Flowserve L75 Series Electric Actuator - Manual (Page 4)

L75 Series Electric Actuator — Modbus RTU FCD LMAIM7502-00 – 07/05

Introduction
The Modbus RTU electronic positioner utilizes the RTU (Remote Terminal Unit) transmission mode to
communicate on standard Modbus networks. The mode and other serial parameters (baud, parity, stop
bits, etc.) must be configured the same for all devices on a Modbus network.
Principles of Operation
The Flowserve Modbus RTU Interface Card is a valve automation and control product that uses the
Modbus communication protocol to operate and monitor position as well as provide predictive and
preventative maintenance functions.
When power is first applied to the board, the motor drive circuits are inactive and the valve will remain
in its current position. A valve position is maintained until a Modbus movement command is received.
Modbus functions are viewed as commands and are available to start or stop movement in a particular
direction, to read the status of the end-of-travel limit switches, and to read the status of the motor drive
circuits. If all three indicator LEDs blink simultaneously when power is first applied, the Modbus address
is not correct and the actuator will not operate. Refer to Modbus Address Selection in the Configuration
section to correct the problem.
Using a Modbus command, the valve shaft can be rotated either clockwise (CW) or counterclockwise
(CCW). A movement command will cause rotation in a specified direction. Valve movement will continue
until either the end-of-travel limit switch opens, or a stop command is received. In full open/close appli-
cations, the stop command is not needed. In other applications, the valve can be stopped in mid-travel
by issuing a stop command before the end-of-travel limit switch opens.
It is not possible to command movement in both CW and CCW directions simultaneously. If this is
attempted, the last positioning command will remain in effect. If a command is issued to move in a
direction opposite to the current direction of movement, the actuator will stop movement in the current
direction, delay for one second, and then begin moving in the specified direction (i.e. a stop command
is not needed to change directions).
General Environmental Information
The L75 Modbus RTU Electronic Positioner is sensitive to electrical noise on communication and power
supply lines. The positioner can also be affected by radiated electrical noise. For best positioner opera-
tion, the electrical noise level should be as low as possible. Follow the wiring guidelines in this manual
carefully.
Shielded, twisted-pair wire is recommended for the communication cable. If shielded, twisted-pair wire
is not available, non-shielded twisted pair cable is the next best alternative to prevent susceptibility to
electrical noise. Unshielded, non-twisted cable is not recommended.