> For the complete documentation index, see [llms.txt](https://docs.lorric.com/qr/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.lorric.com/qr/fu-tx310-ultrasonic-flowmeter-manual-chinese-v2/1.-chan-pin-jie-shao-1/1.5-liang-ce-yuan-li.md).

# 1.5 量測原理

![supersonic-flowmeter-principle](/files/-Lk23WEgWNIZxyYFzN9M)

流體流速為V，聲波在流體中傳遞速度為c，內管徑為D，內管截面為A。當超聲波在水中於探頭A與探頭B之間傳遞時，順流與逆流的方向會產生一個與流速成正比的時間差。

![](/files/-LkbbPm3KWt01yX2hCWa)

流量為Q= v  A， 若內管截面是一個圓，則Q= v＊(d² π/ 4)，故管徑尺寸與流量準確度有很大關係。

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