Set Value Not Attainable - Burkert 8626 Instructions De Service

The result of the autotune function is that the resolution of the controller is optimized
by adapting the internal correcting variable range to the specific pressure conditions.
After completion of the autotune function, the MFC Type 8626 returns to the normal
control mode.
NOTE Every MFC Type 8626 has run through the autotune function in the
works during the final tests at the operating pressure stated on the
calibration record. For reliable control operation in an application,
renewed initiation of this routine after commissioning is not
absolutely necessary. It is only recommended if the operating
pressure differs from the calibration pressure considerably (by
several bar). The autotune should be carried out later only if the
pressure conditions in the installation have substantially changed.

3.4.3 Set value not attainable

In this mode, control proceeds correctly but the MFC Type 8626 can nevertheless
not reach the set value. A permanent positive control deviation (w-x) is present. This
operating mode occurs if the pulse-duty factor of the valve is pulled up to nearly
100%, but the flow rate obtained thereby is insufficient. The cause is usually that the
pressure difference over the MFC Type 8626 is too low, e.g. as a result of collapse of
the supply pressure or heavily contaminated filters.
The LED "Overflow-Y" lights on the front panel.
NOTE
To enable you to react in case of a fault, a signal
is additionally placed on relay output 2 (pins 2
and 5 of the 7-pole round connector).
Operating Instructions-No. 801 147
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