CC BY
61Electronic Journal «Technical Acoustics» http://www .ejta.org
2007, 12
S. Rajagopalan1, S. J. Sharma2, V. M. Ghodki3
1 Department of Electronics, Nagpur University Campus, Nagpur 440 033 (India) e-mail: rajag_ngp@sancharnet.in
2 Department of Electronics, S. K. Porwal College, Kamptee, Nagpur 441 002 (India) e-mail: sjsharma@rediffmail.com
3 Department of Electronics, J. B. Science College, Wardha 442 001 (India) e-mail: nanditag_wda@sancharnet.in
Low cost virtual instrumentation using PC printer port for ultrasonic velocity measurements
Received 01.06.2007, published 03.07.2007
The most popular and effective technique for ultrasonic velocity measurements is the pulse technique. In the present work, PC based single-pulse sender/receiver system is developed using indigenous components and the bi-directional printer port. A program written in C, under the DOS/WINDOWS environment, controls the pulse generation, detection and travel time measurement. A radio frequency burst of 2 MHz of 5 |j,s width is obtained from an external source. This pulse is amplified and sent to the transmitting transducer. The received pulse is detected and is used to stop the counter. The number of pulses is counted using a 32 MHz external crystal source. The count is read by printer port and is further used in determining the travel time and to display the ultrasonic velocity of propagation in the medium on the computer screen. The system developed has been tested for ultrasonic velocity measurements in standard liquids. It has been found that the ultrasonic velocity measurement results obtained using the above system match well with those reported in the literature.
INTRODUCTION
Ultrasonic measurements have been put to use for a variety of applications for many decades now. Initial rapid developments in instrumentation [1, 2] provoked by the technological advances since 1950 continue even today. Through the 1980's and continuing into the present, computers have provided scientists with smaller and more robust instruments with greater capabilities in the measurements of ultrasonic parameters [3]. Numerous techniques and instruments have been designed by researchers to cope up with the requirements of higher accuracy.
The advent of PC have made the researchers to exploit its capabilities to sense, detect, modify, manipulate and display the acquired data [4-6] in user required form. So the conventional instrumentation is being replaced by Virtual Instrumentation (V.I.) [7, 8]. The instruments that were used for ultrasonic measurements are replaced by V.I. In a low cost V.I., data acquired using transducers with necessary signal conditioning is fed to the directional printer port for online or offline processing. All these operations are performed
under the suitable software control. The collected data is processed and displayed in the desired form. The data can be stored for future reference and use, leading to more consistent and accurate measurement.
There are different techniques [9] for measurement of ultrasonic velocity in liquids. The techniques for measurements of ultrasonic velocity in liquids can be classified into pulsed and continuous wave (CW) methods. The pulsed method includes sing around, pulse echo overlap and pulse superposition techniques [10] and continuous wave method includes interferometric technique. CW technique is generally used in low frequency region, and it suffers from number of drawbacks such as presence of complicated modes of vibrations, boundary effects, and large energy dissipation, which results in unwanted heating of the sample. These shortcomings of CW techniques can be overcome using the pulse technique. Woodward and Salman[11] designed a programmable ultrasonic velocity meter using a single pulse transmission technique. There were limitations on the range of values of ultrasonic velocities and digital counter.
In the present work, we have designed a computer based single pulse sender/receiver technique using bidirectional printer port with indigenous components. The system is accurate, reliable, fast and flexible to be operated over a wide range of velocities and frequencies.
A simple graphical user interface designed in VISUAL BASIC [12] at front-end, controls the various functions involved in the measurements. The system developed in our laboratory has been tested for ultrasonic velocity measurements in different standard liquids. The ultrasonic velocity measurements using the above technique, matches well with those reported in the literature.
HARDWARE DESIGN AND SOFWARE
The hardware consists of instrumentation required for measurements and a centronics bidirectional [13] printer port. Each printer port consists of three port addresses: data, status and control port. These addresses are in sequential order. That is, if the data port is at address 0X0378, the corresponding status port is at 0X0379 and the control port is at 0X037a. Fig. 1 and Fig. 2 give the description of printer port pins assignments and port assignments respectively.
View is looking at Connector side of DB-25 Male Connector
Pin Description
1 /Strobe PC Output
2 Data 0 PC Output
3 Data 1 PC Output Pin Assignments
4 Data 2 PC Output
5 Data 3 PC Output Note: 8 Data Outputs
6 Data 4 PC Output 4 Misc Other Outputs
7 Data 5 PC Output
8 Data 6 PC Output 5 Data Inputs
9 Data 7 PC Output
10 /ACK PC Input
11 Busy PC Input Note: Pins 18-25 are
12 Paper Empty PC Input Ground
13 Select PC Input
14 /Autofeed PC Output
15 /Error PC Input
16 Initialize Printer PC Output
17 /Select Input PC Output
Fig. 1. Pin assignments
Data Port Status Port
D7 ►Data 7 D7 «— Busy
D6 ►Data 6 D6 4— /ACK
D5 ►Data 5 D5 4— PE
D4 ►Data 4 D4 4— Select
D3 ►Data 3 D3 4— /Error
D2 ►Data 2 D2 <— /IRQ
D1 ►Data 1 D1 Res.
