Closed loop setup

To use the true stress or strain, it is necessary to measure the cross section or the length of the sample continuously and to have a closed-loop feedback on a (hydraulic) setup. Therefore, most of the time, only cyclic loads or displacements are applied onto the sample. 

The quasi in situ SFM setup utilizes a modified commercial SFM (Dimension 3100 equipped with a NanoScope IV SPM controller and a XY closed-loop scanner, all from Veeco Instruments.). A detailed description of the setup is reported elsewhere [9,32,34], Si3N4 cantilevers from Olympus were used (OMCL-AC160TS, spring constant 40N/m, resonance frequency 200-300kHz). All measurements were performed at free amplitudes of about 30-50 nm and a relative set point of about 0.95. 

Fig. 7.1. Experimental setup of TADPOLE referring closed-loop pulse shape control [7]...

The R D program included two experimental setups both demonstrating helium as a closed-loop Brayton cycle working fluid [44] ... 

Compared with model I, model II performs considerably better during simulation (Fig. 30.21). The manipulated variable i follows the measurements closely, which indicates that the closed loop dynamics of the simulation approximates the actual experimental setup. However, when the controller is switched on, the reflux fraction is increased and becomes larger than one, before it is decreased. This was found to be independent of controller tuning and is caused by the fuzzy model. The result is that there is a slight inverse response in the production curve the production first becomes negative before it increases, which is not possible in practice. The net effect is that the simulated production lags behind the measurements (Fig. 30.21c). Model III performs better than models I and II. Quality control is good and the simulation matches the measurements of i closely. The simulated production curve approximates the measured production well. 

A phase-locked loop is a bit of a hybrid of the oscillator circuit and the propagation measurement system discussed in the previous two sections. The instrumentation setup, shown in Figure 6.14 (page 374), closely resembles that used for propagation measurements. The phase is locked, or rather maintained at a constant value, in the following manner initially, before any perturbation occurs, the phase difference between the two IDTs of the AW device is recorded when a perturbation affects this phase difference, the frequency of the signal from the source is adjusted to return the phase to its initial value. In this way, the source frequency is constantly retuned to the extent dictated by the perturbation, and the phase difference between the two transducers remains locked. ... 

The novel feature of the method is the modification of experimental setup to apply total recirculation of the reaction mixture, as depicted in Fig. 1. By switching the valve from waste to the circulation loop, the system is closed and the steady state - cannot be reached, because of a continuous consumption of substrate in the enzyme reaction. In order to simplify the mathematical description, the following experimental assumptions were made ... 

Most controls, particularly the older ones, are the open loop type. They merely set mechanical or electrical devices to some operating temperature, time, and pressure. If this is all that is required, the control may remain in operation. However, this setup is subject to a variety of hard-to-observe disturbances that are not compensated by open loop controls. Thus process control must close the loop to eliminate the effect of process disturbances. 

The steps involved in sequential experimental design for optimal discrimination and estimation can be represented in a simplified flow diagram as shown in Fig. 2.8-1. The loops can even be closed so that the settings of the independent variables are implemented on the experimental setup directly by the computer. 

The experimental setup used in the study of Guan and Macdonald comprised a closed, circulating loop system as illustrated in Fig. 60, within which the test solution was heated to the desired... 

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