Calibration and Digital Linearization of Ultrasonic Transducer Response

Sensors & Transducers, Vol. 183, Issue 12, December 2014, pp. 48-52 Sensors & Transducers © 2014 by IFSA Publishing, S. L. http://www.sensorsportal.com Calibration and Digital Linearization of Ultrasonic Transducer Response * Warsito, Sri W. Suciyati, Gurum A. Pauzi, Berli L. Putra, Sisca Aprila, Laila Kurniati 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: 21 October 2014 /Accepted: 28 November 2014 /Published: 31 December 2014 Abstract: This paper discusses the calibration and digital linearization method of ultrasonic transducer responses. The system consists of a power supply circuit, a pair of series HC-SR04 ultrasonic transducers (transmitter and receiver), a digital signal conditioning circuit using ATmega16 microcontroller and output monitor using a 16×2 LCD screen. The calibration is done by measuring the water level, and the nonlinearity of ultrasonic transducer responses has been obtained during calibration steps. For linearizing the response, we have performed the segment linearization method and finally we have obtained the fixed nonlinearity equation of transducer responses for all range measurements. The equation of nonlinearity responses is then stored in the microcontroller as a base to respond to the physics input that means the water level. Each physics input that is read by the ultrasonic transducer is further processed digitally by a microcontroller and the results are displayed on the LCD screen. The water level displayed on the LCD screen shows a linear response and is in conformity with the actual value of water level and the theoretical calculation. The average error of calibration and digital linearization compared with the theoretical calculation is 0.299 %. With the system, we can then use directly the transducer to measure and control the water level system. Copyright © 2014 IFSA Publishing, S. L. Keywords: Linearization methods, Ultrasonic transducer, Microcontroller. 1. Introduction Sensor or transducer linearization response is very important performance in application, so it will provide convenience to process subsequent information. Sensor response linearization method has a variety of ways, and it all depends on the type of sensor or transducer used. The step of response linearization can be done at the analog and also at the digital step of signal conditioning circuits. Before performing calibration and linearization phase, sensors and transducers are based on a change of resistance responses, we need firstly convert the 48 resistance change into a change of voltage or current. The various methods for the conversion as well as in the first step of analog linearization have been discussed previously. A simple and universal resistive-bridge sensors interface that is cost effective three-point measuring technique and also does not require any additional active components has been fully discussed [1]. Linearization of nonlinear nature capacitive sensors has been studied by using the polynomial linearization scheme and the improvement in accuracy is obtained by the direct linearization scheme which scales the sensor output by the http://www.sensorsportal.com/HTML/DIGEST/P_2541.htm Sensors & Transducers, Vol. 183, Issue 12, December 2014, pp. 48-52 nonlinear denominator [2]. Sometimes the digital linearization methods are employed in embedded system applications by using the comparison criteria of power dissipation, area, throughput, design time and rate of cost [3]. Linearization of radio-frequency sensors output has been studied by numerical method and he shows that the nonlinearity factor can be regulated by varying the capacitance of a correcting capacitor [4]. Using microcontroller as the principal linearization and calibration instrument has been shown and given the simple method in digital linearization. The equation of non linearity of sensors response can be directly stored in the microcontroller memory in order to process the nonlinearity response of sensor [5]. The lockup table of digital linearization has been minimized in order to obtain the optimal design and to reduce the memory footprint and intermediate table values are estimated by linear interpolation [6]. The dynamic measurement and correction of laser interferometer periodic nonlinearity down to the pedometer level has also been shown. They have used a capacitive sensor to be an external reference for measuring and calculating the periodic interferometer nonlinearity correction function [7]. The method of linearization of such non-linear sensors characteristics using analog electronics has been described and the theoretical explanation of the methods and its verification by experiment has also been stated [8]. Digital linearization method called ‘probability density function’ of the measured data to reduce the number of calibration points, as well as the associated calibration time, for a required level of accuracy has been shown [9]. Lastly, the analog and digital methods of linearization have been shown and the method choice depends fully on sensor type and the designer [10-12], and the 2D digital calibration of transducer response has been also studied [13]. We have also recently shown a different type of sensor linearization methods, and we conclude that the digital type of linearization method is more efficiency, small size and low cost [14–16]. In this paper, we study the calibration and digital linearization for ultrasonic transducer response and characterize the system to find the simplest digital method possible. 2. Methods This section will explain the design of signal conditioning circuit of the system was made. The circuit is very simple because it uses a digital signal conditioner, as has been reviewed previously [5, 9-10, 13-15]. The complete circuit for linearization response of ultrasonic transducer is shown in Fig. 1. Fig. 1. The complete circuit for linearizing of ultrasonic transducer response. 49 Sensors & Transducers, Vol. 183, Issue 12, December 2014, pp. 48-52 The circuit consists of a DC power supply (1), a pair of series HC-SR04 ultrasonic transducers (transmitter and receiver) (2), digital signal conditioner using Atmega16 microcontroller (3), output signal will be on 16×2 LCD screen (4), and buzzer indicator (5). The power supply of an ultrasonic transducer uses a DC voltage which is converted into a digital signal whose frequency (40 kHz) is controlled by a microcontroller through the PB0 port. The ultrasonic waves emitted by the transducer is then received by the receiving transducer and forwarded to the microcontroller through the PB1 port. The ATmega16 microcontroller has an internal ADC, so the analog input can directly be received, it’s different with the AT89C51 microcontroller that we used previously [15]. The signal is then processed by a microcontroller a (...truncated)