Primary controller

The primary control variables at a fixed feed rate, as in the operation pictured in Figure 8, are the cycle time, which is measured by the time required for one complete rotation of the rotary valve (this rotation is the analog of adsorbent circulation rate in an actual moving-bed system), and the Hquid flow rate in Zones 2, 3, and 4. When these control variables are specified, all other net rates to and from the bed and the sequence of rates required at the Hquid... 

Fig. 12. Cascade control signal flow diagram, where SPP = primary control variable setpoint PVP = primary control variable measurement ...

The dynamics of the secondary control loop should be approximately two to four times as fast as the dynamics of the primary control loop in order to achieve stable control. The secondary controller is actually part of the primary controller s process system. Hence, changes in the secondary controller tuning constants change the process system of the primary controller. Therefore, cascade control loops should always be tuned by first tuning the secondary controller and then the primary controller. If the secondary controller tuning is changed for any reason, the primary controller may need to be retuned also. 

Many misconceptions exist about cascade control loops and their purpose. For example, many engineers specify a level-flow cascade for every level control situation. However, if the level controller is tightly tuned, the out-flow bounces around as does the level, regardless of whether the level controller output goes direcdy to a valve or to the setpoint of a flow controller. The secondary controller does not, in itself, smooth the outflow. In fact, the flow controller may actually cause control difficulties because it adds another time constant to the primary control loop, makes the proper functioning of the primary control loop dependent on two process variables rather than one, and requites two properly tuned controllers rather than one to function properly. However, as pointed out previously, the flow controller compensates for the effect of the upstream and downstream pressure variations and, in that respect, improves the performance of the primary control loop. Therefore, such a level-flow cascade may often be justified, but not for the smoothing of out-flow. 

Once an undesirable material is created, the most widely used approach to exhaust emission control is the appHcation of add-on control devices (6). Eor organic vapors, these devices can be one of two types, combustion or capture. AppHcable combustion devices include thermal iaciaerators (qv), ie, rotary kilns, Hquid injection combusters, fixed hearths, and uidi2ed-bed combustors catalytic oxidi2ation devices flares or boilers/process heaters. Primary appHcable capture devices include condensers, adsorbers, and absorbers, although such techniques as precipitation and membrane filtration ate finding increased appHcation. A comparison of the primary control alternatives is shown in Table 1 (see also Absorption Adsorption Membrane technology). 

Depending upon the specifics of the toll, the primary control activity performed by the client during ongoing operations will be auditing the toller. This assures operations are going as planned and... 

Differential temperature as well as differential pressure can be used as a primary control variable. In one instance, it was hard to meet purity on a product in a column having close boiling components. The differential temperature across several bottom section trays was found to be the key to maintaining purity control. So a column side draw flow higher in the column was put on control by the critical temperature differential. This controlled the liquid reflux running down to the critical zone by varying the liquid drawn off at the side draw. This novel scheme solved the control problem. 

Pollutant Loading Pollutant loading is dependent upon the control effectiveness for fine PM of the primary PM control system. Fine PM may, in some cases, comprise up to 90 percent of the total mass of PM emissions from a combustion source, and many primary control technologies have relatively low collection efficiencies for fine PM. 

If primary control by the enclosure is under consideration, the extra wear and tear on electrode holding equipment by the escaping fume must be taken into account. This potential problem is particularly evident on ultra-high-power (UHP) furnaces where the holding equipment would be constantly exposed to high-temperature flame. As a possible solution, the furnace could be equipped with a roof-mounted water-coiled stub stack, which naturally draws fume from the furnace and into the enclosure. This approach would divert the fume and prevent damage to the electrode equipment. 

This type of compressor will continue to compress the air volume in the down-stream system until (1) some component in the system fails, (2) the brake horsepower exceeds the driver s capacity, or (3) a safety valve opens. Therefore, the operator s primary control input should be the compressor s discharge pressure. If the discharge pressure is below the design point, it is a clear indicator that the total down-stream demand is greater than the unit s capacity. If the discharge pressure is too high, the demand is too low and excessive unloading will be required to prevent failure. 

