WIRELESS SENSOR NETWORK PERFORMANCE IN HIGH VOLTAGE AND HARSH INDUSTRIAL ENVIRONMENTS

Transcription

1 WIRELESS SENSOR NETWORK PERFORMANCE IN HIGH VOLTAGE AND HARSH INDUSTRIAL ENVIRONMENTS INAM-UL-HAQ MINHAS This thesis is presented as part of Degree of Master of Science in Electrical Engineering Blekinge Institute of Technology July 2010 Blekinge Institute of Technology School of Engineering Department of Signal Processing Supervisor: Professor Wlodek Kulesza Industrial Supervisor: Jonas Neander Examiner: Professor Wlodek Kulesza

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3 Abstract The applications of wireless sensor networks, WSN, are getting popular in the different areas reaching from daily usage to industrial usage. The performance evaluation of WSN deployed in industrial and high-voltage areas is receiving a great attention and becoming an interesting area of research. This thesis addresses the performance issues of WSN in high-voltage and harsh industrial environments. This study has been carried out at the facilities of High-Voltage Test Lab of ABB. Typically, wireless sensor network contains wireless field devices (nodes) connected to a base station via a central gateway. The gate way centralizes information gathered and processed by the nodes. The nodes can communicate with each other and with the gateway via radio wave. The quality and usability of the data sent by WSN can be degraded due to the packet loss and delay. In the presence of high-voltage, the electromagnetic interference, EMI, can affect the performance of WSN. In this study the performance of WSN is evaluated in terms of packet loss and delay. We also focus on the effect of EMI on hardware devices as well as on signal transmission. EMI was expected at wide frequency band due to harsh industrial and high voltage environments. It was expected that EMIs could increase a bit error rate and/or packet loss. The EMI can also change the sensitivity of the nodes. For the performance evaluation of WSN network throughput, latency, path stability, data reliability and average value of the received signal strength indicator, RSSI, are used and measured. The results show that the electromagnetic frequencies of harsh industrial and high voltage environments affect the wireless sensor network performance. Keywords: WSN, EMI, Latency, Path Stability, Data Reliability, RSSI. 3

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5 Acknowledgements All praises and thanks to Almighty ALLAH, the most beneficent and the most Merciful. I would like to thank my supervisor Wlodek Kulesza from Blekinge Institute of Technology, Jonas Neander from ABB Västerås for their support and kind advices during my work. I would like to thank all ABB CRC Västerås crew. I would like to acknowledge all who played a role in my project either directly or indirectly. Specially thanks to my brother Minhas Tahir Nawaz and my Parents. 5

6 TABLE OF CONTENTS 1 INTRODUCTION USED TERMINOLOGY THESIS STRUCTURE REVIEW OF RELATED WORKS PROBLEM STATEMENT THEORETICAL BACKGROUND OVER VIEW OF USED TECHNOLOGY WIRELESS HART TECHNOLOGY TESTS SCENARIOS AND SET UPS TEST SCENARIOS Non-Industrial Environment Tests Industrial Machine Lab Environment Tests DC High Voltage Environment Tests AC High Voltage Environment Tests - High Voltage Transformer EMI Test in High Voltage and Machine Lab TEST RESULTS AND ANALYSIS NETWORK STATISTICS Analysis of Non Industrial Environments Test Results Analysis of Industrial Machine Lab Test Results Analysis of DC High Voltage Environment Tests Results Analysis of AC High Voltage Environment Tests Results PATH STATISTICS Analysis of Non-Industrial Environment Test Results Analysis Industrial Machines Lab environment Test Results Analysis DC High Voltage Environment Test Result Analysis of AC High Voltage Environment Test Results AVERAGE RSSI VALUE FOR TRANSMISSION ANALYSIS OF EMI TEST RESULTS Spectral Measurements for EMI in 2.4 GHz band Frequency Measurements of EMI in 2.4 GHz Frequency Spectrum in DC High Voltage RESULT ANALYSIS FOR COMPLETE TEST Non Industrial Environments Test Industrial Machines Lab Environment Test AC High Voltage Environment Test All Test Result Summary CONCLUSIONS AND FUTURE WORK REFERENCES APPENDIX

