Integrated temperature sensor product classification 1. Analog Integrated Temperature Sensors Integrated sensors are manufactured using silicon semiconductor integrated processes and are therefore also referred to as silicon sensors or monolithic integrated temperature sensors. The analog integrated temperature sensor was introduced in the 1980s. It is a dedicated IC that integrates temperature sensors on a single chip to perform temperature measurement and analog signal output functions. The main characteristics of the analog integrated temperature sensor are single function (measurement of temperature only), small temperature error, low price, fast response, long transmission distance, small size, micro power consumption, etc. It is suitable for remote temperature measurement and temperature control. Nonlinear calibration is required and the peripheral circuit is simple. It is an integrated sensor that is most commonly used at home and abroad. Typical products include AD590, AD592, TMP17, and LM135.
2. Analog Integrated Temperature Controllers Analog integrated temperature controllers mainly include temperature-controlled switches and programmable temperature controllers. Typical products are the LM56, AD22105, and MAX6509. Some enhanced integrated temperature controllers (such as TC652/653) also include A/D converters and solidified programs, which have some similarities with smart temperature sensors. However, it is a self-contained system and is not controlled by the microprocessor during work. This is the main difference between the two.
3. Smart temperature sensors Smart temperature sensors (also known as digital temperature sensors) were introduced in the mid-1990s. It is the crystallization of microelectronics, computer technology and automatic test technology (ATE). At present, many intelligent temperature sensors have been developed internationally. The smart temperature sensor internally contains a temperature sensor, an A/D converter, a signal processor, a memory (or register), and an interface circuit. Some products also have multiplexers, a central controller (CPU), random access memory (RAM), and read-only memory (ROM). The characteristic of the intelligent temperature sensor is that it can output the temperature data and the related temperature control quantity, and adapt to various microcontrollers (MCU); and it is based on the hardware to realize the test function through the software, and the degree of intelligence depends on it. At the level of software development.
New Trends in the Development of Smart Temperature Sensors After entering the 21st century, smart temperature sensors are moving toward high precision, versatility, bus standardization, high reliability and security, the development of virtual sensors and network sensors, and the development of single-chip temperature measurement systems and other high technologies. The direction of the rapid development.
1. Improve the accuracy of temperature measurement and resolution The first smart temperature sensor introduced in the mid-1990s, using 8-bit A / D converter, the accuracy of low temperature measurement, resolution can only reach 1 °C. At present, foreign countries have introduced a variety of high-precision, high-resolution intelligent temperature sensors, the use of a 9 ~ 12-bit A / D converter, the resolution is generally up to 0.5 ~ 0.0625 °C. The DS1624 high resolution intelligent temperature sensor newly developed by DALLAS Semiconductor, USA, can output 13-bit binary data with a resolution of 0.03125°C and an accuracy of ±0.2°C.
In order to improve the conversion rate of multi-channel smart temperature sensors, some chips also use high-speed successive approximation A/D converters. Taking the AD7817 5-channel smart temperature sensor as an example, the conversion time for the local sensor and each remote sensor is only 27 μs and 9 μs, respectively.
2. Adding Test Functions The test capabilities of the new smart temperature sensors are also increasing. For example, the DS1629 single-wire smart temperature sensor adds a real-time calendar clock (RTC) to make it more functional. The DS1624 also adds a memory function that uses the chip's internal 256-byte E2PROM memory to store user's short messages. In addition, smart temperature sensors are developing from single-channel to multi-channel, which creates favorable conditions for the development and development of multi-channel temperature measurement and control systems.
Smart temperature sensors have a variety of operating modes to choose from, including single conversion mode, continuous conversion mode, and standby mode, and some also increase the low temperature limit expansion mode, the operation is very simple. For some smart temperature sensors, the host (external microprocessor or microcontroller) can also set its A/D conversion rate (typically MAX6654), resolution, and maximum conversion time (typically DS1624).
Smart temperature controllers are developed based on smart temperature sensors. Typical products are DS1620, DS1623, TCN75, LM76, MAX6625. The intelligent temperature controller adapts various microcontrollers to form an intelligent temperature control system; they can also work independently from the microcontroller and constitute a temperature controller by themselves.
3. Standardization and standardization of bus technology At present, the bus technology of smart temperature sensors has also been standardized and standardized. The buses used mainly include single-wire (-Wire) bus, I2C bus, SMBUS, and SPI bus.
