Development trend of the hottest intelligent tempe

Development trend of intelligent temperature sensor

Abstract: This paper introduces the product classification of integrated temperature sensor, and comprehensively and systematically expounds the development trend of intelligent temperature sensor

key words: intelligent temperature sensor; Development trend; Bus; Virtual sensor; The three foundations of modern information technology are information acquisition (sensor technology), information transmission (Communication Technology) and information processing (computer technology). Sensors are cutting-edge products of information technology, especially temperature sensors, which are widely used in industrial and agricultural production, scientific research, life and other fields, and the number of sensors ranks first among all kinds of sensors. In the past hundred years, the development of temperature sensors has roughly experienced the following three stages; (1) Traditional discrete temperature sensor (including sensitive elements); (2) Analog integrated temperature sensor/controller; (3) Intelligent temperature sensor. At present, new temperature sensors in the world are developing from analog to digital, from integration to intelligence and networking

1 product classification of integrated temperature sensors

1.1 analog integrated temperature sensors

integrated sensors are made by silicon semiconductor integration process, so they are also called silicon sensors or monolithic integrated temperature sensors. Analog integrated temperature sensor came out in the 1980s. It is a special IC that integrates the temperature sensor on a chip and can complete the temperature measurement and analog signal output functions. The main characteristics of analog integrated temperature sensor are single function (only measuring temperature), small temperature measurement error, low price, fast response speed, long transmission distance, small volume, micro power consumption, etc. it is suitable for long-distance temperature measurement and control, does not need nonlinear calibration, and the peripheral circuit is simple. It is the most widely used integrated sensor at home and abroad. Typical products include AD590, AD592, tmp17, LM135, etc

1.2 analog integrated temperature controller

analog integrated temperature controller mainly includes temperature control switch and programmable temperature controller. Typical products include LM56, ad22105 and max6509. Some enhanced integrated temperature controllers (such as tc652/653) also include a/d converters and cured programs, which are similar to intelligent temperature sensors. However, it has its own system and is not controlled by the microprocessor when it works, which is the main difference between the two

1.3 intelligent temperature sensor

intelligent temperature sensor (also known as digital temperature sensor) came out in the mid-1990s. It is the crystallization of microelectronics technology, computer technology and automatic test technology (ATE). At present, a variety of intelligent temperature sensor series products have been developed internationally. Inside the intelligent temperature sensor, there are temperature sensors, a/d converters, signal processors, memory steel mills' enthusiasm for pig iron purchasing, moderators (or registers) and interface circuits. Some products also have multiplexers, central controllers (CPUs), random access memory (RAM) and read only memory (ROM). The characteristic of intelligent temperature sensor is that it can output temperature data and related temperature control quantities, and is suitable for various microcontrollers (MCU); And it realizes the test function through software on the basis of hardware, and its intelligence also depends on the level of software development

2 new trend of intelligent temperature sensor development

after entering the 21st century, intelligent temperature sensors are rapidly developing in the direction of high-tech, such as high precision, multi-function, bus standardization, high reliability and security, development of virtual sensors and network sensors, development of single-chip temperature measurement system and so on

2.1 improve the accuracy and resolution of temperature measurement

Zhi 4, which was first launched in the mid-1990s Our company has a spare parts warehouse energy temperature sensor, which adopts an 8-bit a/d converter. Its temperature measurement accuracy is low, and the resolution can only reach 1 ℃. At present, many kinds of high-precision and high-resolution intelligent temperature sensors have been launched abroad. The 9-12 bit a/d converter is used, and the resolution can generally reach 0.5-0.0625 ℃. The DS1624 high-resolution intelligent temperature sensor newly developed by Dallas Semiconductor Company of the United States can output 13 bit binary data, with a resolution of 0.03125 ℃ and a temperature measurement accuracy of ± 0.2 ℃. In order to improve the conversion rate of multi-channel intelligent temperature sensor, some chips also use high-speed successive approximation a/d converter. Taking the ad7817 5-channel intelligent temperature sensor as an example, its conversion time to local sensors and each remote sensor is only 27 μ s、9 μ s。

2.2 add test function

the test function of the new intelligent temperature sensor is also constantly enhanced. For example, ds1629 single wire intelligent temperature sensor adds real-time calendar clock (RTC) to make its function more perfect. DS1624 also adds a storage function, which uses the 256 byte E2PROM memory inside the chip to store users' SMS. In addition, the intelligent temperature sensor is developing from single channel to multi-channel, which creates good conditions for the research and development of multi-channel temperature measurement and control system

intelligent temperature sensors have a variety of working modes to choose from, mainly including single conversion mode, continuous conversion mode, standby mode, and some have added low temperature limit expansion mode, which is very simple to operate. For some intelligent temperature sensors, the host (external microprocessor or single chip microcomputer) can also set its a/d conversion rate (max6654 for typical products), resolution and maximum conversion time (DS1624 for typical products) through corresponding registers

intelligent temperature controller is developed on the basis of intelligent temperature sensor. Typical products include DS1620, ds1623, TCN75, lm76 and max6625. The intelligent temperature controller adapts to various microcontrollers to form an intelligent temperature control system; They can also work independently of the microcontroller and form a temperature controller by themselves