7 LIST OF FIGURE FIGURE 1: SMARTMESH MOTE AND NETWORK MANAGER FIGURE 2: NETWORK TOPOLOGY FOR NON INDUSTRIAL TEST FIGURE 3: ABB LAB WITH TWO MOTOR MACHINES FIGURE 4: MACHINE LAB NETWORK TOPOLOGY FIGURE 5: DC HIGH VOLTAGE TEST SETUP FIGURE 6: THE BLOCK DIAGRAM FOR DC HIGH VOLTAGE TEST CIRCUIT FIGURE 7: THE BLOCK DIAGRAM FOR TRANSFORMER AND METALLIC CAGE FIGURE 8: THE VOLTAGE TEST ALONG TIME FOR HIGH VOLTAGE DC TEST FIGURE 9: BLOCK DIAGRAM OF AC HIGH VOLTAGE TEST SETUP FIGURE 10: AC HIGH VOLTAGE TEST SETUP FIGURE 11: THE CIRCUITRY OF AC HIGH VOLTAGE TEST SETUP FIGURE 12: AC VOLTAGE WITH RESPECT TO TIME FIGURE 13: STABILITY AND LATENCY GRAPH OF NONINDUSTRIAL ENVIRONMENT TEST FIGURE 14: DATA PACKET TRANSMITTED AND FAILED PER TIME SLOT FOR NONINDUSTRIAL ENVIRONMENTS TEST FIGURE 15: STABILITY AND LATENCY GRAPH OF INDUSTRIAL MACHINE LAB TEST FIGURE 16: DATA PACKET TRANSMITTED AND FAILED PER TIME SLOT FOR MACHINE LAB TEST FIGURE 17: STABILITY AND LATENCY GRAPH OF DC HIGH VOLTAGE TEST FIGURE 18: DATA PACKET TRANSMITTED AND FAILED PER TIME SLOT FOR DC HIGH VOLTAGE TEST FIGURE 19: THE VOLTAGE VS. STABILITY AND RELIABILITY FIGURE 20: STABILITY AND LATENCY GRAPH OF AC HIGH VOLTAGE TEST FIGURE 21: DATA PACKET TRANSMITTED AND FAILED PER TIME SLOT FOR AC HIGH VOLTAGE TEST FIGURE 22: PATH STABILITY FOR MODE TO AP IN NONINDUSTRIAL ENVIRONMENT FIGURE 23: PATH STABILITY FOR A MODE TO AP IN MACHINE LAB TEST FIGURE 24: PATH STABILITY FOR A MODE TO AP IN DC HIGH VOLTAGE TEST FIGURE 25: PATH STABILITY FOR A MODE TO AP IN AC HIGH VOLTAGE TEST FIGURE 26: AVERAGE VALUE OF OUTPUT POWER PER TIME SLOT FOR TRANSMISSION IN NON INDUSTRIAL TEST FIGURE 27: AVERAGE VALUE OF OUTPUT POWER FOR TRANSMISSION IN MACHINE LAB TEST FIGURE 28: AVERAGE VALUE OF OUTPUT POWER FOR TRANSMISSION IN DC HIGH VOLTAGE TEST FIGURE 29: AVERAGE VALUE OF OUTPUT POWER FOR TRANSMISSION IN AC HIGH VOLTAGE TEST FIGURE 30: THE 2.4 GHZ SPECTRUM WHEN MACHINES WERE IN OFF STATE FIGURE 31: 2.4 GHZ SPECTRUM WHEN MACHINES ARE OPERATING FIGURE 32: 2.4 GHZ SPECTRUM DC HIGH VOLTAGES TEST

8 LIST OF TABLE TABLE 1. COMPARISON OF WIRELESS HART AND ZIGBEE TABLE 2. OSI LAYER MODEL AND WIRELESS HART STACK TABLE 3. COMPARISON OF STABILITY AND LATENCY - OFF TABLE 4. COMPARISON OF STABILITY AND LATENCY- ON

9 LIST OF ABBREVIATIONS ACK CSMA DSN DSSS EMC EMI FHSS ISM IEMI MAC MIC PHY RSSI TDMA WSN PkRx PkTx Acknowledgment Carries Sense Multiple Access Distributed Sensor Networks Direct Sequence Spread Spectrum Electromagnetic compatibility Electromagnetic Interference Frequency Hopping Spread Spectrum Industrial, Scientific and Medical Intentional Electrometric Interference Medium Access Control Message Integrity Code Physical layer Received Signal Strength Indicator Time division multiple access Wireless Sensor Network Total number of packets received by network motes. Total number of packets transmitted by network motes 9

10 1 INTRODUCTION A wireless sensor network (WSN), consists of wireless field devices called nodes and a central base station. These sensor nodes communicate wirelessly with each other and also with the base station, within their radio communication range. A sensor node is made up of a microprocessor, a small amount of memory, a radio transceiver and one or more sensors. History of sensor networks shows the military application as the beginning of this technology. Distributed Sensor Networks (DSN) project from Defense Advanced Research Projects Agency (DARPA) of the USA during 80 s is one of the first known steps for modern sensor networks. WSN has been lately used and developed not only in the military field, but also in civilian, commercial, medical and industrial application areas. In today s life WSNs are used in monitoring high-security areas, environmental sensing, industrial applications like heating monitoring, home automation or medical application like checking vital signs, patient tracking, etc. WSN, Bluetooth, wireless local area network (WLAN), radio-frequency identification (RFID) s and others technologies operate in 2.4 GHz band which make it overloaded. The 2.4 GHz band is licensed free and available worldwide and has high band width. Due to this, a trend to using 2.4 GHz band is increasing rapidly. For reliable communication within the band, the primary requirement is a minimum interference between devices utilizing this band [5]. However the WSN operations in industrial environment can be also interfered by power grids and heavy machines. The industrial environment characterized by high voltage, high electric and magnetic fields, can cause strong electromagnetic interferences. The main purpose of this thesis is to investigate the performance of WSN in high voltage and harsh industrial environments. High EMIs were expected at different frequency bands in this kind of environments. These EMIs could increase a bit error rate and/or packet loss. In this thesis we thoroughly investigate the impact of EMI on WSN hardware devices and on the radio transmission. The thesis reports results of practical tests which are done by deploying wireless network devices in realistic industrial environments of ABB. In our experiments the wireless HART technology and DUST Network technology products are used to investigate performance of WSN in high voltage and harsh industrial environments. 1.1 Used Terminology In order to study and analyse the performance of a certain given WSN, we can list three key performance parameter; such as reliability, stability and latency. For detail comparison and study of overall network, we consider s: network statistics, path statistics and node statistic, specifically defined as: Network Statistics: Each performance parameter is based on overall WSN within a given time interval. Path Statistics: Each performance parameter is based only for single path between any two nodes. 10

