Current measuring device

In many cases it will suffice to include in the circuit a shunt of appropriately low resistance over which 7/ -drop potential measurements can be made for ready calculation of the magnitude of the current flow. This technique permits measurements to be made as required without opening the circuit even momentarily for the introduction of current-measuring devices. It is also possible to arrange instruments in a circuit so that no measuring resistance is introduced in the galvanic current circuit . 

E2, counter electrode with a constant potential A, current measuring device V, voltage measuring device. 

Fig. 5.8 Schematic diagram of polarographic (or voltammetric) circuits for two-electrode (a) and three-electrode (b) systems. WE(DME) indicator or working electrode (dropping mercury electrode in the case of polarography) RE reference electrode CE counter electrode DC voltage (V) DC voltage source Current (/) current measuring device.

Figure 13-1. Electrode systems, (a) Showing fringing effect and surface conduction in volume resistivity measurement (b) showing volume conduction in surface resistivity measurement (c) electrodes, guard ring and circuit for volume resistivity measurement (d) electrodes, guard plate and circuit for surface resistivity measurement. (G = glavanometer or other current measuring device.)...

The overall dimensions of the electrode system are not really critical, but the size does affect the accuracy of the current measuring device needed, larger sizes being advantageous for higher resistivity materials. IEC 60093 makes no recommendations, whilst the British standards specify two sizes for volume resistivity but suggest several sizes in an appendix for surface resistivity. 

The electrolyte properties of a solution can be measured by a rather simple apparatus consisting of two electrodes, such as graphite rods, dipped into the solution, a battery, and current measuring device (ammeter) all connected with wires or electrical leads (Figure 4.2). If a current is able to flow through the solution, it will register on the ammeter. If the solution cannot conduct a current, the meter will read zero. 

If R and B are nonideal with current depending values, as in an electrolytic electrode system, the DC approach cannot be used. A better approach is to superimpose a small, continuous sine wave voltage on the applied DC voltage. Our current measuring device must then be able to measure both AC current with phase and DC. The battery (being ideal with zero internal resistance) will not influence the AC current, and we consequently measure the resistance of R at AC, but a different R at DC. Because there is no phase shift, we then know that the battery is in the circuit. If we repeat the measurement on many frequencies and the results are identical, we know that there is no capacitor inside the black box. 

Figure 1 Fundamental scheme of a three-electrode polarographic circuit for /Ffdrop correction. RG, ramp generator A, current measurement device V, voltmeter WE, working electrode RE, reference electrode AE, auxiliary electrode.

There have been a number of systems developed to detect current distribution problems and a few have been applied across electrowinning and electrorefming operations for a variety of metals. The most eommon methods include infra-red imaging, cell voltage monitoring, and hand held gauss and individual cathode current measurement devices. 

Ehiring corrosion (oxidation) process, both anodic and cathodic reaction rates are coupled together on the electrode surface at a specific current density known ds icorv This is an electrochemical phenomenon which dictates that both reactions must occur on different sites on the metal/electrolyte interface. For a uniform process under steady state conditions, the current densities at equilibrium are related as o = — c = ieorr Ecorr- Assume that corrosion is uniform and there is no oxide film deposited on the metal electrode surface otherwise, complications would arise making matters very complex. The objective at this point is to determine both Ecorr and icorr either using the Tafel Extrapolation or Linear Polarization techniques. It is important to point out that icorr cannot be measured at Ecorr since ia = —ic and current wfll not flow through an external current-measuring device [3]. 

A current measuring device for monitoring the current produced by the applied potential. The ability of the current measuring device to autorange or to change the scale automatically is also important. 

A conducting cup or chamber that intercepts a charged particle beam and is electrically connected to a current measuring device. 

In rivers, water flows dovmstream due to gravity. The velocity of a river is usually measured directly because rivers are generally accessible and satisfactory current-measuring devices exist. Nevertheless, a great... 

There are two strategies that can be adopted to try and measure such low current levels (1) use a very sensitive current measuring device (a picoammeter or, when suitably configured, an electrometer) or (2) devise some means to amplify the current, thus making it easier to... 

Therefore, the reaction rate may be easily measured by a current-measuring device placed external to the cell. However, the measured current or current density is actually the net current, that is, the difference between forward and reverse current on the electrode. In general, an electrochemical reaction involves either oxidation or reduction of the species ... 

The parameter extraction through equivalent circuit has been applied by several researchers and can help in understanding the material and electrochemical properties of the subcomponents in the MEA. A typical impedance set-up is shown in Fig. 25 that includes a fast Fourier transform (FFT) based frequency response analyzer with a signal generator, an oscilloscope to check the generated waveform, a current measuring device... 

A model CD-I 79 gamma monitor is mounted on the top of the reactor console. This instrument is a sensitive DC current-measuring device with a trip circuit which operates a relay when the current exceeds a preset level. An audible alarm is then given. The CD-179 receives its input from a nitrogen-filled ion chamber lC-34, which is placed near the reactor tank. 

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