How To Use A Fibre Optic Temperature Sensor

Transcription

1 Fibre Optic Distributed Temperature Sensing System

2 Introduction of FODTS The Fibre Optic Distributed Temperature Sensing (DTS) technology using Raman-effect was initially developed in 1980s at Southampton University in England. The DTS method was based on Optical Time-Domain Reflectometer (OTDR) technology. Physical environment such as temperature, pressure and strain affect fibre glass (Silicon Dioxide) internal structure and locally change the way light transverse in the fibre. Thermal effect induces lattice oscillations. When light falls onto these thermally excited molecular lattice, light scatters called Raman scattering. The amplitude of the scattered light is directly related to the intensity of the thermal excitation. The position of the temperature measurement point can also be determined accurately by measuring the round-trip propagation time light / scattered light. This is illustrated in Fig. 1. Fig. 1: Raman-effect to measure temperature points of fibre cable Features of DTS The system detects all temperature sensing points automatically in real time along a fibre optic cable. Alarm signals and reports will be generated if critical temperature limits are exceeded which may mean the operations condition of the host infrastructure is impaired. Database of temperature data, tagged with location and time, are available for use to generate reports and to conduct analysis. Problem areas can be quickly detected and valuable information can be obtained to assist prompt decision making. Our DTS solution provides maximum flexibility to different applications. Different sections of the host system can be defined according to client s requirements (e.g. different sections of power cables, busbars) as different monitoring zones. Individual settings for alarm levels can be applied to different zones to cater for different operations conditions. The DTS user interface is simple and user-friendly. Easy and quick overview of each temperature sensing point is provided. The fibre optic cable route layout can be overlaid on top of the host infrastructure figure to provide instant view of the problem location. Each sensing zone shows in different colour according to real-time surface temperature. Temperature graphs and tables can be customised to facilitate the decision making process.

3 The Science Behind FODTS The technology of our Fibre Optic Distributed Temperature Sensing system involves sending a pulsed laser to an optical fibre and then measures the backscattered light as the pulse propagates through the fiber. The backscattered light is caused by changes in density and composition as well as molecular and bulk vibrations. When light pulse travels in a homogeneous fibre cable, the intensity of the backscattered light decays exponentially with time. The distance of the temperature measurement point can be determined from the time-of-flight of the returning backscattered light. Fig. 2: The technology of FODTS Fig. 3: The Raman backscattering components The Raman backscattering components are caused by thermally influenced molecular vibrations from the propagating light pulse. Thus, their intensity depends on temperature. The Raman backscattered light have two components that lie symmetric to the Rayleigh peak: the Stokes peak and Anti-Stokes peak. The Raman Anti-Stokes Band Components The Intensity (IAS) correlates to temperature. The time of flight of the backscattered light provides information on distance travelled and hence the location of the temperature point.

4 Application One Power Supply Network Application Two In-Building Electrical System Fault Early Stage Detection of Power Cable Faults Avoid Fire Hazards caused by In-Building Electrical Faults The ampacity of a power cable is limited by hightemperature regions (hot spots) that occur along the cable. Optimum use and temperature profile control of power cables can prolong the life of a cable and avoid insulation break downs. Major shopping malls and hotels attract significant people volume utilizing various facilities of the malls and hotels. Theses malls and hotels all require complex and sophisticated electrical systems to support the operations of air-conditioners, heaters, lighting, display, lifts, appliances and building management system. Failures of electrical systems will lead to major interruption of normal operations and cause inconvenience to customers. Further, electrical fault may cause fire to the building and endanger customers of shopping malls and hotels. Depending on the types of insulation material, typical maximum temperatures at the surface of the conductor range from 60 C to 90 C, with an ambient air temperature of 30 C. Monitoring of cable temperature enables early-stage detection of potential cable fault; maximize ampacity of cable system and optimise useable life of cable. Our DTS solution supports real-time detection of hot spots along a cable. Further, the built-in time history temperature analysis capability provides temperature gradients of different sections of a cable to enable prompt identification of potential problems. Our DTS solution provides 24x7 surveillance of inbuilding electrical system including busbars, LV feeder cables and other power equipment. Electrical fault caused by degradation of system can be identified by abnormal change in temperature profiles of the system. The powerful analysis tools of our DTS solution is able to pin point the location and intensity of the abnomality. Appropriate maintenance action can be carried out prior to the occurrence of a fault. When the temperature exceeds the pre-determined limit, alarm system will activate immediately. Fig. 4: A section of a cable has abnormal temperature rise Fig. 5: Busduct temperature monitoring system

