Emerson FM-3 manual Positive Direction Group, Update Rate Group

Setting Up Parameters

Encoder Scaling Check Box

This check box enables the Scaling parameter of the Drive Encoder Output.

Encoder Scaling

This parameter defines the encoder resolution (lines per revolution) of the drive's encoder output. This feature allows you to change the drive encoder output resolution in increments of 1 line per revolution up to the density of the encoder in the motor. If the Encoder Output Scaling parameter is set to a value higher than the motor encoder density, the drive encoder output density will equal that of the motor encoder.

Positive Direction Group

The Positive Direction group consists of a clockwise (CW) Motor Rotation Radio Button or a counter-clockwise (CCW) Motor Rotation Radio Button.

The motion will move in either CW direction or counter-clockwise CCW direction. Perspective of rotation is defined as you face the motor shaft from the front of the motor.

CW Motor Rotation Radio Button

Select this radio button for applications in which CW motor rotation is considered to be motion in the positive direction (increasing absolute position).

CCW Motor Rotation Radio Button

Select this radio button for applications in which CCW motor rotation is considered to be motion in the positive direction (increasing absolute position).

Update Rate Group

This parameter configures the interrupt interval for the FM-3 processor. This defines how often the motion program is interrupted and the Control Loop is processed. In the Control Loop, the feedback information is processed and a new position command is generated. Also in the Control Loop, the I/O is scanned. After Control Loop is complete, all messages are handled. Messages are Modbus data, DeviceNet data, Keypad/Display information, and are only processed if a message is waiting. If no device is querying data from the FM-3 or sending data to the FM-3, then messages do not take up any time. Once messages have been processed, the remainder of the interrupt is dedicated to running the motion programs of user programs.

Available selections for Trajectory Update are 800, 1200, and 1600 microseconds. The longer the update, the more time is dedicated to the user programs, and the less time dedicated to servo performance. The shorter the update , the more precise the servo performance, but less time is available to process user programs. Diagnostics are available on the Status Online tab when online with the device to help select the ideal setting. (See description of Control Loop Group of online parameters for further information)

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