苏ICP备112451047180号-6
温度传感器
在种类繁多的传感器中，温度传感器在其产量和应用两方面都是首屈一指的。热量及与 之相关的温度是一个重要的物理参数，他几乎影响所有的物理、化学和生物医学过程的进行。因此，无论在工业、农业、科学研究、国防和人民日常生活各个方面，温度测量和控制都是极为重要的课题。随着电子技术和材料科学的发展，对各种新型的热敏元件及温度传感器要求结构先进、性能稳定，以满足对温度测量和控制提出的越来越高的要求。
温度传感器的分类按照制造温度传感器的材料及工作原理进行分热敏电阻器工作范围热敏电阻器是指电阻值随温度变化而发生显著的变化的温度传感器，它可以将温度直接转化为电信号。在工作温度范围内，其电阻随着温度的升高而增加的热敏电阻器称为正温度系数热敏制作PTC热敏电阻器通常采用钛酸钡（BaTio3）陶瓷材料，单纯的BaTio3陶瓷在常温度下具有极高的电阻率，在108Ω·m以上，故为绝缘体。若在BaTio3中进行掺杂，可使BaTio3半导体化，例如：掺以0.1%----0.3%的稀土元素，而使其成为在常温下具有0.1----10Ω·m的N行半导体。具有铁电性的半导体的BaTio3，当温度达到居里点Tc时，它由四方晶系转变为立方晶系，此时其电阻率跃增几个数量级（103-----107倍）。正温度系数热敏电阻器(PTC)就是根据这个性质制作的。经半导体化的多晶粒结构的BaTio3中，其晶粒(一般尺寸小约为3—10µm)内部为半导体性质；而晶粒间界为高阻区(具有铁电性)。当样晶外加电压时，电压大部分降落在高阻的晶界层上，因而晶界对材料的导电性能起作用。电子从一晶粒必须穿越晶界阻挡层势垒才能到达另一晶粒。在居里温度Tc以下，BaTio3为四方晶系的强介电相，存在有自发极化很强的内部电场，使电子具有较高的能量，从而穿越晶界势垒容易。而在居里以上，BaTio3由四方晶系变为立方晶系，自发极化消失，内部电场消失，电于穿越势垒困难，因此在居里温废c以上，电阻对于一般半导体材料，电阻率随温废的变化主要是依赖于载流子数目随温度的变化，温度升高，载流子数增加，导电能力增强．从而电阻率F降。对于过渡金属氧化物半导体，例由于它的受主电离能很小，在室温广基本已全部电离，即载流子浓度基本上与温度无关，此时，应主要考虑迁移率与温度之关系。由半导体物理知，迁移率由下式表达：
可见金属氧化物半导体的电阻率随温度的变化主要是有迁移率随温度的变化而引起的。当温度升高时，电阻率下降，呈负温度系数特性。临界温度热敏电阻器（CTR）也属于负温度系数热敏电阻器。在某一临界温度范围内，其阻值随温度上升而急剧下降。
鉴于温度传感器种类繁多，而且其工作机理也不尽相同。本节主要介绍热敏电阻及热敏二极管和热敏晶体管的特性与参数。热敏电阻器可以从结构、材料和阻温特性等多方面进行分类。按结构形状分类：片状、垫圈状、杆状、管状、薄膜状、厚膜状和其他形状。按加热方式分类：直热式和旁热式。按阻温度范围分类有：常温、高温和超低温热敏电阻器。按阻温特性分类有：负温度系数热敏电阻器(NTC)，图4—4中曲线2；开关型正温度热敏电阻器
值与 电阻体温之间的依赖关系，这是热敏电阻
的基本特性之一。
PTC开关型正温度系数热敏电阻器的阻温特性曲线(图4—4曲线4)。室温至居里温度以下的一段温度范围内，表现出和一般半导体相同的NTC特性。从居里点开始，电阻值急剧上升到某一温度附近达到最大值。
PTC热敏电阻器的居里温度TC以通过掺杂来控制。如在BaTio3中掺杂Pb，可使Tc向高温方向移动，在BaTio3中元素后，可使TC向低温方向移动。可根据需要调整居里点TC。热敏电阻器的实际阻值用RT来表示。是在一定环境温度下，采用引起阻值变化不超过0.1％的测量功率所测得的电阻值。实际电阻值又称为零功率电阻值，或称为不发热功率电阻值(冷电阻值)。实际电阻值的大小取决于电阻器的材料和几何形状。
热敏电阻器的实际阻值与其自身温度有如下的关系：为了使用方便，通常取环境温可见，在工作温度范围内，负温度系数热敏电阻器的随温度T的变化有很大的变化，并与材料常数B成正比。因此，通常在给出电阻温度系数的同时，必须指出测量时的温度，正温度系数热敏电阻的aT在数值上等常数A。缓变型正温度系数热敏电阻器的aT值而开关型〔突变型〕正温度系数热敏电阻器的达到60％／℃或更高。
