Int. Journal of Applied Sciences and Engineering Research, Vol. 5, Issue 1, 2016 © 2016 by the authors – Licensee IJASER- Under Creative Commons License 3.0 Research article www.ijaser.com editorial@ijaser.com ISSN 2277 – 9442 Determination of the reliability of a locally made clap activated switch by part count analysis Ehiagwina Ojiemhende Frederick1, Adewunmi Olugbenga Titus2, Bamigboye Oladayo Oladele3, Seluwa Oludare Emmanuel4 Department of Electrical Electronics Engineering School of Engineering Federal Polytechnic, Offa, Kwara State, Nigeria DOI: 10.6088/ijaser.05007 Abstract: In this research work, the reliability of a locally designed and constructed clap activated switch was determined. The sound of clap is detected by a small condenser microphone. The microphone transduces the sound wave to electrical waves which is further amplified by transistor connected in the common emitter configuration. The amplified output from the transistor is then fed to the Bistable Multivibrator circuit. The part count method which assumes typical operating conditions of part or components complexity, ambient temperature, various electrical stresses, operation mode and environment (called reference conditions) was used for the estimation of the reliability of the Clap Activation Switch. It is observed that the reliability of the Clap Activated Switch constructed locally have an estimated reliability that ranges between 0.99706 for the first year of operation to 0.94299 around the twentieth year of operation. Further work can be done by evaluating the reliability of the device using part stress analysis; this will enable the determination of the reliability under actual operating conditions to be carried out. Keywords: Electrical stresses, part count analysis, reliability, switch. 1. Introduction Developing countries of the world are mainly consumers or, at best, assemblers of electronic devices designed by developed nations. There are needs to fast track development and industrialization by encouraging research into designing, construction, testing and mass production of electronic devices in developing countries and Nigeria in particular. The government has shown interest in advancing the country technologically. The clap activated switch can be used to switch ON/OFF devices and they are designed and usually constructed in developed countries and shipped to developing nations. In this research work, a clap activated switch was locally design and construct; hence there is the need to evaluate the reliability of the device. The amplified output from the Bistable Multivibrator is connected to the relay; the contact is connected to the power line and hence turns ON/OFF any electrical devices connected all the way through the relay. 1.1 Reliability analysis In general, reliability designates the ability of a system to perform its assigned function, where past experience helps to form advance estimates of future performance. Reliability is a measuring index for the performance of engineering systems defined reliability as the probability that a device or system will perform its prescribed function adequately for the period of time intended under specified operating conditions (Akinsanmi O. , "Determination of the Comparative Reliability of a Nokia 1200 Mobile Phone ————————————— *Corresponding author (e-mail: frederick.ehiagiwna@fedpoffaonline.edu.ng) Received on January, 2016; Published on February, 2016 62 Determination of the reliability of a locally made clap activated switch by part count analysis Charger", 2009; Abdullahi, Muazu, & Jibril, 2007; Faruk, Ayeni, Abdulkareem, & Moses, 2012). Reliability can be determined through the mathematical concept of probability by identifying the probability of successful performance with the degree of reliability. If a device or system does not fail during the time of service it is said to perform satisfactorily. On the other hand, some devices are expected to fail, be repaired and then returned to service during their entire useful life. In this situation a more appropriate measure of reliability is called availability of the device in question. Therefore, in this work the reliability of the design is evaluated using exponential distribution model. The exponential distribution model is defined in (Akinsanmi, Sha'aban, & Ayo, 2009; Arsenault, 1980). The exponential failure density function f (t) is defined by (1): f t e t (1) The reliability function is defined by (Akinsanmi, Sha'aban, & Ayo, 2009) in the form of (2): Rt e t (2) The generic failure rate, G of each component that makes up the clap activated switch is obtained from the Military Handbook (MIL-HBK-217 Notice 2) (MIL-HDBK-217, 1991), using parts count method of reliability prediction. In this paper, it is assumed that the failure of any components that makes up an electronic system will result to system failure