sensor is a variety of parameters into the computer system, intelligent monitoring, control most of the front end. With the development of science and technology, digitalization and networking
increasingly widespread application of sensor, with its incomparable advantages in the traditional way has become the mainstream trends and technology. Next, we should combine the actual
with the requirements of some of the digital, networked sensors feature selection for your reference.
a number of applications and network cable channel temperature sensor to achieve on-line monitoring
1. Why should cable channel on-line monitoring
cable in the day-to-day production, life can be seen everywhere in the field, factories, laboratories usually a large number of cables on the cable channel, for the convenience of
wiring, maintenance, appearance. With the power of the people dependent on the growth of cable ditch the cable more and more, the probability of the occurrence of fire accidents have
increase accordingly. .
to the electric field, for example, with unit volume increases, a corresponding increase in the level of automation, the more the amount of cable More to come. A 200MW unit,
types of cables up to 200 ~ 300Km. A power plant project a 2 500Mw supercritical generating units parameters, reached by cable 3000Km.
coal-fired power plants in the event of a cable fire, causing serious damage. At present, in the construction of coal-fired power plants in operation, most of them are still using e-
burning cables, cable fire safety issue is particularly prominent.
home, according to the relevant Statistical data, in the past 20 years, China's power plant fire occurred in the cable 140 times, a total of the city from 1986 to 1992, the 7-year
between as many as 75 times. 24 power plant two or more cable fire, the individual plant up to 4 to 6 times. More than 70% of the cable fire
the losses caused by very serious, of which 2 / 5 of the fire caused serious damage. 1975 to 1985, as a result of the extension cable fire caused by burning
a major accident, 60, and then really cause indirect losses of 50 billion yuan.
Shanxi Shentou power cable channel as a result of a fire burning equipment and repair costs of more than 10,000,000 yuan.
1999 Mudanjiang years as a result of the second power cable channel fire, causing the entire power plant accident, direct or indirect losses amounting to 1,000 million.
In addition to the electric field, in large factories and mines, scientific research institutions in the engine room, workshop in the same cable channel there is the potential of fire. 2000 Beijing
high-energy physics of the electron-positron collider surveillance room on the cable channel as a result of the fire was forced down and seriously affected the conduct of scientific research.
the United States in 1965 to 1975 statistics at the 3285 electrical fire, fire on the wire and cable accounted for 30.5 percent, the direct loss of about
4000 million.
Japan had the power, steel, petrochemical, paper-making factories and enterprises, such as surveys, 78% of the units have been on fire lines, which endanger
large extent, accounting for 40% of the accident.
through the electric field of accident The analysis of the wire caused the fire trench as a direct result of cable in the middle in the first run lead to long-term aging, oxidation,
contact resistance is increasing, caused by overheated cables in the first burn insulation, and finally led to the cable trench fires.
a case of: Liaoning power Plant occurred over the first cable fire when fire-fighters tackled the fire just after leaving the scene when the first cable must
edge of breakdown, the recurrence of fire, burn a few people on the spot, resulting in injury accidents group.
two cases: Fulaerji power plant, testing personnel to find fault lines, the use of the morning breakdown capacitance method to find, after the noon break,
cable trench fires occurred, causing a major accident, such as cable configuration on-line monitoring system Accidents can be avoided entirely.
three cases: Hunjiang power plant # 2 recycled water in the middle in the first cable overheating, burning all the trench lines were forced to shutdown caused by the accident, it was learned that on
afternoon was in the middle of the first cable fault from more than 80 meters long on the shafts have been the smell of charred insulation taste , 19:00 minutes off the fire.
four cases: the second Mudanjiang power plant on June 28, 1998, as a result of a machine cycle of water over the first ignition cable in the middle of the cable ditch the
all the cables, causing the whole plant seven aircraft (passenger capacity of 1,030,000 kilowatts capacity) was forced to shut down the power plant accidents.
five cases: Shanghai Power Supply Bureau in 2001 as a result of cable among the first cable tunnel fires caused by overheating, a large area were burning cables, resulting in different departments of urban
plot blackout.
To sum up, cable trench fires was due in large thermal power cables hair in the middle. According to the analysis of the number of accidents found that electricity from
lead to overheating in the first accident, the slow pace of development, more time Long cable through the on-line monitoring system can prevent, eliminate the
types of accidents.
power plant in Jilin years ago summed up the experience, the use of artificial on a daily basis cables in the middle of the first tour gauging the temperature, according to the temperature change in
and analysis of its operation, to spend a lot of human, but to avoid a number of accidents, so that the cable channel on-line monitoring system for power plants
there to see the safe operation of great significance.
