Wednesday, August 13, 2014

Centrifugal Pumps - Typical Types Include Influent, Effluent, and Booster
Required Drive Features:

The drive can control the rate of acceleration and deceleration of the motor and load. These features control the amount of time the drive takes to increase or decrease the output during speed control.

Each application has specific requirements for I/O. Analog I/O is generally used to read process signals and output signals proportional to drive status. Analog I/O is generally Voltage (0-10V) or Current (0(4)-20mA). The type and number required by the application must match the drive.

Applications that involve multiple drives or drives controlled by PLC or other supervisory device often require communications via a defined network.

Some applications have mechanical resonance points that cause the mechanics (shafts, belts, etc.) to oscillate. These oscillations can rapidly cause mechanical failure.

Each application has specific requirements for I/O. Digital I/O is generally used to control the drive (Start, Stop, Jog, etc.) and annunciate the drive status.

Many fan or pump installations have a wide spectrum of flow variations. These include water and sewage systems, process, and other industrial applications. Excellent flow control can be achieved by using a variable speed drive on one fan or pump and using the drive to control other units at fixed speed.

Motors are rated by the manufacturer for the voltage resistance of the insulation system. If this insulation system voltage is too low, voltage reflection from the drive could cause motor failure. This is particularly important if the motor is a long distance from the drive and if the motor is an older motor being retained for the application.

An internal function provides closed loop process control with proportional, integral and derivative (PID) control. The PID function reads an analog input to the drive and compares it to a desired setpoint. The PID loop adjusts the drive output frequency (and therefore the process) to make the input value equal the setpoint.

Applications that control a continuous process cannot afford to stop because of short power outages or dips. The process must continue to run through these outages, typically 2 to 3 cycles long.

A drive is typically speed controlled using a potentiometer or analog input device. If specific repeatable speeds are required, parameters can be used to preset operation of the drive at a pre-determined speed using a digital input.

Applications with significant inertia and low friction tend to coast when stop commands, power interruptions or fault conditions occur. Many of these application require that when the condition disappears, the load must be reconnected at the 'coasting' speed / direction and returned to normal operation.

All applications operate over a given speed range, defined as the ratio of maximum continuous speed to minimum continuous speed.

Applications that do not require significantly more torque than the original motor rating can most often be addressed by a drive using V/Hz algorithms. Loads, such as centrifugal fans and pumps or simple conveyors, are difficult to overload and therefore do not require the performance of other motor control algorithms. Simply maintaining a fixed ratio between drive output voltage and frequency is sufficient.

Applications that depend on accurate speed to accomplish the task require a drive that can control or 'regulate' speed. 

Recommended Choice: ABB ACS150 Series

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