based on series theorem of reliability. (Jones & Hayes, 1999) predicted the reliability of several selected Circuit Board of different types using techniques such as HRD4, Siemens (SN29500), CNET, MIL-HDBK-217E and Bellcore (TR –TSY-00032) models. Part count analysis were performed on the Circuit Board using Published failure rates and the results was compared with observed field performance. It further noted system sensitivity to widely differing parameter such as electrical stress, temperature and other factors . While a framework and procedure for predicting the reliability of electronic equipment at all levels was presented in (IEEE STD, 2003). On the other hand, (Goel & Graves, 2006; Bhargava, Banga, & Singh, 2014) summarized researches in field of electronic system reliability. It reviewed the merits and demerits of traditional reliability prediction models. It pointed out MIL-HDBK-217 as first and widely used predictive models, even as (Jais, Werner, & Das, 2013) highlighted its shortcomings. However, the justification of it use in this research lies in its simplicity and wide acceptability. 1.2 Part count method This is one of the methods used in assessing the reliability of electronic devices. The part count method assumes typical operating conditions of part or components complexity, ambient temperature, various electrical stresses, operation mode and environment (called reference conditions). The failure rate for a part under the reference conditions is calculated by using (3) (MIL-HDBK-217, 1991): n b,i r i (3) i 1 where: r = the failure rate under the reference conditions. Ehiagwina Ojiemhende Frederick et al., Int. Journal of Applied Sciences and Engineering Research, Vol. 5, No. 1, 2016 63 Determination of the reliability of a locally made clap activated switch by part count analysis i the number of components or parts. It is convenient to specify the reliability of electronic equipment by some probability parameters, which give indication of the failure rate of such a system or equipment, and does not depend on the operating time. By using such parameters, it is also possible to compare the performance between different systems with different operating periods. Two of such parameters that are commonly used are the mean time before failure (MTBF) and mean time to failure (MTTF). 1.3 Mean time before failure (MTBF) Systems users are usually concerned with the length of time that a system will run without failure. This is a measure of the reliability of such system. For a repairable system, the time before failure is the critical measure, while for non-repairable systems; the time distribution is exponentially decreasing and the mean time before successful failure of the system. The MTBF can be obtained by running a system for predetermined length of time under specified conditions. Calculating the average length of time before failures could be seen as exponentially decreasing function and MTBF is the mean time before consecutive failures. Hence for the failure rate (is the number of failures per unit time), MTBF is given as (Akinsanmi O. , "Determination of the Comparative Reliability of a Nokia 1200 Mobile Phone Charger", 2009), (Abdullahi, Muazu, & Jibril, 2007): MTBF 1 (4) The reliability of the system ( R ) for a specified period ( t ) of failure free operation is as shown in (2). 1.4 Mean time to failure (MTTF) The mean time to failure MTTF is used for components or items that are not repairable e.g. filament bulbs, resistors, capacitors and so on, which are disposed as soon as they fail. This MTTF can be obtained by stressing a large number of components under known conditions for a period of time and noting the number of failures can obtain the MTTF (Taylor, 1989). 1.5 Equipment Failure Profile Over the years, complex equipment and components have been found to follow a familiar pattern of failure, which has been well documented. Hazard or failure rates have been calculated for equal time interval from installation to replacement. When the failure rate is plotted against a time scale spanning the equipment life time, the resulting graphics, popularly known as ``BATHTUB’’ is obtained as shown in Figure 2. It exhibits three distinct periods or zones- the infant mortality period, the constant failure rate period and the wear out period. Failure rate is usually expressed in failure per hour (or failure per thousand or even per million hours) (Andrew, Jordan, & Lawrence, 1995). 