Response Characteristics

Sources of Error. pH electrodes are subject to fewer iaterfereaces and other types of error than most potentiometric ionic-activity sensors, ie, ion-selective electrodes (see Electro analytical techniques). However, pH electrodes must be used with an awareness of their particular response characteristics, as weU as the potential sources of error that may affect other components of the measurement system, especially the reference electrode. Several common causes of measurement problems are electrode iaterferences and/or fouling of the pH sensor, sample matrix effects, reference electrode iastabiHty, and improper caHbration of the measurement system (12). 

Pneumatic controllers are made of Bourdon tubes, bellows, diaphragms, springs, levers, cams, and other fundamental transducers to accomplish the control function. If operated on clean, diy plant air, they offer good performance and are extremely reliable. Pneumatic controllers are available with one or two stages of pneumatic amphfi-cation, with the two-stage designs having faster dynamic response characteristics. 

FIG. 8-64 Pneumatic controller a) example (h) frequency response characteristic,... 

The reset time, which is nser-adjnstable, can range from 0.05 seconds to 80 minutes or more, depending on controller design. The reset time constant, when converted to frequency 1/2(Tr) Hz (where Tr is the reset time in seconds), determines the frequency where the reset and proportional response characteristics of the controller merge (see Fig. 8-64Z ). Tuning the reset adjustment on the controller moves the reset frequency to the left or right along the frequency axis and thereby affec ts the reset ac tion of the controller. 

Select a positioner with a faster response characteristic. 

This is an important equation that defines the behaviour of a vibrating body under different conditions of applied force or motion F y From this it can be inferred that the response or movement of object x will depend upon t) and 7 is termed the fraction of critical damping and w , the angular natural frequency of the system. With the help of these equations, the response characteristics of an object to a force can be determined. 

S. R, Wilson, G. A. Al-Jumaily, and J. R. McNeil. Nonlinear Characteristics of a Stylus Profilometer. Opt. Eng. 26,953, 1987. This describes modeling stylus profilometer response characteristics and explains their shortcomings. 

Frequency response characteristics of first-order systems... 

The Nichols chart shown in Figure 6.26 is a rectangular plot of open-loop phase on the x-axis against open-loop modulus (dB) on the jr-axis. M and N contours are superimposed so that open-loop and closed-loop frequency response characteristics can be evaluated simultaneously. Like the Bode diagram, the effect of increasing the open-loop gain constant K is to move the open-loop frequency response locus in the y-direction. The Nichols chart is one of the most useful tools in frequency domain analysis. 

Figure 6.39 shows, for both lead compensator designs, the closed-loop frequency response characteristics for the system. 

In addition, a further mechanism of chattering may be introduced in some liquid PR valve installations if the response characteristics of a control valve in the same system are such that hunting between the two occurs. Generally, this can be eliminated by adjustment of instrument settings or by installation of two valves with staggered set points... 

L Wooton, R. O. and H. I. Avci, MARCH (Meltdown Accident Response Characteristics) Code Description and User s Manual, BCL, October 1980. 

Elazard evaluation or the definition of the effects that may occur, including dose-response characteristics and other intrusive processes. 

The term nonlinear in nonlinear programming does not refer to a material or geometric nonlinearity but instead refers to the nonlinearity in the mathematical optimization problem itself. The first step in the optimization process involves answering questions such as what is the buckling response, what is the vibration response, what is the deflection response, and what is the stress response Requirements usually exist for every one of those response variables. Putting those response characteristics and constraints together leads to an equation set that is inherently nonlinear, irrespective of whether the material properties themselves are linear or nonlinear, and that nonlinear equation set is where the term nonlinear programming comes from. 

On the other hand, for aircraft and spacecraft structures, real laminate behavior is pretty typically linear. Laminate behavior is reasonably linear even with some 45° layers which you would expect to contribute their nonlinear shear deformation characteristic to the overall laminate and degrade its relative performance. If you go beyond the behavior of a laminate and look at a large structure, typically the load-response characteristics are linear. Even around a cutout, linear behavior exists. Beyond that apparent linear performance of many laminates, you might not like to operate in some kind of a nonlinear response regime. Certainly not when in a fatigue environment and probably not in a creep environment either would you like to operate in a nonlinear behavior range. 

Two major problems restricting the ability to acquire accurate vibration data at low frequencies are electronic noise and the response characteristics of the transducer. The electronic noise of the monitored machine and the noise floor of the electronics within the vibration analyzer tend to override the actual vibration components found in low-speed machinery. 

The unique natural frequencies of dynamic machine components are determined by the mass, freedom of movement, support stiffness, and other factors. These factors define the response characteristics of the rotor assembly (i.e., rotor dynamics) at various operating conditions. 

In some cases, the stimulus-response characteristics of a system can be manipulated to provide a means to compare maximal responses of agonists (efficacy). 

The discussion of Section 5-1 clearly illustrates that the most important response characteristic of an ISE is selectivity. Depending on the nature of the membrane material used to impart the desired selectivity, ISEs can be divided into three groups glass, liquid, or sohd electrodes. More than two dozen ISEs are commercially available and are widely used (although many more have been reported in the literature). Such electrodes are produced by firms such as Orion Research, Radiometer, Coming Glass, Beckman, Hitachi, or Sensorex. 

Calcium activities as low as 5 x 10 7 M can be measured, with selectivity coefficients ACaMg and ACaK of 0.02 and 0.001, respectively. Such potential response is independent of the pH over the pH range from 5.5 to 11.0. Above pH 11, Ca(OH)+ is formed, while below pH 5.5, protons interfere. Because of its attractive response characteristics, the calcium ISE has proved to be a valuable tool for the determination of calcium ion activity in various biological fluids. 

The response characteristics of enzyme electrodes depend on many variables, and an understanding of the theoretical basis of their function would help to improve their performance. Enzymatic reactions involving a single substrate can be formulated in a general way as... 

Figure 14 shows the computed osmotic volume changes the red cells undergo when suspended in the same four test solutions at room temperature (left side) and when slowly frozen (right side). They are responses characteristic of any cell that behaves as an ideal osmometer. Initially the cells are at normal isotonic volume (relative volume 1.0). After transfer to the test solution, however, they shrink in all... 

The requirements for an instrumental method of specifying reflected color include a light source, the colored object and a detector. What this means is that all we need is a source, an object and a detector. However, since the response characteristics of these optical components are not linear, nor flat, we need an analogue system in order to be able to measure color. 

FABER K A, HUGHES c L JR. (1993) Dose-responsive characteristics of neonatal exposure to genistein on pituitary responsiveness to gonadotrophin releasing hormone and volume of the sexually dimorphic nucleus of the preoptic area (SDN-POA) in postpubertal castrated female rats. Reprod Toxicol. 1 35-9. 

---