Preset value

Operation of the relay may not necessarily start at the preset value due to certain allowable tolerances. As in lEC 60947-4-1, the relay must not trip within two hours at 105% of FLC but it must trip within the next two hours when the current rises to 120% of FLC. Also, it should trip ill two hours in the event of single phasing when the line current in the healthy phases is 115%, but it should not trip in less than two hours during a healthy condition. 

A thermistor is a thermally sensitive, semiconductor solid-state device, which can only sense and not monitor (cannot read) the temperature of a sensitive part of equipment where it is located. It can operate precisely and consistently at the preset value. The response time is low and is of the order of 5-10 seconds. Since it is only a temperature sensor, it does not indicate the temperature of the windings or where it is located but only its preset condition. 

Figure 18.24(b) illustrates the use of a leakage current monitor. The instrument can be used to display or monitor on a computer remotely and store data at intervals as required to provide diagnostic information. Now it is easier to take corrective measures in time. The instrument can also be programmed to give an alarm at a preset value of I, when the actual operating conditions exceed this. 

In the UK. interlock is used to desciibe a device that prevents someone opening one valve while another is open (or closed). Trip describes an auioniaiic device that closes (or opens) a valve when a temperature, pressure, Jlow. etc., reaches a preset value. 

An optimization is complete when it has converged essentially, when the forces are zero, the next step is very small, below some preset value defined by the algorithm, and some other conditions are met. These are the convergence criteria used by Gaussian ... 

In calculation the authors of the model assume that the cube material possesses the complex modulus EX and mechanical loss tangent tg dA which are functions of temperature T. The layer of thickness d is composed of material characterized by a complex modulus Eg = f(T + AT) and tg <5B = f(T + AT). The temperature dependences of Eg and tg SB are similar to those of EX and tg <5A, but are shifted towards higher or lower temperatures by a preset value AT which is equivalent to the change of the glass transition point. By prescibing the structural parameters a and d one simulates the dimensions of the inclusions and the interlayers, and by varying AT one can imitate the relationship between their respective mechanical parameters. 

Comment Instead of calculating a critical tc and comparing it to the experimental one, the experimental t is converted into an estimated error probability, which is then checked against a preset value, e.g., 0.05. The medical and social science communities prefer using the second approach. This algorithm is theoretically underpinned. 

Step 4. Proceed until a simplex that encloses the minimum is found. Stop when the difference between two consecutive function evaluations is less than a preset value (tolerance). 

A sensor to monitor the control variable and provide an output signal when a preset value is exceeded (the instrument). 

A control system is a system of integrated elements whose function is to maintain a process variable at a desired value or within a desired range of values. The control system monitors a process variable or variables, then causes some action to occur to maintain the desired system parameter. In the example of the central heating unit, the system monitors the temperature of the house using a thermostat. When the temperature of the house drops to a preset value, the furnace turns on, providing a heat source. The temperature of the house increases until a switch in the thermostat causes the furnace to turn off. 

Control system output is the actual response obtained from a control system. In the example above, the temperature dropping to a preset value on the thermostat causes the furnace to turn on, providing heat to raise the temperature of the house. 

Chase [2.32] presents an alternative method to monitor and control the freeze drying process by measuring the flow of nitrogen to keep the operation control pressure, pc, constant. The Mass Flow Controller (FMC) consists of a proportional valve, an integral flow meter and a capacitance manometer (CA). The CA measures the total pressure in the plant, the valve opens, if the pressure gets below the preset value and vice versa. The flow of... 

The principle of this method is quite simple The electrode is kept at the equilibrium potential at times t < 0 at t = 0 a potential step of magnitude r) is applied with the aid of a potentiostat (a device that keeps the potential constant at a preset value), and the current transient is recorded. Since the surface concentrations of the reactants change as the reaction proceeds, the current varies with time, and will generally decrease. Transport to and from the electrode is by diffusion. In the case of a simple redox reaction obeying the Butler-Volmer law, the diffusion equation can be solved explicitly, and the transient of the current density j(t) is (see Fig. 13.1) ... 

