Sensors & Transducers
Contents
1. Unit Memory chips are used to store various types of transducer parameters for setting the address range 36 and so many important parameters According to different number of address not only can many sensors and transducers work through parallel bus but also multiple transducers communicate and acquire measured value based on a bus cable and no address conflicts or packet loss can be ensured Memory chip of 24C02 has 1K memory space which can provide ample space for the relevant parameters of transducer to store Calibration of the test data by the temperature can be completed by synchronous detection of ambient temperature of the sensor and transducer The transducer integrated by high precision temperature monitoring unit exports resistance values while putting out temperature of environment at the same time Practice has proved that the integrated temperature sensor DS18B20 has high detection speed high accuracy and good stability 11 12 so that the transducer can not only fully meet the demand of temperature correction but also as intelligent transducer put out multi parameter 2 5 UEWRTS Unbonded elastic wire resistance device is usually buried in the deeper location of the dam or a variety of architectural structures previously Value of resistances of cables is too much to be ignored because cables of sensors are generally long AS shown in Fig 3 Ri and R2 are resistances to be measured r1 r2 r3 r4 and r2. length the cable and Sensors amp Transducers Vol 178 Issue 9 September 2014 pp 34 39 cable resistance More than 32 sensors can be hooked up on the R485 Bus which has greatly improved the reliability of the system and reduced the intensity and difficulty of construction 2 A number of sensors distributed multi cable installation has been solved and convergence of separate cables can be achieved by using communication bus so transmission cables can be extended from 200 meters to more than 1200 meters 3 One to one monitoring mode making installation easy and maintenance free can achieve remote configuration of the parameters and dynamic monitoring sensors online and remotely 4 Local digital process makes the detection accuracy of the sensor fundamental guarantee Digitization and Parameterization make the adaptability and accuracy of differential resistance of the sensor higher which improves the applicability of the differential resistance sensors 5 Reliability and lifetime of the sensor will be greatly extended for there is no longer subjecting to over voltage threats by lightning counterattack This thesis has unique features in the signal conditioning and incenting of differential resistance of the sensor in particular the results put an end to the shortcomings of the differential resistance sensors and improve long term stability and detection accuracy of the differential resistance sensor in the scope of a
3. of measurement Crack variation mm Ea a ie ia is ia ia a oa am aa 2s 0s Pe faa am am as am Pa ars am are am are o 28 oe 2x am 20 38 Table 2 Result of measurement Temperature C value 19 85 19 87 20 35 20 02 20 02 Ez 22 56 22 58 23 84 22 56 22 89 ERE 14 00 14 04 14 59 14 34 14 24 Fig 7 shows the curve of crack length of UEWRTS for one month Gap variation mm Fig 7 Curve of crack length Fig 8 shows the curve of temperature of UEWRTS for one month Temperature C Time Fig 8 Curve of temperatures 6 Conclusions This paper explores the resistance of the sensor signal to achieve one to one place directly converted to high precision digital signal and put out by the RS485 Bus This paper focuses on the technology of signal conditioning and digital bus of resistance type sensor which is widely used in hydraulic construction bridges and other projects Results in the project has a great significance for it can be up to 32 sensor clusters achieve measurement to bus cascade greatly reduce the number of live cable laying and improve the measurement accuracy of the sensor and anti jamming capability According to the practice and the data argument it has been described in this paper that the transducer has the following five technical innovations 1 The application of differential resistance sensor is no longer troubled by
4. EWRTS Communication unit communicates with central sever through RS485 signals Measurement unit is the central part of the transducer It includes signal conditioning and AD acquisition unit and collection of temperature and storage unit As a 24 bit high precision AD acquisition chip ADS1232 transforms the analog signal coming from resistance devices into the digital signal The temperature acquisition chip collects the temperature and compensates for results The memory chip sets address and basic parameters for the transducer The transmission unit transmits the collected information and processing results to the remote server The working current is 25 mA UEWRTS of the hardware is embedded previously in different acquisition positions when the dam is building Five wires of the UEWRTS are extended from the underground to connect with the measurement unit Central Processing UNit MCU Collection of Temperature And Communication Power PE Store gt UEWRTS Unit Management i Signal Conditioning and AD Acquisition Measurement t ee ew booo Fig 1 Block diagram of collector 2 1 Central Processing Unit As the central processing unit microcomputer chip NECuPD78F0881 is responsible for receiving processing and distribution of peripheral signals of devices 9 NECuPD78F0881 is a kind of single chip researched and