11 Node statistics: The node statistics concerns performance of the node individually. Data Reliability of the network is percentage of expected data packets that the base station actually received [3]. So a high reliability ensures that no sensed data has been lost during the communication process. Where PkRx and PkTx are total numbers of packets received and transmitted respectively by the network node. Network / Path Stability of the network is percentage of data packets transmit successfully [3]. (1) (2) Latency is the average time it takes for each data packet from the generating sensor node to the base station [3]. The network manager at base station calculates data latency for each packet by subtracting the time the packet was received at manager from the packet timestamp, which is defined as the packet was generated by the mote [6], here mote is defined as a sensing node which is monitored by the manager. Fail is a measure of number of packets for which no acknowledgement was received. 1.2 Thesis Structure The remainder of this thesis is, section 2, describes the EMI endurance and coexistence in ISM 2.4 GHz band. The effect of electromagnetic interference on wireless sensor network and related work has been described. Whereas, section 3, contains problem statement, research questions, hypotheses and main contribution of this thesis work. In section 4, an overview of wireless sensor networks and the most wide-spread wireless sensor network protocols are given, with special focus on the Wireless HART technology, which represents the central issue for the thesis work. Section 5, which investigates the functionality of wireless radio communication in a high-voltage environment, typically related to industrial processes, transformation stations and other parts of the power distribution grid. Section 6 is the last section, which verifies the functionality of wireless radio communication in high voltage and industrial environments. 11

12 2 REVIEW OF RELATED WORKS Sensor network is one of the most rapidly expanding research areas within information technology. Today we find potential applications for sensor network technology almost everywhere in our everyday life, for example within sports, medicine, process industry, agriculture, energy generation etc. We can surely say that sensor networks would become a part of society critical systems in near future. Due to increasing demand of WSN technology in different areas, a lot of efforts have been done to improve the performance, to make technology faster more accurate and reliable. Different studies have been conducted to evaluate the performance of WSN. In [20] authors investigated the packet loss probability of a link in a sensor network and found that it cannot be predicted accurately using the distance between the nodes. The authors in [22] have studied the packet loss behaviour in a wireless broadcast sensor network and observe that different receivers are likely to experience simultaneous losses. In [23], the authors evaluated the performance of wireless personal network using data throughput, delivery ratio, and received signal strength indication (RSSI) as the performance metrics. Similarly in [24], the authors evaluated the performance of WSN in indoor scenarios; particularly they consider the behavior of RSSI and characterized the performance of WSN in term of end-to-delay and throughput. The reliability and robustness of WSN communications are affected by the possible radio interference like Bluetooth, WLAN, IEEE [19] etc. Most of the industrial WSN devices share the 2.4 GHz ISM band [21]. While exploring interference, researchers have focused on the specific protocols, e.g., IEEE b (WLAN), Bluetooth, and ZigBee [9]. Usually radio interference in WSN causes a serious threat in reliable communication. There are currently several developing technologies with interesting features considering the mitigation of EMI for sensor networks. Encapsulated materials are feasible and are of more interest. Laminate materials like Proof Cap [14] will give both protection for EMI and enables the integration of communication antennas. The threat of EMI is controlled by adopting the practices of electromagnetic compatibility (EMC), which has two complementary aspects: it describes the capacity of electrical and electronic systems to operate without interfering with other systems and also describes the ability of such systems to operate as intended within a specified electromagnetic environment [21]. Interference can propagate from a source to a victim by the main distribution network to which both are connected. This is not well characterized at high frequencies for example connected electrical loads can present virtually any RF impedance at their point of connection [11]. The external interference from a system whose purpose is not data communication might be the effect of industrial environments, grid stations or the environment with strong electric and magnetic fields. This external interference is also known as electrical interference. Most existing studies are based either on over-simplistic environmental models assuming Gaussian background noise, or on the assumption that interference arises from peer [27]. There are two types of disturbance which have received a considerable attention in research under the umbrellas of channel modeling and MAC protocol design, respectively. The third type of disturbance is due to external interference possibly even from a system whose purpose is not data communication has been not much overlooked interference [27]. 12

13 Electrical machinery and lighting systems are main sources of electrical interference [25, 26]. In most cases, the interference results from sparking, arcing and electrical discharges. In a few instances, the interference is caused by electrical control devices such as motor speed controls, temperature controllers and lighting dimmers. High-voltage equipment, especially neon signs, is also a known source of interference [25, 26]. The high voltages in neon systems can also cause leakage discharges, known as corona, which create electrical noise [28]. Other devices that use high voltages are also prone to corona and can cause wireless interference. The discharge in the neon tubes themselves generates surprisingly a little interference under normal circumstances. However, if the tubes are dimmed by lowering the applied voltage, there is a point where they will generate huge amounts of radio interference [25]. In this thesis, we analyze the performance of wireless senor network in the laboratory scenarios at ABB, test scenarios include Machine lab environment, DC high-voltage and AC high-voltage labs environment. Moreover we perform the experiments in the office environment to compare the results. Likewise the [9, 23, 24], we use the throughput, delay, and RSSI as performance indicator to compare the performance of WSN. Furthermore path stability and data reliability was also considered. Contrary to [9, 23, 24] we uses the wireless standard HART [10], which is simple and TDMA-based wireless mesh networking technology. In [8] authors compare the ZigBee and HART wireless technology for industrial use and found that HART is most suitable for this purpose. 13

