AOpen DE7200 Series Betriebsanleitung PDF herunterladen (Seite 47)

OPERATING INSTRUCTIONS

30 Sep 13 4-9

DE-7200VFDCentrifuge

as the torque remains below the set limit. If the slurry is low in viscosity and density, operation will

continue in the flow priority mode. However, conveyor torque may rise if solids volume increases,

as the conveyor may become burdened in moving the increased solids volume at the present

feed rate and bowl speed. When the torque reaches the torque limit setting, the system

automatically switches to torque priority mode, and the background of the Input Torque % Limit

cell becomes green. The feed rate is then reduced to permit the torque to fall. The system will

remain in the torque priority mode once entered. To switch back to flow priority mode, the

operator must click on the flow rate number, and enter a lower flow rate that will not cause an

over-torque condition to re-occur. For more information on the flow priority and torque priority

modes, refer to Section 1.

Bowl Speed

The faster the bowl speed, the faster solids are settled through the pond to the outer wall of the

bowl. A faster bowl speed for a given feed rate results in dryer solids discharge. To reduce

wetness, the slurry must remain in the bowl longer, subjecting it to the settling process for a

longer duration before being conveyed out the solids discharge. Conversely, reducing bowl speed

may be desirable for thick, heavy slurry to extract only high-density materials or larger particles.

Both the bowl speed setting and actual bowl speed are shown on the control panel. The torque

percentage of the bowl is also displayed. This information is useful in optimizing bowl speed to

produce the desired solids dryness and processing speed.

Conveyor Differential Speed

With correct wiring polarity, the conveyor responds properly to settings made on the Operation

screen. Changing the conveyor differential speed adjusts the solids discharge rate. Generally, a

slower differential speed will produce drier solids but reduces the solids discharge rate. Increasing

conveyor speed reduces drying time, leading to wetter discharged solids. Reducing conveyor

speed results in drier solids discharge. However, excessively slow conveyor speed permits solids

to accumulate in the bowl, possibly causing an overload condition. The drying time is reduced by

increasing the conveyor differential speed, which will increase the wetness of the solids. Reducing

the conveyor differential speed raises the settling time, which will produce drier solids.

Both the conveyor speed setting and actual conveyor speed are shown on the control panel. In

addition, the conveyor torque percentage is shown to assist in optimizing conveyor speed to

produce the desired solids dryness and processing speed.

Since the conveyor differential speed is controlled by the PLC relative to the bowl speed setting,

wiring polarity of electrical components is critical. Depending on settings, electrical polarity

determines actual speed and direction of conveyor motor for any bowl speed setting. For

example, with a bowl speed setting of 2000RPM and conveyor differential speed set at 60, the

conveyor motor will rotate in reverse at -1120RPM.

The correct bowl-to-conveyor speed relationship depends on correct wiring polarity. If polarity is

reversed, the same bowl speed setting of 2000RPM described above would result in an actual

conveyor differential speed of about 17 rather than the setting of 60.

Pond Depth

Pond depth can only be adjusted with the centrifuge fully stopped and disabled. For this reason,

pond depth is usually adjusted last. The factory pond depth setting is usually satisfactory when

used in conjunction with feed rate, bowl speed, and conveyor speed adjustments. However, if

desired results cannot be achieved by other means, the pond depth may require re-setting.

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