ELE221 Electronic Measurements (2024-2025) Part 2 Lec 4 PDF

Benha University Faculty of Engineering (Shoubra) Electronics and Communications Engineering ELE221 Electronic Measurements (2024-2025) Part 2 Lec4: Miscellaneous Instruments Dr. Islam Mansour 1 ...

Benha University Faculty of Engineering (Shoubra) Electronics and Communications Engineering ELE221 Electronic Measurements (2024-2025) Part 2 Lec4: Miscellaneous Instruments Dr. Islam Mansour 1  Review 2 © Oxford University Press 2013. All rights reserved.  Review A 10:1 Oscilloscope Probe is used with an oscilloscope with Ri = 1MΩ and Ci = 40 pF. If the probe uses a 9 MΩ series resistor and the coaxial cable has a capacitance of 80 pF, Draw the equivalent circuit of the probe then determine the value of capacitor C1 that should be connected in parallel with the 9MΩ resistor to make the probe compensated. Also, calculate the frequency at which the probe will produce a 3dB reduction in signal from a 500Ω source resistance. Solu: 3 © Oxford University Press 2013. All rights reserved.  Applications of RF Oscillator Frequency modulation (FM) © Oxford University Press 2013. All rights reserved.  Chapter 15 Miscellaneous Instruments © Oxford University Press 2013. All rights reserved.  Outline Permanent (hard copy) records of waveforms can be made by use of a strip-chart recorder or an X-Y recorder. In the strip-chart recorded, a continuously moving strip of paper is passed under a pen or other recording mechanism. The pen is deflected back and forward across the paper in proportion to an input voltage. The X-Y recorder uses a single sheet of paper and has two inputs; one input deflects the pen horizontally and the other produces vertical deflection. A distortion meter measures the total harmonic distortion (THD) content in an input waveform. A spectrum analyzer uses a CRT display to show signal amplitude plotted to a base of frequency. 6 © Oxford University Press 2013. All rights reserved.  Strip-Chart Recorder In a galvanometric (or oscillographic) strip-chart recorder a strip of paper is unrolled and passed under a pen. The pen deflection (or pointer position) is directly proportional to the voltage applied to the moving coil circuit. With the paper passing under the pen at a constant velocity, the waveform of the input voltage is traced out on the paper. Because the movement of the paper is proportional to time, a strip-chart recorder is sometimes termed a YT recorder. Due to the weight of the pointer, the maximum frequency is 200Hz. The pens used are disposable fiber-tipped type. © Oxford University Press 2013. All rights reserved.  Strip-Chart Recorder The deflection system is a small galvanometer with a mirror and light source. A finely focused beam of ultraviolet light is reflected from the mirror onto photographically treated paper, producing an instant trace. The one disadvantage of the light beam system is that special paper is required. A major advantage is that this type of instrument can record waveforms with frequencies up to 5KHz. © Oxford University Press 2013. All rights reserved.  Potentiometric Strip-Chart Recorder The potentiometric strip-chart recorder mechanism is essentially that of a self- balancing potentiometer. The basic arrangement for controlling the pen position. The pen holder makes electrical contact with a potentiometer slide wire which has a DC supply voltage (±E) applied to its terminals. This voltage (Vf) is passed via a voltage follower (A3) to resistor R4, which as part of the summing amplifier. The output voltage of the amplifier (Vo) © Oxford University Press 2013. All rights reserved.  10 © Oxford University Press 2013. All rights reserved.  The accuracy of the potentiometric strip-chart recorder depends on supply voltages ±E. A major disadvantage of the potentiometric strip- chart recorder is its low frequency response. The maximum frequency that may be traced is usually 10Hz. An important advantage of this instrument is that it can be much more accurate than the galvanometric type. Typical accuracies are ±0.2%for potentiometric type, and ±2% for galvanometric instruments. 11 © Oxford University Press 2013. All rights reserved.  Potentiometric Strip-Chart Recorder This type of instrument has five chart speeds ranging from 1cm/min to 2cm/h. Input (voltage or current) waveforms are sampled at a rate of 100 samples/second. Traced quantities are displayed on an LCD meter and recorded on the chart paper. Input ranges are typically 0.1V to 500 V and 10A to 100A. © Oxford University Press 2013. All rights reserved.  X-Y Recorders & Plotters The X-Y recorder mechanism is the same as the potentiometric strip-chart recorder. There are two servomotors, the first servomotor is for the y-direction movement and the second is for the x-direction movement. The control circuits for the X input and Y input are zero control, a summing amplifier, and a voltage follower for the feedback from the slide wire. © Oxford University Press 2013. All rights reserved. X-Y Recorders & Plotters © Oxford University Press 2013. All rights reserved.  Representative X-Y Recorders The X-Y recorder has three input terminals (+,-, and ground) for each (X and Y) section. © Oxford University Press 2013. All rights reserved.  Plotters © Oxford University Press 2013. All rights reserved. Diode Characteristics © Oxford University Press 2013. All rights reserved. Transistor Characteristics © Oxford University Press 2013. All rights reserved.  Distortion Meter Harmonic Distortion A sine-wave input to an electronic circuit may produce an output wave that is distorted instead of being purely sinusoidal. Harmonic distortion consists of the fundamental frequency component and a number of harmonics. One method of determining the harmonic content is to suppress the fundamental component and measure the rms value of the combined harmonics. © Oxford University Press 2013. All rights reserved.  Rejection Amplifier The basic component of a fundamental suppression distortion meter is a notch filter. The notch filter must heavily attenuate the fundamental frequency component while passing all harmonics. © Oxford University Press 2013. All rights reserved.  Spectrum Analyzer A spectrum analyzer separates an AC signal into its frequency component and displays each component as a vertical line on a CRT screen. Tuned radio frequency spectrum analyzer (TRF Spectrum Analyzer) consists of a sweep generator, a voltage-tunable band pass filter, a detector, and a CRT together with vertical and horizontal deflection amplifiers © Oxford University Press 2013. All rights reserved.  Spectrum Analyzer Display Amplitude Suppose modulated that two signal. different The display signals with consists of a frequencies single, large, 200KHz and vertical line, 300KHz. representing the carrier frequenc amplitude, together with two smaller line representing the two sideband frequency components A pure sine wave will display fundamental frequency and higher order harmonics ©with Oxford University small value Press 2013. All rights reserved.  End of Lecture Best Wishes 23 © Oxford University Press 2013. All rights reserved.