14 3 PROBLEM STATEMENT In high voltage and harsh industrial environments, electromagnetic interferences are expected at different frequency bands. These EMIs could increase a bit error rate and data packet loss in wireless communication. In such environment expected EMIs can also affect the WSN device s sensitivity, which causes the packet loss and delay in response time. Our research questions are: How the high voltage and harsh industrial environments do affect the WSN performance? Do the EM frequencies produced due to high voltage and industrial environments, interfere in WSN communication? We assumed that the WSN performance is degraded due to the presence of high voltage and industrial environments. External EM interferences cause time delay and transmission loss. The main contributions of the thesis can thus be summarized: Comparative study of WSN technology. Set up the radio tests for WSN performance. Design the EMI tests for monitoring the EM frequencies in high voltage and industrial environments. Capture and collect the WSN data analyzed with the help of Matlab. 14

15 4 THEORETICAL BACKGROUND OVER VIEW OF USED TECHNOLOGY There are two principal standards for WSN technologies which are realistic choices for a real usage of a WSN: Wireless HART and ZigBee. ZigBee [10] is a set of high-level communication protocols based on the IEEE standard, suited for low data rate WPANs. It aims to provide a simpler and less expensive specification than other WPANs. ZigBee operates in the industrial, medical and scientific radio bands. Typical application areas include home entertainment and control, mobile services, commercial building. The standard specifies the physical, MAC and data link protocol layers. Concerning the physical layer, ZigBee uses direct-sequence spread spectrum (DSSS) like some standards of the IEEE family. ZigBee has been developed to add mesh networking to the IEEE It is particularly suited for embedded systems where reliability and versatility are more important than the bandwidth [13]. The HART Communication foundation (HCF) released the new HART 7 specification on September HART is a master/slave protocol which means that a field (slave) device only acts when called by a master. The HART protocol can be used in various modes for communicating information to/from smart field instruments and central control or monitoring systems. The HART 7 specification includes Wireless HART [12], the first open wireless communication standard designed specifically for industrial environments in which plant applications need reliable, secure and simple wireless communication. For industrial application of WSN the most important argument which makes Wireless HART as our preferred choice for this thesis is that in ZigBee there is no frequency diversity since the entire network shares the same static channel, making it highly susceptible to both unintended and intended jamming. The lack of path diversity means that in a case when a link is broken, a new path from destination has to be set up. Others less significant comparisons like battery life time, etc. are shown in Table 1. Table 1. Comparison of wireless HART and ZigBee Features Wireless HART ZigBee Mesh Architecture Full Mesh Hybrid Star Mesh Self-forming, self-healing network Yes Central network coordinator Battery Years Years Deterministic power Yes No management Reliability and stability in High Low harsh environment Channel hopping Yes No Multiple access scheme Time Synchronized CSMA 15

16 4.1 Wireless HART Technology The key feature of Wireless HART is the combination of direct sequence spread spectrum (DSSS) and frequency hopping spread spectrum (FHSS) which are frequency hopping mechanism that can effectively suppress the sudden interference [2].In wireless HART another technical feature is the combination of Carrier Sense Multiple Access (CSMA) and Dynamic Time Division Multiple Access (TDMA) which gives advantages of TDMA and CSMA [2]. The network layer uses the intelligent mesh network technology. Due to interference when path is interrupted, the device switches on other communication path of good quality [2]. The transport layer uses connection oriented data transmission technology by end to end retransmission mechanism to ensure the high reliability of data transmission [2]. The wireless hart protocol uses the intelligent network management. The other technical features of Wireless HART are: Highly reliable self-organizing network, Using TDMA to avoid message conflicts, Adaptive frequency hopping mechanism, Automatic request retransmission which ensures the success rate of packet transmission, Mesh routing to improve the reliability of end to end communication, High degree of reliability, Use of multiple channels within the band, Very high resistance to active interferers, Higher resistance to passive interferers like multipath, Simultaneous use of more than one channel increases throughput. The Wireless HART protocol is loosely organized around the OSI-7 layered architecture. The protocol defines 5 separate layers - the Physical Layer, the Data-link Layer, the Network Layer, the Transport Layer and the Application Layer. Table 2 shows the Wireless HART layered architecture. The Wireless HART Networks must be managed and connected to the real world. As a central component, the Wireless HART Gateway provides all these functionalities [2]. Table 2. OSI Layer Model and Wireless HART Stack OSI-7 Layer Model Wireless HART Stack Application Layer Command oriented, predefined data types and applications Presentation Layer Not used Session Layer Not used Transport layer Reliable stream transport, negotiated segment sizes, transfer of large data sets Network Layer Power optimized, redundant path, self-healing, wireless mesh network Data link Layer Secure and reliable, Time Synched TDMA/CSMA, Frequency Agile with ARQ Physical Layer 2.4 GHz wireless, based radios, 10 dbm Tx power 16

