Impedance, of cable

Unless we have a system where the detonator is attached directly to the fire set, we must use a cable to transmit current to the detonator. Cables, of course, also have impedance. The impedance of cables is a function of both their construction and their length. Typical cables and their impedance characteristics are shown in Table 25.2. These are the most common cables used for EBW firing systems. 

The input impedance of cable with wiring faults can be given as follows [28], [29] ... 

Most modem potentiostats provide at least four connections to the cell. These connections typically consist of a counter electrode (CE) that provides current to the ceU, a working electrode (WE) that provides measurement of the current through the cell, and at least two reference electrode inputs (RE) for voltage measurement. Potentiostats that have 4-terminal connections are capable of 2, 3 or 4-terminal testing of electrochemical cells (Figure 3.2.2). The 2-terminal test technique is used mainly for the measurement of high impedance materials where the impedance of cables is not significant (see Section 3.2.2.3). 

The phase angle of the zero-sequence current mentioned in Table 3.1 demonstrates that grounding resistance at substations in both cross-bonded and solidly bonded cables significandy affects the zero-sequence current. As a result, there is litde difference in the zero-sequence impedance of the cross-bonded cable and the solidly bonded cable. The results indicate the importance of obtaining an accurate grounding resistance at the substations to derive accurate zero-sequence impedances of cable systems. 

The high-frequency inductive impedance of cables and membrane ohmic resistance components are in series with polarization resistance and double-layer capacitance (expressed as CPE J of either cathode or anode. 

To increase the impedance of the network, a series resistor or reactor is sometimes used to contain the fault level of a system within a desirable limit. This may be required to make the selection of the interrupting device easy, and from the available range, without an extra cost for a new design as well as an economical selection of the interconnecting conductors and cables. Such a situation may arise on HV >66 kV or EFIV > 132. kV transmission networks, when they are being fed by two or more power sources, which may raise the fault level of the system to an unacceptable level. The cost of the interrupting device for such a fault level may become disproportionately high, and sometimes even pose a problem in availability. 

It is equal to the phase impedance of the overhead lines or cables. For low current systems, LT or HT, this impedanee is nearly equal to the resistanee of the circuit, as Due very low A l, the impedance... 

A power system is connected to a number of power supply machines that determine the fault level of that. system (e.g. generators and transformers). The impedances of all such equipment and the impedances of the interconnecting cables and overhead lines etc. are the parameters that limit the fault level of the system. For ease of calculation, when determining the fault level of such a system it is essential to consider any one major component as the base and convert the relevant parameters of the other equipment to that base, for a quicker calculation, to establish the required fault level. Below we provide a few common formulae for the calculation of faults on a p.u. basis. For more details refer to a textbook in the references. 

From the transmitter sensitivity, for a true pressure differential of 5 kN/m2, the transmitter output current iT is 5 mA. Neglecting any resistance in the cables connecting the transmitter and the recorder, the total impedance of the circuit is ... 

The optimum characteristic impedance is dictated by a combination of factors. Interconnections with low characteristic impedance (<40 fl) cause high power dissipation and delay in driver circuits, increased switching noise, and reduced receiver noise tolerance (35). High characteristic impedance causes increased coupling noise and usually has higher loss. Generally, a characteristic impedance of 50-100 fl is optimal for most systems (35), and a ZQ of 50 fl has become standard for a variety of cables, connectors, and PWBs. For a polyimide dielectric with er = 3.5, a 50-fl stripline can be obtained with b = 50 xm, tv = 25 xm, and t = 5 xm. 

We now check whether Eq. (1), with S /3 = e2/ and modified as above to account for finite propagation time, can explain our data. The unknown parameters are the resistance Rq and the effective environment noise temperature Tq. We checked that the impedance of the samples was frequency independent up to 1.2 GHz within 5%. Fig. 2 shows the best fits to the theory, Eq. (1), for all our data. The four curves lead to Ro = 42 12, in agreement with the fact that the electromagnetic environment (amplifier, bias tee, coaxial cable, sample holder) was identical for the two samples. We have measured the impedance Zenv seen by the sample. Due to impedance mismatch between the amplifier and the cable, there are standing waves along the cable. This causes Zenv to be complex with a phase that varies with frequency. We measured that the modulus Zenv varies between 30 12 and 70 12 within the detection bandwidth, in reasonable agreement with f o = 42 12 extracted from the fits. 

Type of cable RCF Natural impedance 50 ohms Resistance ... 

The transmitter amplifier chain consists of a linear, three-stage transistor amplifier from Amplifier Research (10 W), a class C single-stage field effect transistor (FET) amplifier (120 W) custom-built by H. Bonn GmbH, Munich, and a final tube amplifier with two tetrodes 4CX 350A that deliver more than 1.5 kW of pulse power. A special effort was made to match the input and output impedances of this tube amplifier to the characteristic impedance (50 ( ) of the cables connecting it with the probe and the driver, respectively. This impedance matching resulted in the virtually complete disappearance of antisymmetric phase transients (for a discussion of the effects of such phase transients on m.p. spectra, see Haeberlen, 1976, Appendix D). 

With this set-up the absolute value RS(co) and the phase angle y(f0) of the response function is measured as a function of frequency. The response function is the ratio of the voltage drop Um across the resistor Rm to the output voltage of the noise generator Ugen- After data transfer to a PC via an lEEE-interface the impedance of the sample is calculated from these values and the parameters of the set-up (impedance of the cables and the electronic devices of the analyser). 

Use short shielded leads High-frequency bias errors can be seen when the cell impedance is of the same order as the internal impedance of the instrumentation. Under these circumstances, it is essential to minimize the impact of ancillary pieces such as wires. Use of short shielded cables is highly recommended. 

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