5 Application Three Oil & Gas Industries Gas & Oil Pipeline Leak Detection The inherited continuous sensing ability of DTS makes it the ideal solution to quickly detect leak events by monitoring the temperature profile along the complete length of pipeline. For gas line, the escape pressurised gas produces a local cold zone at the surface of the leaked pipe due to Joule- Thompson effect. The change in temperature at the leaked location is immediately detected and measured by our DTS solution to locate precisely the leak. Application Four Heating Ventilation Air Conditioning (HVAC) Tunnel Temperature Monitoring & Ventilation Control Effective tunnel ventilation is necessary to bring fresh air to passengers at the stations and inside the trains. Tunnel temperature monitoring and control enable the operator to optimise the air-flow volume and temperature in the tunnel. The underground railway ventilation system comprises of Ventilation Shafts (above ground structure) which serves as Inlets and Outlets for air movement. A schematic diagram of the tunnel ventilation system is illustrated in Fig. 7. Ground Level 2130m Burst in pipeline DTS Fibre Cable Ventilation Shaft Ventilation Shaft Air Inflow Air Outflow DTS Fibre Optic Cables - attached at different heights of tunnel installation location of DTS FO Cables Temperature (degree C) DTS Temperature - distance plot Drop in temperature at leak location Distance (m) Fig. 6: DTS solution for gas pipeline leak detection Fig. 7: DTS solution for tunnel temperature monitoring Why use DTS to monitor? DTS fibre optic cable is cost effective, immune to interferences in the tunnel & basically maintenance free; Oil pipeline leak will however result in a rise in temperature at the point of leak. In both cases, our DTS solution is able to preciously identify the leak location promptly thereby saving significant cost of leak and time in identification of leak location. DTS provides 24x7 monitoring of tunnel temperature and store up to 1-year data for further analysis; Our DTS can integrate with tunnel ventilation control system to provide full feedback control system supporting both real-time environment data and time-series trend analysis data.

6 Application Five Water Supply & Waste Water System Application Six Hydrology and Geology Hydrology & Geology Water Supply & Waste Water System Storm water is produced from rain (mainly) and sprinklers or other means, that falls and is transported over road / pavement surface into local storm water drain. The storm water will be finally discharged into river, stream or sea. The discharged storm water is UNTREATED. Waste water is any type of water that have been utilised and the utilisation has adversely affected the quality of water. Examples are water that is discharged from households (sanitary), offices and industries. Waste water typically is TREATED before it is discharged. DTS has a wide range of applications in hydrology and geology. Measurement of temperature is always necessary in geological and hydrological processes. In most applications, it is required to measure gradients in temperature in time and space. Governments, Universities and Research Institutions have used DTS to successfully collect temperature data from various geological and hydrological locations including lake, river, underground water streams and surface water streams. Ideally storm water and waste water must be separated. If waste water runs into storm water d ra i n a ge syste m, t h e n i t w i l l ca u s e s e r i o u s environmental and health hazards. DTS solution has been widely used to detect illicit connections in storm sewer systems. The continuous temperature measurements along the in-sewer fibre optic cable creates a detailed representation of temperature anomalies due to illicit discharges. Illegal disposal of waste water Storm water pit e abl c c ipe i e t p op r p pi ter bre ate wa TS fi m w e D tor ag S ew Illegal waste water causes rise in temperature S Fig. 8: DTS solution for illegal disposal of waste water Fig. 9: DTS fibre optic cable along a river Water temperature is of importance to ecological processes. DTS fibre cable installed along the river provides unprecedented precision and resolution of temperature readings along the river. Examples of applications - Understanding and monitoring of stream-aquifer; - Understanding of estuary-aquifer interaction; - Surveillance of aquatic environments; - Computation of energy balance for evaporative loss; - Tracing of convection process; - Understanding of fractured-aquifer hydraulics in boreholes

7 Introduction to OSL Our System Specifications Items Spec DTS System Input Voltage 240 VAC +/- 6% or 24 VDC +/- 0.5% Measurement Accuracy ±1 C Measurement Interval From 0.2m to 1.0m No. of Measurement Channels & Max. Measurement Distance Max. 4 channels (4 separate fibre optic cables) 4km - 10km Update Cycle Time Per Channel 8 seconds per Cycle Measurement Temperature Range -30 C to 105 C Communication Interface Ethernet, RS232, RS485, USB, HDMI System Alarms Comprehensive range of alarms covering all key components Temperature Data Alarms (per Channel) High Temperature Alarm; Temperature Increment Alarm; Zone Temperature Difference Alarm; and other customisable alarms EMI Emission Physical Dimensions of DTS Equipment Operational Environment of DTS Equipment Client Server Design Resistant to EMI Design conforms to IEC mm (w) x 600mm (d) x 1800mm (h) Temperature: C; Relative Humidity: 25-75% DTS system adopts client server design. Temperature data are stored in real-time on a server which can be access remotely from the client module. About Us Optical Sensing Limited (OSL) is a Hong Kong based company. We are located in Science Park, Shatin. We specialise in research, development, manufacture, marketing and provisioning of advanced monitoring / surveillance solutions including Distributed Temperature Sensing solution. We have in-depth knowledge of the operational requirements of different industries; and how our solutions can be deployed to greatly enhance our Clients operations. We provide full service and comprehensive after-sales support. Our solutions have wide range of applications in power network, gas / oil pipeline, sewage system, in-building electrical systems, HVAC applications and geology / hydrology. Contact Us Optical Sensing Limited Tel: (852) / Fax: (852) info@opticalsensing-hk.com Website: Address: Unit 107B, 1/F., Enterprise Place, No.5 Science Park West Avenue, Hong Kong Science Park, Shatin, Hong Kong

8 All rights reserved. No part of this company profile may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or by an information storage and retrieval system without written permission from Optical Sensing Ltd. OSLPB201311