5. Sensors amp Transducers Vol 178 Issue 9 September 2014 pp 34 39 Sensors amp Transducers 2014 by IFSA Publishing S L http www sensorsportal com WWww sensorsportal com Research and Application of Digital Transmission of Unbonded Elastic Wire Resistance Type Sensor Guilin Zheng Zhenjie Wang School of Power and Mechanical Engineering Wuhan University Wuhan 430072 China E mail glzheng whu edu cn wangzhenjie whu edu cn Received 22 June 2014 Accepted 29 August 2014 Published 30 September 2014 Abstract By analyzing different resistance values this collector of this article collects signal of the Unbonded Elastic Wire Resistance Type Sensor UEWRTS in brief acquisition embedded in the dams reservoirs and other hydraulic buildings and monitors the facilities in real time view The position of embedded sensors can be distinguished by setting the address and code The analog signal is one on one converted to digital signals through high precision analog to digital conversion and amplification chips by digitized transducers The digital signals are transported to the central server and the deformation of the structure is estimated by original data in the server Meanwhile it extended the transformer s effective measuring distance from normal analog 200 meters up to digitalized 1200 meters In situation of multi UEWRTS installed field all the output of the transformers can be connected in parallel to eliminate the cabl
6. a is packed and sent to the server After receiving confirm instruction from the server measurement unit and UEWRTS are powered off waiting for the next acquisition instruction If confirm instruction is not received from the server in a certain period of time data is sent in the second time If confirm instruction is still not got measurement unit and UEWRTS are powered off The transducer controlled by remote center of Personal Computer gets collection cycle by configuration according to the need of the project Transducers have four times for collecting daily 6 00 12 00 18 00 and 24 00 6 which can meet the needs of structural telemetry observations When necessary cycle detection can be configured fastest detection to one minute Initialization of hardware Pia Enter standby mode RS485 communication interrupt The check and address is true Get power on Collect the value of resistances and temperature Pack the data and transport to central server Get power down End Fig 4 The program flowchart 4 Stricture of Transducer Unbonded elastic wire resistance device is usually buried within the structure been observed so transducer supporting the design must be of small size rugged construction and can be buried In this article the digital transducer is divided into two parts of signal conditioning and microprocessor ci
7. developed by NEC Corp and its outstanding industrial properties make it stable and reliable in usage This chip has abundant resources 44 pins the built in single supply flash memory the built in watchdog six timers including two 16 and four 8 bit the internal integrated 8 channel 10 resolution AD acquisition module the internal integrated CAN controller In the hardware MCU commands and schedules other unit work which plays the role of control center by exchanging information 2 2 Power Management The transducer is responsible for collecting dam internal parameters periodically and the practical application of the working time is far less than the non working time Considering low power the power part of achieves function of controllable power by using the PMOS transistor switches to supply power on the acquisition part and UEWRTS Power is on under control in the acquisition time Power is off under control after acquisition time and transducer gets into standby mode waiting to be recalled by communication or the timer This design is conducive to extend sensor life while saving energy 35 Sensors amp Transducers Vol 178 Issue 9 September 2014 pp 34 39 2 3 Communication Unit As shown in Fig 2 ADM2483 is of enhanced isolation RS485 transceiver device which includes a three channel isolator a drive controller of tri state output and a receiver of three state input The chip has thermal shutdown protectio
8. e important significance to the lives of dwellers neighboring Previously through resistance sensor the resistance can be got with the indirect method that the line resistance is measured and its value is computed 5 Such method presents the shortcomings such as complex computation occupying a considerable amount of resources bringing great load to MCU Currently the output structure of UEWRTS is five wire system which is taken five lines of different colors as the cable http www sensorsportal com HTML DIGEST P_2349 htm Sensors amp Transducers Vol 178 Issue 9 September 2014 pp 34 39 resistance testing of UEWRTS and the output of mutual resistance measurement 6 7 This essay 1s taken five wire resistance as background high precision ADS1232 as signal processing component and NECuPD78F0881 as processing unit for intelligent signal processing parameterization and bus Meanwhile it takes DC DC as the power supply for the transducer to ensure full power isolation which can resist 2500 Vp back flashover over voltage Additional the output of the sensor photoelectric isolated RS485 signal also has the similar level of isolation voltage The transducer is designed in a metal rod body with 4 centimeters in diameter and 20 centimeters in length which is facilitate to bury According to the embedded micro power high performance microprocessor and the relative signal conditioning circuit the transducer can measure each