The primary controls in the reactor-regenerator section are flow, temperature, pressure, and catalyst level. 

In control situations with more then one measured variable but only one manipulated variable, it is advantageous to use control loops for each measured variable in a master-slave relationship. In this, the output of the primary controller is usually used as a set point for the slave or secondary loop. 

The Study Director is the pivotal person in any GLP study. The sponsor initiates the study and assigns a Study Director to act as the primary control point for all aspects of the study. The Processing Principle Investigator (PPI) acts as an agent of the Study Director and handles the processing phase of the study. The PPI reports directly to the Study Director, and quality assurance (QA) documents resulting from the processing phase are sent to the Study Director for approval. The Study Director has final say in all questions of compliance with GLP and interpretations of the protocol. The... 

A cascade control system can be designed to handle fuel gas disturbance more effectively (Fig. 10.1). In this case, a secondary loop (also called the slave loop) is used to adjust the regulating valve and thus manipulate the fuel gas flow rate. The temperature controller (the master or primary controller) sends its signal, in terms of the desired flow rate, to the secondary flow control loop—in essence, the signal is the set point of the secondary flow controller (FC). 

The modest 10% offset that we have in the slave loop is acceptable under most circumstances. As long as we have integral action in the outer loop, the primary controller can make necessary adjustments in its output and ensure that there is no steady state error in the controlled variable (e.g., the furnace temperature). 

Among other methods, root locus is the most instructive in this case. With a PI primary controller and numerical values, Eq. (10-3) becomes... 

A Routh-Hurwitz analysis can confirm that. The key point is that with cascade control, the system becomes more stable and allows us to use a larger proportional gain in the primary controller. The main reason is the much faster response (smaller time constant) of the actuator in the inner loop.2... 

Handling of disturbance in the inlet process stream temperature is passive. Any changes in this load variable will affect the furnace temperature. The change in furnace temperature is measured by the outlet temperature transducer (TT) and sent to the feedback temperature controller (TC). The primary controller then acts accordingly to reduce the deviation in the furnace temperature. 

The autonomic nervous system exerts the primary control on heart rate. Because the sympathetic and parasympathetic systems have antagonistic effects on the heart, heart rate at any given moment results from the balance or sum of their inputs. The SA node, which is the pacemaker of the heart that determines the rate of spontaneous depolarization, and the AV node are innervated by the sympathetic and parasympathetic systems. The specialized ventricular conduction pathway and ventricular muscle are innervated by the sympathetic system only. 

All antibodies age and therefore have a specific shelf life. Aging may be different for different antibodies, and real aging may be quite different from the expiry dates printed on containers of antibodies. Mixtures of antibodies as are found in secondary antibody cocktails may show distinct aging differences. In other words, over time, one of the species in a secondary cocktail may age at a more rapid rate than the other(s). This would result in a significant decrease in sensitivity for that particular species of primary antibody. A user performing IHC stain runs with multiple tissues, and using primary antibodies from more than one species, must utilize primary controls for each species of primary antibody to detect a change in one of the components of the secondary antibody cocktail. 

The IHC stain procedure is a multistep staining protocol, the various steps intended to provide amplification of stain results. Therefore, a control system must include elements to control each step of the stain process. Such a control should also include a range of reactivities, and that range ideally would encompass the total expression range expected for the measured component. The control should also monitor each step of the multistep protocol. This author has devoted a number of years to this concept, resulting in a patented control for multistep staining processes.14 Such a control provides sufficient information to monitor every IHC stain run, and when the control is evaluated quantitatively, normalization of data from one stain run to another within the same laboratory, and even between laboratories. A process control is a measure of the stain protocol and does not take the place of a control for the primary antibody. While the primary antibody control should include range of expression level detection, a different primary control must be present for every primary antibody used in a stain run (Fig. 10.4). 

Eek J., Gjengedal T., Influence of high wind power penetration on the Nordic power grid primary control response, 2006 CIGRE SESSION, Paris, France, August 27-September 01, 2006. 

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