Question

What is the method of digital multimeter?

Answer 1

A digital multimeter (DMM) is a versatile tool used to measure electrical quantities like voltage, current, and resistance. It works by converting the analog signal (from the electrical circuit) into a digital value, which is then displayed on the screen. Here's how the method of a digital multimeter works:

Basic Operation:

1. Voltage Measurement (DC or AC):
   

   - When measuring voltage, the multimeter is connected across two points of the circuit. It calculates the difference in electrical potential (voltage) between these two points.
   - For DC voltage (direct current), the meter measures how much potential difference exists in a circuit.
   - For AC voltage (alternating current), it measures the average voltage over a period of time.

1. Current Measurement (DC or AC):
   

   - To measure current, the multimeter is connected in series with the circuit, meaning the current flows through the meter.
   - The multimeter measures the amount of current flowing through the circuit.
   - For DC or AC current, the multimeter uses an internal shunt resistor to measure the current. The voltage drop across this resistor is used to calculate the current using Ohm's law.

1. Resistance Measurement:
   

   - When measuring resistance, the multimeter sends a small known voltage through the resistor and measures the resulting current.
   - Using Ohm’s law (V = IR), it calculates the resistance.
   - For resistance, the multimeter also needs to generate its own voltage because no external power source is involved.

1. Other Features:
   

   - Continuity Check: It checks if a circuit is complete. It emits a beep sound when there is continuity (when the circuit is closed).
   - Diode Testing: The multimeter can also check diodes to see if they are functioning properly, by applying a small voltage and checking the forward voltage drop.

Working Principle:

1. Signal Conversion: Inside the digital multimeter, an analog-to-digital converter (ADC) converts the analog signal from the electrical circuit into a digital value.
   

1. Display: The digital value is then displayed on the multimeter’s screen, allowing the user to read the measurement directly.
   

Types of Measurements:

1. DC Voltage (V or VDC): Measures direct current voltage.
   

1. AC Voltage (V~ or VAC): Measures alternating current voltage.
   

1. DC Current (A or ADC): Measures direct current in amperes.
   

1. AC Current (A~ or AAC): Measures alternating current in amperes.
   

1. Resistance (Ω): Measures resistance in ohms.
   

1. Capacitance (F): Measures the capacitance of capacitors (on some models).
   

1. Frequency (Hz): Measures the frequency of an AC signal (on some models).
   

Summary of Key Features:

1. Auto-ranging: Automatically selects the appropriate measurement range.
   

1. Manual ranging: You select the measurement range yourself, which is useful in more precise or specialized measurements.
   

1. Backlight: For easy reading in dark conditions.
   

Digital multimeters are essential tools in electrical and electronics work, providing accurate and quick readings for troubleshooting and testing circuits.