Dc leakage currents

Electrical Measurements. DC leakage current measurements were made as a function of applied bias voltage over a range of -10 to +10 V. Data were obtained with a Keithley Model 616 Digital Electrometer. The voltage source was a battery-regulated potentiometer. 

DC Leakage Current. Under 0% RH, DC leakage currents on clean and contaminated specimens were indistinguishable. Leakage currents of 10 pA were measured under 10 V DC bias, corresponding to a resistance of 10 2 ohms. Resistances were independent of bias between -10 and 10 V. 

The effect of DC bias on a contaminated sample at 100% RH is shown in Figure 5. At bias levels corresponding to threshold and super-threshold levels for electrochemical reactions, the impedance spectrum shows the capacitive loop that intersects the real axis at low frequency (.1 Hz). Zero-DC-bias data, which are not shown, form a similar arc that is large compared to the scale of this plot. This behavior is modelled by a parallel RC circuit, whose resistance decreases from 1 x 10 to 1.6 x 10 and whose capacitance remains constant at approximately 30000 pF, as DC bias is raised from 0 to 3.0 V. The resistances agree with those measured in DC leakage current experiments. The capacitances are 100 times larger than those measured on the clean sample at 100 % RH. 

The heaters commonly consist of a resistive wire or a coaxial heating cable with an insulated heating wire inside bendable metal tubing. These are usually powered by DC supplies. Electrical leads and feedthroughs are designed for minimal leakage currents and stray capacitances. 

For example in the case of DC resistance measurements, leakage currents can introduce errors that are large compared to the uncertainty on the calibration of the measuring equipment. Similarly interment system to these reference materials and the samples being analysed. Work on this is already being carried out in a number of institutes and we are seeing the convergence of approach between physical and chemical measurements. 

Since capacitors do not pass dc current, special steps must be taken to set the charge stored on each capacitor and protect the circuit from drift due to leakage currents, carrier generation, etc. The resistors in Fig. 6.1.8 labelled R s serve this purpose. Additionally, measurements are usually not performed at dc, but rather at some carrier frequency /m, typically a few 100 kHz or MHz. The higher frequencies are needed especially with CMOS circuits to reject the electronics own low frequency flicker noise which often extends to the low MHz. The only exception are applications in which the signal itself is modulated or free from dc content, such as resonant gyroscopes [1] or microphones. Even in those cases modulation is often used. 

In fact, the parasitic capacitance is not connected symmetrically to the two input (rectified) dc rails. So why should the ground leakage current end up being shared equally by the two lines ... 

It must be emphasized that this symmetiy exists over all cells connected in series between the negative and positive poles of the rectifier, not just the cells in a single electrolyzer. Thus, if two bipolar electrolyzers are connected in series in a single DC circuit, the bipolar unit cells with the lowest current will typically be those located near the center of the DC circuit, not those cells at the center of the two electrolyzers. Likewise, if each half of a single electrolyzer is connected in a parallel DC circuit, then the bipolar unit cells with the lowest current will be those located in the center of each half of the electrolyzer, not the ones located in the centers of the electrolyzers. It should be mentioned that leakage currents are also present in monopolar cell circuits. However, their magnitude is very small. 

Capacitors are not ideal drcuit elements. The equivalent circuit of a capadtor (valid from DC up to the low radio frequency range) is shown in Fig. 2.51(a). The shunt resistance Rp (which, in general, is the function of frequency) at DC and low frequendes is referred as the insulation resistance of the capacitor. It accounts for dielectric leakage current and dielectric power losses. When the capacitor is charged to V(0) volts and allowed to discharge through itself, the capacitor voltage is... 

DC test Tests that measure a static parameter, for example, leakage current. 

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