Command signal

Modern subsea trees, manifolds, (EH), etc., are commonly controlled via a complex Electro-Hydraulic System. Electricity is used to power the control system and to allow for communication or command signalling between surface and subsea. Signals sent back to surface will include, for example, subsea valve status and pressure/ temperature sensor outputs. Hydraulics are used to operate valves on the subsea facilities (e.g. subsea tree and manifold valves). The majority of the subsea valves are operated by hydraulically powered actuator units mounted on the valve bodies. 

In the Three Mile Island incident, the command signal to close the reactor relief valve was displayed, not the actual position of the valve (Kletz, 1988). Since the valve was actually open, the incident was worse than otherwise. 

Communication links for data transfer and command signals. 

Fig. 15.18 SFJ test results obtained with a command signal composed of two sine waves, showing that the generated thrust follows the applied command signals through the gas generator pressure and the ramburner pressure.

This is employed when the process is not well-known. The Model Reference Adaptive Controller contains a reference model to which the command signal or set point change is applied as well as to the process itself (Fig. 7.98)<4 ). The output of the reference model is postulated as the desired controlled process output and this is compared with the actual process output. The difference (or error) e , between the two outputs is used to adjust the controller parameters so as to minimise the relevant integral criterion. For example, if the ISE criterion is employed then the quantity... 

Sarvomechanisms. Servomechanisms are part of a broad class of systems that operate on the principle of feedback. In a feedback control system, the output (response) signal is made to conform with the input (command) signal by feeding back to the input a signal that is a function of the output for the purpose of comparison. Should an error exist, a corrective action is automatically initiated to reduce the error toward zero. Thus, thru feedback, output and input signals are made to conform essentially with each other... 

The centrifugal pump directly driven by a variable-speed electric motor is the most commonly used hardware combination for adjustable-speed pumping. The motor is operated by an electronic motor speed controller whose function is to generate the voltage or current waveform required by the motor to make the speed of the motor track the input command signal from the process controller. 

Guided Missile, Antitank. An A/T missile whose path is controlled by a combination of optical sighting and command signals from an automatic computer thru multiple wire command links. It may also contain an IR homing device for final range correction. It is designed to be launched from any type vehicle or ground emplacement. 

Actuation of components in the process through output (command) signals Input (feedback) signals from valves and motors informing the control system that the component in question has been actuated Input (analog) signals from transmitters covering temperature, pressure, and other parameters that provide information on the actual status of process variables... 

To evaluate the proposed adaptive control performance, opening of production choke and flow rate of injected gas at the well-head are random pulses as command signals, as shown in figure 5. The opening value of the production choke Upc also is the manipulated variable of the control strategy. Figure 6 shows noisy measurements and filtering outputs of closed-loop system, where variable variances of measurement noises are apparent. Note that Wpc illustrated the stabilized behavior of closed-loop system. 

Among other kinds of complex systems are those which incorporate high speed computers in the control loop to generate the command signals for the controllers on the basis of broad scale appraisals of operating performance, output requirements, and other pertinent variables. Such systems are not yet completely in being in the process industries, but... 

Figure 22.4 illustrates a different way to adjust the parameters of the controller. We postulate a reference model which tells us how the controlled process output ideally should respond to the command signal (set point). The model output is compared to the actual process output. The difference (error em) between the two outputs is used through a computer to adjust the parameters of the controller in such a way as to minimize the integral square error ... 

It sends out command signals to the various manipulated variables in either analog or digital form. 

Externally powered prostheses use electrical power to provide function. The electrical power is applied via motors located in the terminal device (hand or hook), wrist, and elbow. The grip force of the hand can be in excess of 100 N. Command signals are generated either by voluntary contraction of muscles, so-called myoelectric control, or by using switches of different kinds. For apphcations that are more complex, both the command signals are used for different operations (e.g., control of several degrees of freedom). 

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