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lang=EN-US style='font-size:9.0pt;font-family:Arial;color:#111111'>V </span><span
style='font-size:9.0pt;mso-ascii-font-family:Arial;mso-hansi-font-family:Arial;
mso-bidi-font-family:Arial;color:#111111'>是液体沿管道中心线的速度。考虑到液体流速沿管道直径的不均匀分布，添加一个修正系数</span><span
lang=EN-US style='font-size:9.0pt;font-family:Arial;color:#111111'>K</span><span
style='font-size:9.0pt;mso-ascii-font-family:Arial;mso-hansi-font-family:Arial;
mso-bidi-font-family:Arial;color:#111111'>。根据流体力学，当雷诺数</span><span lang=EN-US
style='font-size:9.0pt;font-family:Arial;color:#111111'>Re </span><span
style='font-size:9.0pt;mso-ascii-font-family:Arial;mso-hansi-font-family:Arial;
mso-bidi-font-family:Arial;color:#111111'>在某一范围内时，</span><span lang=EN-US
style='font-size:9.0pt;font-family:Arial;color:#111111'>K </span><span
style='font-size:9.0pt;mso-ascii-font-family:Arial;mso-hansi-font-family:Arial;
mso-bidi-font-family:Arial;color:#111111'>为定值，在标定过程中确定</span><span lang=EN-US
style='font-size:9.0pt;font-family:Arial;color:#111111'>K </span><span
style='font-size:9.0pt;mso-ascii-font-family:Arial;mso-hansi-font-family:Arial;
mso-bidi-font-family:Arial;color:#111111'>的大小。</span><span lang=EN-US
style='font-size:9.0pt;font-family:Arial;color:#111111'><br>
</span><span style='font-size:9.0pt;mso-ascii-font-family:Arial;mso-hansi-font-family:
Arial;mso-bidi-font-family:Arial;color:#111111'>瞬时流量</span><span lang=EN-US
style='font-size:9.0pt;font-family:Arial;color:#111111'><img border=0
width=123 height=38 id="_x0000_i1032"
src="http://www.dzkf.cn/upimg/allimg/0705/1_18123043.JPG"></span><span
style='font-size:9.0pt;mso-ascii-font-family:Arial;mso-hansi-font-family:Arial;
mso-bidi-font-family:Arial;color:#111111'>（</span><span lang=EN-US
style='font-size:9.0pt;font-family:Arial;color:#111111'>D </span><span
style='font-size:9.0pt;mso-ascii-font-family:Arial;mso-hansi-font-family:Arial;
mso-bidi-font-family:Arial;color:#111111'>为管道直径）</span><span lang=EN-US
style='font-size:9.0pt;font-family:Arial;color:#111111'> (1)<br>
</span><span style='font-size:9.0pt;mso-ascii-font-family:Arial;mso-hansi-font-family:
Arial;mso-bidi-font-family:Arial;color:#111111'>如果已经知道了</span><span lang=EN-US
style='font-size:9.0pt;font-family:Arial;color:#111111'>L</span><span
style='font-size:9.0pt;mso-ascii-font-family:Arial;mso-hansi-font-family:Arial;
mso-bidi-font-family:Arial;color:#111111'>、</span><span lang=EN-US
style='font-size:9.0pt;font-family:Arial;color:#111111'>C</span><span
style='font-size:9.0pt;mso-ascii-font-family:Arial;mso-hansi-font-family:Arial;
mso-bidi-font-family:Arial;color:#111111'>、</span><span lang=EN-US
style='font-size:9.0pt;font-family:Arial;color:#111111'>D </span><span
style='font-size:9.0pt;mso-ascii-font-family:Arial;mso-hansi-font-family:Arial;
mso-bidi-font-family:Arial;color:#111111'>和</span><span lang=EN-US
style='font-size:9.0pt;font-family:Arial;color:#111111'>β </span><span
style='font-size:9.0pt;mso-ascii-font-family:Arial;mso-hansi-font-family:Arial;
