Improving Instrument Data Quality from Excavation sites to ... · Improving Instrument Data Quality...

International Conference and Exhibition on Tunnelling and Trenchless Technology 7-9 March 2006, Subang, Selangor, MALAYSIA

Improving Instrument Data Quality from Excavation sites to the Right person to make the Right Decision at the Right Time

GUAN HONG TAN, YE KONG POH

SysEng (S) Pte Ltd, Singapore [email protected]

CHANG KAAN LOH

Tritech Engineering & Testing (S) Pte Ltd, Singapore [email protected]

JAMES MW BROWNJOHN

University of Sheffield, United Kingdom [email protected]

ABSTRACT As Tunnels are constructed, the demand of the instrumentation monitoring of adjacent buildings and infrastructure increases. These methodologies are used to minimize the project risks and insurance costs. The real time monitoring and alert systems used for monitoring structural and soil movements will also increase. Experience in the Singapore Nicoll Highway excavation site had shown that the instrumentation system used were not effective, as they were difficult to sustain over long monitoring periods and finally ineffective due to its inherent system design, which do not take into account the realities of outdoor site operating conditions in the local context. In modern cities, the infrastructures for the Wire-less communications and Internet have more extensive coverage due to the wide consumer usage of Mobile phones and Internet access. By leveraging this open public infra-structure of Wireless Mobile and Internet, sensor readings in any excavation work can be integrated into a Ubiquitous Real Time Monitoring and Alert system for monitoring tunnels, buildings, structural and soil movements. With the shortening of construction schedules to be cost efficient and time to market, work progresses continuously for 24 hours a day and 7 days a week. Using these technologies, the users can now have these mission-critical information deliver to their personal mobile devices such as Mobile Phones and Pocket PCs. Today wire-less and Internet networks are available in businesses and homes to provide a ubiquitous experience, making these technologies more acceptable to the more traditional construction industry. This ubiquitous information demand will fully automate the monitoring and alert systems to send a higher quality sensor data to the right person to make the right decision at the Right Time for any actions to be taken. Keywords: Data Quality Ubiquitous Wireless Mobile Real Time Monitoring Alert

International Conference & Exhibition on Tunnelling & Trenchless Technology 7-9 March 2006, Kuala Lumpur

1. INTRODUCTION As tunnels and buildings are constructed, the demand of the instrumentation monitoring of adjacent buildings and infrastructure such as gas pipes, water and electrical utility distribution facilities increases. These methodologies are used to minimize the project risks and insurance costs. The real time monitoring and alert systems for structures and soil movements will also increase. Experience in the Singapore Nicoll Highway excavation site incident had shown that the narrow defined real time monitoring system used was not effective, as they were difficult to sustain and finally ineffective due to its inherent system design, as reported by Goh (2004) as their trigger alerts are only done via email. In construction sites, very few engineers carry wire-less devices with email access for alert when they are working in outdoor sites. That system only considers data downloads to but it neglects the important of sensor data upload system from the construction site to the central server. Without the timely sensor data available, no monitoring system can ever work, as it does not have the latest sensor readings. In modern cities, the Internet and Wire-less communication infrastructures have more extensive coverage and access due to the consumer usage of Mobile phones and Internet access. By leveraging this Mobile and Internet infrastructures, sensor readings in any excavation work can be integrated and continuously stream to a server into a Ubiquitous Real Time Monitoring and Alert system for monitoring tunnels, buildings, structural and soil movements. With the shortening of construction schedules, work progresses continuously for 24 hours a day and 7 days a week. The design must consider data upload and data download time critical timings, as both timings must be considered for a True Real Time Monitoring and Alert system. Using these technologies, the users can now have these mission-critical information deliver to their personal mobile devices such as Mobile Phones and Pocket PCs. Today wire-less and Internet networks are available in businesses and homes to provide a ubiquitous experience, making these technologies more acceptable to the more traditional construction industry. 2. THE STATE OF MONITORING SYSTEMS The Quality of any Monitoring system can be divided into two clusters of Quality of Sensor Installation and Quality & Consistency of the Timely Data Collection and Monitoring. Sensor manufacturers usually give the sensor installation methods. The established sensor manufacturers companies do have published guides on their websites. However, none of the manufacturers provide sensor quality checks when it comes to Electro Magnetic Interferences (EMI) on site for tracing the source of noise. It is common knowledge that such electrical noises do affect the sensor readings and sometimes cause false alerts. Some sensors are more sensitive to electrical noise, hence additional quality checks can be done to ensure that the sensor installation location has lower EMI noise. After installation of the sensors, there are three clusters of data collection methods of the manual, semi-automated and the fully automated real time systems. The manual and semi-automated systems form 80~90% of the manpower effort for a monitoring site and


