Tuesday, March 6, 2012

PLC CAN interface ZEUS MicroVertex Detector

The network of CAN-fieldbus that interconnects the control systems of ZEUS MicroVertex Detector (MVD) and the Supervisor of MVD-Controls is utilized by the Supervisor to supervise and control a variety of MVD subsystems. One of the subsystems linked to the network of CAN is the PLC controlled cooling system of the MVD front-end-electronics.

The PLC of the MVD cooling system does not contain an interface to join it straight to a CAN-bus. But it does comprise an interface of RS232, which is utilized to connect it to a module of SPICAN which attributes an interface of RS232 as well as a CAN interface. The module of SPICAN can consequently offer an interface between the CAN and the PLC network. The firmware of custom application has been built for the module of SPICAN to present a communication interface between CAN-bus and RS232.

The Supervisor of MVD-Controls should be capable to monitor the MVD cooling system status, to set a warning and error number limits in the system and be able to state general control over the PLC. All communication will occur with CAN-bus communication.

Monitoring the statuses of PLC Error, Warning and Global
Before the status of PLC and data monitoring can start the node of PLC-CAN has to be set into Operational state with the following 2 databyte CANopen NMT message:

The data of PLC that is subjected to standard monitoring can be interpreted with the mechanism of CANopen PDO. A message of PDO is a non-confirmed CAN-message with one sender and one or more receivers, including no protocol overhead, only data. It is implicit that a PDO receiver’s message knows the importance of the PDO message data content.

PLC-CAN can create two different PDOs, which we will call as PDO1 and PDO2. The parameters of PLC Global Status, Error Status, and Warning Status are found in the block of PLC parameter in the Object Dictionary index 0x2000. They can be integrated in the regular monitoring scan of the PLC parameters as described. Nevertheless, to allow a more regular check or autonomous check of PLC-CAN on the status of PLC words alone, an additional PDO has been identified that includes only these status words (6 bytes in total): PDO1. The data content of PDO1 definition and its mapping can be created in the Object Dictionary at index 0x1A00.

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