Although most of the power plant has long been at a lot of money for cable channel closure of the fire and general fire alarm, but the cable channel fire
still occur, These measures can only be played on fire after the electric wire alleviate the scope of the accident. Does not fundamentally reduce restrictions on the occurrence of fires. Jin
cable channel line-line monitoring is a fundamental limitation of the cable trench fires and effective way.
2. Traditional analog temperature sensors are not suitable for the cable channel temperature
traditional temperature measuring system The structure is usually:
each of the temperature sensor must go through the above link into the system. Therefore, there will be less as follows:
a) need to be hundreds of signal lines (often a communication cable to measure temperature from 200 to 300 points)
b) analog voltage signal during transmission easy to wear and tear, the impact of precision systems, transmission distance and near.
c) the system links more difficult to maintain. And the accuracy of the system vulnerable to the environmental impact is not easy to guarantee.
d) expensive. 200 to 300 points, 10 ~ 200,000
3. The application of new technologies to make the system more convenient for
with the advance of technology, digital, networked sensor technology has become the trend of the mainstream market. DALLAS U.S. companies DS18B20
digital, network-based temperature sensor using unique ideas and successful settlement of the Digital, networked and the cost of the conflict between. So that
the establishment of user-friendly, economic and reliable monitoring system possible.
LTM-8000 digital temperature and humidity environment monitoring system, using the U.S. company DALLAS advanced chip technology, combined with China's situation at the scene
status of the application of intelligent field bus technology, the entire system Only digital signal transmission, and sensors, acquisition module can be networked,
make the system more reliable, more convenient routing. Is structured as follows:
to digital, networked sensors based on the main features of the system:
a) less cable , The sensor can be together through the bus, only a few dozen sensors with a 3-core line. Greatly reducing the cable at the scene to facilitate
wiring at the scene.
b) due to the sensor output is digital signal transmission is no loss of accuracy, the system can ensure accuracy.
c) a small link in the system by the sensor directly from the collector, the system may be the failure of a small link to facilitate maintenance.
d) to adopt Advanced chip technology, a unique concept, as well as large-scale production, greatly reduces system costs and improve reliability.
long-British science and technology LTM-8000 digital temperature and humidity environmental monitoring system has been in power systems, oil, steel and many other fields for the success of
application. Such as:
? Cable channel on-line temperature monitoring and early warning fire
? Temperature high voltage switchboard on-line monitoring
? Electrical junction box and its on-line monitoring of temperature
? Fan and pump bearings on-line monitoring of temperature
? Storage (silos, cold storage, tank) to monitor
? Air-conditioning and Building Automation
4. System
configuration of the system is divided into parts as follows:
1.) PC:
: data processing and user interface
hardware requirements: Pentium 133/32M DRAM / 4.3G or above compatible IPC.
software: the choice of software configuration or custom procedures
2) communications from RS232/485 converter LTM-8520E, With over-voltage, over-current, surge, isolation, lightning protection
3) Field collection module LTM-8003E
features: two-tier communications network between Contact. 1 pair of PC RS-485 network, LTM-8003 as a sub-station modules; another
-class "bus line", LTM-8003 module as a collection center on the measurement of cable digital sensors as a sub-station .
hardware features: an over-voltage, over-current, surge, isolation, lightning protection
4) temperature sensor DS18B20
5. Digital, network-based temperature sensor DS18B20 introduced
the United States Dallas Semiconductor's DS1820 digital temperature sensor is the world's support for a "first-line bus," the interface temperature-
sensor. Bus line and the unique economic characteristics, so that users can easily set up sensor networks, in order to build a measurement system of the new
concept. DS18B20 a new generation of smaller, more economical and more flexible.
DS18B20, measuring temperature ranges from -55 ° C ~ 125 ° C, at -10 ~ 85 ° C range of accuracy ± 0.5 ° C, resolution of 0.0625. On-site
temperature direct "first-line bus," the digital transmission, each carrying an address, greatly reducing the number of cable systems, to improve the system
stability and anti-sexual.
correspond with the traditional concept, which, like a transistor is equivalent to traditional sensors: digital temperature sensor cpu bus protocol and then
mouth.