the most difficult to sustain quality over long periods due to human management fatigue, manpower resignations and monotonous work environment. With such system, data entry errors and time delays are inevitable. With the aid of technology tools, reducing the dependencies of human intervention can minimize such errors and delays. This can be achieved by automating these repetitive processes. The Real Time Monitoring and Alert system is fully man-less. This is used for mission critical monitoring where the data is critical to ensure safety of the project and lower the risk of excavation failure. 2.1 MANUAL DATA COLLECTION The manual data collection is usually used where the instrument readings are required for analysis daily or weekly. The instruments are taken to the monitoring location; the readings are then recorded on a tabulated piece of paper showing person name, instrument identification number, and sensor location, time of recording and sensor values. The data is collected over the construction site and then passed back to a site office where the information is then copied into EXCEL spreadsheet for subsequent analysis by engineers. Sometimes these data is not processed immediately and only done in days delay as the re-keying the data is done manually. These two major sources of errors of manual data entry at site and manual re-keying data at the site office are common challenges in ensure timely data quality.

To improve the Quality of data, the manual system can be improved at the data processing and report generation process. Hence the only source of possible error will come from the manual data entry, which is unavoidable in any manual system even with continuous training. Fig 1 shows a manual data entry collection terminal. These data entry tools are widely used in other industries such in Sales, Property Management, Asset Management and Logistics. All these fall under the Mobile Work Force category. The solution uses a Mobile Phone or a Pocket PC as a data entry terminal, as shown in Fig 2. The use of Mobile phone is similar to the Short Message Text (SMS) method for entry, while the Pocket PC uses the touch screen for data entry. By repackaging the units with

Fig 1. Mobile Data Entry Terminal Fig 2. Mobile Data Entry Devices


water resistant cover, these units can be made more suitable for site work. The user goes on site and then manually keys in the instrument readings taken from the existing instruments like a dial gage, tape indicators. The readings are recorded and stored in the mobile device. At the end of the data collection round, the engineer then download the data from these mobile devices into a site PC for subsequent post processing. This method eliminates re-keying multiple data entries. It also minimizes human errors caused by clerical staff. Post processing calibration and analysis software can be added into the data processing stages so that the entire back end process can be automated. The users get the data in engineering format for decision-making. This will improve the data quality of the sensor information as it minimizes the human errors in the entire process except those of data entries. 2.2 SEMI-AUTOMATED DATA COLLECTION In the Inclinometer, the worker goes to the site and then lowers the inclinometer into a borehole. The readings are recorded and stored in an electronic readout box. One borehole can generate 400 data points inclusive of data verification. This amount of data is impossible to record manually per borehole. The worker then moves to another borehole to collect the data. At the end of the day, he then downloads the readout box data into the PC for processing and analysis. With this method, the bottleneck is the inclinometer readings of the first borehole are analyzed only after the readout box data is down load into a PC. This makes the time delay usually to a day. Any reconfirmation of readings has to be done only in the following day. Fig 3 shows a Geokon inclinometer and readout box. By adding a Wire-less GPRS modem with an embedded computer with the Readout box, the system can be upgraded into a semi-automated Real Time system. The data once stored in the readout box can be upload via GPRS to a central server for post processing and the user then get the inclinometer results in EXCEL format printouts.

