Overshoot-undershoot

Question 2 Is my equipment somehow responsible That is sadly often the case. For example, some electronic loads can show weird glitches in the load profile they present to the converter under dynamic conditions. For example, if we are doing step load testing from 10mA to 200mA, all may be fine. But if we go from 0mA to 200mA, and see an output overshoot/undershoot, it could also be because of the electronic load. We may need to do... 

Note Under very large fine or foad steps, we wilf actually no longer be operating in the domain of the small-signal analysis which we have been performing so far. In that case, the initial overshoot/undershoot at the output is almost completely determined simply by how large a bulk capacitance we have placed at the output. That capacitance is needed to hold the output steady, until the control loop can enter the picture and help stabilize the output. 

A more natural phenomenon seems to be the oligo-oscillation, or the overshoot-undershoot phenomenon. These expressions denote the case when there is only a finite number of local extrema on the concentration versus time functions. Natural as it is, it has rarely been studied in a well-controlled experiment (see, however, Rabai et a/., 1979). It has also rarely been studied from the theoretical point of view. This situation can be explained by the fact that the qualitative theory of differential equations usually makes statements on long-range behaviour and much less on transient behaviour. The only exception seems to be that Pota (1981) has given a complete proof of the statement called Jost s theorem which says in a closed reversible compart-mental system of M components none of the concentrations can have more than M - 2 strict extrema. The methods used by Pota makes it possible to extend this result (see Problem 6 below). Another result of this type, relating nonlinear kinetic differential equations, can also be found among the Problems. 

Pota, Gy. (1981). On a theorem of overshoot-undershoot kinetics. React. Kinet. Catal. Lett., 17, 35-9. 

Rabai, Gy., Bazsa, G. Beck, M. T. (1979). Design of reaction systems exhibiting overshoot-undershoot kinetics. J. Am. Chem. Soc., 131, 6746-8. 

Appreciable pressure overshoots and undershoots are noticeable. The pressure trace at the end of the runner system (P2) at lower levels follows the pattern of the nozzle pressure. 

Considerable difficulty was experienced throughout the entire period of plant-scale operation of the DBBP countercurrent extraction process in adjusting the CAW solution to the desired pH of 0.75. Several factors contributed to these difficulties. Lack of any buffering capacity in the CAW solution made it easy to overshoot or undershoot the desired pH. The two-step neutralization procedure and equipment aided considerably in achieving proper feed acidity. But, even with this approach, inadequate mixing coupled with unsophisticated and insensitive monitoring and control instrumentation made it impossible to routinely achieve reliable adjustment of feed acidity to its optimum range. 

The result for the thermal expansion coefficient, a, which is equal to (dV/dT)/V, is shown in Fig. 13.36 for the cooling and heating process. In the cooling process a decreases gradually from tq to ag. Hysteresis in the volume causes in the subsequent heating process an anomalous effect in the thermal expansion coefficient, depicted by undershoot and overshoot, as also shown in Fig. 13.36. A similar effect occurs in enthalpy H and accordingly in cp, the specific heat capacity, equal to dH/dT. This effect is frequently observed in DSC (Differential Scanning Calorimetry) experiments. 

The velocity aloi the symmetry axis is significantly different an overshoot at the contraction as well as an undershoot downstream of the die exit are observed with the generalized Oldroyd-B model, but only a smooth overshoot is indicated by the multimode Phan-Thien Tanner model. The final value of the velocity after swelling is more important for the PTT, which is consistent with the lower value of swelling observed in Fig 20. 

The scaling, Eq. (9-48), also implies that time-dependent stresses can be rescaled so that data taken at different shear rates collapse onto a single curve. Consider an example in which the sample is sheared at a rate yt until a steady state is reached, and then the shear rate is suddenly increased by a factor of four to y/ — 4yi. After this increase in shear rate, the shear stress undergoes an overshoot and an undershoot, while the first normal stress... 

Although this experimentally observed scaling behavior is correctly predicted by the Doi-Ohta theory, the shape of the transient response curve—in particular, the overshoot and undershoot in the shear stress—are not predicted. This implies that the relaxation expressions chosen by Doi and Ohta, Eqs. (9-46) and (9-47), are inaccurate. This is not very surprising, since Eqs. (9-46) and (9-47) were chosen rather arbitrarily from many possible forms that satisfy the scaling relationship. Optical microscopy suggests that the overshoot and undershoot are caused by elongation of droplets followed by their breakup (Takahashi and Noda 1995). Vinckier et al. (1997) have shown that the stress growth after start-up or... 

It is really a large-signal response issue. The biggest impact on the undershoot/overshoot observed in this case comes simply from the amount of bulk capacitance (and stored energy) present at the output. Because in the initial instant of sudden application of load, the bulk capacitor (Cqut) alone provides the energy being demanded by the load, until the loop finally kicks in to prop up the falling rail. Note that it takes several cycles for the current to ramp up to the new required level in the inductor. So small inductances tend to help in quick recovery and help achieve a fast loop response (of course provided they don t create full-blown instability in the process). 

Incorrect calibration of the pipet (2) temperature different from calibration temperature (3) incorrect filling of the pipet (overshooting or undershooting the mark). 

But sometimes, we do want to know what happens at the moment of application of a stimulus — whether subsequently repetitive, steady, or otherwise. Like the case of the step voltage applied to our RC-network. If this were a power supply, for example, we would want to ensure that the output doesn t overshoot (or undershoot ) too much. 

We see that an optimum feedback loop is neither too slow, nor too fast. If it is too slow, the output will exhibit severe overshoot (or undershoot). And if it is too fast (over-aggressive), the output may ring severely, and even break into full instability (oscillations). 

A very high phase margin may be very stable, with almost no ringing, but there will be greater undershoot/overshoot. 

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