From Feedback Control of Computing Systems


9.6.1   PI Control of the Apache HTTP Server Using
Empirical Methods

This example extends Section 8.7.2 in which proportional control is used to manage
the Apache HTTP Server. As before, KeepAlive (the time that idle HTTP
connections are held) is manipulated so as to regulate CPU (CPU utilizations).
This example describes the use of a PI controller instead of the proportional
controller of Example 8.7.2.

Figure 9.26 displays a block diagram of the Apache HTTP Server with
noise that is modeled as an additive effect on CPU. The operating point is
= (0.58, 11). The input and output offsets are u(k) = KA(k) −
and y(k) = CPU(k) − , respectively. The controller has the transfer function
KP + zKI /(z − 1), and the transfer function of the target system is G(z) =
−0.014/(z − 0.59). Our focus is on noise rejection. The transfer function from
the noise to the output is


Note that FN(1) = 0, so this system should have no steady-state error in response
to a step noise as...

More >> Show More...

Products & Services
Pressure Controllers
Pressure controllers accept input from pressure sensors, transmitters, gauges, and other devices and subsequently control adjustment to the pressure to maintain or achieve the desired pressure level.
Web Controllers
Web controllers maintain control functionality over processes with web or sheet rollers.  Control functionality includes maintaining tension of the web, centering on the track, and material feed rates.
Universal Process Controllers
Universal process controllers constitute a broad area of control devices that may be employed in the monitoring and control of many different process variables, including temperature, pressure, flow and other values.
Audio Amplifiers and Preamplifiers
Audio amplifiers and audio preamplifiers are used to increase the amplitude of sound signals.  Preamplifiers or preamps are designed to amplify low-level signal from a high-impedance device such as a microphone or instrument pick-up. After pre-amplification, the signal is sent to a power amplifier or amp, which provides the higher current necessary to drive the speakers.
Inertial Sensor Chips
Inertial sensors are semiconductor devices used to measure acceleration, changes in inclination, and gyration.

Topics of Interest

9.6.2   Designing a PI Controller for the Apache HTTP Server Using Pole Placement Design This example applies the analytic techniques developed in Section 9.2.4 to the Apache HTTP Server of...

9.2.2   PI Control Design by Pole Placement Consider the closed-loop system with PI control in Figure 9.9. We have four design goals for the PI controller: (1) the closed-loop system is stable;...

*9.7   DESIGNING PI CONTROLLERS IN MATLAB In this section we describe ways to use MATLAB in controller design. In Section 8.8 we introduce the MATLAB functions feedback, pole, zero, dcgain, and...

9.2.3   PI Control Design Using Root Locus In pole placement design, the desired closed-loop poles are determined based on an a priori specification of desired properties of the closed-loop...

9.2   PROPORTIONAL–INTEGRAL CONTROL Proportional–integral (PI) control combines the advantages of integral control (zero steady-state error) with those of proportional control...

Product Announcements
Emerson Automation Solutions – TESCOM Regulators, Valves & Systems