COMPUTER SYSTEM FOR CONTROLLING OF ULTRASONIC LEVEL GAUGE FOR LIQUIDS WITH CIRCULAR MOTION OF ULTRASONIC PULSE



The paper considers a new way of measuring the level of liquids by ultrasonic method, which is based on the circular motion of ultrasonic pulse. The level gauge measuring circuit has two ultrasonic transmitters, one of which is located on a float which floats on the surface of a liquid. The level gauge block diagram is presented, and its operating principle is described. The level gauge has a small dead zone, and twice as wide measuring range.

Keywords: Ultrasound, level,liquid, measuring, transmitter, environment, gas, control, error, sensitivity

The ultrasonic method (USM) of level monitoring is based on determination of time in which an ultrasonic pulse (USP) passes the distance from the ultrasonic transmitter (UST) to the liquid surface [1-3]. Level gauges, which are based on this method, have a sufficiently high precision of measurement (from ±0.25%) and a sufficiently broad measuring control range (MCR) (some of them - up to 120 m) [4,5]. The disadvantages should include the considerable dependence of level monitoring on gas environment (GE) parameters, a sufficiently large dead zone (up to 0.6 meters), the influence of internal structural elements and many others [6-7]. The proposed ultrasonic level gauge (USLG) [8] can have one or two piezoceramic transmitters (UST). Main UST1 is located on the top of the reservoir with liquid and excitedby an electric pulse (EEP), which is formed by an electric measuring circuit (EMC). Secondary UST2 is located on the top of the float which is floating on the liquid surface. UST2 ultrasonic transmitter is excited by an ultrasonic pulse (USP), which is formed by UST1 ultrasonic transmitter. Main and secondary USTs are connected to each other by an insulated metal towrope. The ultrasonic pulse (USP), which is emitted by the secondary UST2 ultrasonic transmitter, passes through the gas environment (GE) in the reservoir and is perceived by an ultrasonic receiver (USR), which converts these pulses into electromotive force (EMF) with an amplitude proportional to the GE thickness, and the electrical signal goes to the programming microcontroller (PMC) of the computer control and management system, which processes the measurement information signal, determines the amplitude of the perceived ultrasonic signal (USS), calculates the time of movement of the ultrasonic pulse (USP) from UST1 ultrasonic transmitter to USR ultrasonic receiver and transmits information to the real-time monitor for display, and sends it to the database formation unit. Due to the fact that the emitted and perceived channels are divided between themselves and create a corresponding circular shape, the following results are achieved:

- the dead zone of the ultrasonic level gauge (USLG) is reduced almost 5 times due to the absence of a reference mechanical device;

- the measuring control range (MCR) of liquid level is increased up to 2 times due to single passing of ultrasonic pulse through the gas environment;

- the precision of liquids level measurement is increased almost twice dueto: a decrease in the distance of passing of an ultrasonic pulse (USP) in the gas environment (GE) by 2 times; a decrease in the secondary ultrasonic effects insideof the reservoir, and the absence of a reference device on the path of an ultrasonic pulse (USP) in the GE.

Ultrasonic level gauges with two ultrasonic transmitters (UST) are designed for measuring control of fuel level in warehouses, refueling stations, etc., as well as other highly inflammable liquids, because ultrasonic pulses of mechanical origin propagate through liquid and gas environment. In cases when nonflammable liquids level is measured, ultrasonic level gauges (USLG) can be built with one ultrasonic transmitter (UST), which is located on the float. A significant advantage of the USLG with circular motion of ultrasonic pulse (USP) is the absence of contact of this pulse with the liquid surface. Fig. 2.1 presents the scheme of an ultrasonic level gauge (USLG), on which the following is marked: 1– UST1 primary transmitter, UST2 secondary transmitter, USR receiver, CU control unit and IDU information display unit.

