Operational amplifier yield

In the direct-reading instruments the emf of the cell is led through an (operational) amplifier across a standard high resistor yielding a current that is measured by a milliammeter calibrated to be read in pH units or millovolts. So, while the null-point system provides a truly potentiometric (non-faradaic) measurement where the off-balance adjustment remains limited to an interrupted temporary current draw-off, the direct-reading system represents an amperometric measurement where a continuous steady-state current draw-off takes place as long as the meter is switched on. In fact, the latter is a deflection method as a pointer indicates the pH units or millivolts by its deflection on the meter scale. 

For controlled-potential coulometry the voltage drop over a standard resistor is measured as a function of time by means of a voltage-to-frequency converter the output signal consists of a time-variant and integrally increasing number of counts (e.g., 10 counts mV-1), which by means of an operational amplifier-capacitor yields the current-time curve and integral158. 

Balancing the ratio-arm bridge is not the only technique yielding cell impedance. It can also be determined by a method that compares the response of an unknown impedance Zy with that of a known reference impedance Zr f. Both impedances are placed at the input and in the feed-back loop of an operational amplifier, respectively. The computer-controlled multiplexer switches the read-out mode of the phase-sensitive detector (the lock-in amplifier) and the unknown conductance is obtained as the inphase output component of the lock-in device. 

In the total interaction diagram of Fig. 13.6, as the system yields for reactive extrusion, several positive feedback loops can be distinguished, due to which a disturbance in a process parameter can be amplified which may lead to an unstable operation. In this way, three different possible sources of instabilities can be distinguished ... 

From these expressions, it becomes clear that operating the chemosensing CP film near its lasing threshold will yield enhancements in fluorescence quenching, thereby enhancing sensitivity. Inspection of Fig. 5.9 shows that optimal sensitivity, at practical pump powers, is obtained when the pump power of the CP is at the onset of amplified stimulated emission (ASE), for the exposed film. Practical implementation of the concept would require rastering of the incident power intensity to locate the pump power that yields the maximum signal response. 

What the raw product should be like to provide suitable yield and quality is dictated as much as anything by the final form of the processed product. The unit operations themselves and the nature of the machines and processing media or chemicals used to implement them have additional requirements and effects. Together they determine, for instance, whether there will be opportunity to exclude undesirable or damaged parts of the fruit, whether the texture needs to be extra firm or the solids content preferably high, and whether such factors as browning rate or juiciness are likely to be problems. Each product seems to have a different combination of requirements, as shown by the ratings in Table 2 and amplified in the text to follow. 

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