Flowserve MX FOUNDATION Fieldbus Field Unit Manuel d'utilisateur télécharger pdf (Page 12)

MX/QX FOUNDATION Fieldbus Field Unit FCD LMENIM2330-01 – 08/11

Figure 2.3 – MX/QX Interface Board

2.2.3 Network Host

The FOUNDATION ﬁeldbus network is connected to the host device, which can be a distributed

control system (DCS), a PC, a PLC, or other microprocessor-based device. The host device can be

the Link Active Scheduler (LAS), which performs the duty of network trafﬁc controller. Networks can

have multiple Link Masters, which have LAS capability, but only one of these can be the LAS at any

time. If the LAS device fails another LAS is automatically created; this redundancy ensures continuing

communication in the event of a failure. The MX/QX FF unit can be conﬁgured for Basic or LAS mode.

In BASIC, the MXa/QX will display COMM LOSS, while in LAS it will display HARDWARE FAILURE, if

power is removed from unit.

2.2.3.1 LAS Tasks

The main task of the LAS is to schedule Compel Data (CD) messages to all devices in turn. The CD

message is directed to one device so it can broadcast (publish) data to all other devices. The LAS

also updates the Live List, which contains all devices on the network with the capability to commu-

nicate, and schedules a Pass Token that allows devices to send unscheduled messages such as

setpoint changes and downloads. The LAS does the following:

• Recognizes and adds new devices to the link

• Removes non-responsive devices from the link

• Polls devices for process data at scheduled times

• Distributes a priority-driven token to devices between scheduled transmissions

• Controls the Publisher/Subscriber process using the CD message

• Controls Server/Client communication between pairs of devices

• Broadcasts a time signal to synchronize all devices on the link

CD Schedule

The CD scheduler contains a list of activities that are scheduled to occur on a cyclic basis. At the

scheduled time, the LAS sends a Compel Data (CD) message to a speciﬁc buffer in a ﬁeldbus device.

The device immediately broadcasts or “publishes” a message to all devices on the ﬁeldbus.

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Flowserve MX FOUNDATION Fieldbus Field Unit Manuel d'utilisateur Page 12