材料常数B是用来描述热敏电阻材料物理特性的—个参数．又称为热灵敏度指标。在工作范围内，B值并不是一个严格的常数，随着温度的升高而略有增大。一般说来，B值大的电阻率也高。不同B值的材料有不同的用途，如普通负温度系数热敏电阻的材料常数B值在2000一5000 K之间。负温度系数热敏电阻器B值可按下式计算：耗散常数H 耗散常数H定义为温度每增加一度所耗散的功率。它用来描述热敏电阻器工作时，电阻体与外界环境进行热交谈的一个物理量。耗散常数H与耗散功率P。温度改变量AT的关系为 热容量和时间常数 热敏电阻器具有一定的热容量C，因此它具有一定的热情性．也就是温度的改变需要一定的时间。当热敏电阻器被加热到了T2温度时，放到温度为T0的环境中，不加电功率，热敏电阻器开始降温，其温度T是时间t的函数，在△t时间内．热敏电阻器向环境耗散的热量可标示为：H（T-T0）△t，这部分热量是由热敏电
式中，ζ＝C/H 称为热敏电阻器的时间常数，单位为S。
时间常数?可定义为：在恒定的静态条件下，热敏电阻器在无功率状态下，当环境温度由一个特定温度向另一个特定湿度突然改变时，电阻体的温度变化了这两个特定温度之差的63.2％所需的时间。通常将这两个特定温度选为85℃和25℃，或者100℃和0℃热敏电阻器用于测温和控温时，一般要求时间常数小。因而，热容量越小越好。电压—电流行性表示在特定温度下，热敏电阻器两端的电压与通过电阻体的稳态电流之间的关系，即伏安特性。伏安特性与热敏电阻器的结构形状有关，还与其阻值、材料常数从所处的环境温度、介质种类等有关。
PTC热敏电阻器的伏安特性曲线如图3—7所示，当所加电压不太高时，PTC热敏电阻的温升不高，流过PTC热敏电阻的电流与电压成正比，服从欧姆定律。随着所加电压的增加，消耗功率增加，电阻体温度超过环境温度时，引起电阻值增大，曲线开始弯曲。当电压增到使电流达到IMAX最大时，如电压继续增加，由温升引起的电阻值增加
超过电压增加的速度，电流反而减小，曲线斜率由正变负。
C热敏电阻器的伏安特性曲线。在开始段同PTC热敏电阻一样也服从欧姆定律。随电流增加，引起热敏电阻温升超过环境温度，则其阻值下降。耗散功率增加，相应的电压变化较为缓慢，出现非线性正阻区b段)。电流继续增加，其电压值增大到最大时，若电流再增加，热敏电阻自身加热剧烈使电阻值减小的速度越过电流增加的热敏电阻的电压降随电流增加而降低，形成段的负阻区。热敏电阻器的其他参数标称电阻值尺R25 标称阻值是热敏电阻器在25℃时的电阻值，其值的大小由热敏电阻的材料与几何尺小决定。最高工作温在规定的技术条件下，热敏电阻器长期连续工作所允许的温度，是热敏电阻器的最高工作温度，它的表达式为：式中T0为环境温度；PR为环境温度时的额定功率额定功率PR 热敏电阻在规定的技术条件下，长期连续工作所允许的耗散功率为额定功率，用PR表示。
Temperature humidity sensor
The sensor in type many sensors, the temperature sensor and applies two aspects in its output both is second to and with it correlation temperature is an important physical parameter, he affects all physical, chemistry and biomedicine process march, regardless of in the industry, the agriculture, the scientific research, the national defense and people's daily life each aspect, the temperature survey and the control all is the extremely important with the electronic technology and the materials science development, to each kind of new thermal element and the temperature sensor request structure advanced, the performance is stable, satisfies the more and more high request which proposed to the temperature survey and the control.