1.6 Infant mortality period This is the running-in period. During this period, the failure rate has been found to be high, due to other design or manufacturing errors, misuse or misapplication of other identifiable causes. It however, falls off Ehiagwina Ojiemhende Frederick et al., Int. Journal of Applied Sciences and Engineering Research, Vol. 5, No. 1, 2016 64 Determination of the reliability of a locally made clap activated switch by part count analysis rapidly with operation. Failures in this period can be avoided during product development through the use of stimulated tests, or by vigorous stressing during commissioning tests. Figure 1: Equipment failure profile (Akinsanmi O. , "Reliability Assessment of UPS Systems in Developing Countries", 2003) 1.7 Constant failure rate period This period follows the running-in period. During this period, the failure rate is lowest and is a function of the basic design. Failure results either through accidents or poor operation or maintenance and they can be reduced by good control of operating and maintenance procedures. In this phase, the mean time to failure (MTTF) is the reciprocal of the (constant) failure rate. 1.8 Wear out Period This period manifests towards the tail end of the equipment component life. During this period, failure is due to old age; various components are worn out, metals become embrittled, insulation dries out and so on. Failure rates can only be reduced by preventive replacement of these components. Generally in some systems, one or two of the phases (usually the early failures and wear out failures) could be more reduced or effectively absent. Therefore, estimates for the parameters that affect the equipment failure profile of the constituent components, especially the length of the constant failure rate period and the associated failure rates are essential ingredients for predicting the reliability (Akinsanmi O. , "Reliability Assessment of UPS Systems in Developing Countries", 2003) 1.9 Equipment availability Equipment availability is the probability that an equipment will perform its required function at a stated instant of time or over a stated period. Availability is a function of the utilization factor (U). The utilization factor of a unit or system is op defined as the ratio of the operating time ( t op ) to the sum of the maintenance time ( t m ) and idle time ( t id ) which may occur between completion of maintenance and use Ehiagwina Ojiemhende Frederick et al., Int. Journal of Applied Sciences and Engineering Research, Vol. 5, No. 1, 2016 65 Determination of the reliability of a locally made clap activated switch by part count analysis due to administrative reasons, and the operating time. Mathematically, the utilization factor U, was given by (Akinsanmi O. , "Determination of the Comparative Reliability of a Nokia 1200 Mobile Phone Charger", 2009; Abdullahi, Muazu, & Jibril, 2007; Oroge, 1991) as expressed in (5). U t op t id t m t op (5) If t id 0 , t m 0 , then U will approach its maximum value and can now be called availability of a unit or system. Mathematically, this can be expressed as shown in (6): U max t op t m t opmin At (6) However, MTBF top min and MTTF top Where MTBF and MTTF is mean time before failure and mean time to failure respectively. Then, the availability is as shown in (7): At MTBF MTBF MTTF (7) And if the availability of equipment is stated as 0.99, it means that the equipment is working satisfactorily for 99% of the time, and under repair for the remaining 1% of the time. 2. Materials and method 2.1 Principle of operation of the clap activated switch The sound of clap is detected by the small condenser microphone that is shown in Figure 2 biased by resistor R1 in the circuit. The microphone transduces the sound wave to electrical waves which is further amplified by transistor Q1 connected in the common emitter configuration. The amplified output from the collector of Q1 is then fed to the Bistable Multivibrator circuit also known as flip-flop. The flip-flop circuit is made by using two transistors Q2 and Q3 . In the flip-flop circuit, only one transistor conducts at a time and the other transistor is cut-off, and when it receives pulse from external source then Q1 is cut-off and Q2 conducts. Thus the output from the flip-flop is either at logic 0 or 1, and it remains in one state 0 or 1 until it receive trigger pulse from external source. The sound energy from the clap which is the trigger for the flip-flop makes changes to the output. The output from the flip-flop is of low current and is unable to drive the relay directly, hence, the output need to be amplified by transistor Q4 . Transistor Q4 is connected to the relay (electromagnetic switch) Ehiagwina Ojiemhende Frederick et al., Int. Journal of Applied Sciences and Engineering Research, Vol. 5, No. 1, 2016 66 Determination of the reliability of a locally made clap activated switch by part count analysis which works as a mechanical switch. The relay contact is connected to the power line and hence turns ON/OFF any electrical devices connected all the way through the relay (Horowity & Hill, 1989; Ojeleke & Olawale, 2014). 