

Chapter 7 Tuning, Manual Operation,

Alarms and Error Codes

Auto-tuning (Heat and/or Cool)

The Series 988LF can automatically tune the PID parameters to fit the
characteristics of your particular thermal system.

Once the auto-tune sequence has begun, all PID values for both heat and
cool are set to [```0] and the control goes into an on/off mode of control
at 90% of the established set point. The displayed set point remains
unchanged.

200

°

Temperature

set point

100

°

process

180

°

auto-tune

begins

auto-tune

complete

90% of

set point

Auto-tuning at a set point of 200

°

F

Time

When the control finishes “learning” the system, it resumes standard PID
control using the PID values established by the auto-tuning process.
Changing the set point during an auto-tune restarts the auto-tune
procedure.

During auto-tuning the process must cross the set point four times within
an 80-minute time span for the Series 988LF to successfully complete the
auto-tune. If this does not happen within the 80-minute time limit, the
Series 988LF chooses PID values based on the 80-minute tuning cycle
performed.

To start auto-tuning:
1. Press the Mode key µ to advance through the Operations menu

until the [`AUt] prompt appears in the lower display.

2. Use the Up-arrow > or Down-arrow < key to select [``On] or

[`OFF].

3. Press the Display key ¥. While the control is in the tuning mode

the lower display alternates every second between the normal
information and the [tunE] prompt.

NOTE:
A useful reference on
tuning is Tuning of
Industrial Control
Systems by Armando B.
Corripio, published by
the Instrument Society of
America

.

Figure 7.1 -
Auto-tuning example

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CAUTION:
If a mechanical relay or
contactor is switching
power to the load, a
longer cycle time may
be desirable to
minimize wear on the
mechanical
components. The
typical life of a
mechanical relay is
100,000 cycles. Verify
that the cycle time
selected is appropriate
for the output device
type. Failure to do so
could result in damage
to equipment and/or
property.