仪表培训教材.doc

仪表培训教材目　 　　录第一章 绪论···························································3第一节 化工测量仪表···············································3第二节 化工仪表的主要品质·········································3第二章 压力测量仪表···················································4第一节 压力测量的根本概念·········································4第二节 压力测量仪表的分类·········································6第三节压力表的安装、使用和维护···································7第三章 流量测量仪表···················································8第一节 流量测量的根本概念·········································8第二节 流量仪表的分类·············································9第三节 差压式流量计···············································9第四节 差压变送器·················································12第五节 漩涡流量计·················································16第六节 质量流量计·················································18第七节 阿牛巴流量计···············································20第八节 电磁流量计·················································21第九节　面积流量计·················································24第四章 物位测量仪表···················································26第一节 物位测量仪表的根本概念·····································26第二节 玻璃液位计·················································27第三节 浮力式液位计···············································28第四节 差压式液位计···············································29第五节 用法兰式差压式液位变送器测量液位···························30第六节 放射性液位计···············································30第五章 温度测量仪表···················································32第一节 温度测量的根本概念·········································32第二节 温标·······················································32第三节 测温仪表的分类·············································33第四节 热电阻温度计···············································34第五节 热电偶温度计···············································36第六节 双金属温度计···············································37第七节 温度变送器·················································38第八节 测温元件的安装·············································39第六章 气动调节阀·····················································40第一节 气动执行机构···············································41第二节 气动调节阀·················································44第三节 气动执行器的特点···········································48第四节 阀门定位器和薄膜调节阀的其他辅助装置·······················51第七章 控制系统简介···················································53第一节 概述·······················································53第二节 工艺控制系统···············································53第三节 停车和联锁·················································54第四节 控制方案简介···············································54第八章　分析仪表简介···················································64第一节 概述·······················································64第二节 PH 分析仪··················································65第三节 电导率分析仪···············································68第四节 CO/CO2 分析仪···············································69第五节 可燃及有毒气体报警器·······································69第一章　绪论第一节　化工测量仪表应用DCS进行过程控制时，需要测量和控制各有关的工艺参数，需要选用各类检测仪表将工艺生产参数转换成DCS系统能识别的并能代表被测量的信号，最后通过执行机构调节工艺参数的变化。

检测仪表包括各种参数的测量和变送仪表，仪表所测参数的不同，可分成压力测量仪表，流量测量仪表， 物位测量仪表，温度测量仪表，成分分析仪表等等被测量的参数直接或间接转换成DCS系统可接受的电模拟信号或脉冲信号仪表测量信号： 电动仪表为4-20mADC；第二节 化工仪表的主要品质指标任何一种产品都要有它的质量标准，仪表也不能例外，来衡量仪表质量好坏的标准，通常叫做品质指标在化工生产中，操作人员住往都是根据仪表显示的数值进行工艺操作的，但仪表指示的数值是不是真实的数值呢？实际上，从被测工艺参数的原始变化，直到最后稳定时的读数，是经过各种不同的仪表元件的转换和传递由于这些元件的性能和制造精度等的影响，在一般情况下，仪表读数和真实的数值，往往是不一样的，因此，仪表读数和真实数值之间就存在著一个差值，我们把这个差值叫做测量误差 可是，其实数值往往是很难测量出来的，因此，人们就把与真实数比拟更接近，更可靠的标准仪表的读数当作真实数值把用于工业测量的仪表和标准仪表对同一参数进行比拟，其读数的差值就叫做仪表的测量误差，误差数值越小，便说明仪表指示值和真实值越近，仪表测量的结果越准确，仪表的品质指标(或质量)就越好。

化工仪表在保证可靠的前提下，主要的品质指标有如下几种 一．根本误差和仪表的准确度 根本误差是指在规定的使用条件下，仪表的最大测量误差与它的测量范围的百分比例如，有一台压力表，测量范围为0—10.0Mpa，它的最大测量误差(或绝对误差)为0.15Mpa，那么它的根本误差：0.15／10　X　100％＝1.5％从仪表的根本误差可以看出仪表的精度等级，上例的压力表，其精度级就是1.5级，或称1.5级表 为了便于表示精度等级，习惯上就是根本误差去掉(％)号的数值仪表的精度级以规定的符号形式标志在仪表的标尺上， 如“0.5〞“1.0〞 等目前，我国生产的仪表精度级有0.005；0.02；0.05；0.1；0.2；0.35；0.5；1.0；1.5；2.5；4.0；等现场用的电动仪表精度大多为0.5级，而气动变送器多为1.0级二．仪表的变差在外界条件不变的情况下，同一台仪表对同一台仪表进行正、反行程(即以最小到最大，再由最大到最小)测量时，其所得到的仪表指示值是不相等的，对同一点所测得的正、反行程的两读数之差就是该点的变差(也可称回差)仪表变差不应越过仪表最大根本允许误差的绝对值变差小，表示仪表的恒定度好，工作可靠。

例如；有一台0—1.0MpaG，1.6级的压力表，在校验0.5MpaG这一刻度点时，压力作正行程校验，仪表指针读数是0.505MpaG，压力作反行程校验，仪表指针读数是0.495MpaG，其变差为： 0.505-0.495=0.01MpaG ，现此表的精度为1.6级，量程为0-1.0MpaG，那么其最大根本允许误差为1.0~1.5％；0.015MpaG因此，这仪表的变量小于0.015MpaG，符合变差规定的要求三．仪表的灵敏度 仪表的灵敏度是指仪表的灵敏程度例如有两台压力表，都通入同样微小的压力信号，其中一个表的指示针不动，另一个表的指针动作，也就是说后一台表要比前一台表灵敏从而可知使仪表指针开始动作的信号越小，仪表的灵敏度就越高四．仪表的稳定性 仪表的稳定性是指仪表的稳定程度在同样的条件下，对同一被测量值经仪表屡次测量，各次测量结果相差越小，仪表的稳定性就越好第二章 压力测量仪表在化工生产过程中，压力不仅影响生产过程的平衡关系和反响速率，而且又影响系统物料平衡的重要参数，在工业生产过程中，有的需要比大气压力高很多的高压，如高压聚乙烯要在150MPAG的高压下进行聚合，而有的那么需要在比大气压力低很多的负压下进行。

如炼油厂的减压蒸馏就是这样PTA化工厂的高压蒸汽压力为8.0MPAG，氧气进料压力约为9.0MPAG，压力测量如此广泛，操作人员应当严格遵守各种压力测量仪表的使用规那么，加强日常维护，任何疏忽和大意都有可能招致巨大的危害和损失，达不到优质，高产，低消耗和平安生产的目的第一节　压力测量的根本概念一．压力的定义在工业生产中，通常所称的压力，就是指均匀而垂直地作用在单位面积上的力，它的大小是由受力面积和垂直作用力的大小决定的用数学式表示为：P＝F/S式中　P为压力F为垂直作用力S为受力面积二．压力的单位在工。