Sensor classification carries on classified resistance type PN according to the manufacture temperature sensor material and the principle of work to tie the type thermoelectricity type radiation formula.
roperating region is refers to the resistance value to have the remarkable change temperature sensor along with the temperature change, it may transform directly the temperature as the electrical the operating temperature scope, its resistance the which increases along with the temperature ascension is called positive temperature coefficient (PTC); Its resistance number the which reduces along with the temperature t ascension is called negative temperature (NTC); The negative temperature which reduces suddenly along with the temperature rise is called critical (CTR) in a warm area internal resistance. 1. PTC principle of the PTC r usually to use the (BaTio3) ceramic material, the pure BaTio3 ceramics have the extremely high electronic resistivity under often the temperature, above 108Ω · m, therefore is the insulator. If carries on the doping in BaTio3, may cause the BaTio3 semiconductor, for example: Mixes by 0.1%----0.3% rare-earth element, but causes it to become has 0.1 under the normal temperature----10Ω·m N line of semiconductors .Has electricity semiconductor BaTio3, when the temperature achieved when Curie temperature T, it transforms by the tetragonal system into the cubic system, this time its electronic resistivity leap increases several magnitudes (103-----107 times).Positive temperature coefficient the (PTC) acts according to this nature manufacture.
After in semiconductor multi-crystal grain structure BaTio3, its crystal grain (general size small is approximately 3-10 µ m) the interior is the semiconductor nature; But the crystal boundary (has f e r r o electricity) for the high-resistance area. When type crystal external voltage, voltage majority of landings on high-resistance crystal boundary level, thus the crystal boundary has an effect to the material electric conductivity .The electron must pass through the crystal boundary barrier potential barrier from a crystal grain to be able to arrive another crystal grain .Below Curie temperature T c, BaTio3 is tetragonal system dielectric, the existence has the spontaneous polarized very strong internal electric field, enable the electron to have the high energy, thus the traversing crystal boundary potential barrier is easy. But above Curie temperature T c, BaTio3 becomes the cubic system by the tetragonal system, polarizes vanishing spontaneously, internal electric field vanishing, the electricity is difficult in the traversing potential barrier, therefore above curie warm waste T c, electronic resistivity sharp increase. When two crystal grains contact mutually, crystal grain barrier potential barrier as shown in Figure 3-2.b is potential barrier level thickness, ø0 is the barrier height .According to the equation, the barrier height ø0 sticks the effective dielectric constant ε e ff between with the crystal the relations is: In the formula, n0 is the density of donors; e is the electronic electric quantity .ε0 is the vacuum coefficient of d i electrical loss. When the electronic overstepping potential barrier enters ø0, the electronic resistivity may write .
When the temperature is lower than Curie temperature TC, ε e ff the value is approximately about 104, therefore ø0 very small, the ceramic electronic resistivity rho approaches in the volume resistivity ρ v, after the temperature surpasses Curie temperature TC, the value drops suddenly, the A value increases, causes rho the value sharp increase, dopes BaTio3 and rho and between the temperature relational like chart .NTC t h r principle of work NTC the r s tor majority is by the transition family metal oxide compound (mainly is with M n, co, Ni, Fe and so on), the agglutination forms the semiconductor metal oxide compound under the controlled condition, they only have the P semiconductor characteristic .Regarding the common semiconducting material, the electronic resistivity mainly is relies on along with the warm waste change the current carrier number along with the temperature change, the temperature increment, the current carrier number increases, electric conduction ability enhancement. Thus electronic resistivity F falls. Regarding transition metal oxide compound semiconductor, for example Ni O, because its acceptor ionizing energy is very small, broad basic ionized completely in the room temperature, namely the current carrier density basically has nothing to do with the temperature, this time, should mainly consider the transport ratio and the temperature relations .By the semiconductor physics knowledge, the transport ratio expresses by the equation below.
In the formula: The d-- oxygen octahedron gap is away from (Ni O is the Na Cl structure); V0-- lattice vibration frequency; The Ei-- activation energy, indicated the electron jumps originally from one in the position the energy which needs to the neighboring atom site. Or rewriting Then the electronic resistivity is: 0Ne-Ei/kT If command, then type changes: rho =ρ0eEi/KT Obviously the metal oxide compound semiconductor electronic resistivity mainly has the transport ratio along with the temperature change to cause along with the temperature change .When temperature increment, the electronic resistivity drops, assumes the negative temperature coefficient characteristic. Critical temperature also belongs to the negative temperature coefficient. But in some critical temperature scope, its resistance number drops suddenly along with the temperature rise .Anti- as shown in Figure 4-4. In the chart the anti- r curve has a resistance number point of discontinuity, approximately for 68℃, resistance number point of discontinuity magnitude generally in 3~7.May carry on the adjustment based on the material ingredient, it is suitable specially in 65℃~75℃ between uses, this kind of resistor may make the constant temperature control and on-off element.