D0 ►Data 0 D0 Res.
Fig. 2. Port assignments
Control Port
D7 Res.
D6 Res.
D5 ► Direction
D4 ► IRQ Enable
D3 ► /Select In
D2 ► INIT
D1 ► /Autofeed
D0 ► /Strobe
In present work data port is used as input port, status port as input port and control port as output port. Table 1 depicts the actual use of each printer port pin.
Table 1
Pin Description Use Type Pin Description Use Type
1 Strobe Clear Output 10 Ack D8 Input
2 Data 0 D0 Input 11 Busy D9 Input
3 Data 1 D1 Input 12 PE D10 Input
4 Data 2 D2 Input 13 Select D11 Input
5 Data 3 D3 Input 14 Autofeed 5 uS Output
6 Data 4 D4 Input 15 Error Not Used
7 Data 5 D5 Input 16 Init S Output
8 Data 6 D6 Input 17 Select in R Output
9 Data 7 D7 Input 18 Ground Gnd Output
Fig. 3 shows the block diagram of a single pulse sender/receiver technique. It consists of IBM compatible PC with bi-directional printer port, RF Amplifier, sample holder with matched piezoelectric transducers, receiver amplifier and pulse shaper circuit. Fig. 4 shows the printer port interface to system. A pulse of 5 ^s is generated using a program. This pulse is given to an AND gate with a 2 MHz source so as to get r.f. carrier pulse of 2 MHz. This is amplified by r.f. amplifier to 24 V peak to peak, is used to drive the transmitting transducer, Tx. The ultrasonic waves generated travel through a sample and are then received by receiving transducer, TR. The received pulse consists of the direct received pulse and the echoes. This pulse is amplified by the receiver amplifier (Fig. 5) to generate pulse of 5 Volts for each echo to trigger the printer port to record the number of pulses, under the program control. This count is used to display the velocity of the liquid under test on the front panel designed using VB.
Fig. 3. Block diagram of a single pulse sender/receiver technique
Software is used to control the total operation of triggering, receiving the pulse corresponding to echo and measuring the travel time. For pulser/receiver circuit printer port pins are used. DOS platform is used to write software in C programming language.
Initially, a reset pulse is generated using the software to activate R input of Flip-Flop to reset the counter. A trigger pulse is generated and sent to the transmitting transducer, simultaneously a pulse is sent to S input of Flip-Flop to activate the counter. The counter (12 bit - 743939) is used to record the counts between the trigger and the first received echo. An external standard frequency source of 32 MHz is used to measure the travel time of the sonic pulse for a given sample length. Counter stops counting of the pulses as soon as the first echo is received. The count is then read using software through bi-directional printer port. It gives the total travel time that includes the total travel time through sample and electronic delay. The electronic delay can be determined using ultrasonic velocity propagation in standard liquid. The ultrasonic velocity in the liquid under study is calculated and displayed on the screen designed (Fig. 6) for V.I. using VB. This procedure can be repeated number of times as per the user’s need. The data corresponding to repetitions are stored in the computer file and can be used for further analysis. The same program calculates the actual velocity in the liquid sample and displays the velocity on the screen.
Fig. 4. Diagram showing the printer port interface
RESULTS
The system has been developed in the laboratory and tested for the ultrasonic velocity measurements in distilled water. It has been found that the ultrasonic velocity measurements carried out using the above system matches well with those reported in the literature. Table 2 shows the results of our measurements carried out for water at various temperatures.
Table 2
Liquid Temperature (C°) Present work (m/s) Literature (m/s) [14]
Water 25.0 1496.69 1496.687
26.4 1500.20 1500.356
27.6 1503.54 1503.384
28.3 1505.24 1505.102
30.5 1510.12 1510.272
31.7 1512.83 1512.949
+9V
From Printer port R Initiai s
Fig. 5. Circuit diagram of a receiver amplifier and pulse shaper
Fig. 6. Screen shot showing the front panel
DISCUSSION
The ultrasonic velocity measurements using the present PC based system are found to be precise and consistent. The system can be used for measurements in different liquids at different temperatures. In the present work, 32 MHz standard external frequency source was used for travel time measurements. Attempts are being made to use higher value frequency sources for better resolution. New systems in binary liquids or gel form are being taken up.
ACKNOWLEDGEMENT
The authors are grateful to Miss Gajbhiye, Head, Department of Electronics, RSTM, Nagpur University, Nagpur to carry out the experimental work. The authors are grateful to Mr. V. R. Vyaghra for useful discussions during the work, to Dr. M. N. Ghoshal and Dr C. D Zanwar for their interest in the work. One of the authors (S. J. Sharma) would like to thank University Grants Commission, New Delhi for the financial assistance provided to carry out the work.
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