AOpen DE7200 Series Instrukcje Operacyjne Pobierz pdf (Strona 15)

INTRODUCTION

20 Sep 12 1-7

DE-7200VFDCentrifuge

Figure 1-4 Centrifuge Operation

CONTROL SYSTEM

Centrifuge operation is supervised by a programmable logic controller (PLC) that interfaces with

the variable frequency drives (VFDs) supplying power to the bowl, conveyor, and feed pump drive

motors. Monitoring and control of the centrifuge may be performed locally or remotely. The

environmentally hardened PLC also offers short-term data storage and a high degree of operating

flexibility. The operator control panel mounted on the control cabinet facilitates communication

with the VFDs and provides real-time access to system operating characteristics. Through the

control panel, the operator may start the centrifuge, enter and adjust speed and torque limits for

bowl and conveyor, set feed rate, shut down the machine, and perform a variety of monitoring and

control functions.

Various inputs including main bearing temperatures, bowl speed, bowl and conveyor torques,

cabinet interior temperature, and vibration are transmitted to the PLC, which then responds with

corresponding outputs to govern centrifuge operation. Critical status information is displayed on

the control panel, as well as alarm and fault messages that inform the operator of any anomalies.

In case of a serious malfunction, the PLC automatically shuts down the centrifuge and displays an

explanatory message for the cause of the shutdown. In addition, the operator may shut down the

centrifuge at any time due to an emergency.

The feed pump is controlled by the PLC, which raises and lowers feed rate to accommodate the

maximum flow and torque limits set by the operator. Flow rate is increased within the set limit until

the torque limit setting is reached. Generally, for maximum throughput flow priority governs

centrifuge operation. However, the PLC defaults to torque priority upon reaching the torque limit

setting. Once torque priority is entered, the system will remain in torque priority even if feed

conditions cause the torque to fall, until flow priority is re-selected by the operator.

The system’s flexibility permits the PLC to raise the feed rate automatically to the set limit unless

the torque limit is reached by either the bowl or conveyor drive motor. Consequently, if feed slurry

properties change, causing the torque to rise, the PLC reduces the feed rate to stay under the

torque limit. The operator control panel displays which priority (flow or torque) is currently in force.

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