温度传感器分类中英文资料

温度传感器分类及原理介绍

英文文献原文

Temperature Sensor ICs Simplify Designs

When you set out to select a temperature sensor, you are no longer limited to either an analog output or a digital output device. There is now a broad selection of sensor types, one of which should match your system's needs.

Until recently, all the temperature sensors on the market provided analog outputs. Thermistors, RTDs, and thermocouples were followed by another analog-output device, the silicon temperature sensor. In most applications, unfortunately, these analog-output devices require a comparator, an ADC, or an amplifier at their output to make them useful.

Thus, when higher levels of integration became feasible, temperature sensors with digital interfaces became available. These ICs are sold in a variety of forms, from simple devices that signal when a specific temperature has been exceeded to those that report both remote and local temperatures while providing warnings at programmed temperature settings. The choice now isn't simply between analog-output and digital-output sensors; there is a broad range of sensor types from which to choose.

Classes of Temperature Sensors

Four temperature-sensor types are illustrated in Figure 1. An ideal analog sensor provides an output voltage that is a perfectly linear function of temperature (A). In the digital I/O class of sensor (B), temperature data in the form of multiple 1s and 0s are passed to the microcontroller, often via a serial bus. Along the same bus, data are sent to the temperature sensor from the microcontroller, usually to set the temperature limit at which the alert pin's digital output will trip. Alert interrupts the microcontroller when the temperature limit has been exceeded. This type of device can also provide fan control.

Figure 1. Sensor and IC manufacturers currently offer four classes of temperature sensors.

"Analog-plus" sensors (C) are available with various types of digital outputs. The V OUT versus temperature curve is for an IC whose digital output switches when a specific temperature

has been exceeded. In this case, the "plus" added to the analog temperature sensor is nothing more than a comparator and a voltage reference. Other types of "plus" parts ship temperature data in the form of the delay time after the part has been strobed, or in the form of the frequency or the period of a square wave, which will be discussed later.

The system monitor (D) is the most complex IC of the four. In addition to the functions provided by the digital I/O type, this type of device commonly monitors the system supply voltages, providing an alarm when voltages rise above or sink below limits set via the I/O bus. Fan monitoring and/or control is sometimes included in this type of IC. In some cases, this class of device is used to determine whether or not a fan is working. More complex versions control the fan as a function of one or more measured temperatures. The system monitor sensor is not discussed here but is briefly mentioned to give a complete picture of the types of temperature sensors available.

Analog-Output Temperature Sensors

Thermistors and silicon temperature sensors are widely used forms of analog-output temperature sensors. Figure 2 clearly shows that when a linear relationship between voltage and temperature is needed, a silicon temperature sensor is a far better choice than a thermistor. Over a narrow temperature range, however, thermistors can provide reasonable linearity and good sensitivity. Many circuits originally constructed with thermistors have over time been updated using silicon temperature sensors.

Figure 2. The linearity of thermistors and silicon temperature sensors, two popular analog-output temperature detectors, is contrasted sharply.

Silicon temperature sensors come with different output scales and offsets. Some, for example, are available with output transfer functions that are proportional to K, others to °C or °F. Some of the °C parts provide an offset so that negative temperatures can be monitored using a single-ended supply.

In most applications, the output of these devices is fed into a comparator or a n A/D converter to convert the temperature data into a digital format. Despite the need for these additional devices,

thermistors and silicon temperature sensors continue to enjoy popularity due to low cost and convenience of use in many situations.

Digital I/O Temperature Sensors

About five years ago, a new type of temperature sensor was introduced. These devices include a digital interface that permits communication with a microcontroller. The interface is usually an I2C or SMBus serial bus, but other serial interfaces such as SPI are common. In addition to reporting temperature readings to the microcontroller, the interface also receives instructions from the microcontroller. Those instructions are often temperature limits, which, if exceeded, activate a digital signal on the temperature sensor IC that interrupts the microcontroller. The microcontroller is then able to adjust fan speed or back off the speed of a microprocessor, for example, to keep temperature under control.

