Electronic Measurements ELE221 - Lec 4 Quiz

Electronic Measurements (ELE221) - Part 2 Lec 4: Miscellaneous Instruments

• The course is Electronic Measurements (ELE221)
• The lecture is Part 2, Lec 4
• The lecturer is Dr. Islam Mansour
• The date of this class is 2024-2025

Review of Miscellaneous Instruments

• A circular display (as in Fig. 11-30(e)) can be made into a dashed-line display by applying a separate signal to the Z input of the oscilloscope.
• The ratio between the highest and lowest frequencies (fm/fp) of the two inputs is equal to the number of gaps in the circle.

Oscilloscope Probe (10:1)

• A 10:1 Oscilloscope Probe is used with an oscilloscope with Ri = 1ΜΩ and Ci = 40 pF.
• The probe uses a 9 ΜΩ series resistor and the coaxial cable has a capacitance of 80 pF.
• The equivalent circuit of the probe needs to be drawn.
• The value of capacitor C1 that should be connected in parallel with the 9ΜΩ resistor to make the probe compensated needs to be determined.
• The frequency at which the probe produces a 3dB reduction in signal from a 500Ω source resistance needs to be calculated.
• The capacitive network attenuates the signal in the same proportion as the resistive network. V_i across R_i equals V_i across C₂.
• The value of C₁ is determined using the formula C₁ = C₂R_i/R₁

Applications of RF Oscillator (Frequency Modulation)

• The VVC diode capacitance (C_D) is in parallel with the oscillator tank circuit capacitor (C₄).
• The LF input alters C_D, by varying the diode reverse bias voltage.
• The tank circuit resonant frequency is altered, and circuit output frequency is modulated.

Chapter 15: Miscellaneous Instruments

• This chapter covers various instruments used in measurements.

Outline of Measuring Instruments

• Permanent records of waveforms can be made using a strip-chart recorder or an X-Y recorder.
• A strip-chart recorder uses a continuously moving strip of paper and a pen. The pen deflection is proportional to the input voltage.
• An X-Y recorder uses a single sheet of paper with two inputs, one for horizontal and one for vertical deflection, of the pen.
• 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 against frequency.

Strip-Chart Recorder

• A galvanometric/oscillographic strip-chart recorder uses a strip of paper that unrolls under a pen.
• Pen deflection (or pointer position) is proportional to the voltage applied to the moving coil circuit.
• Paper moves at a constant velocity, tracing the input waveform.
• Sometimes called a YT recorder (proportional to time).
• The maximum frequency is typically 200Hz.
• Pens are usually disposable fiber-tipped.
• The deflection system uses a galvanometer with a mirror and a light source.
• Light beam strikes photographically treated paper.
• The system advantages include fast measurement up to 5KHz.
• A disadvantage is that special paper is needed

Potentiometric Strip-Chart Recorder

• Mechanism is self-balancing potentiometer, controlling pen position.
• Pen holder contacts a potentiometer slide wire with a DC supply (±E).
• The voltage (Vf) is passed via a voltage follower to resistor R4, which is part of the summing amplifier.
• The output voltage of the amplifier (Vo) is the sum of the input voltages, Vo = R5(I2 + I3 + I4).
• Accuracies are typically ±0.2% for potentiometric type, and ±2% for galvanometric instruments.

X-Y Recorders & Plotters

• X-Y recorder mechanism is similar to potentiometric strip-chart.
• Uses two servomotors (one for X, one for Y movement)
• Control circuits include zero control, summing amplifier, and voltage follower for feedback from the slide wire.
• Input amplifier for X-Y recorder has switch S1 to select the range or Vernier, and S2 to select V/cm deflection sensitivity.
• X-Y recorders have three input terminals (+, -, ground) for each X and Y section.
• X-Y recorders have controls for range, zero, and Vernier for both X and Y inputs.

Plotters

• Plotters move a sheet of paper and pen to draw diagrams.

Diode Characteristics

• Forward and Zener diode characteristics can be traced. The setup includes circuits with specific resistors, like 1kΩ, to measure various input voltages.

Transistor Characteristics

• Circuit for plotting transistor characteristics on an X-Y recorder. Specific components like R1, R2, and C1 are used in the circuit.

Distortion Meter

• Measures harmonic distortion (THD) in waveforms.
• One method determines THD by suppressing the fundamental component, then measuring the rms value of the combined harmonics.
• THD is expressed as a percentage of the complete waveform voltage.

Rejection Amplifier

• A basic component of a fundamental suppression distortion meter is a notch filter.
• The notch filter attenuates the fundamental frequency component while passing all harmonics.
• The Wein bridge is tuned to balance at the fundamental frequency, filtering it out.

Spectrum Analyzer

• Separates an AC signal into its frequency components, displaying each as a vertical line on a CRT screen.
• The instrument has a sweep generator, a voltage-tunable bandpass filter, a detector, CRT, together with vertical and horizontal deflection amplifiers.
• Bands pass filter sweeps frequency range giving different components displaying on CRT connected to a vertical line, for each frequency.
• The analyzer has three input terminals (+, -, ground).

Test your understanding of miscellaneous instruments discussed in Electronic Measurements (ELE221) Part 2, Lecture 4. This quiz covers concepts like circular displays, oscilloscope probes, and the frequency response of instruments. Challenge yourself to apply the theoretical knowledge gained in class.