SPECIAL TOPIC : Actuators & Automation
A Solution to Control Valve Deadband Issues : Shape Memory Alloy Actuators
In industrial settings , control valves serve as critical components , regulating and modulating fluid flows to ensure processes operate within desired parameters . Despite their widespread use , control valves , particularly those operated by traditional electric motorized or pneumatic actuators , face a common challenge : deadband ( Figure 1 ). This phenomenon , the control signal ’ s range that fails to elicit an output , can significantly undermine system performance .
By Adam Nguyen , M . Eng . - Kinitics Automation
Deadband commonly appears in systems that employ electric or pneumatic actuators , due to either the natural mechanical play or as a deliberate design decision . Designers may intentionally introduce deadband to their system processes to reduce motor duty-cycle for maintaining safe motor temperatures or to reduce the consumption of instrument air in pneumatic controllers . Its impact on the process under control is multifaceted , leading to delayed responses , inefficiencies , oscillations , and the potential for increased wear on components leading to more frequent maintenance . In industries like natural gas , where the precise handling of highly valuable and volatile substances is routine , minimizing deadband is not just a matter of efficiency but of safety and economic viability .
The introduction and adoption of Shape Memory Alloy ( SMA ) actuators in the industry offers a solution to the deadband issue . These actuators , benefiting from the unique characteristics of SMA technology , provide high precision and responsiveness . Distinct from their typi-
Figure 1 : Example deadband in an open loop valve control application .
cal electric motorized and pneumatic counterparts , SMA actuators boast the ability to operate at 100 % duty cycle without backlash or slop , effectively minimizing the effects of deadband . This capability is currently being leveraged in the natural gas sector to enhance the performance and reliability of control systems .
Control Valve Problems from Deadband
The phenomenon of deadband within valve control systems presents a series of challenges that directly influence the operational efficacy , precision , and reliability of process control . Deadband is defined by a range of control signal inputs that fail to elicit any adjustment in valve position and is an obstacle in maintaining optimal process conditions . Below are the key challenges associated with deadband , each underscoring the critical need for refined control mechanisms in industrial settings .
• Reduced Sensitivity to Control Signal Variations : The presence of deadband impairs a control system ’ s ability to respond to changes in the control signal . This reduction in sensitivity can lead to the inability to maintain process variables within narrow tolerances , essential for processes that require stringent control over parameters such as pressure and flow rates .
Figure 2 : A Kinitics KVA38 Glove Valve Actuator powered by SMA .
14 Valve World Americas | April 2024 • www . valve-world-americas . net