9. es to only one RS485 Bus as a twisted pair cable and a power line Applications of the transducer in several reservoir dams security monitoring system proof that is of high accuracy reliable strong anti interference solution for all the UEWRTS applications of the relative monitoring and measurement projects The collector has been applied in dam monitoring and achieved good results Copyright 2014 IFSA Publishing S L Keywords Unbonded Elastic Wire Resistance Type Sensor Wire resistance Five wire Transformer Wire resistance Concrete crack Concrete temperature 1 Introduction According to the function Unbonded Elastic Wire Resistance Type Sensor which is used to make long term observation to internal structural parameters of the buildings in all kinds of construction fields can be divided into the stress strain and infiltration pressure temperature crack and so on for observation to different physical quantities 1 2 Through the information collection of resistance sensor the effective analysis for hydraulic structure deformations and internal temperature changes of bridges or dams can be got With the 24 bit high precision Analog to Digital Converter a group of resistances from the sensor can 34 be made accurate measurement 3 4 According to these resistances which are taken into the formula of hydraulic structure detection the internal deformations of several of building fields can be monitored Such has mad
10. n function whose isolation voltage can reach 2500 V and instant high common mold suppression ability can reach 25 kV us These features allow the sensor to have reliable overvoltage over current protection and anti jamming capability In the application and installation system of a multi sensor bus form it plays an important role in protection of the entire communication bus In addition max emission current of the chip is only 2 5 mA Low power design not only conserves energy but also reduces the chip fever thus failures are avoided because of high fever an airtight system r ISOLATION BARRIER TxD DE DIGITAL ISOLATION TRANSCEIVER Fig 2 Schematic of internal serial communication 2 4 Measurement Unit 2 4 1 Signal Conditioning and AD Acquisition Unit Because UEWRTS is five ware structure ADS1232 is chose as acquisition chip ADS1232 is of dual channel high precision 24 bit ADC 10 Integrated programmable gain amplifier PGA is internal of chip ADS1232 which includes a third order modulator a fourth order digital filter and an internal oscillator Its internal structure is able to provide a complete front end solution for the resistance measurement sensor The resistance of a sensor changes from 40 Q to 120 Q According to the range measurement of the resistance of the sensor the full scale measurement range is set as 120 Q 2 4 2 Collection of Temperature and Storage
11. ng two wire resistance temperature detector JEEE Sensors J Vol 6 Dec 2006 pp 1454 1458 S Rescia V Radeka Effect of sense wire resistance on readout noise of large liquid argon time projection chambers in Proceedings of the IEEE Nucl Sci Symp Conf Rec 2009 pp 1932 1935 S Wendong Song J Z Xinjun Design of weighing transmitter in corn yield measurement system in Proceedings of the International Conference on Electric Information and Control Engineering ICEICE I1 2011 pp 324 327 Preliminary user s manual of 78 KO FC2 8 Bit single chip Microcontrollers NEC Electron Corp Tokyo Japan 2005 J Vedral P Fexa ADC and DAC testing using impulse signals in Proceedings of the IEEE Int Mixed Signals Sensors Syst Test Workshop IMS3TW 2011 pp 96 99 L Ping Z Yucai Z Xiangjun A design of the temperature test system based on grouping DS18B20 in Proceedings of the Second IEEE Conf Indust Electron Applic 2007 pp 188 191 Z Xuefeng L Weijie Z Lei Active thermometry based DS18B20 temperature sensor network for offshore pipeline scour monitoring using K means clustering algorithm Int J Distrib Sens Netw Vol 2013 2013 S K Sen T K Pan P Ghosal An improved lead wire compensation technique for conventional four wire resistance temperature detectors RTDs Meas J Int Meas Confed Vol 44 2011 pp 842 846 D Tuan Thanh K Jin Ho N Dung Duc A gateway fo
12. pplication of various types of construction industry So it has a very important reference Acknowledgements This work was supported by the National Natural Science Foundation of China No 61272114 and Marine Renewable Rnergy Projects of State Oceanic Administration 2013 of China No GHME2013JS01 References 1 S Huaizhi L Jinyou H Jiang Analysis and back analysis for temperature field of concrete arch dam during construction period based on JEEE Sensors J Vol 13 2013 pp 1403 1412 2 N M Mohan G Boby K V Jagadeesh Analysis of a sigma delta resistance to digital converter for differential resistive sensors IEEE Trans Instrum Meas Vol 1617 1622 2009 pp 1617 1622 3 M D Ram rez M J S nchez E C Reig Constant current drive for resistive sensors based on generalized impedance converter IEEE Trans Instrum Meas Vol 57 2008 pp 2290 2296 4 11 12 14 16 17 N M Mohan G Boby K V Jagadeesh A sigma delta resistance to digital converter suitable for differential resistive sensors in Proceedings of the Rec IEEE Instrum Meas Technol Conf 2008 pp 1159 1161 N Viet H C Phillip H Anco An analysis of the effect of wire resistance on circuit level performance at the 45 nm technology node in Proceedings of the Int Intercon Technol Conf 2005 pp 191 193 Maiti Tapan Kumar A novel lead wire resistance compensation technique usi
13. r multi device communication between Mechatrolink HI and RS 485 in Proceedings of the 12th International Conference on Control Automation and Systems ICCAS 12 2012 pp 294 299 W Yanfang M Wandui L Jinying A distributed rectifier testing system based on RS 485 in Proceedings of the Sth IEEE Conference on Industrial Electronics and Applications ICIEA I0 2010 pp 779 781 A Bernieri G Betta L Ferrigno Crack depth estimation by using a multi frequency ECT method IEEE Trans Instrum Meas Vol 62 2013 Z Zhiyun A Farhad Fiber optic laser speckle intensity crack sensor for embedment in concrete Sens Actuators A Phys Vol 126 2006 pp 107 111 2014 Copyright International Frequency Sensor Association IFSA Publishing S L All rights reserved http www sensorsportal com 39
