- October 18, 2023
- Emerson
Control and on-off valves are installed throughout process plants and facilities to regulate the flow of liquid and gas media, often in critical applications. Because these valves frequently change position and are in constant contact with process media, wear and tear is inevitable, so their performance and condition must be carefully monitored to ensure proper operation and anticipate any issues.
Control valves are typically operated remotely via a 4-20mA signal from a distributed control or other automation system, with the valve moving to the position commanded by the signal. The signal is usually generated by a PID control loop running in the automation system based on a process variable input received from a flow measurement device installed downstream of the control valve. Ideally, this allows the loop to regulate process media flow so it follows the setpoint, but without feedback from the control valve regarding its position, drift from the setpoint can occur.
As their name implies, on-off valves don’t move through a range of travel to regulate flow to follow a setpoint but are instead either fully open or fully closed. This makes control of these valves simpler, but their operation is no less critical in many plant processes.
To address issues with control and on-off valve monitoring and provide other functionality, digital valve controllers were first introduced to the market back in 1975, with improved versions following over the past few decades, culminating in the Fisher DVC7K, recently introduced by Emerson.
Evolution of valve positioners and controllers
A digital valve controller is a microprocessor-based instrument that is compatible with a variety of communication protocols, such as HART, FOUNDATION fieldbus, and PROFIBUS. The microprocessor enables diagnostics and two-way digital communication to simplify setup and troubleshooting.
In a typical digital valve controller, the output signal from a PID controller in an automation system is read by the microprocessor, processed by a digital algorithm, and converted into a control valve drive current signal to the I/P converter. The microprocessor then executes the position control algorithm—instead of a mechanical beam, cam and flapper assembly.
The first pneumatic valve positioner, designated Fisher 3582i (Figure 1, the photo above), was introduced in 1975, and it pioneered valve control by providing travel feedback in the form of valve stem position proportional to the pneumatic input signal. This allowed the automation system to better regulate valve position so measured flow could follow the setpoint more closely.
The Fisher FIELDVUE DVC5000 was the world’s first digital valve controller when it was released in 1994, and it provided live feedback on the valve travel position so the controller could not only diagnose itself, but also the valve and actuator on which it was mounted.
This was followed by the FIELDVUE DVC6000 digital valve controller in 2000, which modularized components for easier maintenance. Next in line was the FIELDVUE DVC6200 digital valve controller in 2010, which further improved performance and reliability with linkageless feedback (Figure 2).
These advancements each provided significant benefits to end users, but more functionality was needed, resulting in a new controller.
Edge computing enables advancements
The DVC7K digital valve controller was just released in October 2023, and it is built on 30 years of proven field-tested innovation (Figure 3). With over three million FIELDVUE units sold and ten billion hours plus of field operation since the introduction of the FIELDVUE DVC5000 in 1994, long-term reliability and performance is assured, a key requirement as Fisher and other Emerson valves are often used in critical applications. Data and information from the controller can be used to improve the performance, reliability, and uptime of both on-off and control valves, and by extension an entire process plant or facility.
The controller interprets data to create an optimized path to action by combining patented technology, experience-based algorithms, and continuous real-time analytics with flexible connectivity and easy integration. It uses powerful, real-time, and onboard edge computing to analyze issues and create actionable information, providing real-time awareness of valve health by analyzing data locally via its on-board diagnostics. If analysis reveals a problem, an Alert is created, which can be viewed locally or remotely, providing the information required to create streamlined work processes that save time and money. All Alerts include recommended actions to fix the problem, which is a new feature, and one unique to the industry.
All information can be viewed at the controller’s local user interface, nearby via Emerson Secure Bluetooth, or remotely after it is transmitted via a wired digital network to a host, such as a distributed control or asset management system. The local user interface provides indication of valve health at a glance via LEDs, and users can drill down from the interface home screen to find more information. Emerson Secure Bluetooth enables access to one or more digital valve controllers at distances up to 30 feet from any device capable of supporting Bluetooth, such as a smartphone or tablet. Whether the information is viewed locally, nearby, or remotely, plant personnel can use it to drive awareness of valve health.
With more opportunities for remote connectivity and advice at the device, flexibility increases, providing the information needed for fast decisions and quick action to address arising issues. The DVC7K digital valve controller can be specified for all new valve purchases, and it can be retrofitted to most existing valve installations, in either case quickly and easily commissioned via the local user interface.
Control valve applications
Diagnostic data from digital valve controllers plays a critical role by empowering users to operate more safely, identify and minimize process variability, plan smarter maintenance, and reduce process downtime. Until now, this data was only captured during scheduled diagnostic sweeps, or when the valve was out of service and analyzed.
With the always-running, onboard diagnostics on the FIELDVUE DVC7K, diagnostic data is now automatically captured at the time an event occurs, and it is stored and managed onboard the instrument. This new feature allows the instrument to constantly monitor valve operation, and it provide users with access to the most recent and relevant information so they can review and analyze their control valves installed in critical applications.
With 24/7 onboard diagnostic data capture, configurable device Alerts, and recommended actions, the DVC7K empowers users to leverage data and develop work practices for their entire fleet of control valves in ways never before possible with other digital valve controllers.
On-off valve applications
Users with critical isolation valve applications can use the DVC7K when changing from solenoid control to a digital positioner with on/off diagnostics. Stroke time measurements with stroke time degradation tracking, and partial stroke testing, provide monitoring and testing of on/off valves, giving users the ability to address problems before they impact operations. The DVC7K provides these new features, along with other diagnostics, in a new offering specifically designed for high criticality on/off valves.
Along with the added diagnostic data features, the DVC7K also greatly improves reliability as compared to solenoid control, which is often a weak point for these types of applications. Optional built-in position feedback, provided by two limit switches, provides certainty of operation for on/off valves, without the need for additional devices. Utilizing a single device simplifies installation and maintenance, and FIELDVUE mounting kits enable reliable mounting to a wide variety of isolation products, without the need to design and fabricate custom brackets.
Conclusion
Control and on-off valves carry out critical functions in process plants and facilities worldwide, so their performance and condition must be closely monitored. New digital valve controllers provide this functionality, along with other tasks, improving the operation and uptime of these valves. These controllers also enable optimization of maintenance activities by predicting failures well in advance, allowing for proactive instead of reactive actions.
All figures courtesy of Emerson