This type of device is available with a wide variety of features, among them, remote temperature sensing. To enable remote sensing, most high-performance CPUs include an on-chip transistor that provides a voltage analog of the temperature. (Only one of the transistor's two p-n junctions is used.) Figure 3 shows a remote CPU being monitored using this technique. Other applications utilize a discrete transistor to perform the same function.

Figure 3. A user-programmable temperature sensor monitors the temperature of a remote CPU's on-chip p-n junction.

Another important feature found on some of these types of sensors (including the sensor shown in Figure 3) is the ability to interrupt a microcontroller when the measured temperature falls outside a range bounded by high and low limits. On other sensors, an interrupt is generated when the measured temperature exceeds either a high or a low temperature threshold (i.e., not both). For the sensor in Figure 3, those limits are transmitted to the temperature sensor via the SMBus interface. If the temperature moves above or below the circumscribed range, the alert signal interrupts the processor.

Pictured in Figure 4 is a similar device. Instead of monitoring one p-n junction, however, it monitors four junctions and its own internal temperature. Because Maxim's MAX1668 consumes a small amount of power, its internal temperature is close to the ambient temperature. Measuring the ambient temperature gives an indication as to whether or not the system fan is operating properly.

Figure 4. A user-programmable temperature sensor monitors its own local temperature and the temperatures of four remote p-n junctions.

Controlling a fan while monitoring remote temperature is the chief function of the IC shown in Figure 5. Users of this part can choose between two different modes of fan control. In the PWM mode, the microcontroller controls the fan speed as a function of the measured temperature by changing the duty cycle of the signal sent to the fan. This permits the power consumption to be far less than that of the linear mode of control that this part also provides. Because some fans emit an audible sound at the frequency of the PWM signal controlling it, the linear mode can be advantageous, but at the price of higher power consumption and additional circuitry. The added power consumption is a small fraction of the power consumed by the entire system, though.

Figure 5. A fan controller/temperature sensor IC uses either a PWM- or linear-mode control scheme.

This IC provides the alert signal that interrupts the microcontroller when the temperature violates specified limits. A safety feature in the form of the signal called "overt" (an abbreviated version of "over temperature") is also provided. If the microcontroller or the software were to lock up while temperature is rising to a dangerous level, the alert signal would no longer be useful. However, overt, which goes active once the temperature rises above a level set via the SMBus, is typically used to control circuitry without the aid of the microcontroller. Thus, in this

high-temperature scenario with the microcontroller not functioning, overt could be used to shut

down the system power supplies directly, without the microcontroller, and prevent a potentially catastrophic failure.

This digital I/O class of devices finds widespread use in servers, battery packs, and hard-disk drives. Temperature is monitored in numerous locations to increase a server's reliability: at the motherboard (which is essentially the ambient temperature inside the chassis), inside the CPU die, and at other heat-generating components such as graphics accelerators and hard-disk drives. Battery packs incorporate temperature sensors for safety reasons and to optimize charging profiles, which maximizes battery life.

There are two good reasons for monitoring the temperature of a hard-disk drive, which depends primarily on the speed of the spindle motor and the ambient temperature: The read errors in a drive increase at temperature extremes, and a hard disk's MTBF is improved significantly through temperature control. By measuring the temperature within the system, you can control motor speed to optimize reliability and performance. The drive can also be shut down. In high-end systems, alerts can be generated for the system administrator to indicate temperature extremes or situations where data loss is possible.

Analog-Plus Temperature Sensors

"Analog-plus" sensors are generally suited to simpler measurement applications. These ICs generate a logic output derived from the measured temperature and are distinguished from digital I/O sensors primarily because they output data on a single line, as opposed to a serial bus.

In the simplest instance of an analog-plus sensor, the logic output trips when a specific temperature is exceeded. Some of these devices are tripped when temperature rises above a preset threshold, others, when temperature drops below a threshold. Some of these sensors allow the temperature threshold to be adjusted with a resistor, whereas others have fixed thresholds.