17 5 TESTS SCENARIOS AND SETUPS In this chapter we present the test scenario and results for deploying wireless sensor notes in real high voltage and industrial machine environments. At the start we perform experiments in normal office environments during night time to reduce the chances of interference from wireless communication sources. We use these results as reference for office environments and we compare these results with all other scenarios i.e. deploying the wireless sensor network in high voltage and industrial environments. The WSN uses DUST SmartMesh network technology. Dust SmartMesh technology is based on Wireless HART, the technical features of used technology are explained in chapter 4. SmartMesh network has one manager and can have up to 250 nodes [3]. SmartMesh networks are reliable, ultra low power. The used DUST SmartMesh products are The SmartMesh IA-510 D2510 Network Manager, The SmartMesh Motes. Figure 1: SmartMesh Mote and Network Manager The SmartMesh network manager is responsible for network configuration, management, and gateway functionality for field devices or nodes. SmartMesh network managers allow programmatic access to network control commands, by using host interface application via XML API and Serial API. In other words, the SmartMesh Mote is more intelligent than a network node. The SmartMesh M2510 motes are ultra low-power wireless transceivers and onboard radio to send packets [3]. (For specification of products see Appendix). For monitoring and measurement DUST s SmartMesh Console Software and DUST s SmartMesh API and Command Line Interface are used. For measurement of interference FSH view software and FSH 6, a remote spectrum analyzer is used [6]. The collected data are analyzed using Matlab. 17

18 5.1 Test Scenarios To observe the WSN performance in high voltage and harsh industrial environments we used ABB labs. As a reference we perform the same experiments in nonindustrial environments to observe the radio performs without the disturbances. In order to observe the effect of high voltage and industrial environments on wireless sensor network communication we divide our experimenters in five scenarios Non-Industrial Environment Tests In 1 st scenario, we perform test in office environments called non industrial tests and being a reference for other tests. In this scenario we deploy wireless senor network in office environments at night time and collect data using wireless hart technology and dust network instruments. The efforts are taken to achieve maximum stability and minimum legacy. There is one issue needed to consider during experiments: the behavior of network manger up time defined as the time when nodes start stable communication or build stable network. Non-industrial environment does not mean that the environment is completely free from interferences. Some known external interference like WLAN, Wireless devices, RFID s is working in the environment. We cannot ignore these external interferences. The tests were performed at ABB AB Corporate Research, in the office environment. The tests were repeated for several times to make the readings reliable. We used five wireless field devices for this test in which node 1 was working as gateway. The distance of field devices was not more than seven meters from access point. Figure 2: Network topology for non industrial test Figure 2 shows the network topology of the wireless sensor network deployed in office environment. Where AP is access point or gateway and M12, M13, M19, M20 are wireless nodes and small m depicts the distance in meter between nodes and between nodes and a gateway. 18

19 5.1.2 Industrial Machine Lab Environment Tests In 2 nd scenario we select the laboratory room of ABB for real industrial environments which has two machines of 550 kw and 450 kw and some small machines shown in figure 3.The detail topology and experiments environment is presented in following sections. The main reason to select this environment is to observe how wireless sensor network communication behaves in continues lower band frequencies noise and to observe if there is any sudden emission of frequency in the range 2.4 G Hz band (which big machine produce) and impact of such emission on wireless communication or wireless devises. We deployed five field devices which are shown in Figure 3. Among the five wireless field devices node 1 is working as gateway. The distance of field devices is not more than ten meters from access point. The test is divided into three steps. 1- Test in the lab when machines are not running. 2- Test in the lab when machines are running. 3- Test to monitor EM frequencies in lab when machines are running. Figure 3: ABB Lab with two motor machines 19

20 Figure 4: Machine lab network topology Figure 4 shows the network topology of the wireless sensor network deployed in industrial machine lab tests, where AP is access point and gateway and M12, M13, M19, M20 are wireless nodes and small m depicts distance in meter between nodes and between nodes and a gateway. Machines 1 and 2 are machines of 550 kw, 523 A, 690 V and 450 kw, 230 A, 9300 V respectively DC High Voltage Environment Tests The test setup in the DC High Voltage Lab consists of a transformer to control the voltage, and a secondary transformer to increase the voltage and then a rectifier circuit to convert AC into DC. The high voltage environments may produce a corona, which is sparking or lightning due to ionization in the air. 20

21 Figure 5: DC high voltage test setup In Figure 5 the network topology of the wireless sensor network deployed in DC High Voltage Lab is shown along with a metallic cage in which lighting effect is produced. AP is access point gateway and M12 and M13 are wireless nodes and small m depicts distance in meters between nodes and between nodes and a gateway. The arrow from original setup to topology shows were the nodes are placed in original test setup. We used three wireless field devices in this experiment, but one of them is working as gate way node and the remaining two are field devices which are placed on DC high voltage experimental equipment. The distance of field devices is not more than ten meters from access point. The test is divided into three steps. 1. WSN performance test in the DC High Voltage Lab. 2. WSN performance test when DC high voltage is increasing step by step. 3. Test to monitor EM frequencies in lab. 21

