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PPC: Programmable Process Controller

The Programmable Process Controller (PPC) is the main controller component of DXS.PPC is responsible for executing control strategies, communicating with higher layer, as well as, peer networks (FF HSE), communicating with Fieldbus devices (FF H1 and HART), and performing the required conventional I/O functions. The PPC supports full redundancy in processing, I/O and communications (both internal and external). The DXS PPC is designed to fulfill the requirements of the most demanding process control applications. Competent in handling thousands of I/O points and the corresponding control strategies per single controller, the system can scale up to tens of thousands of I/O points through a series of networked controllers using powerful communication mechanisms built into its system hardware and software.


At the heart of the PPC lies the MPU (Main Processing Unit) which is responsible for receiving and storing PPC configuration information, execution of control strategies, all communications in controller level, and the management of I/O modules. MPU’s are formed around a family of powerful 32-bit RISC CPUs.

I/O Modules

I/O modules are the main interface between PPC’s and conventional non-smart sensors and actuators. These modules are fully compatible with IEC61131-2 recommendations. They are fully isolated and have self-diagnostic and status report functionality. A comprehensive set of analog and digital input and output modules are available in DXS. The I/O modules can be used in redundant configuration, eliminating single points of failure in the I/O subsystem of the PPC.

FOUNDATION Fieldbus HSE Connectivity

FOUNDATION Fieldbus HSE is the control level bus for a FOUNDATION Fieldbus system. It enables the construction of control cascades between instruments on different H1 segments. It also serves as the more conventional communications pathway to all field instruments. In the DXS architecture, HSE acts as the universal protocol between various control elements, providing fast and reliable communication among PPC’s, and also between PPC’s and field instruments through so-called Linking Devices.

HART capability

Along with the state of the art FOUNDATION Fieldbus connectivity, APAT has developed solutions that provide the connections between the DXS control system, HART field instruments, and the asset management system. The HART-enabled I/O modules of DXS PPC support HART-6 universal, common practice, and device-specific commands. Multi-drop networks and burst mode are also supported. The I/O modules can operate either in manual command or auto-polling modes.

Modbus Connectivity

The PPC Controller can operate in either Modbus Master or Modbus Slave mode to communicate with remote MODBUS devices. The controller can be configured as a Modbus Master to control and obtain information from Modbus Slaves (such as PLC’s used for control of stand-alone packages). The serial ports can also be configured as Modbus Slave, accepting commands from Modbus Master devices and providing the requested data.

Controller and Network Redundancy

Redundant controllers are used for critical control applications. The main and backup controllers operate in parallel, checking each other’s status by exchanging various synchronization messages in each control cycle assuring a bumpless transfer to backup controller in case of main controller failure. In addition to controller redundancy, the DXS PPC has two high-speed Ethernet ports to provide alternate paths of communication. Each port can be connected to an independent LAN. In case of a network failure detected on the main port, traffic is immediately switched to the other LAN to ensure uninterrupted flow of information.