Tanks capacitance

With the advent of inexpensive, fast frequency counters, which count the individual cycles over a precisely fixed period (usually 1 s) and display the frequency digitally, it is more convenient to connect the radio-frequency output of the variable-frequency oscillator directly to the frequency counter and determine the total capacitance with the aid of Eq. (27). This technique is highly suitable for the present experiment if a WTW Dipol-meter or another LC oscillator is available or can be constructed. (With the Dipolmeter only the variable-frequency oscillator is used.) A simple LC oscillator circuit that can be constructed from inexpensive components has been described by Bonilla and Vassos this circuit, with a small modification to provide for one side of the tank to be grounded, is shown in Fig. 2. In this circuit, as in the WTW Dipolmeter circuit, all tank capacitances are in parallel. [This is not true of the circuit described in Ref. 4 of Exp. 30, as that circuit incorporates some series capacitance. If that circuit is employed, Eqs. (28) to (30) are not valid and Eqs. (30-3) to (30-5) must be used instead, unless the null mode is employed.]... 

With the cell capacitor and cell beaker clean and dry, assemble the cell and mount it in a constant-temperature bath set at 25°C. Set the cell capacitor at the open position (a). Turn on the oscillator and the frequency counter, and adjust the tank capacitance Cj to yield a frequency in the range of 1.3 to 1.5 MHz. Wait a while to make sure that the apparatus is operating stably and not drifting in frequency. Determine the frequencies and 4 in alternation at intervals of 30 s by alternating the position of the pointer knob between (a) and (b) until four to six frequency values have been recorded at each position. Make certain that you do not alter Cj or move the leads so as to affect Cs during either set of measurements. 

In nonmetaUic vessels, the second plate of the capacitor is missing and must be suppHed. A stiUweU probe, one with a concentric metal tube, is utilized. The concentric tube suppHes the second plate. StiUweU probes have numerous other uses. In appHcations of nonconductive media, a stiUweU probe is more sensitive and suppHes a greater amount of capacitance because the ground reference is so close to the probe. Further, if a tank waU offers a ground reference that is a varyiag distance to the probe, eg, a horizontal cylinder, the stiUweU offers a much more consistent (linear) ground reference. 

As the tank fills the capacitance increases while the leakage resistance decreases in proportion to the wetted area. The conservative case is to consider only the floor area. Assume that the charging current Iq < 10 pA and that the gas involved is hydrogen, whose LMIE W = 0.016 mJ. Eor lining thickness d = 2 mm, dielectric constant = 4, and floor area A = 10 m, the... 

To apply these data and equations to the problem of ground resistance, the maximum anticipated current must first be estimated. For practical industrial situations, Iq varies in the range 0.01-100/rA. The upper value represents extreme cases such as microfiltration and the lower value to slow flow in pipe. Typical charging currents for tank tmck loading are of the order 1 /rA (5-3.1.1). As an example, consider a system such as a tank with a capacitance less than 1000 pF. First, consider the minimum ignition voltages in Table A-4-1.3b. From Eq. (2), f L = In the case of hydrogen the mini-... 

In many cases it is inconvenient to use a dipstick, due to the position or location of the tank, and there are a variety of direct and remote contents gauges available, including gauge glasses, float and weight, float and swing arm, float and indicator, hydrostatic, electrical capacitance, etc. 

This is called an integrating (also capacitive or non-self-regulating) process. We can associate the name with charging a capacitor or filling up a tank. 

A common method of level measurement is to use a capacitance bridge. A typical arrangement is shown in Fig. 6.31a in which the sensor consists of two concentric metal cylinders. In the case of a circular tank, the wall of the tank can be employed as the outer cylinder of the sensor. The capacitance of the sensor is ... 

Measurements of liquid density are closely related to quantity and liquid-level measurements since both are often required simultaneously to establish the mass contents of a tank, and the same physical principle may often be used for either measurement, since liquid-level detectors sense the steep density gradient at the liquid-vapor interface. Thus, the methods of density determination include the following techniques direct weighing, differential pressure, capacitance, optical, acoustic, and nuclear radiation attenuation. In general, the various liquid level principles apply to density measurement techniques as well. 

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