The Research And Design Of Electronic Soap Film Flow Meter

The research and design of Electronic Soap Film Flow Meter This paper introduces a gas flow measurement apparatus - electronic soap film flow meter, which is mainly used for small flow rate of gas flow measurement. Soap film flowmeter has many advantages: good stability, simple structure and measuring accuracy. This electronic soap film flow meter combined the single chip technology and infrared sensor technology, while also used air pressure, temperature sensor to guarantee the measurement accuracy. The article elaborates on the ideas of its research, design methods and choices of various functional devices.Flow meter is a fluid (gas and liquid) flow velocity measure meter, which is an important instrument of industrial measurement. The so-called gas flow, that is, gas flowing through a cross-section of the gas volume per unit time. Calculated as follows: Qv (gas flow rate) = V (gas volume) / t (by time).Different ambient temperature and pressure can cause quite different gas flow, for uniform comparison and analysis, the flow value should be converted to standard conditions.Qv is gas flow converted to standard conditions by this formula: Qs = Qv×Ts×[(P-Pv) / (Ps×T)].For the traditional soap film flowmeter, t (the time) is counted by a stopwatch, the staff watched it and manually read out the soap film movement time, this can not only make the test slow, but the data accuracy is low, manual timing makes the experimental accuracy very limited.This design improves the traditional stopwatch timer by the use of photoelectric detection method, photoelectric detection signal can be processed, timed and conversed automaticly.Use the temperature sensors and pressure sensors to measure and compensate the flow meter's environment temperature and pressure,which can greatly improve work efficiency, measurement accuracy and precision.Electronic soap film flowmeter system consists of 6 parts:control system hardware (STC89C58RD+),soap membrane test module, temperature and pressure measurement module, display module and operation module.Soap film flow meter works summarized as follows: Source of the gas flow into the air intake tube at the bottom, squeez a rubber ball with liquid soap (or other methods) to let soap move up to the branch pipe, the gas blow soap film drum, and the pressure will push the soap film tube up in the glass .How to detect soap film's location? Selected two appropriate locations, note the two fixed values of the locations and draw two engraved lines,then install two pairs of photoelectric tubes, so volume between the tube can be fixed (V). Adjust the output voltage of the optical receiving part to 4.6V or so, then wait for soap film to go through the process, when the soap film rose to the next groove, the optical output voltage of the tube turn to 2.5V or so, this is to detecte soap film, then cause an immediate interrupt, microcontroller timer starts to time, when the soap film rise to the carved line stops timing. So can get the time t.As we has been knowned the time t and volume V, the actual instantaneous flow of gas Q can be calculated according to the formula.Next is the measurement of gas pressure. Pressure measurement module consists of two parts:the pressure signal detection and signal conversion. The design used Motorola chip MPX4100AP to measure atmospheric pressure,, the output voltage and the measured pressure has normally a good linear relationship. MPX4100 output voltage is transfered into TLC549 ADC chip to get a digital value.For temperature measurement I used the temperature sensor DS18B20. DS18B20 is produced by the U.S. DALLAS Company.It is a digital temperature sensor. It has wide range of temperature measurement and the temperature measurement error is small;It has nine programmable 12-bit ADC precision, temperature measurement resolution can be up to 1 / 16 (0.0625℃), the sensor meets the application requirements of this research. It also has a significant advantage:unique single interface mode: DS18B20's connection with the microprocessor requires only one line; signed 16-bit digital serial output hand down to the microprocessor, therefore, it is particularly convenient to use and can saves MCU interface resources.In this study, we use the microcontroller STC89C58RD+ to control the whole system.It has high processing speed and RAM is sufficiently large (1280 bytes,more than the ordinary 512 bytes), it is only 8-bit microcontroller, however,with large storage space: an internal 8K E2PROM, 32K FLASH memory, the clock frequency is up to 80 MHz, 40-pin chip package in which output I / O port resources is highly confidential, there are eight interrupt sources.The above characteristics fully meet the design's computing and storage requirements.Finally,use LCD12864 to display the output:the test of time, gas temperature, pressure and other measured parameters, gas flow calculated from the MCU, the converted standard flow. And use the function keys to manually input users'commands,so to control the boot, measurement, translation start, display, reset and other functions.About the system software design, the first thing is to master the timing requirements of the various devices. For any device, before its programming process, we must first view the timing diagram about its operations,and the programming sequence should be written in strict accordance with the regulations, so as to ensure the work components to function properly. The Whole system used a number of electronic components,as their representation this paper presented only a small part of them: the timing requirements and procedures of the A / D converter chip and LCD12864. Then introduced flow chart of the entire electronic soap film flowmeter system's software design:when the measurement is started,we first see the initial interface LCD screen, then use the keys to select operation according to the instructions displayed on the screen.Next when manual measurements begin, produce soap film according to the methods described earlier. If everything is ready, you can ensure the success of the soap film through blowing air, so start to measure the gas flow. Then the system measure and display time, temperature, pressure and other required data, microcontroller can calculate the actual measured gas flow, also show it on the 12864 screen. Finally gas flow is converted to standard state and shown on the LCD. At the end of the experement judge whether to show the data or not, if you don't want to show the datas and results,can return to the initial state, waiting for the next measurement.The design of electronic soap film flow meter meet the estimated demand parameters, error and precision are within acceptable range, after further refinement and improvement,can produce finished product and test its effectiveness in the market.