Question

Please write in computer or write clearly, so I can understand

Answer completely, is just one exercise

• Construct block diagrams to represent the major control mechanisms involved.
• Clearly identify the physiological correlates of the controller, the plant, and the feedback element, as well as the controlling, controlled, and feedback variables.
• Describe how negative (or positive) feedback is achieved in each case.

2.) A prolonged reduction in blood pressure due to massive loss of blood can lead to "hemorrhagic shock" in which the decreased blood volume lowers mean systemic pressure, venous return and thus, cardiac output. Consequently, arterial blood pressure is also decreased, leading to decreased coronary blood flow, reduction in myocardial oxygenation, loss in the pumping ability of the heart, and therefore, further reduction in cardiac output. The decreased cardiac output also leads to decreased oxygenation of the peripheral tissues, which can increase capillary permeability, thereby allowing fluid to be lost from the blood to the extravascular spaces. This produces further loss of blood volume and mean systemic pressure, and therefore, further reduction in cardiac outp

Answer 1

Prior to analysing or designing a control system, it is useful to define explicitly the major variables and structures involved in the problem. One common way of doing this is toconstruct a block diagram. The block diagram captures in schematic form the relationshipsamong the variables and processes that comprise the control system in question. blockdiagrams thatrepresent open-loop and closed-loop control systems in canonicalform. Consider first the open-loop system Here, the controller component ofthe system translates the input (r) into a controller action (u), which affects the controlledsystem or "plant" thereby influencing the system output (y). At the same time, however,external disturbances (x) also affect plant behavior; thus, any changes in y reflect contributions from both the controller and the external disturbances. If we consider this open-loopsystem in the context of our previous example of the heating system, the heaterwould be the controller and the roomwould represent the plant. Since the function of this control system is to regulate the temperature of the room, it is useful to define a set-point, which correspond to the desired room temperature. In the ideal situation of no fluctuations in external temperature (i.e., x = 0), a particular input voltage setting would place the room temperature exactly at the set-point. This input level may be referred to as the reference input value. In linear control systems analysis, it is useful (and often preferable from a computational viewpoint) to consider the system variables in terms of changes from these reference levels instead of their absolute values. Thus, in our example, the input (r) and controller action (u) would represent the deviation from the reference input value and the corresponding change in heat generated by the heater, respectively, while the output (y) would reflect the resulting change in room temperature. Due to the influence of changes in external temperature (x), r must be adjusted continually to offset the effect of these disturbances on y. As mentioned earlier, we can circumvent this limitation by "closing the loop." Figure

l.lb shows the closed-loop configuration. The change in room temperature (y) is now measured and transduced into the feedback signal (z) by means of a feedback sensor, i.e., the thermostat, The feedback signal is subsequently subtracted from the reference input and the error signal (e) is used to change the controller output. If room temperature falls below the set-point (i.e., y becomes negative), the feedback signal (z) would also be negative. This feedback signal is subtracted from the reference input setting (r = 0) at the mixing point or comparator (shown as the circular object in Figure 1.1b), producing the error signal (e), which is used to adjust the heater setting. Since z is negative, e will be positive. Thus, the heater setting will be raised, increasing the flow of heat to the room and consequently raising the room temperature. Conversely, if room temperature becomes higher than its set-point, the feedback signal now becomes positive, leading to a negative error signal which in turn lowers heateroutput. This kindof closed-loop system is said to have negative feedback, since any changes in systemoutput are compensated for by changes in controller action in the opposite direction. Negative feedback is the key attribute that allows closed-loop control systems to act as regulators. Whatwould happen if, ratherthanbeingsubtracted, the feedback signal were to be added to the input? Going back to our example, if the roomtemperature wereto rise and the feedback signalwere to be added at the comparator, the errorsignal would become positive. The heater setting would be raised and the heat flow into the room would be increased, thereby increasing the room temperature further. This, in tum, would increase the feedback signal and the errorsignal, and thus produce evenfurther increases in room temperature. This kind of situation represents the runaway effect that can result from positivefeedback. In lay language, one would refer to this as a vicious cycle of events. Dangerous as it may seem, positive feedback is actually employed in many physiological processes. However, in these processes, there are constraints built in that limitthe extentto whichthe system variables can change. Nevertheless, there are also many positive feedback processes (e.g., circulatory shock) that in extreme circumstances can lead to the shut-down of various system components, leading eventually to the demise of the organism.