Capacitors location

Figure 23.34 Capacitor locations for individual for group loads...

The probe tuning rods are long extensions of the variable capacitors located at the top of the probe, near the probe coil. The capacitors are delicate and there are two ends of the travel of the knob If any force at all is applied at the end of the travel, the capacitor will break. This will usually require that the probe be sent back to the manufacturer for repair, a process requiring a week or two and costing many thousands of dollars. For this reason many NMR labs do not allow users to tune the probe ... 

We measure the current through the interface of the working electrode as a function of the potential difference at it. This current is either a displacement current or a real current. The displacement current, which is an undesirable effect in nearly all electroanalytical work, can be described as a charging of a capacitor, located at the interface, and one speaks about the capacitive current. The other, more important, part is due to electrochemical processes, in which ions or electrons are transferred from the electrode to the solution or vice versa. As these processes are governed by Faraday s law, one speaks of faradaic currents. Faraday s law states that the electrochemical conversion of m moles yields an amount of electricity of mnP coulombs, where n is the number of electrons released or taken up in the reaction and F the Faraday constant, with a value of about 10 coulombs/mole. This high value of the electrochemical equivalent is, of course, very attractive from the analytical point of view. The measurement of picocoulombs of electricity is extremely simple nowadays and detection limits of 10 mole could be expected from this simple calculation. 

Bypass capacitors are required at the power connections to the IC, the reference signal inputs, and the analog inputs to minimize noise that is induced by the digital signals. Each manufacturer specifies the recommended bypass capacitor locations and values in the data sheet. The manufacturers recommendations should be followed to ensure proper performance. 

The Series 1151 differential pressure transmitter manufactured by Rosemount (MinneapoHs, Minnesota) uses a capacitance sensor in which capacitor plates are located on both sides of a stretched metal-sensing diaphragm. This diaphragm is displaced by an amount proportional to the differential process pressure, and the differential capacitance between the sensing diaphragm and the capacitor plates is converted electronically to a 4—20 m A d-c output. 

Refer to a typical distribution network shown in Figure 2.5..5 I. The capacitor is of maximum use when located as near to the load-point as possible, especially in induction motors, because ... 

Diversity When a tiumber of motor loads are connected on a common bus. normally not all the motors will be operating at a time. A capacitor bank near the MCC w oidd permit the use of lesser total kVAr than if the capaeitors were located separately at each individual load. 

Figure 23.34 suggests possible locations where the capacitor banks can be installed for individual or group controls, depending upon cost and simplicity. Location 1 will be suited for individual loads and is effective when there are not many load points. For group controls, locatioti... 

The capacitors are shown in the centre of the line which being the best location. But they can be provided near the receiving end transformer also. 

Concentration of capacitor banks at one point in a system may cause amplification of harmonics, selfexcitation of machines, overvoltages due to switching and unsatisfactory working of audiofrequency remote-control apparatus. To overcome this, a concentration of capacitor banks at one point must be avoided as far as possible. These may be installed at different locations in the system. 

One last factor is the physical layout of the output stage when more than one output filter capacitor is used. The capacitors should be located radially symmetric from the output rectifier, and the printed circuit traces for the rectified voltage and the grounds should be of similar trace-widths and lengths. Any dissimilarity of these traces causes more series resistance and inductance to the... 

These ac current loops should be routed before any other traces in the power supply. The three major components that make up each loop the filter capacitor, the power switch or rectifier, and the inductor or transformer must be located adjacent to one another. The components must also be oriented such that the current path between them is as short as possible. A good example of a layout of the power section of a buck (or step-down) converter can be seen in Figure 3-60. 

The first compensating pole will be located at the capacitor s ESR frequency (4,020 Hz). 

Locate the compensating error amplifier pole at the lowest anticipated zero frequency caused by the ESR of the capacitor or... 

The location of the lower of the two error amplifier zeros (/epi) is placed at the location of the estimated zero of the output capacitor and its ESR. Hence,... 

This causes the control-to-output characteristic to add gain and phase above the location of this zero. This can be a problem with respect to the stability of the supply. Unfortunately, many capacitor manufacturers do not present the value of the ESR for their capacitors. Typically, the zero caused by the output filter capacitor falls in the following range ... 

The zero attributed to the output filter capacitor is still present in the control-to-output characteristics. Its location is found in Section B.2.1 and Equation B.9. 

The location of the error amplifier s pole is used to counteract the effects of the output filter capacitor s zero caused by the ESR. The error amplifier s pole should be located by... 

Another major source of noise is the loop consisting of the output rectifiers, the output filter capacitor, and the transformer secondary windings. Once again, high-peak valued trapezoidal current waveforms flow between these components. The output Alter capacitor and rectifier also want to be located as physically close to the transformer as possible to minimize the radiated noise. This source also generates common-mode conducted noise mainly on the output lines of the power supply. 

When connected as switchable banks the rating of each step of the capacitor bank must be selected with care. It is important that the control relay settings are matched to the ratings of each capacitance step in order to prevent hunting (i.e. continuously switching in and out at a particular load point). When capacitors are connected to one particular load (usually a motor) the capacitor bank can be located at the motor, adjacent to but separate from the control switchgear or within the control switchgear itself. 

When located at the motor the capacitor bank will be normally cabled from the motor terminal box, so that the size of the motor cable can then be selected on the basis of the reduced-power factor corrected current drawn by... 

Take a look at some data I extracted from the Murata database in Figure 4-5. All these are 1 pi 725 V capacitors in the 1206 size, but I am varying their material. You see that though their resonant frequency does not change with material, the better materials have better ESRs, too. So X7R could give you an ESR almost 10 times lower. However, the difference in ESR due to material was not so obvious for lower values of capacitance (probably because then a major part of the ESR is located outside of the actual material (in the interconnects, terminations, etc.). 

---