4. Reliability and Security Design Most traditional A/D converters use integral or successive comparison conversion techniques. Their noise margin is low, and the ability to suppress aliasing noise and quantization noise is poor. New smart temperature sensors (such as the TMP03/04, LM74, and LM83) commonly use high-performance sigma-delta A/D converters that convert analog signals to high sample rates and low sample resolution Digital signals, oversampling, noise shaping, and digital filtering techniques are used to increase the effective resolution. The Σ-Δ A/D converter not only filters out quantization noise, but also has low requirements on the accuracy of the external components. In order to avoid malfunction when the temperature control system is disturbed by noise, a programmable "fault queue" counter is set inside the intelligent temperature sensors such as the AD7416/7417/7817, LM75/76, and MAX6625/6626. , It is used to set the allowable temperature value to exceed the upper and lower limits. The interrupt is only triggered when the measured temperature continuously exceeds the upper limit or falls below the lower limit for a number of times (n = 1 to 4). If the number of faults does not meet the above conditions or the fault does not occur continuously, the fault counter is reset without triggering the interrupt. This means that assuming n=3, then accidentally subject to one or two noise disturbances will not affect the normal operation of the temperature control system.
The LM76 intelligent temperature sensor adds a temperature window comparator and is ideal for designing a temperature control system that conforms to the Advanced Configuration and Power Interface (ACPI) specification. This kind of system has perfect overheat protection function, can be used for monitoring CPU and main circuit temperature in notebook computer and server. The maximum operating temperature of the microprocessor is specified as tH, the desktop computer is generally 75°C, and the high-end notebook computer has a dedicated CPU up to 100°C.
Once the temperature of the CPU or main circuit exceeds the set upper and lower limits, the INT terminal immediately causes the host to generate an interrupt, and then 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 severe over-temperature alarm output (T_CRIT_A) can also directly shut off the main power supply, and this end can also cut off the main power supply through an independent hardware shutdown circuit to prevent the main power supply from being controlled. Failure. The above-mentioned triple safety protection measures have become a new concept in designing temperature control systems internationally.
To prevent damage to the chip due to human body electrostatic discharge (ESD). Some intelligent temperature sensors also increase the ESD protection circuit, and generally can withstand electrostatic discharge voltage of 1000-4000V. Generally, the human body is equivalent to a circuit model in which 100 PF capacitors and 1.2 K ohm resistors are connected in series. When the human body is discharged, the serial interface terminal of the TCN75 intelligent temperature sensor, the signal output terminal of the interrupt/comparator, and the address input terminal are all Can withstand 1000V electrostatic discharge voltage. The LM83 intelligent temperature sensor can withstand an electrostatic discharge voltage of 4000V.
The newly developed smart temperature sensors (such as the MAX6654 and LM83) also include a sensor fault detection function that automatically detects an open-circuit or short-circuit fault of an external transistor temperature sensor (also called a remote sensor). The MAX6654 also features a "Parasitic Resistance Cancellation" (PRC) mode that counteracts the temperature measurement error caused by the remote sensor's lead impedance. Even if the lead impedance reaches 100 ohms, it does not affect the measurement accuracy. The remote sensor leads can be twisted pair or shielded twisted pair.
5. Virtual Temperature Sensors and Network Temperature Sensors (1) Virtual Temperature Sensors Virtual temperature sensors are based on sensor hardware and computer platforms and have been developed through software. The software can be used to calibrate and calibrate the sensor to achieve the best performance. Recently, B&K Corporation of the United States has developed a TEDS-based virtual sensor based on software settings. Its main feature is that each sensor has a unique product serial number, and a floppy disk is stored. The floppy disk stores the calibration of the sensor. Relevant data. When used, the sensor is connected to the computer through the data collector. First, the serial number of the sensor is input from the computer, and the relevant data is read out from the floppy disk. Then the sensor inspection, sensor parameter reading, sensor setting and recording are automatically completed. jobs.
(2) Network temperature sensor The network temperature sensor is a new generation of smart sensors that contain digital sensors, network interfaces, and processing units. The digital sensor first converts the measured temperature into a digital quantity, and then sends it to the micro-controller. The result is transmitted to the network in order to realize data exchange and resource sharing between each sensor, between the sensor and the actuator, and between the sensor and the system. Sensors do not need to be calibrated and calibrated, and can be “plug & playâ€, which greatly facilitates the user.
6. The single-chip temperature measurement system (System On Chip) is a high-tech product in the 21st century. It integrates a system or subsystem on the chip, and its integration degree will be as high as 108 to 109 devices/chips, which will bring epoch-making progress to the IC industry and IC applications. At present, some well-known IC manufacturers in the world have begun to develop a single-piece temperature measurement system and believe that it will be available in the near future.
The trend of smart temperature sensors
The three basics of modern information technology are: information acquisition (ie, sensor technology), information transmission (communication technology), and information processing (computer technology). Sensors belong to the cutting-edge products of information technology, especially temperature sensors are widely used in industrial and agricultural production, scientific research and life and other fields, the number of the highest in a variety of sensors. In the past 100 years, the development of temperature sensors has generally gone through the following three phases: (1) Traditional discrete temperature sensors (including sensitive elements); (2) Analog integrated temperature sensors/controllers; (3) Intelligent temperature sensors. At present, new types of temperature sensors in the world are developing from analog to digital, from integrated to intelligent, and networked.