Geokon Inclinometer

Fig 3. Semi-Automated Monitoring System with Wire-less and Internet communication support to achieve real time results form site

Inclinometer Graphs


In this system, the data from the Readout box is uploaded and then its raw data is automatically processed into inclinometer information via a central server. With this method, the data quality is always ensured with speed. Any error or repeat of readings is required, the Geotechnical Engineer will phone the site staff for a repeat reading for confirmation, incase the limits are breached and alerts have to send out. Any repeat of data collection in the same bore hole can be done within minutes as the processed inclinometer is available to the Geotechnical Engineer at the office which can be hundreds of kilometers within 10 minutes once the readings are taken at that borehole. This provides efficiencies to the Geotechnical Engineer for decision-making. 2.3 FULLY AUTOMATED REAL TIME AND ALERT SYSTEM Vibrating Wire Strain Gages (VWSG) are installed at the struts to measure the strut forces. In the past the real time system usually has no definition of the speed of information flow as some real time system are called real time only when the data is available at the central computer. This narrow definition neglects the critical time taken for the sensor readings to reach the computer. In the new Nicoll Highway Monitoring Contract C8255, the real time monitoring system defines that the strain gage readings from construction sites are monitored at every 10 minutes intervals and then upload to a website. Contracts of Singapore Circle Line C821 and C8242 also use this system extensively. Any breach of trigger limits, the system will automatically alert users through the mobile phones. The Geotechnical and Structural designers require the data for analyzing the behavior of the construction sequence and system. The data from the same VSWG sensors from sites can now be shared. The site staff now can make real time judgment during the excavation process, where the reaction time is very short for remedial action. Figure 4 shows the Real Time Monitoring and Alert system described by Tan (2004) using Machine-to-Machine (M2M) technologies. In this system, a wire-less General Packet Radio Service (GPRS) modem is used to transmit the data from the data logger to the central server. GPRS is used as an always-connected wire-less communication system. In this system, the monitoring and alert response time is in the order of minutes time scale. Real time is only meaningful when the actual sensor readings are taken and then send to the end-users in minutes. The GPRS data speed is 32,000 bps, which is very much faster than the GSM of 9,600 bps. This makes it suitable for wire-less real time monitoring and alert systems. The cost for using GPRS network depends on the amount of data transfer. The data logger is always connected to the central server. Data can be transmitted between the logger and server immediately when the last channel of sensor is measured. Hence, there is no connection time delay. The information can then be access by multiple users through the Internet. Through the use of Infocomm Technologies (IT) and Internet technologies in instrumentation and monitoring, engineers and decision makers could access to the data from their desktops or notebooks from anywhere in the world as mentioned by Alaghehbandian (2003) and Radulescu (2003). With Real Time Monitoring, the sensor data streams into the central server system at a high data rate. Traditional manual monitoring and alert system will experience user


Fig 4. Real Time Monitoring and Alert System from site sensor to user

information overload if a manual EXCEL spreadsheet based system is used. The computer system will slow down and manually the user cannot cope up with the high data rate. Hence a fully automated information flow system is a solution to overcome such a challenge.

In a Real Time Monitoring site in a excavation site, the Real Time Monitoring and Alert system monitors 810 Vibrating Wire Strain Gage (VW SG) and 44 Load Cells readings every 10 minutes. Two VW SGs monitor a strut with its individual temperature sensor and the Load Cell has 4 VW SGs and 1 Temperature sensor. Hence there is a total of 810 VW+ 810T + 44 x 4 VWSG + 44 T = 1840 sensor readings per 10 minute measurement cycle. The data rate is then 1840 x 6 x 24 = 264,960 data points per day! In an EXCEL spreadsheet system, the system will be overloaded. One solution to overcome EXCEL limitations is to use a more efficient software development platform such as C.

Fig 5. Sensor Level movements in time sequence At high-volume data rate in the real time system, any sensor noise or intermittent failure will cause unnecessary alerts. Fig 5 shows sensor level movements in time sequence. In Real Time Monitoring system, when the sensor level exceeds the Alert Trigger Level,


