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Several Factors Affecting Measurement Accuracy of Ultrasonic Water Meter

Views: 0     Author: Site Editor     Publish Time: 2022-03-11      Origin: Site

Several Factors Affecting Measurement Accuracy of Ultrasonic Water Meter


 The measurement of static water flow is relatively difficult, especially for large pipe diameters, the flow change caused by dripping water is very small, so it needs a great measurement resolution to achieve the measurement of static water flow with large pipe diameters. At present, the ultrasonic water flow measurement scheme is mostly used on the market. At present, it can achieve the stability of the TOF value change within 60ps, which makes it possible to measure the water flow with high precision, laying a solid foundation for the intelligent water meter network. foundation. Here are several factors that affect the stability of the TOF value during static water flow. Users can learn from it when designing an ultrasonic water meter with a chip for time-of-flight measurement.

Influencing factors of static water flow stability:

A. water vapor

Before the overall test, please ensure that the waterproof performance reaches IP68. Water vapor will affect the normal operation of the PCB, especially when the static water flow measurement is easy to cause interference.

B. Transducer

The working stability of the transducer directly affects the calculation of the TOF time difference, to ensure that the time interval of the transducer transmitting sound waves remains stable and the intensity of the sound wave remains stable, and the transducer is tested in advance before the overall performance test.

C. Power

At present, there are many cases of abnormal measurement caused by the power supply. The small signal output by the power supply has a relatively large impact on the water flow. Therefore, the output signal of the power supply should be tested first. If the power supply effect is not good, an additional LDO can be added.

D. Circuit board heat buildup

The heat accumulation of the circuit board mainly affects the junction temperature of the chip and makes the semiconductor work abnormally. Therefore, after the circuit is designed, the overall temperature needs to be verified, and the output of the signal at different temperatures is tested to see if there is any abnormality in the zero drift and TOF stability. .

E. The influence of high frequency signal of the circuit

In many cases, high-frequency devices such as analog switches are used in circuit design, which is not a problem when measuring large flow, but it is prone to interference when switching to static water flow, so try to avoid a large number of high-frequency components.

F. Water temperature

Water temperature mainly affects the propagation rate of sound waves in water and thus affects the zero point of the water meter. When the medium is tap water, the zero point difference between 20°C water and 70°C water is about 11%, which is a considerable impact; especially For large water pipes for long-distance transmission, they are often exposed in the wild, and are susceptible to zero-point drift caused by factors such as day and night temperature difference, sunshine, altitude, etc. Therefore, for such water meters that work in environments with large temperature differences, it is best to The method is to perform temperature compensation.

G. Reasonable Design

Some important considerations for wiring are as follows:

i. Place the crystal oscillator as close to the chip as possible

ii. Please do not bridge the SPI communication line with the Load or IO pin traces

iii. Please do not bridge the crystal line and the load line

iv. Please place the double-pass C2 and C3 decoupling capacitors close to the power pins of GP21

v. Please make the temperature measurement traces as short and symmetrical as possible

If possible, please use copper layer GND to surround the crystal oscillator

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Summary

 Ultrasonic water meters and ultrasonic heat meters have brought many advantages and expanded functions to our lives. It provides information that helps reduce design time and avoid circuit problems caused by incorrect component values or incorrect configuration. We recommend following the layout diagram and the demo board schematic when designing for best performance.


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