Low Frequency Measurement of Mechanical Vibration Using Optocoupler Sensor and Cantilever System

Sensors & Transducers, Vol. 172, Issue 6, June 2014, pp. 91-97 Sensors & Transducers © 2014 by IFSA Publishing, S. L. http://www.sensorsportal.com Low Frequency Measurement of Mechanical Vibration Using Optocoupler Sensor and Cantilever System Warsito, Sri Wahyu Suciyati, Novi Irawan Physics Department, Faculty of Mathematics and Natural Sciences, University of Lampung Jl. Sumantri Brojonegoro 1, Bandar Lampung – Indonesia 35145 Tel.: +62 8154056557, fax: +62 721 704625 E-mail: Received: 28 March 2014 /Accepted: 30 May 2014 /Published: 30 June 2014 Abstract: It has been realized and characterized the instrument for low frequency measurement of mechanical vibration by using optocoupler sensors and cantilever system. The realized optocoupler sensor system consists of light emitting diode (LED) and phototransistor. The LED is placed on the end of cantilever and phototransistor is placed on the fixed axe as reference point. The frequency of mechanical vibration on the vertical direction can be shown directly by recording the signal detected by phototransistor. The cantilever used is produced from stainlesstel razor blade that gives a 2.98 Hz natural frequency for 0.28 × 10-3 kg of sample weight (mp) and 0.21 × 10-3 kg of cantilever weight (mk). The possible measured frequencies are ranged from 1 – 2.98 Hz. The output of measurement system is directly given in computer by serial interfacing employing microcontroller AT89C51 and MAX232 circuit. Copyright © 2014 IFSA Publishing, S. L. Keywords: Vibration, Optocoupler, Razor blade cantilever. 1. Introduction The mechanical vibration is the importance physical quantity in industries that is characterized by two principal quantities; frequency and amplitude. The vibration transducer has been developed in different manners; piezoelectric system [1-3], magnetic sensor, optical system and cantilever system [4-10]. The use of piezoelectric ceramics patches as sensors and actuators to suppress the vibration of the smart flexible clamped plate was introduced [1]. The vibration of cantilever has been reduced by combining positive position feedback and proportional-derivative control. The use of fiber optic system in measuring of structural vibration has been developed [11]. The smart structure system based on fiber optic vibration sensors was introduced for monitoring the structural damage based on the detection of spatial speckle of a multimode optical with a diameter of 200/230 μm [12]. The measuring accuracy of temperature and vibration measurement using the fiber optic system is practically independent of the properties of the fiberoptic system such as fiber length, fiber diameter and type of connectors used [13]. The accuracy of system in temperature measurement is 0.5 °C in the temperature range 0 to +200°C and a 0.05 g resolution for vibration measurements and a dynamic range of 70 dB has introduced [13], the same value of resolution has also obtained [14]. The Micro-Electro-Mechanical Systems of a laser Doppler interferometric system for measuring motion of vibrating combs have been improved [15]. Fiber optic displacement sensor for the measurement of amplitude and frequency of vibration has been also developed [16]. In measuring of vibration amplitude, the system possess the sensitivity of 0.893 V/mm 91 http://www.sensorsportal.com/HTML/DIGEST/P_2107.htm Sensors & Transducers, Vol. 172, Issue 6, June 2014, pp. 91-97 over 0.6 to 2.1 mm range within a frequency range of 75 to 275 Hz. Recently, the low vibration frequencies measurement by using the Michelson interferometry system has been developed [17]. The use of razor blade combined with a commercial silicon nitride cantilever in carbon nanotube (CNT) probe investigation has been also developed for obtaining nanometer scale resolution of friction measurement by using atomic force microscope [18]. In this research, we have developed the simple system for measurement the low frequency of mechanical vibration by using optocoupler sensors and razor blade cantilever system. We use the light emitting diode (LED) for the illumination source of optocoupler that has also introduced [19]. As receiver of LED illumination, we use the simple phototransistor. The cantilever system has been realized by using stainlesstel razor blade [20]. The system has been also fully equipped by computer serial acquisition system. 2. Methods 2.1. Design of Vibration Transducer System The cantilever system by using capacitive sensing has developed [21]. Here in this research, we use the optocoupler system. The vibration transducer system works by displacing of LED placed on the end of cantilever to the fixed phototransistor sensor. A cantilever used is a beam supported on only one end as shown in Fig. 1. Fixed plate Casing Phototransistor LED Cantilever Fig. 1. Design of Vibration Transducer System. The beam carries the load to the support where it is resisted by moment and shear stress of cantilever. The material used as cantilever in this research is stainless steel razor blade fabricated from steel alloy with a minimum of 10.5 % - 11 % chromium content by mass. The cantilever posses 0.2 × 10-3 kg of weight (mk). In order to minimize the external light noise, the casing has been fully painted in black colour. 2.2. Hardware Design The hardware designed is configurated by vibration transducers system, analog signal conditioning, ADC 0804 circuit, AT89C51 microcontroller and MAX-232 converter (Fig. 2). 92 Vibration Transducer System Analog Signal Conditioner ADC 0804 AT89C51 Microcontroller Computer MAX -232 Fig. 2. Design of mechanical vibration acquisition system. The vibration transducer system is used to convert the physical vibration quantities to electric quantities. The output signal of vibration transducer system is very small, it will be amplify by analog signal conditioning circuit ranged from 0 to 5 Volt. This analog signal will be converted to digital signal by ADC0804 circuit. The parallel digital signal will be commuted to serial signal by AT89C51 microcontroller circuit and MAX-232 circuit. The level of output signal from MAX-232 circuit has been in RS232 serial signal level and will be easily adapted to the computer serial port. In the signal conditioning circuit, the output voltage obtained by phototransistor sensor is very low ranged from 0.1 – 0.5 Volt, this value is not yet adaptable to the ADC analog input. We use the non inverting amplifier in order to gain the output signal ranged from 1 – 5 Volt. The positive analog signal is connected to Vin (+) of ADC, the negative analog signal is connected to Vin (-) and we must be guaranteed that all of ground signal in the same level or in one point. The pin 11 to 18 are the digital output of ADC 0804 then will be connected directly to port 1 of AT89C51 microcontroller as shown in Fig. 3. The signal clock of ADC is produced by connecting a 10 kOhm of resistor to pin 19 and 150 pF of capacitor to pin 19 and ground. In thi (...truncated)