Connect-Tek Transa PRO 17 Manual de Instruções descarregar pdf (Página 41)

3–19 Auto tuning

The auto-tuning process is performed at the set point.

The process will oscillate around the set point during the

tuning process. Set the set point to 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. Use the default values

for PID before tuning.

The default values are: PB1=PB2=18.0°F

TI1=TI2=100 seconds, TD1=TD2=25.0 sec-

onds.

Of course, you can use other reasonable values

for PID before tuning according to your previ-

ous experiences. But don’t use a zero value for

PB1 and TI1 or PB2 and TI2, otherwise, the

auto-tuning program will be disabled.

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 until appears

on the display.

5. Press for at least 3 seconds. The upper

display will begin to flash and the auto-tuning

procedure is beginning.

NOTE: Ramping function, remote set point,

or pump function, if used, will be disabled

once auto-tuning is proceeding.

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). See figure 3.22.

If auto-tuning begins apart from the set point (cold start), the unit

enters warm-up cycle. As the process reaches the set point value,

the unit enters a waiting cycle. The waiting

cycle elapses for a double integral time (TI1 or

TI2, dependent on the selection, see section

4.1), then it enters a learning cycle. The double

integral time is introduced to allow the process

to reach a stable state. Before the learning cycle,

the unit performs a pre-tune function with PID

control. While in the learning cycle, the unit

performs a post-tune function with an ON-OFF

control. The learning cycle is used to test the characteristics of the

process. The data is measured and used to determine the optimal

PID values. At the end of the two successive ON-OFF cycles, the

PID values are obtained and automatically stored in the non-

volatile memory. Once the auto-tuning procedures are completed,

the process display will cease to flash and the unit will revert to

PID control using its new PID values. During the pre-tune stage

the PID values will be modified if any unstable phenomenon

which is caused by incorrect PID values is detected. Without the

pre-tune stage, like other conventional controllers, the tuning

result will be strongly related to the time when the auto-tuning is

applied. Hence, different values will be obtained every time auto-

tuning is completed without pre-tune. It is particularly true when

auto-tuning is applied using cold start and warm start.

If auto-tuning begins near the set point (warm start), the unit

skips the warm-up cycle and enters the waiting cycle. Afterward,

the procedures are the same as described for cold start.

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;

• or if the event input state is changed so that the set point

value is changed.

Solutions to

1. Try auto-tuning again.

2. Don’t change the set point value during the auto-tuning

procedure.

3. Don’t change the event input state during the auto-tuning

procedure.

4. Use manual tuning instead of auto-tuning. (See section 3-20)

5. Touch any key to reset message.

Pre-tune

function

advantage:

Consistent

tuning results

can be

obtained

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