Valve Terminals and Electronics
Manufacturers-that rely on pneumatics are constantly on the lookout for ways to reduce downtime and operating costs and, ultimately, improve productivity. To meet these goals, they want faster setup, more efficient operations, and streamlined troubleshooting with less downtime from their pneumatic systems.
Valve terminals are evolving to help meet these demands. When first introduced more than a decade ago, fieldbus valvemanifold systems offered several advantages over traditional systems, the most notable being lower installation costs. Conventional systems containing a series of stand-alone valves generally require extensive wiring, making installation expensive and presenting plenty of opportunities for miswiring. More connections also mean lower reliability.
Valve terminals require substantially less wiring than an equal number of stand-alone valves and, thus, reduce installation costs. Also, IP65 ratings mean manufacturers need fewer protective enclosures or can eliminate them altogether. For applications heavily focused on output signals, a single scanner card can replace many individual output cards, at substantial cost savings. And because valve terminals can be positioned close to the actuators, rather than near the controller, shorter lengths of I/O wiring and pneumatic tubing can be used. Shorter tubing pressurizes faster and actuators respond quicker.
The first valve terminals often had standard valves simply mounted on a manifold and wired to a "black-box" fieldbus node, with individual solenoids controlled over the network.
The node also provided I/O, but the main benefit was connecting discrete solenoids to the fieldbus. In terms of troubleshooting, one shortcoming of these systems was the entire fieldbus valve terminal appeared as a single block of data to the controller. This limited the ability to pinpoint a fault. For instance, data blocks did not differentiate between solenoids and outputs. And the procedures to set up and configure a fieldbus system usually varied among PLC vendors — and even among different PLCs from the same vendor — so it often required multivendor support.
Most leading PLC manufacturers and fieldbus organizations are developing systems that improve the configuration of fieldbus devices. And valve terminals are evolving to keep up with these advancements in programming and control.
The main breakthrough has been the implementation of a dedicated, high-speed bus embedded within the valve terminal. This lets users plug in various pneumatic and electronic modules — such as fieldbus and I/O modules — and configure the precise system needed for a particular application.
The internal bus ties the modules together. It increases data capacity and communication speed compared-with discretely wired versions, and has the capacity to handle additional data, such as diagnostics for solenoid valves. The modular approach also makes it easy to expand a system, saving setup and commissioning time.
The design conforms to modular configuration schemes dictated by advanced control and fieldbus systems. Users can configure valve terminals by individual modules and take advantage of the latest visual configuration tools, such as RSNetworx for DeviceNet using modular EDS, or Com Profibus.
A significant benefit advanced valve terminals offer is that physical connections no longer limit the number of solenoid coils, as in the past. The quantity is logical, based on the capacity of the serial bus. Some valve terminals now support 64 or more valves. Also, specialty modules that support pneumatics can be incorporated into systems. For example, a diagnostic server module could monitor, diagnose, and report pneumatic failures using sensors for pressure differential, spool position, and so on. The internal serial bus easily transports the added diagnostic data.
An example of an advanced valve terminal is Festo's CPX/MPA. It uses embedded bus technology to offer the industry's highest concentration of solenoid valves per manifold. It features more than 64 solenoids on the main unit, plus additional manifolds per custom-distributed CANbus interface. Options for the design engineer include several different types and sizes of pneumatic valves, with bicolored LEDs that indicate the solenoid is on, off, or faulted.
The integrated bus can also control power distribution throughout the manifold to each module, and isolate solenoids from control electronics. Solenoid valves require a certain amount of current to initiate movement but substantially less to hold them open or closed. Controlling power in this manner can reduce operating costs and extend solenoid life.
In addition to pneumatic units, the CPX holds up to 10 electronic modules of all types, including digital and analog I/O; DeviceNet, Profibus, Ethernet/IP, and other fieldbus and Ethernet nodes; special modules for distributed control; and so on. The CPX can handle 512 bits of input and 512 bits of output. An ASIC on every module coordinates internal bus traffic at the optimum speed and capacity.
Electronic datasheets let technicians quickly configure the terminals in most contemporary control systems, and simplify service and field modifications. Valves and I/O devices can be configured block by block, onscreen, with visual editors. The visual-block-programming approach differentiates between solenoids, digital and analog input and output devices, and other data types, making setup and troubleshooting straightforward.
The CPX also accepts "intelligent" modules. For example, if there is the need to process data quickly, say in a precise dosing application, an onboard logic controller can preprocess the data and perform its function independent of the latency time introduced by the fieldbus.
Users can also access dedicated diagnostics. Because of the embedded bus, all system data is immediately available to the fieldbus. For instance, it can detect if a device is not connected or upper or lower voltage limits are exceeded. In addition, the system retains the last 40 diagnostic events, and timestamps them from the last power cycle. The system records faults via modules and, in most cases, via channels within modules for single-point diagnostics. Thus it increases uptime by immediately localizing faults, saving troubleshooting time and speeding repair.
An HMI is available for troubleshooting, commissioning, and configuration. This provides a window into the CPX operating system and lets technicians easily identify trouble spots by module or channel. Improvements to the control architecture, and the valve terminal's ability to supply data, also will make it easier to diagnose problems. This can be done with the HMI, or with an Ethernet module over the Web from anywhere in the world.
Festo Corp., (800) 99-Festo, festo.com