Practical Physics Laboratory Work: Introduction to Multimeters, Signal Generators, and Oscilloscopes

Purpose of Practical Work N°01

• Handling a multimeter.
• Operating a GBF (base frequency generator), which is a low-frequency signal generator.
• Learning to use the oscilloscope.

The Multimeter

• Definition and Functionality: A multimeter is a universal controller or tester that enables the performance of several types of electrical measurements within a single device.
• Primary Measurement Modes:     - Voltmeter: Measuring electrical potential.     - Ammeter: Measuring current flow.     - Ohmmeter: Measuring resistance.
• Applications: Measuring voltage in direct current (DC) or alternating current (AC), testing electrical resistors or components, and measuring low-current circuits.
• Types of Multimeters:     - Digital Multimeter: Features a constant-current generator allowing it to function as an Ohmmeter, Ammeter, current-to-voltage converter, and a digital Voltmeter.     - Analog Multimeter: Includes a voltage-current converter and a magnetoelectric ammeter. Unlike digital models, it requires no batteries for current and voltage measurements.
• Terminal Connections:     - Common (COM): Also referred to as the minus (-) terminal. The black wire is always connected to this terminal regardless of the measurement type.     - Voltage Terminal (V): Marked as (+) or "V". This is where the red wire is connected to measure voltage.     - Resistance Terminal ($\Omega$): Marked with the omega symbol. This is the input for the red wire when measuring resistance.     - Amperage Terminal (A): This is the input for the red wire when measuring current (amperage).
• Measurement Parameters and Accuracy:     - Choosing the Gauge (Size): The chosen gauge influences measurement accuracy. There is an inverse relationship where the smaller the gauge, the greater the accuracy.     - Threshold Rule: For a measurement to be successful, the gauge must remain greater than the value being measured (e.g., resistance). If the measurement exceeds the gauge, no value is displayed.
• Reading Measurements:     - Digital Readout: The value displayed on the screen is expressed in the same units as the selected gauge.     - Analog Readout: The voltage measurement is calculated using the following formula:     $U = \text{the size} \times \text{reading the wick}$
• Manipulation 1:     - Step 1: Create an assembly as shown in the provided figure (lamp circuit).     - Step 2: Read and record the voltage value at the lamp terminal.

Base Frequency Generator (GBF)

• Definition: A device that delivers periodic electrical signals over a wide range of frequencies. It also offers the option of superimposing a continuous (DC) signal.
• Setting Parameters:     - Frequency: Configured via a range selector (FREQUENCY) with increments such as $10\,Hz$, $100\,Hz$, $1000\,Hz$, etc., and a rotary knob for fine-tuning values between $0.2$ and $2.0$.     - Signal Shape: Options include square, triangular, and sinusoidal waves.     - Amplitude: Adjusted using the "level" or "amplitude" buttons.
• Manipulation 2:     - Step 1: Set up a circuit where the voltmeter is connected to the generator terminals.     - Step 2: Ensure correct polarity by connecting the voltmeter's "V" terminal to the generator's (+) terminal and the voltmeter's "COM" terminal to the generator's (-) terminal.     - Step 3: Select the appropriate voltmeter rating and power on the voltmeter.     - Step 4: Switch on the generator and use the potentiometer to set its voltage to $5\,V$.     - Step 5: Observe the voltage displayed on the voltmeter and compare it to the generator's setting for discussion.

The Oscilloscope

• Definition: A measuring device that displays variations in voltage as a function of time ($V = f(t)$) or as a function of another voltage ($XY$ mode). It is essential for studying alternating voltages.
• Capabilities: It accepts two input channels, allowing for the simultaneous study and comparison of two distinct electrical signals regarding amplitudes, periods, and phase shifts.
• Voltage Measurement Procedure:     - Apply a sinusoidal voltage from a GBF to the input of Channel 1.     - Select the appropriate rating to ensure correct signal display.     - Task 1: Measure the peak-to-peak amplitude ($V_{c-\grave{a}-c}$) of the signal.     - Task 2: Measure the voltage using a multimeter.     - Recording Data (Table 1): Include Calibre oscill ($V/cm$), $V_{c-\grave{a}-c}$ (volts), $V_{max}$ (volts), $V_{multim\grave{e}tre}$ (volts), and $V_{effe}$ (volts) for sinusoidal, triangular, and square-wave signals.
• Frequency Measurement Procedure:     - Apply a sinusoidal signal ($f > 100\,Hz$) from a GBF to Channel 1.     - Adjust calibrators for a clear signal display.     - Task 1: Measure the period ($T$) of the signal.     - Recording Data (Table 2): Include $Fr\grave{e}q.GBF$ ($Hz$), Calibre de temps (time base), Nbre de cm (number of cm/divisions for $T$), $T(s)$, and calculate frequency using the formula:     $f = \frac{1}{T}\,Hz$
• Phase Shift Measurement (Time Reference Method):     - Step 1: Assemble a circuit using a resistor $R$ and a capacitor $C = 4.7\,\mu F$.     - Step 2: Press the GD (ground) keys to ground the input signals, then adjust the traces to superimpose them perfectly on the x-axis.     - Step 3: Vary the resistance $R$ ($100\,\Omega$, $500\,\Omega$, $1000\,\Omega$) and determine the phase shift ($\phi$) for each value using the formula provided in Table 3:     $\phi = \frac{t}{T} \times 360$     - Required data: $R (\Omega)$, $t (cm)$, $T (cm)$.

Lissajous Method

• Two Signals of the Same Frequency:     - Step 1: Set the oscilloscope to horizontal sweep by pressing the X-Y button.     - Step 2: Press the GD buttons on both channels and fix the spotlight in the center of the axes.     - Step 3: For the same R-C circuit, determine phase shift for values of $R$ ($100\,\Omega$, $500\,\Omega$, $1000\,\Omega$).     - Calculation (Table 4):     $\sin(\phi) = \frac{a}{b}$$\phi = \arcsin\left(\frac{a}{b}\right)$     - Required variables: $a (cm)$ (intercept on y-axis) and $b (cm)$ (maximum vertical deflection).
• Two Signals of Different Frequencies:     - Step 1: Set the oscilloscope to horizontal sweep by pressing the Hor.ext. button.     - Step 2: Press GD buttons and center the spotlight.     - Step 3: Apply the signal from GBF1 to channel 1 and the signal from GBF2 to channel 2.     - Step 4: Vary the GBF2 frequency ($100\,Hz$, $180\,Hz$, $200\,Hz$) until a stable figure is obtained on the screen.     - Calculation (Table 5): Identify the number of tangency points on the x-axis ($N_x$) and y-axis ($N_y$) to find the ratio $N_x/N_y$. Calculate the unknown frequency ($F_x$) relative to a reference frequency ($F_0$):     $F_x = F_0 \times \frac{N_x}{N_y}$

Institutional and Course Information

• Institution: University of Algiers 1, Faculty of Science, Department SM (L1).
• Module: Practical physical work 2 (electricity).
• Academic Year: 2025/2026.
• Instructor: Dr. AIT KAIETZ.
• Document Title: PW N°01 : INTRODUCTION.