Intelligent fieldbus connectors for valves

Asco Joucomatic's Mike Reece looks at a recent development that puts more intelligence into fieldbus connected valves and actuators.

Fieldbus systems like interbus-s or Profibus-DP are being used more and more in installations to connect inputs and actuators to a PC or PLC controller. The Valve Connection System, VCS, recently introduced by Asco Joucomatic is made up of a connector for each valve/actuator, a 2-wire profiled cable (the VCS line) and an interface. It links actuators together simply, quickly and economically and is ideal for large installations and machines.

Up to 127 connectors for spool valves with two solenoid coils each (bistable valves) and up to 254 sensor inputs can be connected with a single cable, spanning a length of up to 2.5km.

The VCS has been designed precisely with these new trends in mind and the interface acts as a communication centre for a PLC, a fieldbus and up to 127 VCS connectors organised in loop. Data from the fieldbus passes through the interface and is transmitted to valves through the VCS line. Corresponding feedback from digital inputs (limit switches) is transmitted over the line to the interface and on to the fieldbus system.

Simple cabling Valves and actuators with a VCS connector are referred to as participants. These participants are connected to each other and to the VCS interface over a 2-wire profiled cable supplying both power and data. When the lid of the connector is closed, the vampire-type plug automatically enables immediate contact and the participant is connected. This system eliminates the need for cable stripping or fastening and no tools are needed to fasten the lid.

Each connector is equipped with a data repeater suitable for a distance of up to 20m between two valves. In addition to technological features such as automatic cuffing and vampire-type plugging, all the electronics used to extract data from valves and to transmit input data from sensors is integrated within the connector, rendering it intelligent. This has been achieved by the used of a newly developed, economical and compact ASIC which is at the heart of the VCS electronic system.

An advantage of using a loop is that transmitted data is fed back and analysed, and an output is switched only after transmitted data and feedback data are fully compatible. If faulty data blocks are detected then transmission is repeated and valve actuators only operate after data has been verified. A loop structure results in automatic addressing since each valve is recognised by its position in the loop, making time consuming manual addressing unnecessary and avoiding double assignments.

The system's intelligence is in the interface which controls data transmission from the fieldbus to the VCS line. Depending on which fieldbus system is being used, the interface is equipped with a corresponding fieldbus module, and these are available for standard protocols such as Profibus-DP, lnterbus-S and DeviceNet.

• Asco Joucomatic
  Email b103@industrialnetworking.co.uk
  

C1: The VCS links actuators together simply, quickly and economically, with a single cable spanning a length of up to 2.5km. The system's intelligence is in the interface which controls data transmission from the fieldbus to the VCS line