SMS will be sent out. However, if the sensor data only exceeds this threshold only once, it is most likely that this sensor reading contains false readings caused by noise. But on the other hand, if the sensor readings maintain above the Alert Trigger limit, then the sensor reading must trigger an SMS alert. With a manual system, the amount of data is insufficient and slow to provide a re-confirmation within minutes that there is a trigger alert as the manual data collection and analysis cycle time is usually in the order of hours. There is a need for a Monitoring System Design Strategy to overcome false alert and prevent user overload. In a manual system where the readings are done twice per day, there will be 3,680 readings per day. A 0.1% false reading means 4 false alerts. For the same 0.1% false readings in 264,960 real time data, it will mean 265 false readings, which are unacceptable for Quality data. Using a Real time monitoring and alert system will improve the Quality standards of the instrument service provider, as the user will have higher quality expectation in the whole process of sensor installation, cabling, grounding, system setup, commissioning and monitoring. A monitoring system deployed by the authors was used in an excavation site over 18 months and had 145,078,400 VWSG data collected. The total false alert readings over that period was 1,203 and they were mainly in the initial stage of familiarization by the contractor. This works out to be 8 false readings per million readings as a Data Quality index. As the sensors and electronics are used in outdoor environment, noise is a perpetual problem causing false SMS alerts. Noise can cause the sensor readings to increase or decrease from their actual values. Hence the alert levels have upper and lower bounds assigned to each sensor. 3. ELECTRICAL NOISE SOURCE CAUSING ERRORS IN SENSOR READINGS In any sensor installation noise checks can be done to ensure data quality when the values are recorded. Currently there are no tools available for checking the noise levels pickup by the sensors. This makes it very difficult to trace the source of false alerts. When sensor readings are recorded in data loggers, the tendency is to trust the data recorded is more accurate than those taken manually. This “blind” trust is based upon the notion that computers don’t lie! Fig 6 shows the analogue signal flow from the sensor, signal conditioner and then to be digitized in a data logger. When the sensor reading is recorded as 1.1, there is no indication about the noise contribution in the value. In the area of instrumentation, Signal to Noise ratio is an important parameter to check the Quality of measured data. In a Vibrating Wire sensor is made up of the vibrating wire and the drive coil as shown in Fig 7. Fig 8 shows the Vibrating wire sensor coil and the wire, which is enclosed in the steel protective enclosure.


Fig 6. Sensor Level movements in time sequence

Fig 7. Vibrating Wire sensor components Fig 8. Vibrating Wire Strain Gage Due to the construction of the coil, which also acts as the frequency measurement device, the same coil can also pick up other unwanted signals. Fig 9 shows the spectrum analysis measured at the out put of the coil. This means that the coils while behaving as a measuring coil is also a noise pickup coil itself. The electronics measuring circuit cannot differentiate between unwanted and wanted signal in this case if it happens to fall within the same frequency spectrum and no amount for filtering can help as filtering is essentially removes noise and does not improve accuracies. Some data loggers also provide the averaging function; this averaging is a statistical method and also increases the measurement time. The measurement method of the vibrating wire strain gage count pulse timing which is less prone to noise, but having signals, which can inject noise via overloads, and additional unwanted pulses can cause the data logger to measure lower or higher frequencies, hence in turn affecting the strain levels. This method of tracing noise spectrum give engineer the tools to investigate to trace the noise source to ensure the sensor data quality. There is no point measuring the sensor if the sensor readings have high noise content, making it unreliable to make any engineering judgment.


Fig 9 shows the Time Series and the Spectrum Analysis plots from an output of the drive coil without any excitation in a power station Fig 9 is an output from a vibrating wire strain gage coil signal recorded via a Digital Fast Fourier Transform Analyzer. In one Power station, strain measurements were required within the transformer room. Hence such advanced Digital Signal Processing Instrumentation technology was used to trace for a suitable sensor location where 50Hz magnetic noise was the lowest. Shielding using high permeability steel could be used with additional expense. With this tool, the sensor was relocated to a suitable strain-monitoring site with a lower noise level. 4. UBIQUITOUS ENVIRONMENT FOR DELIVERING PROCESED ENGINERING INFORMATION INTO THE HANDS OF THE END USERS AT THE RIGHT TIME In Fig 10, the users receive SMS text alerts on their mobile phones and they require a PC connected to the Internet to view and analyze the sensor historical trend. Fig 11 shows the SMS Alert text message while the time chart data is taken from a PC website screen shot. By linking the server data to the new generation of Mobile phones and Pocket PCs, which have larger graphical displays, the sensor charts can now be delivered as shown in Fig 11. Both mobile devices are growing tremendously and this platform makes it easier for the sensor data to be delivered in the Ubiquitous environment on the same unit.


