Required Drive Features
Applications often require a precise measurement of load speed. Typically, an encoder is mounted to the motor shaft and its signal is used to indicate shaft speed. The drive can then adjust its output to the desired condition. Closed loop offers the highest accuracy and performance.
Requires: A drive with feedback capability, either as standard or as a plug-in option card.
Applications that involve multiple drives or drives controlled by PLC or other supervisory device often require communications via a defined network.
Requires: A drive that has a standard or optional connection to the desired network.
Digital I/O
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.
Requires: A drive that offers sufficient I/O and needed flexibility to perform all required func¬tions.
Applications that require rapid deceleration or quick stops can regenerate energy back to the drive. A dynamic brake dissipates this energy through a resistor as heat.
Requires: A drive that has an internal DB chopper and connectable resistor or has an external DB kit.
Dynamic Response
High performance applications often demand nearly instant response to changes in speed or torque commands or input status changes. The higher the dynamic response, the more capable the drive is in meeting these demands.
Requires: A drive that meets the response demands.
Mechanical Brake Control
A mechanical brake is used for holding the motor and driven machinery at zero speed when the drive is stopped or not powered.
Requires: A drive with mechanical brake control.
Overload Torque
Applications may require varying degrees of overload capacity for starting, accelerating, or intermittent duty. This overload capacity must be supplied by the drive as current and by the motor as torque.
Requires: A drive that has sufficient overload capacity.
PID Loop
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.
Requires: A drive with one or more internal PID loops to eliminate the need for external hardware.
Power Loss Ride-Through
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.
Requires: A drive that has sufficient power loss ride-through capability.
Slip Compensation
A squirrel-cage motor slips under load. To compensate for this, the frequency can be increased as the motor torque increases.
Requires: A drive that provides adjustable slip compensation.
Speed Range (100:1)
All applications operate over a given speed range, defined as the ratio of maximum continuous speed to minimum continuous speed.
Requires: A drive that can produce the needed torque and speed torque regulation (accuracy) over the required speed range.
Torque Proving
Some applications, like cranes, hoists and elevators, use mechanical brakes to hold the motor and driven machinery stationary while the drive is stopped. Prior to the release of this brake, the drive senses adequate current supplied to the motor to prevent dropping the driven machinery when the mechanical brake is released.
Requires: A drive that provides torque proving.
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