It’s said that nothing succeeds like success, but after years and decades pile up, initially successful innovations can result in huge installed bases that can be challenging to service and maintain.
For instance, Emerson’s Fisher Instruments has been producing its Wizard pneumatic controllers since the 1940s, refining and revamping them every 20 years or so. Along the way, the company produced its electro-pneumatic controllers, and more recently developed its Fisher Fieldvue digital pneumatic controllers (DPC). In all, Emerson estimates there are more than 1 million of its pneumatic controllers presently operating.
However, despite their longtime service regulating valve actions, pneumatic controllers have many limitations. Using them typically results in closed-loop control that’s sluggish and imprecise, causes frequent deviations from setpoint, and degrades performance as their mechanical components wear out. This degradation impedes reliability, requires excessive onsite maintenance, and increases staff travel and safety issues.
“A wholly pneumatic controller is a standalone device, but today’s users want to establish setpoints remotely, so they don’t have to drive out to them all the time,” says Jerry Van Staalduine, senior product manager at Fisher Instruments. “They also want to communicate with their pneumatic controllers, monitor them from their SCADA systems, and automate troubleshooting to save time by knowing what issues they’re facing and what tools and parts to take when they do have to visit devices.”
To provide the capabilities that can alleviate these difficulties, Emerson is launching its Fisher Fieldvue DPC2K digital process controller that can be retrofitted where Fisher Wizards, other pneumatic controllers and pneumatic controllers are installed on control valves—regardless of manufacturer. Because it’s configurable, the same base model can be used in a variety of applications, including but not limited to pressure, flow, level, temperature, percentage, volume and rate control.
DPC2K improves closed-loop control with configurable loop types, more than 150 units of supported measurements, 50-millisecond scan and update rates, configurable deadband, anti-reset windup and dynamic reset limiting. These features cooperate to keep process variables (PV), such as pressure, flow, level or temperature, close to their setpoints, as well as improve recovery from saturated conditions.
DPC2K has an integral, sealed gauge pressure sensor that’s available with 0-30, 0-100, 0-300, 0-600, or 0-1,500 psi ranges. Its pneumatic output has a low-bleed of less than 3.0 SCFH. DPC2K is rated for Class 1 Div 1 or Zone 1 hazardous areas. Its operating temperature range of -40 to 80 °C. Input voltages of 9-28 VDC are accommodated, with a typical power draw of only 1 watt. High-speed, two-way digital remote access is provided by Modbus TCP and HART IP Ethernet protocols or via Modbus RTU RS-485 serial protocol, which allow access to all discrete and analog variables in the controller from any host application.
“DPC2K is different because it’s flexible at the valve and can connect to many different sizes,” explains Van Staalduine. “We’ve taken RTU, PLC and DCS functions that used to be separate in the electro-pneumatic space, and put them all together right on the valve.”
DPC2K is configured with LoopConnect software that’s free to download and enables remote access. It’s designed to run for years with no required maintenance, but it’s easily done with modular replacement parts when maintenance is finally needed. DPC2K is also easy to interact with locally or remotely. At the controller, users interact with its menu-driven LCD and six-button user interface. It allows users to: display setpoint versus process variable; view alarms, alerts and status; pick manual/remote setpoint; select auto/manual output control; set up communications; and lockout or exercise the valve.
DPC2K performs local closed-loop, digital control using its integral PID controller, and can accept a 4-20 mA input from transmitters that typically provide a PV. Setpoints can be set locally or via a remote, 4-20mA or digital signal. To close the PID loop, a 4-20mA manipulated variable output is available to regulate the final control element. The PID controller uses valve travel and position to make sure the manipulated variable output is at the correct value, reducing PV deviation from setpoint. If the pneumatic manipulated variable output option is used, it controls the final control element, and the 4-20 mA output becomes available to transmit PV or other internal variables.
“DPC2K is a single-loop controller, but now it’s also a preconfigured device that doesn’t need so much programming, which makes its user experience simple and makes it easier to support,” adds Van Staalduine. “It can go on a skid, be shipped anywhere, and users can still access it. Many users still think of PID control as a voodoo art, but we’ve made DPC2K easy to implement and as simple as possible to use.”
For more information, visit Emerson.com/FisherDPC2K.