mso-bidi-font-family:Arial;color:#111111'>，只要能够测得顺流和逆流传播时间差（</span><span
lang=EN-US style='font-size:9.0pt;font-family:Arial;color:#111111'> ΔT </span><span
style='font-size:9.0pt;mso-ascii-font-family:Arial;mso-hansi-font-family:Arial;
mso-bidi-font-family:Arial;color:#111111'>）就可以求出速度</span><span lang=EN-US
style='font-size:9.0pt;font-family:Arial;color:#111111'>V</span><span
style='font-size:9.0pt;mso-ascii-font-family:Arial;mso-hansi-font-family:Arial;
mso-bidi-font-family:Arial;color:#111111'>，进而得到瞬时流量。</span><span lang=EN-US
style='font-size:9.0pt;font-family:Arial;color:#111111'><br>
<br>
2.2 </span><span style='font-size:9.0pt;mso-ascii-font-family:Arial;mso-hansi-font-family:
Arial;mso-bidi-font-family:Arial;color:#111111'>影响流量计测量精度的因素和解决方法</span><span
lang=EN-US style='font-size:9.0pt;font-family:Arial;color:#111111'>1<br>
</span><span style='font-size:9.0pt;mso-ascii-font-family:Arial;mso-hansi-font-family:
Arial;mso-bidi-font-family:Arial;color:#111111'>精度是测量仪表的重要指标，在时差法超声波流量计流量测量中，误差来源主要来自以下几方面：</span><span
lang=EN-US style='font-size:9.0pt;font-family:Arial;color:#111111'><o:p></o:p></span></p>
<p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;
margin-left:0cm;text-indent:-18.0pt;line-height:18.0pt;mso-list:l1 level1 lfo3;
tab-stops:list 36.0pt;background:white'><![if !supportLists]><span lang=EN-US
style='font-size:9.0pt;font-family:Arial;mso-fareast-font-family:Arial;
color:#111111'><span style='mso-list:Ignore'>1.<span style='font:7.0pt "Times New Roman"'>
</span></span></span><![endif]><span style='font-size:9.0pt;mso-ascii-font-family:
Arial;mso-hansi-font-family:Arial;mso-bidi-font-family:Arial;color:#111111'>加工精度及温度变化对机械尺寸的影响。</span><span
lang=EN-US style='font-size:9.0pt;font-family:Arial;color:#111111'><br>
</span><span style='font-size:9.0pt;mso-ascii-font-family:Arial;mso-hansi-font-family:
Arial;mso-bidi-font-family:Arial;color:#111111'>声路角</span><span lang=EN-US
style='font-size:9.0pt;font-family:Arial;color:#111111'>β </span><span
style='font-size:9.0pt;mso-ascii-font-family:Arial;mso-hansi-font-family:Arial;
mso-bidi-font-family:Arial;color:#111111'>、管道直径</span><span lang=EN-US
style='font-size:9.0pt;font-family:Arial;color:#111111'>D</span><span
style='font-size:9.0pt;mso-ascii-font-family:Arial;mso-hansi-font-family:Arial;
mso-bidi-font-family:Arial;color:#111111'>、声程</span><span lang=EN-US
style='font-size:9.0pt;font-family:Arial;color:#111111'>L </span><span
style='font-size:9.0pt;mso-ascii-font-family:Arial;mso-hansi-font-family:Arial;
mso-bidi-font-family:Arial;color:#111111'>等机械参数的加工精度、温度稳定性对流量的测量有直接的影响。在测量过程中，它们会随着温度的变化而变化。这种误差可以通过精密加工，合理选材以及合理的结构设计使影响减到最小。</span><span
lang=EN-US style='font-size:9.0pt;font-family:Arial;color:#111111'><o:p></o:p></span></p>
<p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;
margin-left:0cm;text-indent:-18.0pt;line-height:18.0pt;mso-list:l1 level1 lfo3;
tab-stops:list 36.0pt;background:white'><![if !supportLists]><span lang=EN-US
style='font-size:9.0pt;font-family:Arial;mso-fareast-font-family:Arial;
color:#111111'><span style='mso-list:Ignore'>2.<span style='font:7.0pt "Times New Roman"'>