22 Figure 6: The block diagram for DC High Voltage Test Circuit The setup as shown in the Figure 6 consists consist of an adjustable transformer to control the voltage, a secondary transformer to increase the voltage, a rectifier circuit made of diodes to turn AC into DC current, a conductor of about 6 meters and a termination point which leaves a gap between the line and the ground. The termination, the gap (no. 1 in the diagram) and the ground are surrounded by a metallic cage as seen in Figure 7 in order to simplify the geometry for other tests that were made at the same time. Therefore some collateral Faraday box isolation effects can be founded. With this set-up it is possible to measure the effects of DC current installations and corona of this type of environments as well. Corona is a typical electrical discharge, or sparking, produced by the ionization of the air nearby where the high voltage is present. Figure 7: The block diagram for transformer and metallic cage 22

23 Test voltage DC Voltage ( kv ) :00:00 14:24:00 16:48:00 19:12:00 21:36:00 00:00:00 02:24:00 04:48:00 07:12:00 09:36:00 Time "Voltage" Figure 8: The voltage test along time for High Voltage DC Test In the Figure 8, we can see that the test voltage was progressively modifying along the time, later on it maintain fixed level at 300 kv AC High Voltage Environment Tests - High Voltage Transformer This test investigates how the WSN behaves on proximity to high voltage transformers. The setup shown in Figure 9 consists of an exciter transformer, a tunable reactor, which is a high voltage series resonant test system of variable inductance to test resonant loads, a voltage divisor to measure and a simple load. Figure 9: Block Diagram of AC high voltage test setup The test is divided into two steps. 1. WSN performance test in the lab without high voltage. 2. WSN performance test in the lab when high voltage is increasing. 23

24 Figure 10: AC High voltage test setup The topology of AC high voltage test is shown in Figure 10.The same as in the previous test, we use three wireless field devices for this test in which the first node is working as gate way and the remaining two filed devices are placed on experimental equipment as shown in Figure 10. The distance of field devices from access point is not more than sixteen meters. Figure 11: The circuitry of AC high voltage test setup 24

25 The test took 7 hours, where the first 6 hours transformer system worked with an output load of 77 kv. The last hour the power was switched off in order to study if the laboratory environment caused any effect on the network behavior Voltage (kv) 09:07 10:19 11:31 12:43 13:55 15:07 Figure 12: AC Voltage with respect to time Voltage (kv) EMI Test in High Voltage and Machine Lab For measurement of EMI in high voltage and industrial environment we design EMI test in same environments as mention in and where we investigate the WSN performance. We divided EMI tests in following sub scenarios. 1- Measurements of EMI in 2.4 GHz Frequency Spectrum in machine lab, 2- Measurements of EMI in 2.4 GHz Frequency Spectrum in DC high voltage. In both sub scenarios we use two test setups. 1- When WSN filed devises are transmitting, 2- When WSN filed devises are disabled. 25

26 6 TEST RESULTS AND ANALYSIS In this section we analyze the tests result from the all four scenarios and finally we compare them with each other. 6.1 Network Statistics Analysis of Non Industrial Environments Test Results N e t w o rk S t a t is t ic s % Network Stability Latency in second T im e " 1 5 m in u t e s E a c h In t e rva l" Figure 13: Stability and latency graph of nonindustrial environment test In Figure 13 the x-axis shows time t interval, and each interval is fifteen minutes. Along y-axis the percentage network stability and latency in seconds are plotted. From Figure 13 we observe that the network stability is above % and latency is below 0.6 second, which is very close to expected result in non industrial environment. During the test the data reliability of the network is 100%, which means that the manager receives all expected data. The average value of network stability is 99.7 % with variance 0.08 during nonindustrial environment test. 26

27 Packet Tx Network Statistics " Tx & Fail " Time interval(15 min each interval) Fail Time " 15 minutes Each Interval" Figure 14: Data Packet Transmitted and Failed per time slot for nonindustrial environments test In Figure 14 the x-axis shows time t interval, each interval is fifteen minutes. Along y-axis the number of packets transmitted and the number of packet failed to get ACK are plotted. From Figure 14 we can see that in each time interval the number of packets for which no acknowledgement was received is less than 10 packets per time slot with a total average around 5 packets per time slot. 27

28 6.1.2 Analysis of Industrial Machine Lab Test Results 100 Network Statistics 99 % Network Stability Latency in second Time interval(15 min each interval) Figure 15: Stability and latency graph of Industrial Machine lab test In Figure 15 the x-axis shows time t interval, each interval is fifteen minutes. Along y-axis the percentage network stability and latency in seconds are plotted. In Figure 15 the blue line shows the network stability when machines were not running, and red line shows the network stability when machines were running. The graph shows that the stability is around 99.5% when machines are not running and when the machine are in running state, the network stability drop down with minimum value 96.5% and an average of 97.8%. More than 2% stability decreasing shows that the machines running environment affect the WSN performance. The green line in latency graph from Figure 15 is the average latency of the WSN before the machines were running with average 0.57 seconds and the red line is the latency when machines were running, it shows an average latency of 0.68 seconds. An increase in latency shows the WSN performance degradation in machines running environments. The average value of network stability is % with variance during industrial environment test. 28

