Enhanced Modbus connectivity for electric actuators

Enhanced Modbus connectivity for electric actuators

12/01/2004

Rotork electric valve actuators are now available with improved connectivity to the popular Modbus automation protocol, facilitating an increased range of control and communication information including historical operating data.

Fitted within the environmentally sealed actuator enclosure for maximum reliability, the Rotork Modbus card uses the familiar Modbus RTU protocol on a low cost RS485 communication network. With the card fitted, all the normal commands associated with moving the actuator become available on the Modbus multi-drop highway for PLC supervision. When fitted to Rotork IQ intelligent actuators the Modbus card also makes available a subset of the standard data logger feedback information. A torque profile is provided for every valve operation together with the total number of times that the motor starter has been energised in each direction. This information can be accessed periodically to update the control system with the latest data.

Generally, up to thirty-two actuators can be connected to a single RS485 network with a typical cable length of one and a half kilometres and a data transfer speed of 9600 baud, making Rotork Modbus installations ideally suitable for the centralised control of small to medium sized processes such as water treatment plants.

Three versions of the card are available  single channel, with and without repeater, and dual channel. The single channel is the simplest implementation, connecting the actuator to one RS485 highway and including an additional input for a standard analogue instrument signal. The single channel with repeater module includes an internal repeater to allow the Modbus highway to be extended over greater distances or for applications where a ring is to be constructed. The dual channel module caters for applications where redundant highways are used for high integrity field connection. The two channels are isolated from each other and provide independent communications.

Modbus connectivity is available for all Rotork current range electric actuators, either as a factory fitted option for new units or retrofitted on existing installations.