</span></span></span><![endif]><span style='font-size:9.0pt;mso-ascii-font-family:
Arial;mso-hansi-font-family:Arial;mso-bidi-font-family:Arial;color:#111111'>温度变化对流速的影响。</span><span
lang=EN-US style='font-size:9.0pt;font-family:Arial;color:#111111'><br>
</span><span style='font-size:9.0pt;mso-ascii-font-family:Arial;mso-hansi-font-family:
Arial;mso-bidi-font-family:Arial;color:#111111'>超声波的传播速度随流体的温度的升高而升高，因而会给测量带来误差。流体温度变化对精度的影响可以采用温度补偿方法通过测量流体的温度和温度补偿数学模型的计算实现自动补偿。</span><span
lang=EN-US style='font-size:9.0pt;font-family:Arial;color:#111111'><o:p></o:p></span></p>
<p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;
margin-left:0cm;text-indent:-18.0pt;line-height:18.0pt;mso-list:l1 level1 lfo3;
tab-stops:list 36.0pt;background:white'><![if !supportLists]><span lang=EN-US
style='font-size:9.0pt;font-family:Arial;mso-fareast-font-family:Arial;
color:#111111'><span style='mso-list:Ignore'>3.<span style='font:7.0pt "Times New Roman"'>
</span></span></span><![endif]><span style='font-size:9.0pt;mso-ascii-font-family:
Arial;mso-hansi-font-family:Arial;mso-bidi-font-family:Arial;color:#111111'>电气特性上的误差。</span><span
lang=EN-US style='font-size:9.0pt;font-family:Arial;color:#111111'><br>
</span><span style='font-size:9.0pt;mso-ascii-font-family:Arial;mso-hansi-font-family:
Arial;mso-bidi-font-family:Arial;color:#111111'>器件工作不稳定、计数电路精度低会给流量测量带来误差。为了减小该误差，我们选用</span><span
lang=EN-US style='font-size:9.0pt;font-family:Arial;color:#111111'>100MHz</span><span
style='font-size:9.0pt;mso-ascii-font-family:Arial;mso-hansi-font-family:Arial;
mso-bidi-font-family:Arial;color:#111111'>、高精度、高稳定性的石英晶体振荡器作为时钟基准信号，选用大规模高速可编程逻辑器件</span><span
lang=EN-US style='font-size:9.0pt;font-family:Arial;color:#111111'>(CPLD)</span><span
style='font-size:9.0pt;mso-ascii-font-family:Arial;mso-hansi-font-family:Arial;
mso-bidi-font-family:Arial;color:#111111'>来实现复杂的逻辑控制和高精度计时功能，以达到系统的稳定性和可靠性。</span><span
lang=EN-US style='font-size:9.0pt;font-family:Arial;color:#111111'><o:p></o:p></span></p>
<p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;
margin-left:0cm;text-indent:-18.0pt;line-height:18.0pt;mso-list:l1 level1 lfo3;
tab-stops:list 36.0pt;background:white'><![if !supportLists]><span lang=EN-US
style='font-size:9.0pt;font-family:Arial;mso-fareast-font-family:Arial;
color:#111111'><span style='mso-list:Ignore'>4.<span style='font:7.0pt "Times New Roman"'>
</span></span></span><![endif]><span style='font-size:9.0pt;mso-ascii-font-family:
Arial;mso-hansi-font-family:Arial;mso-bidi-font-family:Arial;color:#111111'>回波波形变化和幅值变化带来误差</span><span
lang=EN-US style='font-size:9.0pt;font-family:Arial;color:#111111'><br>
</span><span style='font-size:9.0pt;mso-ascii-font-family:Arial;mso-hansi-font-family:
Arial;mso-bidi-font-family:Arial;color:#111111'>该变化会使二值化电路的计时比较点发生变化，造成波形误差。这种误差用硬件方法很难克服，必须借助于软件方法引入智能分析算法加以解决。</span><span
lang=EN-US style='font-size:9.0pt;font-family:Arial;color:#111111'><o:p></o:p></span></p>
<p style='line-height:18.0pt;background:white'><strong><span lang=EN-US
