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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Ultrasonic gasoline octane meter. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Measuring technology Many modern cars are equipped with an electronic ignition system with a computer control unit for fuel supply and injection. One of the parameters important for the correct operation of the control unit is the octane number of gasoline. If it does not comply with the standard, the engine will not be able to operate in the optimal mode, the fuel injection control process will be disrupted, up to an emergency loss of power. Therefore, the presence of a simple and affordable device for all motorists to control the octane number of gasoline poured into a fuel tank is very important today. There are many different methods for measuring the octane number of gasoline [1], on the basis of which the production of octanomers has been mastered. For example, the ZX101C device widely used in Russia by Zeltex uses a method for measuring octane number based on the absorption of infrared radiation by gasoline in the range of 800...1100 nm. The patented optical design of the device contains 14 light filters, resulting in 14 readings of the absorption spectrum in the specified range. Next, based on the calibration model, the octane number is calculated. A laboratory analyzer XX-440 is also produced, designed for express analysis of the octane number of gasoline. It is easy to use and has high reliability due to the most sophisticated modern technologies and patented technical solutions used in its creation. After each switch-on, the device self-tests to achieve maximum accuracy. The measurement results are displayed on the display and can be printed on the built-in printer indicating the sample number, date and time of the test. But the cost of such a device is measured in tens of thousands of US dollars. It is very difficult even for a very experienced radio amateur to create similar octanomers at home. To create a small-sized and cheap device for the operational control of fuel quality, one can use the ultrasonic method for determining the octane number of gasoline [2], which is based on measuring the speed of propagation of ultrasound in gasoline. On the basis of this method, the domestic industry already produces octanomers AC-98, SHATOX SX-150, OKTAN-IM, etc. The octane meter considered below does not claim to be highly accurate in determining the octane number of gasoline compared to the declared accuracy of industrial devices, but nevertheless it makes it possible to distinguish good gasoline from bad. This is important for a car enthusiast, since the quality of gasoline at many gas stations, unfortunately, does not meet the standards. In addition, such an octanomer is easy to manufacture, requires minimal adjustment, and uses a cheap element base.
The block diagram of the ultrasonic octane meter is shown in fig. 1. At the output of the single pulse generator, a pulse (1) is formed, which the transmitter transfers to the resonant frequency of the ultrasound emitter (2). For the most common currently produced ultrasonic emitters, this frequency is 40, 200 or 400 kHz [3]. The pulse is radiated into the car's gas tank. On the opposite side of the gas tank, an ultrasonic receiver receives this pulse (3), and a selective detector converts it into a direct current pulse (4), delayed relative to the pulse (1) by the time the ultrasound propagates in gasoline. This time is equal Δt = L/V, where L is the distance between the emitter and receiver of ultrasound; V is the speed of propagation of ultrasound in the analyzed gasoline. Along the fronts of the emitted and received pulses, a pulse (5) is formed, the duration of which is equal to Δt. By measuring it and knowing the distance between the transmitter and the receiver, you can calculate the speed V and use it to estimate the octane number of gasoline. To measure the duration, the pulse is filled with the following counting pulses with a known period and their number is counted. Then this number is compared with the reference constants for different brands of gasoline, and based on the results of the comparison, displayed on the LED indicator, a conclusion is made about the brand and quality of gasoline. The values of the speed of propagation of ultrasound at different temperatures in gasoline, currently used in automobile engines and in the air, are given in Table. 1. Table 1
Since the speed of propagation of ultrasound in gasoline depends significantly on temperature, the measuring installation is equipped with a thermostat, having built a temperature sensor and a heater into the gasoline tank. This significantly improves the measurement accuracy, especially in winter. A schematic diagram of an octanomer operating according to the described principle is shown in fig. 2. The transmitter and selective ultrasonic signal detector are based on the LM567 (DA2) tone decoder chip. This microcircuit is a synchronous detector, the reference oscillator of which is covered by a PLL loop. The generator can be tuned to any frequency F from 100 Hz to 500 kHz by selecting the appropriate parameters of elements C6, R9 and R10: F = 1/(1,1·C6·(R9+R10)). Since the device uses ultrasonic transducers MA40S4R (VM1) and MA40S4S (BA1) with a resonant frequency of 40 kHz [3], the frequency of the generator should be the same. By using the same generator for generating the emitted pulse and detecting the received one, a stable tuning of the receiver to the transmitter signal is ensured.
