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The development trend of intelligent temperature sensor

Modern information technology is based on information collected three (ie, sensor technology), information transfer (ICT) and information processing (computer technology). Sensors are the forefront of cutting-edge information technology products, especially the temperature sensors are widely used in industrial and agricultural production, scientific research and life in areas such as the number of ranking first in a variety of sensors. The past century, the development of the temperature sensor has gone through three phases; (1) the traditional discrete temperature sensors (including sensor); (2) analog integrated temperature sensor / controller; (3) smart temperature sensor. Currently, the international new temperature sensor is moving from analog to digital, from the integrated to the intelligent, the direction of network development。

An integrated temperature sensor product category
1.1 analog integrated temperature sensor
Integrated Sensor is a silicon semiconductor integrated process and made, and therefore also known as monolithic integration of silicon sensors or temperature sensors. Analog integrated temperature sensor is 80 years came in the 20th century, it is the temperature sensor integrated on a chip, to be completed by the temperature measurement and analog signal output of the dedicated IC. Analog integrated temperature sensor is characterized by a single function (only measure temperature), temperature measurement error is small, low price, fast response, transmission distance, small size, low power consumption, etc., suitable for remote temperature measurement, temperature control, no the need for non-linear calibration, the external circuit is simple. It is most common in the domestic application of an integrated sensor, the typical products AD590, AD592, TMP17, LM135, etc。

1.2 analog integrated temperature controller
Analog Integrated temperature controller includes temperature control switches, programmable temperature controller, a typical product LM56, AD22105 and MAX6509. Some of the enhanced integrated temperature controller (such as TC652/653) also contains the A / D converter and curing a good program, which is smart temperature sensor has some similarities. But it is a system, work is not subject to the control of the microprocessor, which is the main difference between the two。

1.3 Smart temperature sensor
Smart temperature sensor (also known as digital temperature sensor) is in the 20th century, the mid-90s came out. It is the micro-electronics technology, computer technology and automated testing techniques (ATE) of crystallization. At present, the international community has developed a variety of smart temperature sensor products. Smart temperature sensor internal temperature sensor is included, A / D converter, signal processor, memory (or registers) and the interface circuit. Some products also with multiplexer, the central controller (cpu), random access memory (RAM) and read-only memory (ROM). Smart temperature sensor output temperature data is characterized and related to the temperature control variable, fit a variety of micro-controller (MCU); and it is based on the hardware through software to achieve the test function, which depends on the degree of intelligence in the software development level。

2 smart new development trend of the temperature sensor
In the 21st century, high-precision smart temperature sensor is moving, multi-functional, bus standard, high reliability and security, development of virtual sensors and network sensors, temperature measurement systems, single-chip high-tech development direction of the rapid development。

2.1 to improve temperature measurement accuracy and resolution
In the 20th century, first introduced in the mid 90's smart temperature sensor, using 8-bit A / D converter, the low temperature measurement accuracy, resolution can only reach 1 ° C. At present, foreign countries have launched a variety of high-precision, high resolution intelligent temperature sensor is used in 9 to 12-bit A / D converter, the general resolution of up to 0.5 ~ 0.0625 ° C. DALLAS Semiconductor, Inc. by the United States developed a new type of high-resolution intelligent DS1624 temperature sensor that can output 13-bit binary data, and its resolution as high as 0.03125 ° C, temperature accuracy of ± 0.2 ° C. In order to improve multi-channel intelligent temperature sensor conversion rate, and some chip high-speed successive approximation A / D converter. The AD7817 5-Channel Temperature Sensor, for example, its local sensors, remote sensors for each road, respectively, the conversion time of only 27us, 9us。

2.2 increase in test function
New intelligent temperature sensor test capability is also growing. For example, DS1629 temperature sensor type single intelligent real-time calendar clock increased (RTC), to function more perfect. DS1624 also increased the storage capabilities, the use of 256 bytes of E2PROM chip memory, can store the user's text messages. In addition, the smart temperature sensor is moving from single to multi-channel direction, which for the research and development of multi-channel temperature control system has created good conditions。

Smart temperature sensors are available with a variety of operating modes, including single conversion mode, continuous conversion mode, standby mode, and some also increased the low temperature limit expansion mode, operation is very simple. Some smart temperature sensor, the host (an external microprocessor or microcontroller) can also register to set its corresponding A / D conversion rate (typical products MAX6654), the maximum resolution and conversion time (typical products DS1624)。

To the temperature controller is a smart temperature sensor based on evolution. Typical products DS1620, DS1623, TCN75, LM76, MAX6625. Intelligent Temperature Controller Adapter various micro controllers, intelligent temperature control system constituted; they can also work out a separate micro-controller, self-constituting a temperature controller。

2.3 bus technology, the normalization and standardization
Currently, the smart temperature sensor bus technology to achieve the standardization, using the bus are single (1-Wire) bus, I2C bus, SMBus bus and spI bus. Temperature sensor can be dedicated as a slave bus interface for communication with the host。

