Sensing instantaneous current

Instantaneous current sensing is used to proteet the power semieonduetors. A eurrent sensing resistor is plaeed in the power switeh eurrent path and its voltage represents the instantaneous eurrent flowing through the power deviee. This... 

A CT is provided in series with the spark gap to sense its operation during a line fault. As soon as there is arcing, it provides an instantaneous command to a short-circuit relay. The relay, in turn, closes the bypass breaker, within 3 to 5 cycles, leaving only the natural line impedance in the faulty eircuit. Now = 0, which limits the fault current to the natural level of the system, as if the capacitors were not connected. The shorting device is restored to its original status as soon as the fault condition is cleared. The device must be capable of interrupting the line fault... 

Process Stability and Control. Operationally, automatic control of the crystal radius by varying either the input power to the heater or the crystal pull rate has been necessary for the reproducible growth of crystals with constant radius. Techniques for automatic diameter control have been used since the establishment of Czochralski growth. Optical imaging of the crystal or direct measurement of the crystal weight has been used to determine the instantaneous radius. Hurle (156) reviewed the techniques currently used for sensing the radius. Bardsley et al. (157,158) described control based on the measurement of the crystal weight. 

A schematic of the apparatus is shown in Figure 2. The series resistor senses current. When the overall circuit RC (R and C are circuit resistance and capacitance, respectively) time constant is short compared with the voltage developed on the sensing resistor is proportional to the instantaneous... 

Electronic Measurements Ltd. at www.pemuk.com. These probes are not the usual current transformer type. The output from a Rogowski probe depends not on the instantaneous current enclosed, but on the rate of change of current. So, instead of just placing several turns around the wire to be sensed, as in a typical current transformer, the Rogowski probe effectively takes an air-cored solenoid and then bends that in a circle around the sensed wire (like a doughnut). Such probes are also considered virtually noninvasive. 

Many of these meters will, at the flip of a switch, show instantaneous voltage or current values or even both in the same display. The price goes up as more features—low-volt-age disconnect, alarms, load shunting, etc.—are added in other models. These aren t bells and whistles. They re the eyes and ears of your system, and will help you make good decisions and spot trouble early. At best, it will make you master of your energy-generating system. At least, it provides a solid sense of security when it comes to energy matters. 

In a short-circuit condition, magnetic action, accomplished by an electromagnet in each breaker pole, causes the breaker to trip instantaneously. In a magnetic-only breaker, the thermal sensing bimetal is left ont. Sohd-state breakers utilize current transformers and soUd-state circuitry in place of the thermal and magnetic trip units. 

For electrochemical actuators driven by flow of a constant current (/), any change of the working energetic (U) conditions (mechanical, thermal, chemical, electrical) will be sensed by the instantaneous adaptation of the device potential (E) evolution, during acmation, to the new working energetic conditions potentio-metric sensors. 

The ideal non-polarized electrode is one which allows free and unimpeded exchange of electrons or ions across the electrode-solution interface. The reversible electrodes considered in an earlier chapter approximate in behaviour to these, the rapid establishment of thermodynamic equilibrium being consequent upon such rapid interchange. When charge crosses an ideally reversible electrode, the electrochemical changes which take place do so with such rapidity that the equilibrium situation is instantaneously restored. Such an electrode is non-polarizable in the sense that its potential, for small currents, has remained stable. This potential, for a fixed temperature and pressure, is... 

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