The devices shown in Figure 6 are purchased with a specific internal temperature threshold. The three circuits illustrate common uses for this type of device: providing a warning, shutting down a piece of equipment, or turning on a fan.

Figure 6. ICs that signal when a temperature has been exceeded are well suited for

over/undertemperature alarms and simple on/off fan control.

When an actual temperature reading is needed, and a microcontroller is available, sensors that transmit the reading on a single line can be useful. With the microcontroller's internal counter measuring time, the signals from this type of temperature sensor are readily transformed to a measure of temperature. The sensor in Figure 7 outputs a square wave whose frequency is proportional to the ambient temperature in Kelvin. The device in Figure 8 is similar, but the

period of the square wave is proportional to the ambient temperature in kelvins.

Figure 7. A temperature sensor that transmits a square wave whose frequency is proportional to

the measured temperature in Kelvin forms part of a heater controller circuit.

Figure 8. This temperature sensor transmits a square wave whose period is proportional to the measured temperature in Kelvin. Because only a single line is needed to send temperature information, just a single optoisolator is required to isolate the signal path.

Figure 9, a truly novel approach, allows up to eight temperature sensors to be connected on this common line. The process of extracting temperature data from these sensors begins when the microcontroller's I/O port strobes all the sensors on the line simultaneously. The microcontroller is then quickly reconfigured as an input in order to receive data from each of the sensors. The data are encoded as the amount of time that transpires after the sensors are strobed. Each of the sensors encodes this time after the strobe pulse within a specific range of time. Collisions are avoided by assigning each sensor its own permissible time range.

Figure 9. A microcontroller strobes up to eight temperature sensors connected on a common line and receives the temperature data transmitted from each sensor on the same line.

The accuracy achieved by this method is surprisingly high: 0.8°C is typical at room temperature, precisely matching that of the IC that encodes temperature data in the form of the frequency of the transmitted square wave. The same is true of the device that uses the period of the square wave.

These devices are outstanding in wire-limited applications. For example, when a temperature sensor must be isolated from the microcontroller, costs are kept to a minimum because only one optoisolator is needed. These sensors are also of great utility in automotive and HVAC applications, because they reduce the amount of copper running over distances.

Anticipated Temperature Sensor Developments

IC temperature sensors provide a varied array of functions and interfaces. As these devices

continue to evolve, system designers will see more application-specific features as well as new ways of interfacing the sensors to the system. Finally, the ability of chip designers to integrate more electronics in the same die area ensures that temperature sensors will soon include new functions and special interfaces.

中文翻译

温度传感器芯片简化设计

当选择一个温度传感器时，将不再局限于模拟输出或数字输出设备。现在有的传感器类型，会让你有很大的选择空间。在市场上的所有的温度传感器提供模拟输出。热敏电阻、 RTDs 和热电偶是另一种模拟输出设备，硅温度传感器。在大多数应用程序中，不幸的是，这些模拟输出设备需要比较器、 ADC 或在他们的输出放大器。因此，当更高的级别，集成的变得可行，数字接口的温度传感器成为可用。这些芯片在多种形式出售，从简单信号在特定温度时的设备已超过那些报告同时提供警告在升温设置的远程和本地的温度。选择现在不是简单地之间模拟输出和数字输出的传感器；有范围广泛的传感器类型可供选择。

温度传感器的种类

图 1。传感器和 IC 制造商目前提供温度传感器的四的类。

在图1中举例说明四种温度传感器类型。一种理想的模拟传感器提供输出电压，这是一个完美的线性温度（A）的功能。在数字 I/O 类的传感器 (B) 中，温度多 1 和 0 的表单中的数据传递到微控制器，通常是通过串行总线。沿着相同的总线，数据被发送到温度传感器的微控制器，通常设置的警报针的数字输出将旅行的温度限制。警报中断微控制器时已经超过温度限制。这种类型的设备，还可以提供风扇控制。

