A method for liquid fuel rockets fueling level sensors parameters determining by the AC technique
Korolev Rocket and Space Corporation «Energia», 4а, Lenin str., Korolev, Moscow region, 141070, Russia
Methods for parameters determining of various objects based on the judgment on the measuring object according to its mathematical model and associated with analysis of alternating current passage through these objects gain more and more proliferation .
These methods found widespread occurrence in space rocket industry in particular. Abandonment of the CE5002 AC bridge, which was widely employed on technical complexes of space-rocket products, was the reason for new measuring techniques developing.
Dielectric liquids and cryogenic liquefied gases, reaching the temperatures about −253°C, are rocket fuel componentThe fueling level sensor represents a cylindrical air capacitor in double version in accordance with Fig. 1. Thus, the capacitive measuring method became widely spread in space-rocket products due to the possibility of operation in a boiling component, linearity of characteristic, movable parts absence etc. The fueling level sensor represents a cylindrical air capacitor in double version in accordance with Fig. 1.
A universal meter for impedance parameters' analyzer for performing studies in the field of materials analysis of ferroelectromagnetic phenomena, ion and superionic conductivity etc.  was developed at V. A. Trapeznikov Institute of Control Sciences of Russian Academy of Sciences.
The measuring devices for impedance measurements such as materials analysis, ferroelectricity, ionic and superionic conductivity etc. was developed in V. A. Trapeznikov Institute of Control Sciences of Russian Academy of Sciences.
In this transducer, computer controls measuring sequence and connects phase frequency detector (PFD) and analog to digital converter (ADC) firstly to the measuring object, and then to the reference with excitation voltage phase step of
, where n is integer. As a result, after each measuring cycle the value Uij (i = 1, 2; j = 1 … n), representing projection of measured voltage vector on the reference voltage, is formed at the ADC output:
Where T is integration interval; Uij(t) is PFD input signal; Gj(t) reference signal.
Computer receives the codes carrying information on Uij(t), and computes real and imaginary part of the voltage at the tested object and measure.
The developed device allows measuring fueling level sensor parameters with high accuracy, but the main restriction while its application is the presence of a long double-wire cable communication link, reaching the length of 500 m. With such a cable link length, the phase measurements are extremely difficult to be realized due to the parasitic components of the communication line.
That is why the authors took another path aimed at developing a new technique for fueling level sensor parameters determining.
As long as the fueling level sensor (FLS) is a two elements two-pole, its parameters determining consists in alternating current impact at the two specified frequencies firstly on fueling level sensor, and then of the reference.
According to the given FLS equivalent circuit we have the following equations to determine its parameters:
where CW is working capacity of the sensor;
RL is leakage resistance of sensor;
RR is reference resistance;
ω1, ω2 is excitation frequencies;
are measured currents via capacity sensor and reference at two frequencies.
However, operation results revealed that currents induced by the communication line length fr om the external sources, as well as AC frequencies difference value affect measuring results, namely, the more the AC frequencies separated, the higher the measuring accuracy.
Thus, the goal of the new measuring approach is increasing measuring accuracy due to bias currents compensation and providing one measurement at the direct current excitation using the following equations:
wh ere sign of Δ denotes bias currents compensation, which were measured at turned-off AC and DC current sources.
The Xilinx FPGAs were employed for the newly developed technique realization, on which base measuring data processing and computation blocks, and functional blocks of analog measuring channel, including analog-to-digital converter of integrating type, sine voltage generator, frequency and scale of amplification control circuit.
The developed measuring technique allowed create a unit for ensuring FLS parameters measuring on the technical complex instead of out of production CE5002 AC bridge.
The technique described in the article may be applied for parameters measuring of two-poles, employed as physical processes sensors (temperature, pressure, level of liquid and granular media, etc.) at the industrial objects, transportation means and, above all, in the systems for measuring fueling level of liquid fuelled rocket carriers in the space-rocketry.
Keywords:fueling level sensor, measuring, two-pole parameters, alternating current, precision, space rocket efficiency, dielectric permittivity, electrical capacity
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