The crystal oscillator on the logic element DD8.4 generates counting pulses with a frequency of 1 MHz, which, using the element DD8.3, fill the pulse of the difference between the emitted and received signals, which is formed at the output of the dD8 element. 1. Thus, the number of pulses that have passed through the element DD8.3 is equal to the duration of the passage of ultrasound measured segment in gasoline, expressed in microseconds. For gasoline of different grades at a temperature of 20 оWith and the length of the measured segment 1 m, this number (N) is indicated in Table. 2. Table 2
The pulses are counted by the counter DD1. Since only seven of its digits are used, which can contain a number not exceeding 127, they overflow many times during the counting process and, upon completion, they contain the remainder of dividing the number of counted pulses by 128 (N mod 128) . These residues are also listed in Table. 2. Since the difference between the maximum and minimum possible values of the residuals of the number of pulses does not exceed 127, there is no ambiguity in the count when analyzing the state of only seven digits of the counter. The number from the outputs of the counter is fed to one of the inputs of the digital comparator on the DD3 and DD5 microcircuits. On the second input of the comparator using the switch SA1 alternately serves the numbers corresponding to the reference duration of the delay for four grades of gasoline. These numbers are set at the inputs of the buffer elements DD2, DD4, DD6 and DD9 in inverse binary code, since these elements are inverting. Since the outputs of these elements have three states, they can be combined into a common bus, which is done in the octane meter. With a different length of the measured segment (the length of the gas tank), the exemplary numbers N change proportionally, then the remainders of their division by 128 are taken. Starting to measure the octane number of gasoline, you should set the SA1 switch to the "AI-80" position. Then reset the counter by pressing the SB1 button and, by pressing the SB2 button, take a measurement. If the octane number of gasoline is less than the reference for gasoline of this brand, then the red LED HL3 will turn on. If it is equal to the reference, the yellow LED HL2 will turn on. If more, then the green LED HL1 will be turned on. In the latter case, switch SA1 should be sequentially moved to positions corresponding to high octane numbers, while continuing to observe the LEDs. Establishing the device comes down to setting the frequency to 40 kHz at pin 5 of the DA3 chip using the trimming resistor R9. If higher frequency ultrasonic transducers of 100 or 200 kHz are used, then the generator frequency must be increased accordingly. However, it should be borne in mind that with an increase in the frequency of ultrasound, its attenuation in gasoline increases. Therefore, the dimensions of the tank in which measurements are made will have to be reduced, and this will increase the error of the instrument. The digital microcircuits used in the octanomer can be replaced by their imported analogues of the 4000 and 74HC series. Instead of the LT3013EFE voltage regulator, any linear regulator with an adjustable or fixed output voltage of 5 V and a maximum load current of at least 100 mA will work. Since the power dissipated on the stabilizer is about 0,7 W, it must be equipped with a heat sink. The thermostat circuit is shown in fig. 3. It is built on a dedicated thermostat IC LM56BIM (DA1), which has a built-in temperature sensor and a reference voltage source of 1,25 V (pin 1). The heater on and off temperatures are set by the voltage values at the inputs UTL (pin 3) and UTH (pin 2), respectively, which should be equal [4]: UTL = 0,0062 TL + 0,395 UTH = 0,0062 TH + 0,395, XNUMX, where TL and tH - set values of temperature, respectively, turning on and off the heater, °C.
These voltages are obtained from the reference voltage Uref (pin 1) using a resistive voltage divider R1-R3. Given the value of RΣ\u1d R2 + R3 + RXNUMX, the resistances of these resistors can be calculated using the formulas: R2=UTLRΣ / 1,25 R1 = (UTHRΣ / 1,25) - R2 R3=RΣ - R1 - R2 The ratings of resistors R1-R3 indicated in the diagram provide a heater switch-on temperature of about 18 оC, and the temperature of its shutdown is about 26 оC. If the temperature of gasoline is less than 18 оC, then the HL2 LED lights up and the heating element EK1 turns on. If the temperature is above 26 оC, the heater turns off, but the HL1 LED turns on. Therefore, when any of the LEDs is on, it is not worth measuring the octane number of gasoline. To correctly measure the temperature of gasoline, the LM56BIM chip package must have good thermal contact with the gas tank. Self-adhesive heating foils were used to heat the gas tank [5]. Literature
Author: A. Kornev
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