Control band, dead

Core power level The uncertainty of the core power level represents the cahbration error in core power measurements and the control system dead band. A typical error of 2% of the nominal value is used to determine the maximum and minimum bounds, and this error is usually taken as 2normal distribution and v cr for a uniform distribution. Therefore, the standard deviation [Pg.186]

In order to get an extremely high resolution and a small dead zone" (after the transmitter pulse) single amplifier states must have a bandwidth up to 90 MHz ( ), and a total bandwidth of 35 MHz (-3 dB) can be reached (HILL-SCAN 3010HF). High- and low-pass filters can be combined to band-passes and provide optimal A-scans. All parameters are controlled by software. 

In addition to energy conservation, the variable speed drives offer better control because of a faster response, ie, reduced dead band. They are also sometimes chosen for safety reasons because of elimination of the control station and accompanying valving. The capital saved by use of a smaller motor and elimination of the control valve partially compensates for the cost of the drive. 

With the exception of the dead-band booster, the application of booster relavs has diminished sornewEat bv the increased use of ciir-rent-to-pressiire transducers, electropneiirnatic positioners, and electronic control svsterns. Transducers and valve positioners serve much the same fiinctionalitv as the booster relav in addition to interfacing with the electronic process controller. 

Dead band A range of the controlled variable in which no corrective action is taken. 

A three-state controller is used to drive either a pair of independent two-state actuators, such as heating and cooling valves, or a Didirec-tional motorized actuator. The controller is comprised of two on/off controllers, each with dead band, separated by a dead zone. While the controlled variable lies within the dead zone, neither output is energized. This controller can drive a motorized valve to the point where the manipulated variable matches the load, thereby avoiding cycling. 

FIG. 8-88 Dead-band booster relay. (Courtesy Fisher Controls International LLC.)... 

From a dynamic response standpoint, the electronic adjustable-speed pump has a dynamic characteristic that is more suitable in process control applications than those characteristics of control valves. The small amplitude response of an adjustable-speed pump does not contain the dead band or the dead time commonly found in the small amplitude response of the control valve. Nonlinearities associated with friction in the valve and discontinuities in the pneumatic portion of the control valve instrumentation are not present with electronic variable-speed drive technology. As a result, process control with the adjustable-speed pump does not exhibit limit cycles, problems related to low controller gain, and generally degraded process loop performance caused by control valve nonlinearities. 

Unless sophisticated speed control power electronics is used, position modulation is achieved via bang-zero-bang control. Mechanical inertia causes overshoot, which is (1) minimized by braking and/or (2) hidden by adding dead band to the position control. Without these... 

Most common metal oxide and metal chalcogenide semiconductors have valence-band edges that lie positive of the oxidation potentials of most organic functional groups, and thermodynamics will thus favor photocatalytic oxidation. For efficient processes to take place, an easily oxidizable donor is required, but a whole range of substrates have been shown to be useful for this application. For example, a Japanese group has shown that this purpose is served not only by pure compounds, but even by wastes such as polyvinyl chloride, algae, protein, dead insects, and animal excrement, which function as electron sources [104]. Thus, synthetic utility is attained only if this wide reactivity is controlled. In practice, selectivity is best controlled by the adsorption and oxidation potential effects [105],... 

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