Fig 10 SMS Alert on a mobile phone and screen shot of a PC Internet Web interface Fig 11 Crack sensor time chart displayed on an Ericsson Mobile phone and a HP iPAQ Pocket PC 5. BENEFITS OF UBIQUITOUS REAL TIME MONITORING AND ALERT SYSTEM With the Mobile devices as data entry terminals and adding Wire-less communication devices into the Inclinometer readout box, the monitoring system can now be made more efficient and getting data is timely with less human errors. This processed data can also be download to assigned users via GPRS so that the users on the move can obtain critical information for decision making globally. The main advantage of the Ubiquitous Real Time Monitoring and Alert system is obviously the Real Time alert where the site staff gets urgent data instantly when sensors exceed their limits. The other benefit is to provide the users and designers the actual on-


site forces acting on the struts when construction works progresses. This increases the productivity of the Geotechnical consultants by having their verification of the design via the Internet instead of visiting the site, which could be hours drive away. The data is also shared with multiple users and this makes collaborative work easier across the globe. This brings the important site data into the hands of the users via wire-less communication technologies of Mobile Internet, hence reducing the unproductive time of traveling to site to retrieve data or requiring a PC for data access. It also helps to raise the Data Quality standards as it impose new challenges to provide Reliable Data timely to all stake holders of the project. 6. CONCLUSION With the use of Mobile devices, Internet and Wire-less communications, IT technologies, the entire monitoring system can be made more efficient and less prone to human errors if the appropriate technologies are used. Experiences have shown just the use of data loggers for data collection do not necessary lead to a comprehensive real time monitoring. Such use of data loggers are mainly used for design verification, monitoring, investigation works and research. Only with the deployment of other M2M technologies of wireless communications, Mobile Internet devices and services, these monitoring systems have evolved into a Ubiquitous Real Time Monitoring and Alert systems, where the information are needed in a matter of minutes to give the Right Data to the Right Person to make the Right Decision at the Right Time. Using available proven technologies, Mission Critical Real Time Monitoring and Alert systems are used to monitor and deliver information from the sensor until the end users in a matter minutes, rather than hours or days. When the sensor readings exceed their predefined limits, the system automatically sends SMS alerts to multiple users within minutes. These alerts can also be used in the manual collection work as the data processing and alert can also be made automated. The Ubiquitous system delivers the important information onto the mobile devices of the users. This compression of the total delivery time, from the remote site sensor to the user, is useful to inform site problems immediately for critical projects so that preventive actions can be mobilized faster. It gives users more reaction time to organize, to investigate and to prevent collapses or failures rather than having data to confirm that the site had problems. With the wider acceptance of Mobile Internet technologies by the consumer sector, the relevant technologies have become easily accessible for wider deployment in the civil engineering sector. This forms a new cluster of Ubiquitous mission critical monitoring and real time alert systems based upon the M2M technologies.


REFERENCES Goh Chin Lian and Woon Wui Teck. The Straits Times, 13th August 2004, Page H6. “Judge notes lapses by sub-contractor”. Tan G.H. Ng T.G. and Brownjohn, J., 2004. Real Time Monitoring and Alerts Systems for Civil Engineering Applications using Machine-to-Machine Technologies, International Conference on Structural and Foundation Failures, 2 – 4 August 2004. Alaghehbandian, A., Abe, M. and Fujino, Y., 2003. An Internet Orientated Platform for Structural Health Monitoring, Proceedings of First International Conference on Structural Health Monitoring and Intelligent Infrastructure, 13-15 November 2003, Tokyo, Japan, pp. 339-344. Radulescu, D.C., Radulescu, C. and Sereci, A.M. ,2003 Structural health monitoring 24/7 broadcasting system, Proceedings of First International Conference on Structural Health Monitoring and Intelligent Infrastructure 13-15 November 2003, Tokyo, Japan, pp. 971-976

Improving Instrument Data Quality from Excavation sites to ... · Improving Instrument Data Quality...

Documents

Transcript of Improving Instrument Data Quality from Excavation sites to ... · Improving Instrument Data Quality...