29 Packet Tx Fail Network Statistics "Tx & Fail" Time interval(15 min each interval) Figure 16: Data Packet Transmitted and Failed per time slot for machine lab test In Figure 16 the x-axis shows time t interval, each interval is fifteen minutes. Along y-axis the number of packets transmitted and the number of packets failed to get ACK are plotted. The Figure 16 shows that less than 10 packets per time slot fails to get ACK when machines are not running but when the machines are running the number of packets fails to get acknowledgement increased up to maximum 46 packets per time slot, with an average of 30 packets per time slot Analysis of DC High Voltage Environment Tests Results In our hypothesis we assume that high voltage environments can affect the wireless communication and wireless devices which produce different level of electromagnetic frequencies by increasing and decreasing voltage and current level and sparking or lighting effects. Such high level electromagnetic frequencies can produce interference in wireless sensor network communication band. 29

30 100 Network Statistics 99 %Network Stability Latency in second Time " 15 minutes Each Interval" Figure 17: Stability and latency graph of DC High voltage test In Figure 17 the x-axis shows time t interval, each interval is fifteen minutes. Along y-axis the percentage network stability and latency in seconds are plotted. In Figure 17a the blue line shows the network stability of the network when voltage level from experimental setup is zero or no voltage. Red line shows the network stability when DC high voltage is present in setup and is increasing step by step from 0 up to 400 kv. The graph shows that the stability is around 99% when voltage level is zero but when DC high voltage is present in experimental setup we can see the degradation in stability drops down to 3%. In Figure 17 the latency graph is plotted with green line which is the average latency of the WSN when voltage level is zero, which is average 0.6 seconds. In the latency graph, the red line shows the latency when DC high voltage is present, which is 0.77 seconds on average. An increase of seconds in latency shows that the WSN performance decreases. The average value of network stability is 97.2 % with variance 5.78 during nonindustrial environment test. 30

31 750 Network Statistics " Tx & Fail" 725 Packet Tx Fail Time "15 minutes Each Interval") Figure 18: Data Packet Transmitted and Failed per time slot for DC high voltage test In Figure 18 the x-axis shows time t interval, each interval is fifteen minutes. Along y-axis the number of packets transmitted and the number of packets failed to get ACK are plotted. Figure 18 shows that when voltage level is zero, then less than 10 packets fail in the test in each time interval. But when DC high voltage is applied and increased step by step the number of packets failed to get acknowledgement increased up to 32 packets per time slot with an average of about 25 packets per time slot. 31

32 Voltage Vs. Stability & Reliability 100,00% ,00% 80,00% 70,00% 60,00% 50,00% 40,00% 30,00% 20,00% 10,00% Stability Reliability Voltage DC Voltage ( kv ) ,00% 0 12:00 14:24 16:48 19:12 21:36 00:00 02:24 04:48 07:12 09:36 time Figure 19: The voltage vs. stability and Reliability 32

33 6.1.4 Analysis of AC High Voltage Environment Tests Results 100 Network Statistics 99 % Network Stability Latency in second Time " 15 minutes Each Interval" Figure 20: Stability and latency graph of AC High voltage test In Figure 20 the x-axis shows time t interval, each interval is fifteen minutes. Along y-axis the percentage network stability and latency in seconds are plotted. When AC voltage is increasing during the test, at one point, the both nodes stop transmission and SmartMesh software shows that the nodes are lost. When test voltage stopped after a few minutes, then the both nodes reconnected the WSN and started transmitting. We did not use any reboot command to reboot nodes or manager and waited until the nodes itself reconnected the WSN. As this test was not repeated, therefore we cannot say anything about the event which might not be detected by the mote and what is the probability of such event. In Figure 20a the green line shows the network stability of the network when voltage level is zero or no voltage. Red line shows the network stability when AC high voltage is present in setup and increasing steps by step. The graph shows that the stability is around 99% while the voltage level is zero but as voltage level increases, the stability reaches value around 95.1 %. The Latency graph is shown in Figure 20b, the green line shows the average latency of the WSN when voltage level is zero, which is average 0.7 seconds where as red line, shows the latency when AC high voltage is present, which increased up to maximum 1.4 seconds. The average value of network stability is % with variance during AC high voltage environment test. 33

34 750 Network Statistics " Tx & Fail" 725 Packet Tx Fail Time "15 minutes Each Interval" Figure 21: Data Packet Transmitted and Failed per time slot for AC high voltage test In Figure 21 the x-axis shows time t interval, each interval is fifteen minutes. Along y-axis Figure 21a shows the number of packets transmitted and Figure 21b shows the number of packets failed to get ACK. In Figure 21a we can see that when voltage level is zero, the blue line shows that less than 10 packets fail to get ACK per time slot. Red line shows the graph when voltage is present in equipment and increasing step by step, it shows that the number of packets failed to get acknowledgement is up to 35 packets per time slot with an average of about 25 packets per time slot. As the number of fails increase the number of transmitted packets also increased. When nodes reconnect, again number of fails starts decreasing. As explained above, due to re transmission, the protocol supports the retransmission of packet which fails to get ACK to get maximum reliability. 34