Figure 1 - Scheme of the ultrasonic level gauge with the circular motion of ultrasonic pulse

Measuring of liquid level in the reservoir is performed by means of the secondary UST2 which emits ultrasonic pulses (USP) and transmits them through the gas environment (GE) with R thickness to the ultrasonic receiver (USR). Since the distance from the primary UST1 to UST2 is constantand determined by the towrope length, and the distance from UST2 ultrasonic transmitter to USR ultrasonic receiver is determined by R thickness, then the time of ultrasonic pulse (USP) passing of this distance will depend on L liquid level. Since the UST1 output signal is proportional to the UST2 signal, and the time of USP passing along the metal towrope is constant and much less than the timeof USP passing through the gas environment (GE), then this time has almost no effect on the measurement result. The time by which the liquid level is determined, consists of ${{\tau }_{1}}$ time of feeding of a single electric pulse (EEP)to the piezoceramic element (PCE1) of UST1, ${{\tau }_{2}}$ time of ultrasonic pulse (USP) formation by the first transmitter, ${{\tau }_{3}}$ time of USP passing along a metal towrope to UST2, $\tau g$ time of USP passing of the gas environment (GE), and ${{\tau }_{4}}$ time of perception by the ultrasonic receiver (USR), transformation into voltage and amplification of the latter. UST2 ultrasonic transmitter has receiving and emitting metal membranes in its structure, between which there is a PCE2 which serves as a receiver-transmitter of initial ultrasonic pulses (USP). Due to single passing by USP of R distance in the GE, the liquid level measurement error, which is caused by changes in temperature, pressure and composition, is reduced almost twice. Since ultrasonic pulse (USP) weakening in the GE decreases almost twice, then the level measurement range is increased by the same amount compared to an analog. The computer measuring system consists of the following two units: the control unit (CU) and the measurement information display unit (IDU). The IDU includes: microcontroller (MC) 1; signal conversion unit 2; memory unit 3 and real-time monitor 5. The control unit includes: signal conversion unit 5; managing microcontroller (MMC) 6; adjustable source of excitation pulses (ASEP)7; reference-voltage source (RVS) 8; comparator 9; USR EMF amplitude determining unit 10 and amplifier 11. The ultrasonic level gauge (USLG) operates in the following way. After its putting into operation, managing microcontroller (MMC) 6 producesa control signal to adjustable source of excitation pulses (ASEP) 7, which forms and produces a single electric pulse (EEP) to UST1 ultrasonic transmitter. Simultaneously, the timing-pulses counter (TPC) resets to zero and turns on. Atthat, UST1 generates an ultrasonic pulse (USP) at maximum amplitude, which goesto UST2 along the insulated metal towrope. The latter creates USP, which is sent to the GE. After passing through the GE, this USP is perceived by the ultrasonic receiver (USR), in which EMF with ${{}_{R}}$ voltage is created. The latter, after amplification in amplifier 11, is fed to comparator 9, where it is compared with a pre-set ${{}_{0}}_{R}$ reference voltage, which is formed by reference-voltage source (RVS) 7. If the difference in these voltages is notzero (${{}_{R}}-{{}_{0R}}\ne 0$), then comparator 9 produces a signal to the adjustable source of excitation pulses (ASEP), which reduces or increases the amplitude of the single electric pulse (EEP) until ${{}_{R}}-{{}_{0R}}=0$ equation is valid. When ${{}_{R}}-{{}_{0R}}=0$, then the comparator permits managing microcontroller (MMC) 6 to turn the timing-pulses counter (TPC) on and calculate the liquid level value. The timing-pulses counter (TPC) is working until the perceiving signal of the next level-measuring cycle comes to the comparator, and the measured time, the calculated level value, the temperature of the GE and the liquid, as well as the pressure in the reservoir and the atmospheric pressureare displayed on the monitor screen 4. The absolute error of the measurement control is also displayed on the monitor screen.

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  • Рецензент: д.т.н., проф., зав. каф. Комп'ютерно-інтегрованих систем управління Східноукраїнського національного університету ім. В. Даля Й.І. Стенцель
May 26, 2016