Process control controlled-cycling operation mode

PSA systems are moderately reliable. The numerous valves associated with the process can cause unexpected shutdowns. The new PSAs are designed with alternate modes of operation, in which 100% of design capacity can be achieved while bypassing any failed valve or instrument, with only a slight loss of recovery. Failures are automatically detected and bypassed by the microprocessor-based control system. However, stronger and periodic control cycles are required. 

Reliability takes into account the on-stream factors which can cause unscheduled shut-downs. Membrane systems are extremely reliable with respect to the on-stream factor. The membrane separation process is continuous and few control components can cause a shut-down. Typically, the response to unscheduled shut-downs is rapid for GS whereas PSA systems are moderately reliable owing to the numerous valves associated with the process which can cause unexpected shut-downs. The new PSA are designed with alternative modes of operation, in which 100% of design capacity can be achieved while by-passing any failed valve or instrument, with only a slight recovery loss. Failures are automatically detected and by-passed by the microprocessor-based control system. Flowever, stronger and periodic control cycles are required. The cryogenic process is considered by refiners to be less reliable than PSA or membrane... 

To maintain control of the computer system throughout its conception, implementation, and operational use in a GMP environment, it is required that the computer system application must be validated in a way that will establish auditable documented evidence that the computer system does what it is expected to do. As applicable, this needs to be carried out in conjunction with plant equipment to provide a high degree of assurance that a specific process will consistently produce a product meeting its predetermined specifications and quality attributes. The methodology to achieve this is based on a recognized life-cycle mode. 

While the chemical kinetics of the thermal autoignition process are relatively well understood, means of controlling the ignition timing in the engine cycle when operating in the HCCI mode are still elusive. Chemists and chemical engineers will need to help overcome this obstacle if HCCI is to be executable in automotive practice. 

Two-Position Control. The simplest case is two-position (on-off) control. Here, any deviation of the measured value from a set point drives the final control-operator to either a full-on or full-off position. This forces the measured value back and forth across the set point, and the measurement signal cycles about this point. The amplitude and frequency of this cycle depend on the response characteristics of the process. As the process dead-time becomes small, the frequency of the cycle becomes high likewise, as the process capacitance becomes high, the amplitude of the cycle becomes small. This mode of control is used only for processes in which this cycling effect can be tolerated it is most successful with those having large capacitance. 

If only one cycle is to be executed, the controls are in the semiautomatic mode. If a practically unlimited number of cycles are to be executed, the eontrols are in the frdly-automatie mode. The machine operator must start the process by pressing a button. Usually the process will start only if all machine components are in their respective starting conditions. If this is not so, the controls issue an appropriate error message or automatically restore the components to their starting conditions. 

In summary, punches and dies with the desired shapes, angular orientation, and proper die clearances are loaded into the turrets, the part program is brought into active memory in the control, the work sheet is properly located on the machine table and into the work clamps, and the machine control is placed in the automatic mode. Next, the operator starts the part program by pushing Cycle Start and the fabrication process is underway. 

Laser SNMS requires the operation with properly selected duty cycles that control the delay times between the primary ion pulse, a pulsed extraction voltage for separating the secondary ions from post-ionized neutrals, and the firing of the postionizing laser pulse. Such duty cycles have, in addition, to be synchronized with the stepwise motion of the pulsed primary ion beam across the sample surface in the microprobe mode of laser SNMS. The selection of appropriate duration and decay times of the ion and laser pulses, of the laser intensity, and beam shape is important to make the photoion yields independent on the sputtered particle velocities. The detection volume must be matched to the entrance ion optics of the TOP such that it becomes independent of the individual ionization process. Usually, laser intensities in the range from 10 to lO Wcm are applied. While the particle density in the detection volume is monitored at small laser intensities, the particle flux is measured at high photon densities. 

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