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Hardware anti-interference techniques used in ultrasonic flowmeter measurement system

by:Sincerity     2020-10-16
1. Interference sources in the ultrasonic flowmeter measurement system, the interference sources of interference are a lot of kinds, mainly include: (1) meter installation environment may have larger electric field and magnetic field interference; (2) close to the water pump water pump when installation of close to the ultrasonic signal noise; (3) the power supply noise interference, the use of commonly used power filtering technology can eliminate the effect; (4) launch signal to interference from the received signal. Bigger transmitting power, through the circuit harmony road can be coupled to receive circuit, if the diameter is very small, very close to the distance between the transducer, the interference between the tail will receive, wave waveform, which seriously affect the received signal. 2. Anti-interference measures, 1) The power supply. Use of all kinds of dc power supply system ( Such as + 5 v) The input end of the jumper 1 10 ~ 100 & mu; Electrolytic capacitor and 1 0 F. 01 ~ - 0. 1μ F ceramic filter capacitor to suppress the power peak interference, sending and receiving circuit with two sets of isolated power supply. ( 2) Receive the range gate. Receive door can prevent transmitting and switching action brings to the received signal interference. ( 3) Automatic gain technology. Automatic raised beneficial technology besides to facilitate measurement signal, also can effectively suppress noise interference. ( 4) The watchdog circuit. Application will be caused by disturbance in the process of running out of control and cause program flying, or into & other; Infinite loop & throughout; At this time, ZUI directly anti-interference method is to use hardware & other; Guard dog & throughout; Circuit. The reset pulse can make the system reset, to restart the running program. X5045 integrated chip is used to implement the watchdog function. X5045 pin function is as follows: CS for optional signal; SO for the serial output; SI for serial input; SCR for the serial clock input; WP to an EPROM write protect input; RESET to RESET signal output; Vss for; Vc for the power supply voltage. X5045 using three serial line bus ( SPI) Peripheral interface, to manipulate all the chip operation code, byte address and write data is input by ST pin, write data in serial clock SCT up along the latch; The data read from the chip serial output by the SO pin. And voltage monitor chip control timer of single chip microcomputer to provide independent protection, when the power supply voltage to 4. The RESET pin is below 5 v, immediately produce high level RESET signal automatically, and keep to the supply voltage has been returned to normal; When the system power on or off the electricity, the RESET pin also automatically generate a high level RESET signal; When a system failure occurs, as long as the control to the programmable timer timeout limit, automatic RESET pin immediately produce a continuous high level of 200 ms RESET signal. In this way, can effectively prevent freezes any clerical error, data and failure such as wrong operation. ( 5) Reasonable wiring technology. Analog signal and digital signal lines are relatively separate, signal is separated from the power cord; PCB wiring will be public ground wire and power cable to widen as far as possible, and make them as much as possible close to the power supply circuit; To minimize the length of the power cord and ground wire, to minimize the public impedance between the two, reduce the coupling of dry resistance; Avoid in the process of wiring circuits have repeat area, to reduce the mutual induction. ( 6) Grounding technology. To digital and analog separate, they are on the point, two probe using their independent ground, reducing ground interference coupling, instrument and probe ground. ( 7) Shielding technology. Using shielding technology can be isolated through space coupling electromagnetic interference, the measures is to use metal machine 売 will encapsulate measurement circuit. 3. Conclusion the accuracy of ultrasonic flowmeter measurement largely depends on the system of ultrasonic signal correctly, ultrasonic flowmeter work environment is usually bad, however, are susceptible to the influence of various interference. Not only for measuring system, the interference may affect the data collection, all kinds of control signals of the state, and RAM, speaking, reading and writing will also affect the normal work of the program counter, make the program failure, therefore, must take effective measures to reduce interference.
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