过程控制第2章02(热电偶、热电阻2013)

主要内容

温度检测热电偶热电阻测温元件的选型及安装热电偶（Thermocouple）

工业过程中使用范围很广的一种测温元件。特点：其热电动势与温度在小范围内基本上呈单值、线性关系；稳定性好；测温范围宽，高温热电偶测温上限可达2800℃；精度较高。热电偶外形图铠装热电偶具有能弯曲、耐高压、热响应时间快和坚固耐用等许多优点。热电偶温度变送器常用热电偶型号基本为定型生产，有标准化分度表。

常用型号：铂铑30-铂铑6热电偶（也称双铂铑热电偶，分度号B）；测温范围300-1600℃。铂铑10-铂电偶（分度号S）；测温范围0-1300℃。镍铬-镍硅（镍铬-镍铝，分度号K）热电偶；测温范围-50-1000℃。将两种不同材质的导体或半导线在其端点实现物理接触；当回路两端温度不同时，回路中出现电势差。AB热电偶产生的直流热电势与温度有准确的单值对应关系，且幅值不超过几十毫伏。热电偶------基于热电效应实现温度检测.冷端热端AB热电偶的总热电动势=接触电动势+温差电动势忽略温差电动势热电偶冷端温度对被测温度的影响

只有当热电偶冷端温度T0保持不变时，热电势才是被测温度T的单值函数：EAB(t，t0)=EAB(t)-EAB(t0)冷端温度能恒定吗？反例说明：1.热端温度恒定，冷端变动；

2.同一个热电势，可以对应无穷多组冷热端温度。只有将冷端温度保持为0℃，或者进行一定的修正才能得到准确的测量结果。该过程称为热电偶的冷端温度补偿。关于热电偶的分度表。热电偶的冷端温度补偿热电偶的分度表（K型）热电偶的分度表（K型）热电偶的分度表（K型）热电偶的分度表（K型）热电偶的分度表（K型）如何固定冷端温度？用普通导线连接可以吗？为什么？热电偶的补偿导线注意：补偿导线并没有补偿作用，其实质是延伸热电偶。此时显示仪表能显示准确的温度值吗？热电偶冷端补偿方法1.冰浴法2.查表法（计算法）依据：热电偶的中间温度定律

EAB(t，0)=EAB(t，t0)+EAB(t0，0)热电偶冷端补偿方法热电偶冷端计算法补偿例题用分度号为K的镍铬-镍硅热电偶测量温度，在没有采取冷端温度补偿的情况下，显示仪表指示值为500℃，而这时冷端温度为60℃。试问：实际温度应为多少？如果热端温度不变，设法使冷端温度保持在20℃，此时显示仪表的指示值应为多少？

热电偶冷端计算法补偿例题显示仪表指示值为500时，查表可得此时显示仪表的实际输入电势为20.64mV，即

冷端温度为60℃产生的电势：由23.076mV查表可得：t=557℃。即实际温度为557℃。

热电偶冷端计算法补偿例题当热端为557℃，冷端为20℃时，由于E（20，0）=0.798mV,故有：查表可得显示仪表指示值应为538.4℃。大家想想：此种方法在实际中如何实现？