2.4 Reliability and security design
Traditional A / D converter they use integral or successive approximation conversion technique, the noise margin is low, inhibition of aliasing noise and quantization noise of the capacity is relatively poor. New Intelligent Temperature Sensor (for example TMP03/04, LM74, LM83) the widespread adoption of high-performance type Σ-Δ A / D converter can sample at high sampling rate and low resolution of analog signals into digital signal, and then use oversampling, noise shaping and digital filtering techniques to improve the effective resolution. Σ-Δ type A / D converter can not only filter out quantization noise and the accuracy of the external components that require low; the use of digital feedback mode, the comparator offset voltage and zero temperature drift will not affect the conversion accuracy. The smart temperature sensors both series mode interference suppression capability, high resolution, good linearity and low cost。

In order to avoid interference by the noise in the temperature control system malfunction arising in AD7416/7417/7817, LM75/76, MAX6625/6626 internal temperature sensors and other intelligent, have set a programmable "fault line (fAultqueue)" Counter , dedicated to the set to allow the measured temperature exceeds the lower limit of the number of times. Only when the measured temperature of the upper or lower limit exceeded the number of times meet or exceed the set number of times n (n = 1 ~ 4) when the client can trigger the interrupt. If the number of failures does not meet the above conditions are not continuous or fault occurs, the fault counter to reset and will not interrupt client. This means that assuming n = 3, then once or twice by accident by the noise will not affect the normal operation of temperature control system。

LM76 temperature sensor adds intelligent temperature window comparator, ideal for designing a consistent ACPI (AdvAnced ConfigurAtion And Power InterfAce, the "Advanced Configuration and Power Interface") standard temperature control system. This system has perfect thermal protection, can be used to monitor the laptop computer and the server CPU and the main circuit temperature. Microprocessor can withstand the highest operating temperature of the provisions of tH, desktop computer usually 75 ° C, high-end notebook computers dedicated CPU up to 100 ° C. Once the CPU or the main circuit exceeds the set temperature, the lower limit, INT interrupt the host side immediately, and then send a signal through the power controller to quickly turn off the main power supply for protection. In addition, when the temperature exceeds the limits of CPU temperature, severe over-temperature alarm output terminal (T_CRIT_A) can also be directly off the main power, and the client can also independent of the hardware to cut off the main power circuit in case the main power control failure. Triple security protection measures mentioned above have become international design the new concept of temperature control system。

To prevent the human body electrostatic discharge (ESD) and damage to the chip. Some smart temperature sensor has also increased the ESD protection circuits can typically withstand 1000 ~ 4000V ESD voltage. The body is usually equivalent to the 100PF capacitor and 1.2K ohm resistor in series circuit model, when the body discharge, TCN75 intelligent temperature sensor serial interface port, interrupt / comparator output signal and address inputs are ESD withstand voltage of 1000V. LM83 temperature sensor can be intelligent ESD withstand voltage of 4000V。

The newly developed Intelligent Temperature Sensor (for example, MAX6654, LM83) also increased the sensor fault detection, can automatically detect the external transistor temperature sensor (also known as remote sensors) in open or short. MAX6654 also has a choice "parasitic impedance offset" (PArAsitic ResistAnce CAncellAtion, the English abbreviation for the prc) model, to offset long-range sensors lead impedance measurement error caused, even if the lead impedance of 100 ohms, it will not affect measurement accuracy. Remote sensors can be used ordinary twisted pair wire or shielded twisted pair。

2.5 virtual temperature sensor and temperature sensor networks
(1) virtual sensors
Virtual sensor is a sensor-based hardware and computer platforms and software to develop. To be completed by the software sensor calibration and calibration to achieve optimal performance. Recently, the U.S. B & K has developed a software-based set of Virtual TEDS sensor, its main feature is the product of each sensor has a unique serial number and comes with a floppy disk, floppy disk storing the calibration of the sensor relevant data. When used, the sensor data acquisition by computers connected to the first input of the sensor from the computer serial number, and then read out from the floppy disk data, then automatically check the sensor, the sensor reads the parameters, sensors and record set work。

(2) Network temperature sensor
Network digital sensor temperature sensor is included, the network interface and processing unit of the new generation of smart sensors. First, the measured temperature digital sensor into a digital number, and then sent to the microcontroller for data processing. Finally, the measurement results transmitted to the network in order to achieve between the various sensors, between sensors and actuators, sensors and data exchange between systems and resource sharing in the replacement of sensors without the need for calibration and calibration can be "plug and that use (Plug & PlAy) ", thus greatly facilitate the users。

2.6 single-chip temperature measurement system
SoC (System On Chip) is a 21st century high-tech products. It is integrated on the chip of a system or subsystem, the integrated components will be as high as 108 ~ 109 / piece, which will bring IC industry and IC applications epoch-making progress. Semiconductor Industry Association (SIA) on-chip system integration forecasts in Table 1. At present, some well-known international manufacturers have started to develop the IC chip temperature measurement system that can be available in the near future。

Table 1 predict the development of integrated circuit chip system
Year 2001 2002 2007 2010
Minimum line width /um 0.18 0.13 0.1 0.07
Contains the number of transistors / chip 1.3X108 2.5X108 5X108 9X108
Cost / (transistors / mm cents) 0.2 0.1 0.05 0.02
Chip size/mm2 750 900 1100 1400
Supply voltage/V 1.8 1.5 1.2 0.9
Film I / O number 2000 2600 3600 4800

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