New Development
trend of Intelligent temperature Sensor
After
the 21st century, the intelligent temperature sensor is developing rapidly in
the direction of high precision, multi-function, bus standardization, high
reliability and security, development of virtual sensor and network sensor, and
the development of a single-chip temperature measuring system.
1. Improving the accuracy and resolution of
temperature measurement
In the
mid-1990s, the first intelligent temperature sensor was introduced, and the
8-bit A/ D converter is adopted. The temperature measurement accuracy is low
and the resolution can only reach 1 ° C. At present, a variety of high-precision and high-resolution
intelligent temperature sensors have been introduced in the world. The 9-12-bit
A/ D converter is used, and the resolution is generally in the range of
0.5-0.0625 ° C. The DS1624 high-resolution intelligent
temperature sensor developed by the DALLAS semiconductor company in the United
States can output 13-bit binary data with a resolution of up to 0.03125 ° C. In order to improve the conversion rate of the multichannel
intelligent temperature sensor, the high-speed successive approximation A/ D
converter is adopted in the chip. Taking the AD7817 type 5-channel intelligent
temperature sensor as an example, the conversion time of the remote sensor is
27us and 9us, respectively.
2. Add test function
The
testing function of the new intelligent temperature sensor is also increasing.
For example, DS1629 single-wire intelligent temperature sensor adds real-time
calendar clock (RTC), to make its function more perfect. DS1624 also adds
storage function, which can store user's short message by using 256 bytes
E2PROM memory inside the chip. In addition, intelligent temperature sensors are
developing from single channel to multichannel, which creates good conditions
for the research and development of multichannel temperature measurement and
control system.
The
energy temperature controller is developed on the basis of intelligent
temperature sensor. Typical products are DS1620,DS1623,TCN75,LM76,MAX6625. The
intelligent temperature controller is adapted to all kinds of micro controllers
to form an intelligent temperature control system, and they can also work
independently from the micro-controller and form a temperature control
instrument by themselves.
3. Standardization and Standardization of bus
Technology
At present, the bus technology of intelligent
temperature sensor has also been standardized and standardized. The main buses
used are single-wire (1-Wire) bus, I2C bus, SMBus bus and spI bus. As a slave,
the temperature sensor can communicate with the host computer through the special
bus interface.
4. Reliability and safety design
Most of the traditional A ≤ D converters use integral or
successive comparison conversion technology, which has low noise tolerance and
poor ability to suppress aliasing noise and quantitative noise. The new
intelligent temperature sensor (such as TMP03/04,LM74,LM83) generally adopts
high performance Σ-Δ A ≤ D converter, which can convert analog signal into digital signal
with high sampling rate and low sampling resolution, and then improve effective
resolution by using oversampling, noise shaping and digital filtering
technology. Σ-Δ A ≤ D converter can not only filter out quantitative noise. Moreover,
the accuracy of the peripheral components is low. Because of the digital
feedback mode, the misalignment voltage and zero drift of the comparer will not
affect the conversion accuracy of temperature. The intelligent temperature
sensor has the advantages of strong ability to suppress serial mode
interference, high resolution, good linearity and low cost.
In order to avoid malfunction when the
temperature control system is disturbed by noise, a programmable``f Aultqueue''
counter is provided in the interior of 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 exceeds the upper and lower
limit. The interrupt end can only be triggered if the measured temperature
continuously exceeds the upper limit or is lower than the lower limit and
reaches or exceeds the set number of times n(n=1~4). If the number of failures
fails to meet the above conditions or the fault does not occur continuously,
the fault counter is reset without triggering the interrupt terminal. This
means that, assuming n=3, no accidental noise interference will affect the
normal operation of the temperature control system.
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 remote sensor). Max6654
also has the choice of "parasitic impedance cancellation" (PArAsitic
ResistAnce CAncellAtion, abbreviated as prc) mode, which can offset the temperature
measurement error caused by the lead impedance of the remote sensor, even if
the lead impedance reaches 100ohm. Nor will it affect the measurement accuracy.
Remote sensor leads can use ordinary twisted-pair wire or twisted-pair wire
with shield layer.
5.Virtual temperature Sensor and Network
temperature Sensor
(1)Virtual sensor
The virtual sensor is based on sensor hardware
and computer platform and is developed by software development. The calibration
and calibration of the sensor can be completed with the software to achieve the
best performance index. Recently, U.S. B & K has developed a software-based
TEDS-based virtual sensor featuring a unique product serial number per sensor
and a floppy disk that stores data on the sensor to be calibrated. When in use,
the sensor is connected to a computer through a data collector, the product
serial number of the sensor is first input from a computer, the related data is
read out from the magnetic disk, and then the inspection of the sensor, the
reading of the sensor parameters, the sensor setting and the recording
operation are automatically completed.
(2)Network temperature sensor
The network temperature sensor is a new
generation of smart sensors that include a digital sensor, a network interface,
and a processing unit. The digital sensor first converts the measured
temperature into a digital quantity and then sends it to the micro-controller
for data processing. And finally, the measurement result is transmitted to the
network so as to realize data exchange and resource sharing among the sensors,
between the sensor and the actuator, between the sensor and the system, and
when the sensor is replaced, the calibration and the calibration are not
required, so that the "Plug & Play" can be realized, so that the
user is greatly facilitated.
6.Single chip temperature measurement system
System On Chip is a science and technology
product in the 21st century. It is the integration of a system or sub-system on
the chip, and the integration level will be as high as 108-109 elements/
pieces, which will bring an epoch-making progress to the IC industry and the IC
application. The predictions made by the Semiconductor Industry Association
(SIA) for the integration of the system are presented in Table 1. At present,
some famous IC manufacturers in the world have started to develop a single-chip
temperature measuring system, which is believed to be ready in the near future.