Second, the digital profile, network-based humidity sensor
United DALLAS "bus line" with its DS18X20 temperature sensor hardware interface simple, stable performance by the majority of the customers well, the British chief technology
also for the different needs of our customers to develop a range of products. But also found in the application of its communication protocols are more complex, less easy to use. The
at the scene and the demand for a wide range, DALLAS the product appears to be insufficient, DALLAS, after all, only a Device manufacturers, products and the practical application of the
there is still gap between the demand.
long-British science and technology based on customer demand, combined with years of experience in applications, the use of chip technology, new technologies, as far as possible be retained in the system DALLAS excellent
point of the premise, as far as possible to make up for its shortcomings. LTM8901 develop digital, networked degrees and humidity sensors.
1. The lack of humidity sensors traditional
traditional humidity sensors are basically divided into resistance and capacitance. And then through the transmitter voltage or current mode to connect to the mining
-set,
so:
a) interchangeable Sensors poor to Honeywell 3605L for Cases, each of its sensors attached to a table the amendment so that users
according to table the amendment. Very convenient to exchange.
b) analog voltage signal during transmission easy to wear and tear, the impact of precision systems, transmission distance and near.
c) the general need for additional transmitter power supply and power requirements of high accuracy, or affect the accuracy of the system.
d) the system links more difficult to maintain. And the accuracy of the system vulnerable to the environmental impact is not easy to guarantee.
e) difficult to calibrate the accuracy, so that better accuracy of the sensors, the price Expensive. VISSALA famous 3% of the accuracy of
as long as the sensor on every thousand dollars.
f) for each sensor to the transmitter, the transmitter to the collector at least two lines, multi-point system wiring is very difficult
2. Digital, networked sensors and humidity LTM8901 features of
a) good interchangeability, as amended smart technology, the sensor can be any swap.
b) due to the sensor output is digital signal transmission is no loss of accuracy, the system can ensure accuracy. And
a relatively short transmission distance.
c) use of low-power design, by the collector unified power supply, no additional power supply.
d) a small link in the system by the sensor directly from the collector, the system may be the failure of a small link to facilitate maintenance.
e) amendments to adopt intelligent technology, a unique concept, as well as large-scale production, greatly reduced costs and improved reliability.
f) less cable , The sensor can be together through the bus, only a dozen sensors with a 3-core line. Greatly reducing the line at the scene
cable for wiring at the scene.
3. Digital, networked sensors and humidity of the LTM8901 About
a) LTM8901 application interface connection
PC CPU only has a two-way I / O pins, according to the following circuit connection, you can communication with the LTM8901.
the MCU request I / O pin for the door OC output (or three-state output) and at the same time you have input. Most of today's MCU
the I / O pin has this feature.
b) LTM8901 typical characteristics of
? Operating temperature range: -25 ~ +85
? Humidity measurement resolution: 0.5% RH
? Humidity measurements Range: 1% ~ 99% RH
? Humidity measurement accuracy: ± 3.0% RH (typical)
? Backlash: ± 2.0% RH (typical)
? Year drift: ± 0.5% RH (typical)
? Response time: 5s (typical)
? Operating voltage range: 4.5 ~ 5.5V
? Appearance size: 70 × 50 × 25mm3
three or digital, networked sensors applications About the structure of
1. Digital, networked sensor applications, the structure of
applications are usually composed by the three networks:
a) sensor networks by a variety of sensors, the regional distribution of 200 to 300 meters.
b) fieldbus network from a variety of bus collector, such as: LTM8000 Department of temperature and humidity module collection and distribution of the region in 1000 ~
2000 meters.
c) local area network and wide area network, usually by a variety of PC and workstation, through the INTERNET to remote monitoring and control.
2. Digital, networked sensors and the structure of the application system Application diagram
four other digital, networked sensors and related products and applications About
1. Digital, networked counter DS2423
applications: multi-family program presentation
features: just a 3-core line will be able to water, electricity and gas meter data Transmission unit to the collector.
each unit for the single-chip design, RS485 network than the traditional way of low-cost, traditional pulse wiring simple way out of households.
2. Digital, networked Smoke Alarm
Application: Fire Monitoring
characteristics: the use of power transmission line alarm signal, just more than two sensor networking line.
3. Information button DS1991
Application: prepaid water meters, electricity meters, and so on, parking management systems, access control systems, Patrol System
characteristics: with the use of digital, networked sensors of the same network protocols can be easily integrated with the intelligent system area.
|
Testing instrument with the temperature
Sensor Principle and the working process