Diagnosis – The third generation of decentralisation

1987 – Festo invents the valve terminal, thus heralding the first generation of decentralisation. Decentralised installation of I/O's outside of the central control cabinet is possible via fieldbus systems. The valve terminal supports greater machine complexity – including tubing, wiring and control.

1997 – Festo has a well-established market for direct machine mounting of I/O's to IP65. The development of subsystems and more compact valve terminals such as the CPV for direct machine mounting marks the start of the second generation of decentralisation. Hybrid lines supply power and data to subordinate I/O modules and valve terminals. Machines are more compact and shorter tubing enhances performance. All components have integrated diagnostic services. Another example is the cylinder/valve combination DNCV from Festo, which functions as a subsystem with integrated diagnostics.

2005 – Pre-processing functions and enhanced function-oriented diagnostic services are decentralised from the central control system to the field devices. Complex programming is replaced by straightforward parameterisation. These improvements in efficiency have only become possible with the integration of mechanical, electrical and pneumatic components, combined with the specific mechatronic applications expertise of the company. Built-in ASICS create an intelligent pneumatic control sequence that extends from the monitored valve to the actuator and back to the inputs via the sensors. Fieldbus systems are responsible for data communication via standardised diagnostics channels.

With the integration of the Festo front-end controller CPX-FEC as an electronic bridge to the valve terminal, the third generation of decentralisation has finally begun. Function-oriented diagnosis increases machine availability. Additional built-in pre-processing relieves the central PLC and provides IT services such as SMS/e-mail alert, web server and Ethernet for the valve terminal.

Out of the control cabinet

As more and more functions move from the control cabinet and the control system into the field and the corresponding field devices, the trend toward decentralisation shows no sign of abating. Function and technology modules are following the route taken by I/O modules. The variable nature of field device hardware is no longer an issue thanks to the introduction of software-based parameterisation functions. Pre-processing functions – in particular diagnostic and monitoring functions – are also being deployed.

Synergies are being created in diagnostic functions through the field-oriented control of complete control chains. Valve terminals play a special role in pneumatics in this context. Only with the advent of decentralisation has it become possible to have pre-processing diagnostic functions. These functions incorporate a complete control chain for the actuation of valves, monitoring of the load voltage supply for valves, assigned sensors and outputs. A central control system or a neutral remote I/O would not have been capable of providing these functions.

Component diagnosis

Component diagnosis allows detailed monitoring of fault causes in pneumatic valves and in the sensors and actuators connected to a terminal.

Possible fault causes include:

• Communication errors such as disconnected fieldbuses
• Faults in the power supply such as unstable voltage or compressed air supply
• Device errors such as a faulty module or faulty internal connections
• Peripherals errors such as faulty wiring, sensors or actuators
• Process errors such as run-time or context faults
• Errors by operating and service staff
• Accidental errors

Highlights

Errors by operating and service staff as well as accidental errors frequently lead to long and expensive downtimes. Identification of a mechanical manual override with detent can be evaluated electronically and communicated to a master controller as diagnostic information via LED display, on site via a handheld device or via fieldbus. This is done on a channel-specific basis with clear localisation of fault causes. The identified fault causes as well as all conventional errors are logged in a diagnostic trace on the terminal by default. This algorithm provides a simple means of identifying sporadic faults. No other controller manufacturer or supplier of field devices has previously offered this feature.

Preventive maintenance functions

These are the latest addition to the Festo diagnostics concept. A condition counter is implemented for each solenoid coil for this purpose. This is an electronic maintenance plan for status monitoring, which generates a maintenance signal that can be precisely parameterised by the user in accordance with the control chain.

Status and diagnostic information about the process, the devices and the peripherals is not just saved as bits and bytes, but is instead displayed as normal text and images. Browser technology and e-mail alerts bring greater transparency to the production process – irrespective of current location.

The Festo diagnostics concept is flexible. As a solution based on partnership, it supports connections to controllers and systems from market leaders as well as all IE protocols such as Modbus TCP/IP, Ethernet/IP and – in the near future – ProfiNet.

Mechatronics integration

The diagnostics concept provides function units for the complete control and monitoring of sub-functions of machines and systems. Mechatronics integration contributes to lower installation costs, while the integration of specific diagnostic functions reduces operating costs and downtimes.