14. rcuit design and the upper and lower parts are fixed by pins which is easy to fix within the tubular shell The thickness of shell is 5 mm of metallic materials As shown in Fig 5 and Fig 6 show the transducer can be directly buried near the resistance for its solid structure so it can complete digital transmission of analog sensors in the nearest place advanced isolation technology of power supply and digital output communication interface of the transducer has been taken electrical standards of capacity of counter attack voltage 2500 Vpp in RS485 and power supply against lightning can be achieved 15 grade IP68 of the waterproof from overall structure of the transducer can be reached capacity of bearing 400 kg cm geotechnical engineering requirements can be achieved Fig 6 Top view of internal structure 5 Practical Application and Analysis Taking one used in a large reservoir spillway as an example the transducer of the research the spillway has 18 resistive sensors buried in the construction process The buried sensors are divided into two categories first class for the deformation detection second class of observations for the temperature After the transducers are digitalized respectively corresponding addresses are address 01 to 15 for the first category address 16 to 18 for the second category Set resistances as R and Ro of a resistance sensor The usual method of detection is to calculate ratio Z of
15. resistance s value and its change within sensors and cable lines accurately With the coordination and administration of the microprocessor the transducer can achieve automatic measurement and complete correction In addition 8 all the parameters can be set remotely by RS485 communication The adoptive AD chip within the transducer achieves a high resolution of 24 bit The embedded temperature chip is applied to monitor and compare the environmental parameters of the measured structure With the AD conversion technology the transducer can wipe off the influence and error affecting on measurement results which are caused by different lengths of resistive sensors output cables and changes in environmental temperature In this context this paper takes the collector installed in spillway dam Wuhan Daoguan River Reservoir in China for example and the transducer collection and calculation of the resistance value through the embedded sensors to complete analysis the deformation and temperature of the dam 2 Part of the Hardware As shown in the Fig 1 the hardware includes five parts central processing unit power management unit communication unit measurement unit and five wire UEWRTS Central processing unit is made up of Micro Control Unit MUC which is the control center Degree of intelligence is depended on MCU Power management unit is used to support controllable energy for the communication unit measurement unit and U
16. s are all resistances of the cable lines It is because of five wire configuration resistances of the cables can be measured and errors are available to be avoided in the final results 13 Ri Ro Fig 3 Five wire Resistance 3 The Programming As shown in Fig 4 the program flowchart of the transducer and different sensors are distinguished by setting different addresses The number of address of sensors can be set from 01 to 32 by digital interface of RS485 Bus It should be noted that addresses of sensors must be assigned one to one before connecting with the bus and a same address of different sensors is not allowed After the address is assigned the RS485 cables of the transducers connect with the central server as a bus and master slave mode is used in communication between multiple sensors and central Sensors amp Transducers Vol 178 Issue 9 September 2014 pp 34 39 server and multiple sensors 14 Transducer responds to the central server according to the address of an instruction When the address of the command does not match the sensor takes no action The first type is the core of the instruction after receiving the order the transducer begins to collect temperature and resistance value then transfer the value back to the collection center When acquisition instruction is got from central service measurement unit and UEWRTS are powered on Values of temperature and resistances are collected and dat
17. two resistances Z 10000x R R and detection of resistance and R is 37 Sensors amp Transducers Vol 178 Issue 9 September 2014 pp 34 39 R R R When the dam is built the crack length of the dam is measured as basic value The data calculated by UEWRTS is actually crack variation 16 17 Set the crack variation as L T as the observed temperature f as minimum readings for the sensor b as resistance reference value for the temperature correction coefficient t as the temperature Ro as benchmark when UEWRTS is just out from the factory t as the temperature constant when R gt Ro to as temperature when constant R lt Ro Zo as baseline resistance ratio when resistance sensor was just out from the factory So detection function of temperature T and crack length L are as follows T tx R R 1 If R gt R t ty If R lt R t L f x Z Z bx T T 2 Formula of the second class is shown as 1 In this subject f b to ti Zo To and Ro are known quantities Formula 1 is used in second category and 1 and 2 in first category According to one day of sunshine and dam temperatures 4 observation time points 6 00 12 00 18 00 and the 24 00 are set and the data of following two tables were collected on July Tables 1 2 Change of the dam can be seen from different points in every day is not significantly which proves that the collector is working stable and reliable Table 1 Result
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