2.3 standardization and standardization of bus technology

at present, the bus technology of intelligent temperature sensor has also achieved standardization and standardization. The buses used mainly include single wire (-wire) bus, I2C bus, SMBus bus and SPI bus

2.4 reliability and safety design

traditional a/d converters mostly use integral or successive comparison conversion technology, which has low noise tolerance and poor ability to suppress aliasing noise and quantization noise. New intelligent temperature sensors (such as tmp03/04, lm74, LM83) generally adopt high-performance Σ－Δ Type A/D converter, which can convert analog signals into digital signals with high sampling rate and low sampling resolution, and then use oversampling, noise shaping and digital filtering technology to improve the effective resolution. Σ－Δ Type A/D converter can not only filter quantization noise, but also has low accuracy requirements for peripheral components. In order to avoid misoperation when the temperature control system is disturbed by noise, a programmable "faultqueue" counter is set inside the intelligent temperature sensors such as ad7416/7417/7817, LM75/76, max6625/6626, which is specially used to set the number of times that the measured temperature value is allowed to exceed the upper and lower limits. Only when the measured temperature continuously exceeds the upper limit or is lower than the lower limit for the number of times to reach or exceed the set number of times n (n=1~4), can the interrupt end be triggered. If the number of faults does not meet the above conditions or the faults do not occur continuously, the fault counter will reset without triggering the interrupt end. This means that if n=3 is assumed, the normal operation of the temperature control system will not be affected by accidental noise interference once or twice

lm76 intelligent temperature sensor adds a temperature window comparator, which is very suitable for designing a temperature control system that conforms to the specification of ACPI (advanced configuration and power interface). This system has perfect overheat protection function and can be used to monitor the temperature of CPU and main circuit in notebook computers and servers. The maximum working temperature that the microprocessor can withstand is specified as R - the compressive strength of the test piece, th. Desktop computers are generally 75 ℃, and the special CPU of high-end notebook computers can reach 100 ℃. Once the temperature of CPU or main circuit exceeds the set upper and lower limits, even if the host is interrupted, the int terminal sends a signal through the power controller to quickly turn off the main power supply for protection. In addition, when the temperature exceeds the limit temperature of the CPU, the serious over temperature alarm output terminal (t_crit_a) can also directly turn off the main power supply, and this terminal can also cut off the main power supply through an independent hardware shutdown circuit to prevent the main power control failure. The above triple safety protection measures have become a new concept in the international design of temperature control systems

to prevent chip damage due to human electrostatic discharge (ESD). Some intelligent temperature sensors have also added ESD protection circuits, which can generally withstand the electrostatic discharge voltage of 1000~4000v. Generally, the human body is equivalent to a circuit model composed of 100pF capacitor and 1.2k ohm resistor in series. When the human body discharges, the serial interface terminal, interrupt/comparator signal output terminal and address input terminal of TCN75 intelligent temperature sensor can withstand 1000V electrostatic discharge voltage. LM83 intelligent temperature sensor can withstand 4000V electrostatic discharge voltage

the newly developed intelligent temperature sensor (such as max6654, LM83) also adds the sensor fault detection function, which can automatically detect the open circuit or short circuit fault of the external transistor temperature sensor (also known as the remote sensor). Max6654 also has the option of "parasitic impedance cancellation" (PRC) mode, which can offset the temperature measurement error caused by the lead impedance of the remote sensor. Even if the lead impedance reaches 100 ohms, the measurement accuracy will not be affected. The remote sensor lead can be ordinary twisted pair or twisted pair with shielding layer

2.5 virtual temperature sensor and network temperature sensor

(1) virtual sensor

virtual sensor is based on sensor hardware and computer platform, and is developed through software. The calibration and calibration of the sensor can be completed by using the software to achieve the best performance index. Recently, B & K Company of the United States has developed a TEDS virtual sensor based on software settings. Its main feature is that each sensor has a unique product serial number and is attached with a floppy disk, which stores the relevant data for calibrating the sensor. When in use, the sensor is connected to the computer through the data collector. First, the product serial number of the sensor is input from the computer, and then the relevant data is read out from the floppy disk, and then the sensor inspection, sensor parameter reading, sensor setting and recording are automatically completed

(2) network temperature sensor

network temperature sensor is a new generation of intelligent sensor including digital sensor, network interface and processing unit. The digital sensor first converts the measured temperature into a digital quantity, and then sends it to the microcontroller for data processing. Finally, the measurement results are transmitted to the network, so as to realize the data exchange and resource sharing among sensors, sensors and actuators, sensors and systems. When replacing sensors, there is no need to calibrate and calibrate, so that "plug&plug" can be achieved, and the original products can be continuously improved, which greatly facilitates users

2.6 single chip temperature measurement system

system on chip is a high-tech product in the 21st century. It integrates a system or subsystem on a chip, and its integration degree will be as high as 108~109 components/chip, which will bring epoch-making progress to the IC industry and IC applications. The predictions made by the semiconductor industry association (SIA) for monolithic system integration are shown in the table. At present, some famous IC manufacturers in the world