On Mason reset-based control and the scale of integration

关键词:  Mason Reset · Scale of integration · Gain scale · Time scale · Reset windup · Integrator windup · Mason Reset Based control

Key words:  Mason Reset · Scale of integration · Gain scale · Time scale · Reset windup · Integrator windup · Mason Reset Based control

摘要:

Mason Reset (MR), a groundbreaking invention by Clesson E. Mason in 1930 that later became a part of “the universal approach to process control instrumentation”, is revisited in this paper and is shown to consists of three actions: fast (errorcorrection), medium (negative feedback for expanded proportional band) and slow (reset for zero steady-state error). The focus of the paper is on the reset action, generated from a positive feedback loop, and its underlying principles with profound implications to our understanding and practice of automatic control, both basic and advanced. For example, we note that reset control and integral control, contrary to common belief, differ fundamentally in design principle and in practicality. Such difference comes to a head in the event of integrator windup: while reset windup is a problem of actuator saturation, the integrator windup is a runaway situation due to controller instability. In fact, there is no advantage gained in replacing MR with an integrator. In other words, one should not integrate the error directly as in standard PID, since doing so makes the closed-loop system internally unstable. With MR-based control formulated in this paper, there is no such threat of instability and, therefore, no need for any anti-windup mechanisms. Furthermore, the integral control is made scalable in this framework as a tradeoff between the steady-state accuracy and the controller stability. This leads to a novel MR-based control design, scalable in gain and in time to accommodate various process characteristics and design specifications. Simple in construction and transparent in principle, this MR-based control, as a basic framework of design, is readily deployable in scale.

Abstract:

Mason Reset (MR), a groundbreaking invention by Clesson E. Mason in 1930 that later became a part of “the universal approach to process control instrumentation”, is revisited in this paper and is shown to consists of three actions: fast (errorcorrection), medium (negative feedback for expanded proportional band) and slow (reset for zero steady-state error). The focus of the paper is on the reset action, generated from a positive feedback loop, and its underlying principles with profound implications to our understanding and practice of automatic control, both basic and advanced. For example, we note that reset control and integral control, contrary to common belief, differ fundamentally in design principle and in practicality. Such difference comes to a head in the event of integrator windup: while reset windup is a problem of actuator saturation, the integrator windup is a runaway situation due to controller instability. In fact, there is no advantage gained in replacing MR with an integrator. In other words, one should not integrate the error directly as in standard PID, since doing so makes the closed-loop system internally unstable. With MR-based control formulated in this paper, there is no such threat of instability and, therefore, no need for any anti-windup mechanisms. Furthermore, the integral control is made scalable in this framework as a tradeoff between the steady-state accuracy and the controller stability. This leads to a novel MR-based control design, scalable in gain and in time to accommodate various process characteristics and design specifications. Simple in construction and transparent in principle, this MR-based control, as a basic framework of design, is readily deployable in scale.