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mso-ascii-font-family:Arial;mso-hansi-font-family:Arial;mso-bidi-font-family:
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</span><span style='font-family:宋体;mso-ascii-font-family:Verdana;mso-hansi-font-family:
Verdana;mso-bidi-font-family:Arial;color:#111111'>技术在时差法超声波流量计中的应用</span><span
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style='font-size:9.0pt;mso-ascii-font-family:Arial;mso-hansi-font-family:Arial;
mso-bidi-font-family:Arial;color:#111111'>作者：王玉辉</span><span lang=EN-US
style='font-size:9.0pt;font-family:Arial;color:#111111'> </span><span
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mso-bidi-font-family:Arial;color:#111111'>日期：</span><st1:chsdate
IsROCDate="False" IsLunarDate="False" Day="18" Month="5" Year="2007" w:st="on"><span
lang=EN-US style='font-size:9.0pt;font-family:Arial;color:#111111'>2007-05-18</span></st1:chsdate><span
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<p style='line-height:18.0pt;background:white'><strong><span lang=EN-US
style='font-size:9.0pt;font-family:Arial;color:#111111'>1 </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'>概述</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'>时差法超声波流量计由于精度高，换能器结构简单，不影响流体流动形态而被广泛应用。本设计中的超声波流量计是一套由计算机控制的多通道时差法超声波流量测量系统，可用于测量多个通道液体流速、瞬时流量和累计流量。</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'>设计中采用了</span><span
lang=EN-US style='font-size:9.0pt;font-family:Arial;color:#111111'>ALTERA </span><span
style='font-size:9.0pt;mso-ascii-font-family:Arial;mso-hansi-font-family:Arial;
mso-bidi-font-family:Arial;color:#111111'>公司生产的大规模复杂可编程逻辑器件（</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'>）：</span><span lang=EN-US
style='font-size:9.0pt;font-family:Arial;color:#111111'>MAX7000S</span><span
style='font-size:9.0pt;mso-ascii-font-family:Arial;mso-hansi-font-family:Arial;
mso-bidi-font-family:Arial;color:#111111'>系列</span><span lang=EN-US
style='font-size:9.0pt;font-family:Arial;color:#111111'>EPM7128S</span><span
style='font-size:9.0pt;mso-ascii-font-family:Arial;mso-hansi-font-family:Arial;
mso-bidi-font-family:Arial;color:#111111'>。为了提高测量精度和稳定性，利用</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'>大规模复杂可编程特点，在逻辑电路中设计了发射波抑制电路、激励脉宽可电调整电路和数字倍频计数器电路。发射波抑制电路有效地抑制了发射激励波的干扰；激励脉宽可电调整电路能够方便地适配不同特性探头对激励脉宽的要求；数字倍频计数器电路提高了计时精度。由于</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'>高速、高稳定性、高可靠性和现场可编程的特点，大大提高了超声波流量计测量系统的精度和可靠性。</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'>主机使用新型高性能、低功耗、</span><span
lang=EN-US style='font-size:9.0pt;font-family:Arial;color:#111111'>RISC </span><span
style='font-size:9.0pt;mso-ascii-font-family:Arial;mso-hansi-font-family:Arial;
mso-bidi-font-family:Arial;color:#111111'>结构、内载</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'>的</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'>。</span><span lang=EN-US
style='font-size:9.0pt;font-family:Arial;color:#111111'>8515 </span><span
style='font-size:9.0pt;mso-ascii-font-family:Arial;mso-hansi-font-family:Arial;
mso-bidi-font-family:Arial;color:#111111'>带有一个全双工的通用串行异步收发器，可方便的与多台仪表进行通讯，从而实现分布式测量系统。</span><span
lang=EN-US style='font-size:9.0pt;font-family:Arial;color:#111111'><br>
EPM7128S </span><span style='font-size:9.0pt;mso-ascii-font-family:
Arial;mso-hansi-font-family:Arial;mso-bidi-font-family:Arial;color:#111111'>内部还设计有</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'>的外扩总线、译码电路和输入输出等接口。</span><span
lang=EN-US style='font-size:9.0pt;font-family:Arial;color:#111111'>8515</span><span
style='font-size:9.0pt;mso-ascii-font-family:Arial;mso-hansi-font-family:Arial;
mso-bidi-font-family:Arial;color:#111111'>以外扩</span><span lang=EN-US
style='font-size:9.0pt;font-family:Arial;color:#111111'>RAM </span><span
style='font-size:9.0pt;mso-ascii-font-family:Arial;mso-hansi-font-family:Arial;
mso-bidi-font-family:Arial;color:#111111'>的访问形式操作</span><span lang=EN-US
style='font-size:9.0pt;font-family:Arial;color:#111111'>EPM7128S </span><span
style='font-size:9.0pt;mso-ascii-font-family:Arial;mso-hansi-font-family:Arial;
mso-bidi-font-family:Arial;color:#111111'>内部所有资源，进行通道切换、控制采样过程、读取键盘等操作。</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'>实现的主要功能有：测量</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'>个通道的流速、瞬时流量、累计流量，显示出错报警等信息。</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'>2 </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'>时差法超声波流量计的测量原理和影响测量精度的因素分析</span></strong><span
lang=EN-US style='font-size:9.0pt;font-family:Arial;color:#111111'><br>
2.1 </span><span style='font-size:9.0pt;mso-ascii-font-family:Arial;mso-hansi-font-family:
Arial;mso-bidi-font-family:Arial;color:#111111'>时差法超声波流量计的测量原理</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'>超声波在流体中的传播速度与流体流动速度有关，据此，可以实现流量测量。超声波的发射和接收采用双探头方式，发射和接收传感器的材料和结构完全相同，可以互换使用或进行双向收发。结构原理图见图</span><span
lang=EN-US style='font-size:9.0pt;font-family:Arial;color:#111111'>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'>。</span><span lang=EN-US
style='font-size:9.0pt;font-family:Arial;color:#111111'><br>
<img border=0 width=188 height=118 id="_x0000_i1030"
src="http://www.dzkf.cn/upimg/allimg/0705/1_18122908.JPG"><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'>由于篇幅有限，有关公式推导见参考文献</span><span
lang=EN-US style='font-size:9.0pt;font-family:Arial;color:#111111'>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'>，这里只给出结论。</span><span lang=EN-US
style='font-size:9.0pt;font-family:Arial;color:#111111'><br>
<img border=0 width=145 height=52 id="_x0000_i1031"
src="http://www.dzkf.cn/upimg/allimg/0705/1_18122934.JPG"><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'>其中，</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'>为声速，</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'>为顺逆流传播时间差，</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'>为声路角，</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'>为声程。</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'>需要特别说明的是，</span><span
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