style='font-size:9.0pt;font-family:Arial;color:#111111'>3 </span></strong><strong><span
style='font-size:9.0pt;font-family:宋体;mso-ascii-font-family:Arial;mso-hansi-font-family:
Arial;mso-bidi-font-family:Arial;color:#111111'>系统硬件组成</span></strong><b><span
lang=EN-US style='font-size:9.0pt;font-family:Arial;color:#111111'><br>
</span></b><span lang=EN-US style='font-size:9.0pt;font-family:Arial;
color:#111111'> </span><span style='font-size:9.0pt;
mso-ascii-font-family:Arial;mso-hansi-font-family:Arial;mso-bidi-font-family:
Arial;color:#111111'>超声波流量计测量系统原理框图如图</span><span lang=EN-US style='font-size:
9.0pt;font-family:Arial;color:#111111'>2 </span><span style='font-size:9.0pt;
mso-ascii-font-family:Arial;mso-hansi-font-family:Arial;mso-bidi-font-family:
Arial;color:#111111'>所示。</span><span lang=EN-US style='font-size:9.0pt;
font-family:Arial;color:#111111'><br>
<a href="http://www.dzkf.cn/upimg/allimg/0705/1_18123755.JPG" target="_blank"><img
border=0 width=403 height=291 id="_x0000_i1033"
src="http://www.dzkf.cn/upimg/allimg/0705/1_18123755.JPG"></a> <br>
</span><span style='font-size:9.0pt;mso-ascii-font-family:Arial;mso-hansi-font-family:
Arial;mso-bidi-font-family:Arial;color:#111111'>图</span><span lang=EN-US
style='font-size:9.0pt;font-family:Arial;color:#111111'> 2 </span><span
style='font-size:9.0pt;mso-ascii-font-family:Arial;mso-hansi-font-family:Arial;
mso-bidi-font-family:Arial;color:#111111'>超声波流量计原理框图</span><span lang=EN-US
style='font-size:9.0pt;font-family:Arial;color:#111111'><br>
3.1 </span><span style='font-size:9.0pt;mso-ascii-font-family:Arial;mso-hansi-font-family:
Arial;mso-bidi-font-family:Arial;color:#111111'>流量计主机硬件设计</span><span
lang=EN-US style='font-size:9.0pt;font-family:Arial;color:#111111'><br>
</span><span style='font-size:9.0pt;mso-ascii-font-family:
Arial;mso-hansi-font-family:Arial;mso-bidi-font-family:Arial;color:#111111'>在设计中，微处理器采用</span><span
lang=EN-US style='font-size:9.0pt;font-family:Arial;color:#111111'>ATMEL </span><span
style='font-size:9.0pt;mso-ascii-font-family:Arial;mso-hansi-font-family:Arial;
mso-bidi-font-family:Arial;color:#111111'>公司高性能</span><span lang=EN-US
style='font-size:9.0pt;font-family:Arial;color:#111111'>AVR </span><span
style='font-size:9.0pt;mso-ascii-font-family:Arial;mso-hansi-font-family:Arial;
mso-bidi-font-family:Arial;color:#111111'>单片机</span><span lang=EN-US
style='font-size:9.0pt;font-family:Arial;color:#111111'>AT90S8515</span><span
style='font-size:9.0pt;mso-ascii-font-family:Arial;mso-hansi-font-family:Arial;
mso-bidi-font-family:Arial;color:#111111'>，芯片内可下载的</span><span lang=EN-US
style='font-size:9.0pt;font-family:Arial;color:#111111'>FLASH </span><span
style='font-size:9.0pt;mso-ascii-font-family:Arial;mso-hansi-font-family:Arial;
mso-bidi-font-family:Arial;color:#111111'>存储器可通过</span><span lang=EN-US
style='font-size:9.0pt;font-family:Arial;color:#111111'>SPI</span><span
style='font-size:9.0pt;mso-ascii-font-family:Arial;mso-hansi-font-family:Arial;
mso-bidi-font-family:Arial;color:#111111'>串行接口对程序存储器进行系统内的重新编程。主要功能如下：</span><span