There are several commercial packages that realise the above strategy for molecularly realistic systems. It is useful to discuss some of the limitations. Ideally, one would like to do simulations on macroscopic systems. However, it is impossible to use a computer to deal with numbers of degrees of freedom on the order of /Vav. In lipid systems, where the computations of all the interactions in the system are expensive, a typical system can contain of the order of tens of thousands of particles. Recently, massive systems with up to a million particles have been considered [33], Even for these large simulations, this still means that the system size is limited to the order of 10 nm. Because of this small size, one refers to this volume as a box, although the system boundaries are typically not box-like. Usually the box has periodic boundary conditions. This implies that molecules that move out of the box on one side will enter the box on the opposite side. In such a way, finite size effects are minimised. In sophisticated simulations, i.e. (N, p, y, Tj-ensembles, there are rules defined which allow the box size and shape to vary in such a way that the intensive parameters (p, y) can assume a preset value. 

Summing up, a robust and easy to handle SMB-design uses 4 zones, a recycling pump fixed in respect to the columns and two pumps for the control of the outlet flow rates. Extremely high precision of all technical components of the SMB is needed. All pumps and valves have to be exactly synchronized. The flow rates should not vary by more thanl % from the preset value. All connections between the different parts of the system must be carefully optimized in order to minimize the dead volume. All columns should be stable and nearly identical in performance. If the SMB-technology is to be used in Biotechnology, GMP issues (cleaning, process and software validation) also have to be considered. In addition and as with any continuous process in that particular area, the definition of a batch could be a problem. 

For every decade of input, the output changes about 120 mV. In commercial logarithmic amplifiers, a subsequent linear amplification stage further amplifies the output voltage to a preset value. A typical input-output characteristic of a commercial logarithmic amplifier is shown in Fig. 11.4. 

Temperature and pressure are calculated from standard formulas from statistical mechanics (equipartition kinetic energy and virial, respectively), and are regulated at preset values by computational thermostats and barostats. 

Monitoring the effluent of a smoke stack, or the concentration of a drug in a patient requires that the sampling rate is as low as possible and that can be predicted with a known probability that between the sampling times no fatal concentration change will occur. If it is expected that the monitored value will exceed a preset value a simple action can prevent that administer some drug, open or close a value, etc. 

The objective of control is quite different. The purpose of control is to keep a process property, e.g. the composition, as close to a preset value as is technically possible and economically desirable. The deviation from the set point is caused by intentional or random fluctuations of the process condition. In order to control the fluctuating process, samples must be taken with such frequency and analyzed with such reproducibility and speed that the process condition can be reconstructed. From this reconstruction predictions can be made for the near future and control action can be optimal. Another goal can be the detection of nonrandom deviations, like drift or cyclic variations. This also sets the conditions for sampling frequency and sample size. 

The sample, a reverse-biased p-n or metal-semiconductor junction, is placed in a capacitance bridge and the quiescent capacitance signal nulled out. The diode is then repetitively pulsed, either to lower reverse bias or into forward bias, and the transient due to the emission of trapped carriers is analyzed. As discussed in the preceding section, for a single deep state with JVT Nd the transient is exponential with an initial amplitude that gives the trap concentration, and a time constant, its emission rate. The capacitance signal is processed by a rate window whose output peaks when the time constant of the input transient matches a preset value. The temperature of the sample is then scanned (usually from 77 to 450°K) and the output of the rate window plotted as a function of the temperature. This produces a trap spectrum that peaks when the emission rate of carriers equals the value determined by the window and is zero otherwise. If there are several traps present, the transient will be a sum of exponentials, each having a time... 

In feedback control, after an offset of the controlled variable from a preset value has been generated, the controller acts to eliminate or reduce the offset. Usually there is produced an oscillation in the value of the controlled variable whose amplitude, period, damping and permanent offset depend on the nature of the system and the... 

Figure 3.10. Condensers, (a) Condenser on temperature control of the PF condensate. Throttling of the flow of the HTM may make it too hot. (b) Condenser on pressure control of the HTM flow. Throttling of the flow of the HTM may make it too hot. (c) Flow rate of condensate controlled by pressure of PF vapor. If the pressure rises, the condensate flow rate increases and the amount of unflooded surface increases, thereby increasing the rate of condensation and lowering the pressure to the correct value, (d) Condenser with vapor bypass to the accumulator drum. The condenser and drum become partially flooded with subcooled condensate. When the pressure falls, the vapor valve opens, and the vapor flows directly to the drum and heats up the liquid there. The resulting increase in vapor pressure forces some of the liquid back into the condenser so that the rate of condensation is decreased and the pressure consequently is restored to the preset value. With sufficient subcooling, a difference of 10-15 ft in levels of drum and condenser is sufficient for good control by this method.

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