35 6.2 Path Statistics Analysis of Non-Industrial Environment Test Results 100 Path Statistics % Path Stability Time "15 minutes Each interval" Figure 22: Path stability for Mode to AP in nonindustrial Environment In Figure 22 the x-axis shows time t interval, each interval is fifteen minutes, y-axis shows percentage path stability (Path M13 to M1 as shown in Figure 2). Here path stability is not for the whole network, just for single path from a node to the access point. The path stability varies from 100% to 98.5% in non industrial environments for node to access point path. 35

36 6.2.2 Analysis Industrial Machines Lab environment Test Results 100 Path Statistics %Path Stability Time "15 minutes Each Interval" Figure 23: Path stability for a mode to AP in machine lab test In Figure 23, the x-axis shows time t interval, each interval is fifteen minutes (Path M20 to M1 as shown in Figure 4). In Figure 23 the path stability of the WSN field devices before the machines were running is more than 99% whereas when the machines were running the path stability decreases up 89%. The decrease in path stability up to 10% shows that some factor in environments creates disturbance in WSN. 36

37 6.2.3 Analysis DC High Voltage Environment Test Result 100 Path Statistics % Path Stability Time "15 minutes Each Interval" Figure 24: Path stability for a mode to AP in DC High voltage test In Figure 24 the x-axis shows time t interval, each interval is fifteen minutes, y-axis shows percentage path stability (Path M13 to M1 as shown in Figure 5). In Figure 24 the path stability of the WSN field devices is around 99% when voltage level is zero. When the DC high voltage is present and increasing the path stability decreases up to 89%. The decrease in path stability up to 10% shows that some factor in environments creates disturbance in WSN. 37

38 6.2.4 Analysis of AC High Voltage Environment Test Results 100 Path Statistics %Path Stability Time interval(15 min each interval) Figure 25: Path stability for a mode to AP in AC high Voltage Test In Figure 25 the x-axis shows time t interval, each interval is fifteen minutes, y-axis shows percentage path stability (path between M20 and M1 as shown in Figure 10). In Figure 25 we can see that the path stability of the WSN field devices during AC high voltage test is dropped up to 86% with an average of 90%. The red line corresponds to a case when WSN is operating under AC high voltage and gap is when devices lost connection or signalling due some unknown effect which we mention in previous section for a case when discharge produced lot of lighting and which can may be due to increased temperature. 38

39 6.3 Average RSSI value for Transmission Path Statistics "Average RSSI values for Transmissions A->B Power B->A Power A->B & B->A Power-dBm Time "15 minutes Each interval" Figure 26: Average value of output power per time slot for transmission in non industrial test In Figure 26 the x-axis shows time t interval, each interval is fifteen minutes, y-axis shows power is in dbm. In Figure 26 we can see that in nonindustrial environment tests the total average RSSI values of transmission about dbm. 39

40 -50 Path Statistics "Average RSSI values for Transmissions A->B & B->A Power-dBm Time interval(15 minute Each interval) Figure 27: Average value of output power for transmission in machine lab test In Figure 27 the x-axis shows time t interval, each interval is fifteen minutes, y-axis shows power is in dbm. In Figure 27 we can see that in industrial machines lab environment tests the total average RSSI values of transmission is dbm. Typical RSSI values for network radio strength paths within these distances, indoors in a free-ofdisturbances environment are up to -50 dbm. 40

41 -50 Path Statistics "Average RSSI values for Transmissions A->B & B->A Power-dBm Time interval(15 minute Each interval) Figure 28: Average value of output power for transmission in DC High voltage test -45 Path Statistics "Average RSSI values for Transmissions A->B Power B->A Power -50 A->B & B->A Power-dBm Time interval(15 minute Each interval) Figure 29: Average value of output power for transmission in AC High voltage test 41

42 In Figure 28 and 29 the x-axis shows time t interval, each interval is fifteen minutes, y-axis shows power is in dbm. In Figure 28 we can see that in DC high voltage test the total average RSSI values of transmission is about dbm. In Figure 29 we can notice that there is no considerable change in RSSI value of transmission in high voltage test during the first 15 minutes interval. In 1 st time slot its value is around -63 dbm, and -65 dbm. Average RSSI value of transmission from node to gate way more affected by increasing distance then by any other factors or environmental condition. 6.4 Analysis of EMI Test Results Spectral Measurements for EMI in 2.4 GHz band Frequency For measurement of interference FSH view software and FSH 6, a remote spectrum analyzer up to 6GHz used. Measurements of interference are taken in machine lab environment for both cases that are when WSN devices are transmitting and when they are disabled and not in transmitting mode. Figure 30: The 2.4 GHz Spectrum when machines were in off state In 1st case we observe some interference in 2.4 GHz frequency band when wireless field devices are operating in environment, because WSN field devices used in these experiments are operated in 2.4 GHz frequency band. In 2nd case, when WSN devices are completely in off state and machines are running in full intensity and we didn't observe any interference in 2.4 GHz band. However we observed electromagnetic interference in the khz level. 42

43 Figure 31: 2.4 GHz Spectrum when machines are operating For measuring the frequency range which suffers interference while machines are running, we use the test setup with remote spectrum analyzer and antenna is placed very near of running machines and monitor all around the machines. But we did not observe any interference in 2.4 GHz band but we observed electromagnetic frequencies in the khz level. 43