3.电桥补偿法热电偶冷端补偿方法明白为什么要这样补偿？如何补偿的？RCU采用了什么接法？热电阻（RTD）

在中、低温区，热电偶输出的热电动势很小,并且冷端温度不易得到完全补偿；而在中、低温区，用热电阻比用热电偶做为测温元件时的测量精确度更高；热电阻特点：性能稳定、测量精度高，一般可在-270～900℃范围内使用（推荐在150℃以下时选用）。热电阻外形不同热电阻特点及分度号铂在氧化介质或高温时，物理、化学性质稳定。分度号有Pt100、Pt10。测温范围-200-850℃。铜在-50-150℃稳定性好，超过100℃易被氧化。分度号有Cu50、Cu100。测温范围-50-150℃。镍在我国含量少，不常用。分度号有Ni100、Ni300和Ni500。测温范围-60-180℃。三种热电阻中，铂（特别是Pt100）使用最广）0200400600800-2001234CuPtNit/℃价格便宜，线性程度好，但温度高易于氧化。精度高、稳定性好、性能可靠、耐氧化能力强、测温范围宽。但电阻温度系数比较小，电阻值与温度之间呈非线性关系，且价格较贵。不同热电阻的特性（线性度）Pt100分度表温度℃电阻值（Ω）（JJG229-87）R0=100.00Ω0123456789-20018.49----------19022.8022.3721.9421.5121.0820.6520.2219.7919.3618.93-18027.0826.6526.2325.8025.3724.9424.5224.0923.6623.23-17031.3230.9030.4730.0529.6329.2028.7828.3527.9327.50-16035.5335.1134.6934.2733.8533.4333.0132.5932.1631.74-15039.7139.3038.8838.4638.0437.6337.2136.7936.3735.95-14043.8743.4543.0442.6342.2141.7941.3840.9640.5540.13-13048.0047.5947.1846.7646.3545.9445.5245.1144.7044.28-12052.1151.7051.2050.8850.4750.0649.6449.2348.8248.41-11056.1955.7855.3854.9754.5654.1553.7453.3352.9252.52-10060.2559.8559.4459.0458.6358.2257.8257.4157.0056.60-9064.3063.9063.4963.0962.6862.2861.8761.4761.0660.66-8068.3367.9267.5267.1266.7266.3165.9165.5165.1164.70-7072.3371.9371.5371.1370.7370.3369.9369.5369.1368.73-6076.3375.9375.5375.1374.7374.3373.9373.5373.1372.73-5080.3179.9179.5179.1178.7278.3277.9277.5277.1376.73-4084.2783.8883.4883.0882.6982.2981.8981.5081.1080.70-3088.2287.8387.4387.0486.6486.2585.8585.4685.0684.67-2092.1691.7791.3790.9890.5990.1989.8089.4089.0188.62Pt100分度表0100.00100.39100.78101.17101.56101.95102.34102.73103.12103.5110103.90104.29104.68105.07105.46105.85106.24106.63107.02107.4020107.79108.18108.57108.96109.35109.73110.12110.51110.90111.2830111.67112.06112.45112.83113.22113.61113.99114.38114.77115.1540115.54115.93116.31116.70117.08117.47117.85118.24118.62119.0150119.40119.78120.16120.55120.93121.32121.70122.09122.47122.8660123.24123.62124.01124.39124.77125.16125.54125.92126.31126.6970127.07127.45127.84128.22128.60128.98129.37129.75130.13130.5180130.89131.27131.66132.04132.42132.80133.18133.56133.94134.3290134.70135.08135.46135.84136.22136.60136.98137.36137.74138.12100138.50138.88139.26139.64140.02140.39140.77141.15141.53141.91110142.29142.66143.04143.42143.80144.17144.55144.93145.31145.68120146.06146.44146.81147.19147.57147.94148.32148.70149.07149.45130149.82150.20150.57150.95151.33151.70152.08152.45152.83153.20140153.58153.95154.32154.70155.07155.45155.82156.19156.57156.94150157.31157.69158.06158.43158.81159.18159.55159.93160.30160.67160161.04161.42161.79162.16162.53162.90163.27163.65164.02164.39170164.76165.13165.50165.87166.14166.61166.98167.35167.72168.09180168.46168.83169.20169.57169.94170.31170.68171.05171.42171.79190172.16172.53172.90173.26173.63174.00174.37174.74175.10175.47Pt100分度表680338.92339.23339.54339.85340.16340.48340.79341.10341.41341.72690342.03342.34342.65342.96343.27343.58343.89344.20344.51344.82700345.13345.44345.75346.06346.37346.68346.99347.30347.60347.91710348.22348.53348.84349.15349.45349.76350.07350.38350.69350.99720351.30351.61351.91352.22352.53352.83353.14353.45353.75354.06730354.37354.67354.98355.28355.59355.90356.20356.51356.81357.12740357.42357.73358.03358.34358.64358.95359.25359.55359.86360.16750360.47360.77361.07361.38361.68361.98362.29362.59362.89363.19760363.50368.80364.10364.40364.71365.01365.31365.61365.91366.22770366.52366.82367.12367.42367.72368.02368.32368.63368.93369.23780369.53369.83370.13370.43370.73371.03371.33371.63371.93372.22790372.52372.82373.12373.42373.72374.02374.32374.61374.91375.21800375.51375.81376.10376.40376.70377.00377.20377.59377.89378.19810378.48378.78379.08379.37379.67379.97380.26380.56380.85381.15820381.45381.74382.04382.33382.63382.92383.22383.51383.81384.10830384.40384.69384.98385.28385.57385.87386.16386.45386.75387.04840387.34387.63387.92388.21388.51388.80389.09389.39389.68389.97850390.26---------Cu50分度表Cu50分度表T℃0-1-2-3-4-5-6-7-8-905049.78649.57149.35649.14248.92748.71348.49848.28448.069-1047.85447.63947.42547.2146.99546.7846.56646.35146.13645.921-2045.70645.49145.27645.06144.84644.63144.41644.243.98543.77-3043.55543.34943.12442.90942.69342.47842.26242.04741.83141.616-4041.441.18440.96940.75340.53740.32240.10639.8939.67439.458-5039.242

05050.21450.42950.64350.85851.07251.28651.50151.71551.9291052.14452.35852.57252.7865353.21553.42953.64353.85754.0712054.28554.554.71454.92855.14255.35655.5755.78455.99856.2123056.42656.6456.85457.06857.28257.49657.7157.92458.13758.3514058.56558.77958.99359.20759.42159.63559.84860.06260.27660.495060.70460.91861.13261.34561.55961.77361.98762.20162.41562.6286062.84263.05663.2763.48463.69863.91164.12564.33964.55364.7677064.98165.19465.40865.62265.83666.0566.26466.47866.69266.9068067.1267.33367.54767.76167.97568.18968.40368.61768.83169.0459069.25969.47369.68769.90170.11570.32970.54470.76270.97271.18610071.471.61471.82872.04272.25772.47172.68572.