2.2 System description Figure 2: Circuit diagram of the Clap Activated switch (Ojeleke & Olawale, 2014) The clap activated switch of Fig. 1 is made up of one step-down transformer T1 rated 240/12V, with a secondary current of 300mA. The transformer steps down the supplied voltage to 12V a.c., half wave rectification was employed using a single diode D1 and the output is connected to a capacitor C1 rated 1000 F / 16V for filtering purpose in order to have a smoothened DC voltage supply. The condenser microphone is connected with resistors [ R1 R3 ] in series as a potential divider, which is then connected to transistor Q1 (BC548) whose current is limited by R4 the output from Q1 is connected to Bistable Multivibrator comprising of transistors Q2 and Q3 , resistors [ R5 R12 ], diodes D2 and D3 , and capacitors C 3 and C 4 . The weak output from the Bistable Multivibrator is amplified by transistor Q4 biased by R13 . Diode D4 prevents current from flowing back to the Bistable Multivibrator. The output from Q4 is designed to control relay K 1 which performs the switching operation when a clap is made. Ehiagwina Ojiemhende Frederick et al., Int. Journal of Applied Sciences and Engineering Research, Vol. 5, No. 1, 2016 67 Determination of the reliability of a locally made clap activated switch by part count analysis 3. Reliability assessment of electronic equipment The expression for the parts count method of assessing reliability of the clap activated switch is given in (8) as: n CAS i nR R nC C nQ Q nT T nD D nK K nCON CON nMIC MIC (8) i 1 where: n R Number of resistors in the clap activated switch nC Number of capacitors in the clap activated switch nQ Number of transistors in the clap activated switch nT Number of transformers in the clap activated switch n D Number of diodes in the clap activated switch n K Number of keys or relay in the clap activated switch nCON Number of connectors in the clap activated switch nMIC Number of microphones in the clap activated switch R Failure rate of the resistors C Failure rate of the capacitors Q Failure rate of the transistors T Failure rate of the transformers D Failure rate of the diodes K Failure rate of the keys or relay CON Failure rate of the connectors MIC Failure rate of the microphones CAS Failure rate of the clap activated switch By substituting (8) in (2), the reliability of the clap activated switch is given as (9): RCAS t e tCAS (9) Ehiagwina Ojiemhende Frederick et al., Int. Journal of Applied Sciences and Engineering Research, Vol. 5, No. 1, 2016 68 Determination of the reliability of a locally made clap activated switch by part count analysis 4. Results and discussion The design criteria presented above will be used to assess the locally constructed clap activated switch. We can now obtain the failure rate. The conclusions arrived at will be used to assess the reliability, RCAS t of the clap activated switch, with the generic failure rate which has taken care of the environmental factors, and the results of the failure rates are as shown in Table 1 below. From the Table 1 the total failure rate is obtained to be 0.33503 10 6 Table 1: Failure rate of the component parts of the clap activated switch Components of the clap activated switch (a) Quantity ( ni ) (b) Failure rate of the generic part Failure Rate of the components 10 10 (c) (d) = (b) *(c) 6 6 Resistors 16 0.00370 0.05920 Mica capacitors 7 0.00057 0.00399 MOSFET 1 0.01200 0.01200 Electrolytic 1 0.01300 0.01300 Diodes 5 0.00345 0.01725 Transistors 1 0.00015 0.00015 Transformer 4 0.00061 0.00244 Relay 1 0.04900 0.04900 Connectors 60 0.00130 0.07800 Switch 1 0.10000 0.10000 Total failure rate (CAS ) d 0.33503 Reliability of the clap activated switch plotted against time can be obtained for the period of twenty (20) years as shown in Figure 3, which indicates that the reliability of the clap activated switch decreases with age. A reliability value of not less than 0.98 is expected for the first six (6) year of operation. 5. Conclusion It is observed that the reliability of the Clap Activated Switch constructed locally have an estimated reliability that ranges between 0.99706 for the first year of operation to 0.94299 around the twentieth year of operation. Further work can be done by evaluating the reliability of the device using part stress analysis; this will enable the determination of the reliability under actual operating conditions to be carried out. Ehiagwina Ojiemhende Frederick et al., Int. Journal of Applied Sciences and Engineering Research, Vol. 5, No. 1, 2016 69 Determination of the reliability of a locally made clap activated switch by part count analysis Figure 3: Estimated Reliability of the locally constructed clap activated switch 6. References 1. Abdullahi M. I., Muazu O., & Jibril Y. 2007. Reliability Assessment of an Electronic System: A Case Study of a British Siren in Nigeria, Journal of Applied Sciences Research, 3(12), 1671-1678. 2. Akinsanmi O. 2003. 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