lang=EN-US style='font-size:9.0pt;font-family:Arial;color:#111111'><br>
⑴</span><span style='font-size:9.0pt;mso-ascii-font-family:Arial;mso-hansi-font-family:
Arial;mso-bidi-font-family:Arial;color:#111111'>人机接口：系统参数设置和存贮，液体流速、瞬时流量和累计流量显示，出错报警。</span><span
lang=EN-US style='font-size:9.0pt;font-family:Arial;color:#111111'><br>
⑵</span><span style='font-size:9.0pt;mso-ascii-font-family:Arial;mso-hansi-font-family:
Arial;mso-bidi-font-family:Arial;color:#111111'>通讯接口：利用</span><span lang=EN-US
style='font-size:9.0pt;font-family:Arial;color:#111111'>RS485 </span><span
style='font-size:9.0pt;mso-ascii-font-family:Arial;mso-hansi-font-family:Arial;
mso-bidi-font-family:Arial;color:#111111'>通讯接口与上位机通讯。例如：修改参数、回传测量值、监控工作状态等。</span><span
lang=EN-US style='font-size:9.0pt;font-family:Arial;color:#111111'>RS485 </span><span
style='font-size:9.0pt;mso-ascii-font-family:Arial;mso-hansi-font-family:Arial;
mso-bidi-font-family:Arial;color:#111111'>接口可与</span><span lang=EN-US
style='font-size:9.0pt;font-family:Arial;color:#111111'>PC </span><span
style='font-size:9.0pt;mso-ascii-font-family:Arial;mso-hansi-font-family:Arial;
mso-bidi-font-family:Arial;color:#111111'>计算机实现点对多点通讯，组成多达</span><span
lang=EN-US style='font-size:9.0pt;font-family:Arial;color:#111111'>8×128 </span><span
style='font-size:9.0pt;mso-ascii-font-family:Arial;mso-hansi-font-family:Arial;
mso-bidi-font-family:Arial;color:#111111'>点的流量测量系统。</span><span lang=EN-US
style='font-size:9.0pt;font-family:Arial;color:#111111'><br>
<br>
3.2 </span><span style='font-size:9.0pt;mso-ascii-font-family:Arial;mso-hansi-font-family:
Arial;mso-bidi-font-family:Arial;color:#111111'>功能电路设计</span><span lang=EN-US
style='font-size:9.0pt;font-family:Arial;color:#111111'><br>
⑴ </span><span style='font-size:9.0pt;mso-ascii-font-family:Arial;mso-hansi-font-family:
Arial;mso-bidi-font-family:Arial;color:#111111'>超声波换能器：采用双探头完成超声波信号的发送与接收。探头频率为</span><span
lang=EN-US style='font-size:9.0pt;font-family:Arial;color:#111111'>2.5MHz</span><span
style='font-size:9.0pt;mso-ascii-font-family:Arial;mso-hansi-font-family:Arial;
mso-bidi-font-family:Arial;color:#111111'>。</span><span lang=EN-US
style='font-size:9.0pt;font-family:Arial;color:#111111'><br>
⑵ </span><span style='font-size:9.0pt;mso-ascii-font-family:Arial;mso-hansi-font-family:
Arial;mso-bidi-font-family:Arial;color:#111111'>通道切换电路：</span><span lang=EN-US
style='font-size:9.0pt;font-family:Arial;color:#111111'>8 </span><span
style='font-size:9.0pt;mso-ascii-font-family:Arial;mso-hansi-font-family:Arial;
mso-bidi-font-family:Arial;color:#111111'>路电磁继电器实现通道选择，实现指定通道或循环各通道采样。</span><span
lang=EN-US style='font-size:9.0pt;font-family:Arial;color:#111111'><br>
⑶ </span><span style='font-size:9.0pt;mso-ascii-font-family:Arial;mso-hansi-font-family:
Arial;mso-bidi-font-family:Arial;color:#111111'>方向切换电路：利用一个电磁继电器切换传感器方向，实现顺流和逆流时间测量。</span><span
lang=EN-US style='font-size:9.0pt;font-family:Arial;color:#111111'><br>
⑷ D/A </span><span style='font-size:9.0pt;mso-ascii-font-family:Arial;
mso-hansi-font-family:Arial;mso-bidi-font-family:Arial;color:#111111'>电压调节有三个作用：</span><span