The CTR r usually uses the glass semiconductor processing, take the vanadium as the main material. Mixes in certain materials and so on oxide compound like CaO, BaO,SO or P2O5, TiO2 becomes after the hot dissolve. 3.2 temperature sensor basic characteristic in view of the fact that the temperature sensor type is many, moreover its work mechanism is also different. This mainly introduces t the hot sensitive diode and the hot sensitive transistor characteristic and the parameter. 3.2.1 from the s the material and anti- and so on carry on the classification variously. According to structure shape classification: Laminated shape, gasket shape, rod-shaped, tubular, thin membrane, thick membranous and other shapes. Includes according to the anti- temperature ra classification: Normal temperature, high temperature and ultralow temperature hot sensitive resistor. Includes according to the anti- classification: Negative temperature coefficient r (NTC), switch temperature r (PTC); Slow aberration positive temperature coefficient r (PTC), the critical negative temperature coefficient, the platinum resistor limits the temperature curve like chart 4-4 curvature 1.1st, resistance - temperature characteristic anti-is refers to between the actual resistance value and the resistance body temperature dependent relations, this is one of basic characteristics.
PTC switch positive temperature coefficient anti- curve. value rises suddenly to some temperature nearby the maximizing.
Through the doping .If dopes Pb in BaTio3, may cause Tc to the high temperature traverse, mixes in elements and so on Sr or Sn after BaTio3, may cause TC to the low temperature traverse. May according to need to adjust t Curie temperature TC. The actual resistance number expressed with RT. Is under certain ambient temperature, uses causes the resistance number change not to surpass the resistance value which 0.1% survey power actual resistance value is called the zero energy resistance value, or is called does not give off heat the power resistance value (cold resistance value).The actual resistance value size is decided by the resistor material and the geometry shape. If the actual resistance number own temperature has the following relations: NTC In the formula: RT time 11 temperature T actual resistance value; R1 and resistance geometry shape with material related constant B,A 11 material constants. For the easy to operate, usually takes the ambient temperature for 25℃ to take the reference temperature, then has: NTC puts the resistor hotly: RT/R25=exp[B(1/T-1/298)] PTC g change along with the temperature
T change, and is proportional with material constant B. Therefore, usually while gives the resistance temperature coefficient, must point out when the survey temperature, positive temperature coefficient t a T in value superior constant A. Slow aberration positive temperature coefficient value in 0.5%/℃ 110%/℃ between. But the switch (mutant) positive temperature co efficient T may achieve 60%/℃ or higher. Material constant B is uses for to describe the t material physical property - parameter. Also is called the thermal sensitivity target. In the operating region, the B value is not a strict constant, has slightly along with the temperature ascension increases .In general, the B value great electronic resistivity is also high. The different B value material has the different use, like ordinary negative temperature coefficient material constant B value between 2000yi5000 K. The negative temperature coefficient B value may according to the equation below computation: Positive temperature coefficient resistor, its A value according to equation below computation: In the formula, R1 R2 respectively is time thermodynamic temperature T1 and the T2 resistance value. 2. thermal properties (1) dissipation constant H dissipation constant H defined as the temperature each increase once diffusion power .It uses for when describes work, the resistance element and the external environment carry on the hot conversation a physical quantity. Dissipation constant H and dissipated power P .The temperature increment AT relations are
The H size and the t structure, locates the environment medium type, the velocity of movement, the pressure and the heat conduction performance and so on related, when ambient temperature change, H has the change.(2) capacity and the time-constant r appliance has certain calorific capacity C, therefore it has certain warm. Also is the temperature change needs certain time. When the is heated up the T2 temperature, puts to the temperature is in the T0 environment, does not add the electric power, the starts to decrease temperature, its temperature T is the time t function, in △t time. The may indicate to the environment diffusion quantity of heat is: H(T-T0)△t, this part of quantity of heat is provides by the temperature decrease. Its value for - C△T, therefore has:
