Circuit Under Test

An important point to be considered when the instrument is used for A.C. voltage measurement is the terminal connections. One terminal will be clearly designated as the high-potential connection, and this should be adhered to. The HT terminal will have a low value of capacitance to other bodies and to earth while the corresponding capacitance of the other is high. If the instrument is in a metallic case this should be connected to the mains earth as a safety precaution. In some cases, the low-voltage terminal is also connected to the metallic case. If this is so, the instrument will effectively earth the circuit under test, which may give rise to problems. 

The spark test apparatus shall be inserted in the circuit under test at each point where it is considered that an interruption or interconnection may occur. Tests shall be made with the circuit in normal operation, and also with one or two faults, as appropriate to the category of electrical apparatus..., and with the maximum values of the external capacitance (C0) and inductance (L0) or inductance to resistance ratio (LJR0) for which the apparatus is designed. 

Radiation experiments are the closest designers can get to real space radiation. It is possible, at ground level, to use different kinds of energized particles to emulate the particles present in space. In order to do so, particles are accelerated and thrown at the circuit under test. Examples of particles ate protons, neutron, alpha particles, and heavy ions, such as cobalt. Such experiments deal with radioactive elements and accelerated particles that can cause severe damage to human beings and the environment. Because of that, such experiments must have an extremely controlled testing facilities (most of them controlled by the estate), and therefore can be very expensive. 

Practical limitations are imposed at low frequencies, however, where the rectification-smoothing function necessary to transduce the ac voltage magnirnde to a dc level becomes inaccurate. Ac voltmeters typically become seriously in error at frequencies below 20Hz. To obtain an accurate KK transform, it is necessary to extend the measurement frequency range significantly beyond the limits of frequency needed to elucidate the equivalent circuit under test. Thus, the method described here is not appropriate for aqueous electrochenfical systems for which the diffusional impedance is prominent. This method can be useful for systems in which the lowest frequency of interest is greater than 50 Hz or so, as is usually the case for solid ionic conductors, oxide films, and semiconductor surfaces. 

Make sure only the conductor from the circuit under test is within the jaws of the clamp. 

Input impedance Impedance that a circuit under test sees when an instrument is connected to it. Input impedance is usually specified as a parallel resistance and capacitance combination, such as 1 MS2 shunted by 15 pF. 

Supply to Ground Short Pulser Current Tracer Remove power from circuit under test Disconnect electrolytic bypass capaators Pulse xross Vcc and ground using accessory connectors provided Trace current to lault... 

The signal is present at the input of a certain circuit and is no longer present at the output. The circuit under test has an interruption on the signal path. 

The heat generated by a current-caiTying component or conductor is its watt loss and is expressed by R, where / is the current and R the resistance of the circuit under consideration. The watt loss of each current-carrying component installed in the test assembly is estimated and added to arrive at the approximate watt loss during the actual operation. Based on this loss is calculated of the total heaters required. These heaters are then suitably located in the test assembly to represent all the incoming and outgoing feeders, their power cables and any other current-carrying component. 

The Nernst equation shows that the glass electrode potential for a given pH value will be dependent upon the temperature of the solution. A pH meter, therefore, includes a biasing control so that the scale of the meter can be adjusted to correspond to the temperature of the solution under test. This may take the form of a manual control, calibrated in 0 C, and which is set to the temperature of the solution as determined with an ordinary mercury thermometer. In some instruments, arrangements are made for automatic temperature compensation by inserting a temperature probe (a resistance thermometer) into the solution, and the output from this is fed into the pH meter circuit. 

In the null-point instruments use is made of the well-known compensating method according to Poggendorf, by which the emf of the cell under test is compared with that of a standard cell. The circuit diagram of such a method54 is illustrated in Fig. 2.14. 

EIS data is generally interpreted based on defining an appropriate equivalent circuit model that best fits the acquired data. The elements of the circuit model involve a specific arrangement of resistors, capacitors, and inductors that tacitly represent the physicochemical reality of the device under test. Under these circumstances the numerical value for chemical properties of the system can be extracted by fitting the data to the equivalent circuit model. Impedance measurements are typically described by one of two models ... 

The waveguide system used to measure the dielectric parameters of water and other lossy liquids has been described previously (3J. Basically it involves the measurement of the power profile of a wave reflected from a movable short circuit as it traverses the liquid under test. 

For a process occurring with a not small characteristic time, the plot is a semicircle of radius, Rpl2, which meets the x -axis both at x = R0 + Rp/2 for co=0 and x=R0- Rpl2 for co=°° (see Figure 8.21) [75]. The time constant of this simple circuit is defined with the help of Equation 8.89, where fm = com/2jt is also the frequency of the maximum of the semicircle. This relaxation time also corresponds to the characteristic relaxation time of the electrochemical process under test. 

The high impedance of the parallel resonance circuit is transformed to 50 Q nominally by the second variable capacitor. Both variable capacitors are Johan son 5341 which are piston air capacitors with Be-Cu stators and Ag rotors. They work very nicely except for the problem of high voltage breakdown. The dc breakdown under test conditions is listed as 1200 volts at sea level but that number has to be severely derated for radio frequency and altitude. (The latter problem is serious at Los Alamos where the atmospheric pressure is 590 mm Hg and the altitude correction to the breakdown is about 10%.)... 

The basic corrosion instrumentation requirement involves the measurement of potential difference. Currents are measured as the potential across a resistor (R ) as shown in Fig. 1.2, where the potential difference is again determined with an operational amplifier. More sophisticated measurements such as polarisation characteristics and zero resistance ammetry involve the use of potentiostats which again use operational amplifiers in a differential mode. The potentiostat is an instrument for maintaining the potential of an electrode under test at a fixed potential compared with a reference cell, and the basic circuit is similar to that for potential measurement with the earth return circuit broken to an auxiliary electrode in the electrochemical cell. Such a circuit would maintain the potential of the test electrode at the reference cell potential. This potential may be varied by inserting a variable potential source (V ) in the input circuit as shown in Fig. 1.3. The actual cell potential (V ) and the current required to polarise the test electrode to this potential may be measured using the basic circuits shown in Figs. 1.1 and 1.2 respectively. 

Impedance Detection, Fig. 31 Basic circuits for contacting the material under test using electrodes (a) two-electrode (bipolar) interface and (b) four-electrode (tetrapolar) interface... 

After the test-outcome droplets are read serially, the capacitive-sensing circuit generates a pulse sequence corresponding to the detection of these droplets. An additional evaluation step is required to analyze these pulse sequences to determine whether the microfluidic array under test has a defect. For example, if a row/column of an array is faulty, there is no generated pulse in... 

Fig. 6 illustrates the average resistance change as a function of time under test conditions for the control, PSS and HMDS (plasma) coated substrates. This graph is based on the circuits which survived the 1000 hours at high temperature and humidity. 

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