下图是锅炉水位、压力控制方案图。试选择给水阀和蒸气阀的气开气闭形式,并选择液位控制器(LC)和压力控制器(PC)的正反作用形式,并说明理由。

<p class="MsoNormal"><span lang="EN-US">1</span><span style="font-family:宋体; mso-ascii-font-family:&quot;Times New Roman&quot;;mso-hansi-font-family:&quot;Times New Roman&quot;">）从安全原则考虑，信号中断时，给水阀应处于全开位置较为安全，以防锅炉烧干，因此给水阀选择气关阀；蒸汽阀此时应处于全开状态以防锅炉内压力过大引起事故，因此蒸汽阀选择气关阀。</span></p> <p class="MsoNormal"><span lang="EN-US">&nbsp;</span></p> <p class="MsoNormal" style="text-indent:21.75pt"><span lang="EN-US">2</span><span style="font-family:宋体;mso-ascii-font-family:&quot;Times New Roman&quot;;mso-hansi-font-family: &quot;Times New Roman&quot;">）液位控制器</span><span lang="EN-US">:</span><span style="font-family:宋体;mso-ascii-font-family:&quot;Times New Roman&quot;;mso-hansi-font-family: &quot;Times New Roman&quot;">阀为气关阀，则</span><span lang="EN-US">kv </span><span style="font-family:宋体;mso-ascii-font-family:&quot;Times New Roman&quot;;mso-hansi-font-family: &quot;Times New Roman&quot;">选“－”，进水量增多时，液位上升，则</span><span lang="EN-US">kp</span><span style="font-family:宋体;mso-ascii-font-family:&quot;Times New Roman&quot;;mso-hansi-font-family: &quot;Times New Roman&quot;">选“</span><span lang="EN-US">+</span><span style="font-family: 宋体;mso-ascii-font-family:&quot;Times New Roman&quot;;mso-hansi-font-family:&quot;Times New Roman&quot;">”，根据负反馈原则，</span><span lang="EN-US">kc</span><span style="font-family:宋体;mso-ascii-font-family:&quot;Times New Roman&quot;; mso-hansi-font-family:&quot;Times New Roman&quot;">应为“</span><span lang="EN-US">+</span><span style="font-family:宋体;mso-ascii-font-family:&quot;Times New Roman&quot;;mso-hansi-font-family: &quot;Times New Roman&quot;">”，所以液位控制器应选择正作用。</span></p> <span lang="EN-US" style="font-size:10.5pt;mso-bidi-font-size:12.0pt;font-family: &quot;Times New Roman&quot;,&quot;serif&quot;;mso-fareast-font-family:宋体;mso-font-kerning:1.0pt; mso-ansi-language:EN-US;mso-fareast-language:ZH-CN;mso-bidi-language:AR-SA">&nbsp; </span><span style="font-size:10.5pt; mso-bidi-font-size:12.0pt;font-family:宋体;mso-ascii-font-family:&quot;Times New Roman&quot;; mso-hansi-font-family:&quot;Times New Roman&quot;;mso-bidi-font-family:&quot;Times New Roman&quot;; mso-font-kerning:1.0pt;mso-ansi-language:EN-US;mso-fareast-language:ZH-CN; mso-bidi-language:AR-SA">压力控制器：阀为气关阀，则</span><span lang="EN-US" style="font-size: 10.5pt;mso-bidi-font-size:12.0pt;font-family:&quot;Times New Roman&quot;,&quot;serif&quot;; mso-fareast-font-family:宋体;mso-font-kerning:1.0pt;mso-ansi-language:EN-US; mso-fareast-language:ZH-CN;mso-bidi-language:AR-SA">kv </span><span style="font-size:10.5pt;mso-bidi-font-size:12.0pt;font-family:宋体;mso-ascii-font-family: &quot;Times New Roman&quot;;mso-hansi-font-family:&quot;Times New Roman&quot;;mso-bidi-font-family: &quot;Times New Roman&quot;;mso-font-kerning:1.0pt;mso-ansi-language:EN-US;mso-fareast-language: ZH-CN;mso-bidi-language:AR-SA">选“－”，蒸汽量加大时，压力减小，则</span><span lang="EN-US" style="font-size:10.5pt;mso-bidi-font-size:12.0pt;font-family:&quot;Times New Roman&quot;,&quot;serif&quot;; mso-fareast-font-family:宋体;mso-font-kerning:1.0pt;mso-ansi-language:EN-US; mso-fareast-language:ZH-CN;mso-bidi-language:AR-SA">kp</span><span style="font-size:10.5pt;mso-bidi-font-size:12.0pt;font-family:宋体;mso-ascii-font-family: &quot;Times New Roman&quot;;mso-hansi-font-family:&quot;Times New Roman&quot;;mso-bidi-font-family: &quot;Times New Roman&quot;;mso-font-kerning:1.0pt;mso-ansi-language:EN-US;mso-fareast-language: ZH-CN;mso-bidi-language:AR-SA">选“－”，根据负反馈原则，</span><span lang="EN-US" style="font-size:10.5pt;mso-bidi-font-size:12.0pt;font-family:&quot;Times New Roman&quot;,&quot;serif&quot;; mso-fareast-font-family:宋体;mso-font-kerning:1.0pt;mso-ansi-language:EN-US; mso-fareast-language:ZH-CN;mso-bidi-language:AR-SA">kc</span><span style="font-size:10.5pt;mso-bidi-font-size:12.0pt;font-family:宋体;mso-ascii-font-family: &quot;Times New Roman&quot;;mso-hansi-font-family:&quot;Times New Roman&quot;;mso-bidi-font-family: &quot;Times New Roman&quot;;mso-font-kerning:1.0pt;mso-ansi-language:EN-US;mso-fareast-language: ZH-CN;mso-bidi-language:AR-SA">应为“－”，所以压力控制器应选择反作用。</span><br>