Expressed in the environment atmosphere the steam content physical quantity is a y. The humidity expression method has two kinds, namely absolute humidity and relative h um (RH).The absolute humidity is refers to in the atmosphere the water content absolute value, the relative humidity is refers to in the atmosphere the steam to press with the identical temperature under ratio of the saturated steam tension, expressed with the percentage. The humidity sensor or the dew cell are refer to the paraphrase to the humidity sensitive part, it may be the wet sensitive resistor, also may be the wet sensitive capacitor or other dew cells. The humidity sensor classification classifies according to the feeling wet physical quantity, the humidity sensor may divide into three big kinds, namely wet sensitive resistor, wet sensitive capacitor and wet sensitive transistor. The humidity resistor makes which according to the use different material may divide into: Metal oxide compound semiconductor ceramics wet sensitive resistor, for example: MgCr2O4 series, ZnO-Cr2O3 series; Element material wet sensitive resistor, for example: Semiconductor Ge, Si, Se and C element; Compound wet sensitive resistor, for example: Li Cl, CaSO4, and fluoride and iodide and so on; High polymer wet sensitive resistor and so on. The wet sensitive capacitor mainly is the porous Al2O3 material makes as the medium. The wet sensitive transistor divides into the wet sensitive diode and the wet sensitive three levels of tubes. The wet sensitive resistor principle of work and the characteristic 1, the metal oxide compound semiconductor ceramics wet sensitive resistor (1) principle of work porous metal oxide compound semiconductor ceramics, in the crystal plane and the crystal boundary place, very easy to adsorb t drone. Because the water is one strong polar dielectric medium, nearby the h y drone hydrogen atom has the very strong electric field, has the very big electron affinity. When hy drone adheres to stick cohere when the semiconductor ceramics surface, will form the energy level very deep attachment surface acceptor condition, but from semiconductor ceramics surface capture electron, but will form the bound state in the ceramic surface the negative space charge, correspondingly will appear the hole in the near surface layer to accumulate, thus will cause the semiconductor ceramics electronic resistivity depression.
Moreover, according to the ion electric conductance principle, the structure not compact semiconductor ceramics crystal grain has certain crevice, reveals the porous capillarity tubular .The drone may adsorbs through this kind of pore between various crystal grains surface and the crystal grain, because adsorbs the e separable relieves the massive electric conduction ion, these ions are playing the electric charge transportation role in the water adsorbed layer. along with humidity increase, material electronic resistivity drop. oxide compound semiconductor ceramics wet sensitive resistor principal variety and structure The metal oxide compound semiconductor ceramics wet sensitive resistor typical product includes: MgCr2O4-TiO2wet sensitive resistor, ZnO-Cr2O3 wet sensitive resistor, ZnO-Li2O3-V2O5 wet sensitive resistor and so on. For example: The ZnO-Li2O3-V2O5 wet sensitive resistance, is take Zn O as the main material, is joining a price, two prices, three prices and so on other metal oxide compound burns the ceramics semiconducting material, the survey humidity scope is 5%~100%RH, the measuring accuracy is 2%, is one kind of more ideal dew cell, and may make the miniaturization, the structure is simple. 2nd, element material wet sensitive resistor kind of wet sensitive resistor is a part which the element semiconducting material or the element material make.
The carbon wet sensitive resistor is one resistance - humidity characteristic is the dew cell. With the organic matter polypropylene plastic piece or the stick are substrates, spreads cloth one to include the conductive carbon granule organic textile fiber constitution. This kind of wet sensitive resistor craft is simple, is advantageous for the uses the organic material absorption of moisture, the volume expansion, between the carbon granule distance increases, thus the resistance value increases principle. The element semiconductor, have on the honeycomb electrode ceramic substrate, is composed [granule diameter by the characteristic in the Fe3O4 colloid by the particle approximately for (100~250)×10-8m], each pellet only then a magnetic domain, therefore, the co current pellet attracts the union mutually, thus does not need the high polymer material to make the colloid bond, but can obtain the good performance and the long service life. Figure 4-1 is the Fe3O4 colloid wet sensitive resistor structure drawing. Figure 4-2 is the Fe3O4 wet sensitive resistor resistance humidity characteristic curve, displays for the negative feeling wet characteristic. 4th, the wet sensitive resistor characteristic (1) resistance - humidity characteristic wet sensitive resistor resistance number along with the humidity change is generally the index relations change.