lang=EN-US style='font-size:9.0pt;font-family:Arial;color:#111111'><br>
(a) </span><span style='font-size:9.0pt;mso-ascii-font-family:Arial;mso-hansi-font-family:
Arial;mso-bidi-font-family:Arial;color:#111111'>调节高压，产生</span><span lang=EN-US
style='font-size:9.0pt;font-family:Arial;color:#111111'>400</span><span
style='font-size:9.0pt;mso-ascii-font-family:Arial;mso-hansi-font-family:Arial;
mso-bidi-font-family:Arial;color:#111111'>～</span><span lang=EN-US
style='font-size:9.0pt;font-family:Arial;color:#111111'>600V </span><span
style='font-size:9.0pt;mso-ascii-font-family:Arial;mso-hansi-font-family:Arial;
mso-bidi-font-family:Arial;color:#111111'>的激励电压调节范围，用来形成发射电路所需发射功率。</span><span
lang=EN-US style='font-size:9.0pt;font-family:Arial;color:#111111'><br>
(b) </span><span style='font-size:9.0pt;mso-ascii-font-family:Arial;mso-hansi-font-family:
Arial;mso-bidi-font-family:Arial;color:#111111'>调节放大电路增益，实现信号的增益控制。增益调整范围：</span><span
lang=EN-US style='font-size:9.0pt;font-family:Arial;color:#111111'>10</span><span
style='font-size:9.0pt;mso-ascii-font-family:Arial;mso-hansi-font-family:Arial;
mso-bidi-font-family:Arial;color:#111111'>～</span><span lang=EN-US
style='font-size:9.0pt;font-family:Arial;color:#111111'>30dB</span><span
style='font-size:9.0pt;mso-ascii-font-family:Arial;mso-hansi-font-family:Arial;
mso-bidi-font-family:Arial;color:#111111'>。</span><span lang=EN-US
style='font-size:9.0pt;font-family:Arial;color:#111111'><br>
(c) </span><span style='font-size:9.0pt;mso-ascii-font-family:Arial;mso-hansi-font-family:
Arial;mso-bidi-font-family:Arial;color:#111111'>调节二值化电路的参考端输入电压。使之与放大后的回波信号相比较。</span><span
lang=EN-US style='font-size:9.0pt;font-family:Arial;color:#111111'><br>
⑸ 8 </span><span style='font-size:9.0pt;mso-ascii-font-family:Arial;mso-hansi-font-family:
Arial;mso-bidi-font-family:Arial;color:#111111'>个独立式键盘可以进行功能选择、参数设置、通道切换、显示切换等操作。</span><span
lang=EN-US style='font-size:9.0pt;font-family:Arial;color:#111111'><br>
⑹ </span><span style='font-size:9.0pt;mso-ascii-font-family:Arial;mso-hansi-font-family:
Arial;mso-bidi-font-family:Arial;color:#111111'>显示器采用</span><span lang=EN-US
style='font-size:9.0pt;font-family:Arial;color:#111111'>LED </span><span
style='font-size:9.0pt;mso-ascii-font-family:Arial;mso-hansi-font-family:Arial;
mso-bidi-font-family:Arial;color:#111111'>显示。可显示液体流速、瞬时流量、累计流量及报警等信息。</span><span
lang=EN-US style='font-size:9.0pt;font-family:Arial;color:#111111'><br>
⑺ CPLD </span><span style='font-size:9.0pt;mso-ascii-font-family:Arial;
mso-hansi-font-family:Arial;mso-bidi-font-family:Arial;color:#111111'>实现在单片机的控制下的超声波激励、计时测量以及与单片机接口。</span><span
lang=EN-US style='font-size:9.0pt;font-family:Arial;color:#111111'><br>
<br>
3.3 </span><span style='font-size:9.0pt;mso-ascii-font-family:Arial;mso-hansi-font-family:
Arial;mso-bidi-font-family:Arial;color:#111111'>超声波信号处理电路</span><span
lang=EN-US style='font-size:9.0pt;font-family:Arial;color:#111111'><br>
</span><span style='font-size:9.0pt;mso-ascii-font-family:
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