Valve terminals have come a long way from early beginnings of adding a multipin connector onto a manifold. Valve terminals now combine pneumatic valves, digital and analog I/O, and even advanced functions like servocontrol into a single automation platform with a network adapter. The adapter lets users make a single connection to a fieldbus or Ethernet network and control the entire system from a PLC. Valve terminals drastically reduce the amount of labor required to install and commission an automation platform — by up to 65% as compared to conventional hard-wired systems.
The pullout screen shows operating parameters for a VPPM proportional valve.The complexity of modern valve terminals does pose a challenge to engineers who commission and control the I/O devices that the valve terminals handle. For instance, an advanced valve terminal like Festo’s CPX supports up to 512 I/O per fieldbus node. Complex functions, variable data types, and many kinds of messages have to be managed. Fortunately, some manufacturers have developed software tools that help engineers manage the data and make commissioning more efficient.
One example of this is the L5K Export option of the Festo Maintenance Tool. This feature offers several benefits to controls engineers using Ethernet/IP with Rockwell Logix5000-based controllers. It adds descriptions to the tag names associated with every function of the valve terminal. For example, if 2 bytes are required to read a temperature input from a thermocouple module, the description field will be labeled with the module number, byte order (high or low), and input’s channel number. All this is readily available and saves the programmer time.
Another L5K Export feature adds parameter data to the valve-terminal configuration. Parameters such as operating limits and alarms can be stored in an I/O device, but this often becomes a problem in a disaster recovery situation. If hardware is damaged due to an unforeseen incident, a replacement module will not have its parameters set out of the box. If installed parameters are unknown or not readily available, getting the machine up and running will take some time. Setting parameters inside the PLC and having them pushed to the valve terminal is a much more secure and reliable method for handling parameter data.
Let’s look at an example. Consider a handling operation that deals with a number of different parts. Because of the variety, actuators must generate varying forces. Rapid axis movements are required to meet cycle times. And directional valves are needed to activate clamps.
A CPX valve terminal can be configured to perform all the required operations: Servopneumatics for rapid axis positioning; integrated proportional-pressure regulators for controlling a zone of valves that vary pressure to change actuator forces on the fly; and additional valves and analog I/O to complete the necessary operations, including monitoring.
The manifold can be modeled in the Festo Maintenance Tool software, as shown in the screen image on the previous page. Once modeled, the user then sets parameters for the necessary operating functions. For example, the pullout screen for Module #8 (a VPPM proportional valve) lets the user program the pressure regulator in psi units and set an upper-limit warning of 90 psi. In this configuration, a program value of 605dec will command the regulator to go to 60.5 psi. It requires no scaling on the part of the user, which makes programming easier and minimizes chances of mistakes.
By exporting this model to an L5K format, the Logix 5000 software can subsequently import data when needed. The first benefit for the user is that it automatically populates the Generic configuration table, shown above. The software calculates I/O size and configuration data for the application, which eliminates configuration- related errors.
Configuration data is stored as a project in the Logix 5000, and will be pushed to the CPX each time Ethernet/ IP establishes a connection. Storing data in this manner, rather than in the CPX, makes disaster recovery relatively simple.
In addition, Logix 5000 description fields are annotated, making it easy to rapidly identify tag names for the CPX system. In the example below, CPX output data byte 0 is easily identified as the least significant byte of the VPPM in slot #8. This also eliminates errors and reduces programming time.
Users taking advantage of the integrated functions that modern valve terminals provide no longer face complex programming tasks. Software tools make commissioning easier than ever and provide benefits like disaster recovery and programming without scaling.