"模拟正量"传感器(C)被应用在多种类型的数字输出上。当超过特定温度的时候，V out 对温度曲线是一个数字输出。在这种情况下，增加到模拟温度传感器的“正信号”只不过是一个比较器的参考电压。其他的类型“正信号”部分在以频率和方波的形式储存以后被延迟，这些将会在以后讨论。

系统监视器（D）是四种类型当中最复杂的集成电路。除了功能由数字 I/O 类型提供外，当电压上升或下降到通过I/O 总线设置的极限的时候这类型装置的监测系统会报警。风扇监控和/或控制包含在这种类型中的集成电路。在某些情况下，此类设备用于决定一个风扇是否正在工作。更多复杂控制风扇如一或更多量过的温度的功能。系统监视器传感器这里不讨论，但简短提到温度传感器的类型。

模拟输出温度传感器

热电阻和硅温度传感器被广泛地应用在模拟输出温度传感器上。图 2 清楚地显示当需

要时电压和温度的线性关系，硅温度传感器是比热敏电阻好得多。在狭窄的温度范围之内，热敏电阻可以提供合理的线性和良好的敏感特性。许多构成原始电路的热敏电阻已经被硅温度传感器代替。

图 2。热敏电阻和硅温度传感器这两个模拟输出温度探测器的比较。

硅温度传感器有不同的输出刻度和偏移量。例如，与绝对温度成比例的输出转换功能，还有其他与摄氏温度和华氏温度成比例。摄氏温度部分提供一种组合以便温度能被单端补给传感器测试。

在大多数应用程序中，这些装置的输出被装入一个比较器或 A/D 转换器的温度数据转换为数字格式。这些附加的装置，热电阻和硅温度传感器继续被使用是由于在很多情况下它的成本低和使用方便。

数字 I/O 温度传感器

大约在五年前，一种新型温度传感器出现了。这种装置包括一个允许与微控制器进行通信的数字接口。接口通常是 I2C 或 SMBus 的串行总线，但其他的串行接口，如 SPI 是共用的。除了要报告的微控制器，温度读数，该接口也从微控制器接收指令。这些指令通常温度限制，如果超出，将中断微控制器的温度传感器在集成电路上的数字信号。然后微控制器可以调整风扇速度，或减慢微处理器的速度，例如，保持温度在控制下。

这种类型装置有多样性的特点。远程温度传感，为了能够远程测量，大多数的高效处理器提供一个温度的模拟电压芯片晶体。（晶体管的两个 p-n 结仅被使用）。图 3 显示了一个使用这种技术检测的处理器。其他应用利用离散的晶体管实现相同的功能。

图 3。设计的温度传感器可远程测试处理器芯片上的p-n结温度。

这种类型的传感器的另一个重要特征是测量温度在高或低极限外有中断微控制器的能力（包括在图 3 中所示的传感器）。在其他的传感器上，当测量的温度超过极限的时候，它

会产生一个高或低的温度门限，对於在图 3 中的传感器，那些极限经由SMBus 接口被传送到温度传感器。如果温度移动到周围画线范围上面或下面，报警信号会中断处理器。

在图 4 中画一种类似的装置。而不是监测一个p-n结温度，它会检测四个结和其内部的温度。因为Maxim的 MAX1668 消耗很小的能量，它内部的温度接近周围温度。周围温度的测量给出关于系统风扇是否正常工作的指示。

图 4。温度传感器可检测自己本地的温度和四个远程 p-n 结的温度。

在图5中显示，控制风扇是在远程温度监测时集成电路的主要功能。这一部分的使用能在风扇控制的两种不同的模式之间进行选择。在 PWM 模式中，微控制器控制风扇转速是通过更改发送到风扇的信号周期测量温度的一种功能。它允许电力消耗远少于该部分的线性模式控制所提供的。因为某些风扇在PWM信号控制它的频率下发出一种听得见的声音，这种线性模式可以是有利的，但是需要较高功率的消耗和附加的电路。额外的功耗是整个系统功耗的一小部分。

图 5。风扇控制器/温度传感器集成电路也可使用PWM或一个线性模式控制方案。

当温度超出指定界限的时候，在这个集成电路提供中断微控制器的警告信号。这个被叫做过热温度的信号形式里，安全特征也被提供。如果温度升到一个危险级别的时候或软件被锁定，警报信号将不再有用。然而，温度经由 SMBus升高到一个水平，过热能被直接用去关闭这个系统电源，没有控制和阻止潜在的灾难性故障。

这种数字设备的 I/O 类广泛使用在查找服务器、电池组和硬磁盘驱动器中。为了增加服务器的可靠性，温度在很多位置被检测：在主板（本质上是在底盘内部的周围温度），在

处理器钢模之内，和在其他发热原件例如图形加速器和硬磁盘驱动器。出于安全原因电池组结合温度传感器和使其最优化以达到电池最大寿命。

检测依靠中心马达的速度和周围温度的硬盘驱动器的温度有两个好的理由：在驱动器中读取错误增加温度极限。而且硬盘 MTBF 大大改善温度控制。通过测量系统里面的温度，就能控制马达速度将可靠性和性能最佳化。驱动器也能被关闭。在高端系统中，警告能为系统管理员指出温度极限或数据可能丢失的状况。

模拟正温度感应器

“模拟正量”传感器通常匹配比较简单的测量应用软件。这些集成电路产生逻辑输出量来自被测温度，而且区别于数字输入/输出传感器，因为他们在一条单线上输出数据，与串行总线相对。

在一个模拟正量传感器的最简单的实例中，当特定的温度被超过时，逻辑输出出错；其它，是当温度降到一个温度极限的时候。当其他传感器有确定的极限的时候，这些传感器中的一些允许使用电阻去校正温度极限。

在图6中，装置显示购买一个特定的内在温度极限。这三个电路说明这种类型的设备的常见用途：提供警告，关闭仪器，或开启风扇。

图 6.温度超过某一界限的时候，集成电路信号能报警和进行简单的开/关风扇控制。

当需要读实际温度时，微控制器是可以利用的，在单线上传送数据的传感器可能是有用的。用微处理器的内部计数器，来自于这个类型温度传感器的信号容易被转换的温度来测量。图7中传感器输出频率与周围温度成正比例的方波。图8中的设备很相似，但方波周期是与周围温度成比例的。

图 7.热控制电路部分在绝对温标形式下，频率与被测温度成比例的产生方波的温度传感器。

图 8。这个温度传感器传送它的周期与被测温度成正比例的方波。因为只发送温度数据需要一条单一线，就需要单一光绝缘体隔离信道。

图9，在这条公共线上允许连接达到8 个温度传感器。当微控制器的 I/O端口同时关闭在这根线上的所有传感器的时候，开始提取来自这些传感器的温度数据。微控制器很快地重新装载接受来自每个传感器的数据。在传感器关闭期间，数据被编码。在特定时间范围内每个传感器对闸门脉冲之后的时间编码。分配给每个传感器自己允许的时间范围，这样可以避免碰撞。

图 9。用一条公共线与8个温度传感器连接的微控制器，而且从同一条线上接收每个传

感器传送得温度数据。

通过这个方法达到的准确性令人惊讶：0.8 ° C 是典型的室温，正好与被传送方波频率的电路相匹配，同样适用于方波周期的装置。

这些装置在电线应用中非常突出的。例如，当一个温度传感器被微控制器隔离的时候，成本被保持在一个最小量，因为只需要一个光绝缘体。这些传感器在汽车制造HVAC应用中也是很有效的，因为它们减少了铜的损耗数量。

预期的温度传感器发展

集成电路温度传感器提供各式各样的功能和接口。同样的这些装置继续发展，系统设计师将会看到更多特殊应用就像传感器与系统接口连接的新方式一样。最后，在相同的钢模区域内集成更多电子元件，芯片设计师的能力将确保温度传感器很快会包括新功能和特殊的接口。