Short Answer:

An analog multimeter works using a moving coil mechanism called a galvanometer. When electrical current flows through the coil, it interacts with a magnetic field and creates a deflecting torque that moves a pointer over a calibrated scale. This movement shows the measured value of voltage, current, or resistance.

Different internal circuits are used to allow the analog multimeter to measure AC, DC, and resistance. The user manually selects the desired range and function using a rotary switch. The needle’s position on the scale gives the reading, which must be interpreted carefully for accuracy.

Detailed Explanation:

Working of analog multimeter

An analog multimeter is a type of measuring instrument used to measure voltage (volts), current (amperes), and resistance (ohms). It is called “analog” because it uses a pointer and scale instead of a digital display. The core of an analog multimeter is a moving coil galvanometer, which is a sensitive device that detects small electrical currents and converts them into needle movements.

The working of an analog multimeter depends on the deflection of a pointer due to the flow of electric current through a coil placed in a magnetic field. The pointer moves over a graduated scale that is marked for different electrical quantities. The amount of pointer movement is proportional to the current flowing through the coil.

Basic Components and Functioning:

Galvanometer (Moving Coil):
This is the main part that detects current. It consists of a coil of wire suspended in a magnetic field. When current passes through the coil, it experiences a force that causes it to move, rotating a pointer over the scale.
Pointer and Scale:
The needle attached to the coil moves across a marked scale. The scale has different markings for voltage, current, and resistance, often in multiple ranges.
Range Selector Switch:
This rotary switch allows the user to select what quantity to measure (V, A, or Ω) and the range (e.g., 10V, 50V, 250V).
Multiplier Resistors:
These are used when measuring voltage. They are connected in series with the galvanometer to allow the meter to measure higher voltages safely.
Shunt Resistors:
When measuring current, low-resistance shunts are connected in parallel with the galvanometer to bypass most of the current.
Battery and Series Resistor (for Resistance Measurement):
A small battery inside the meter provides the power needed to measure resistance. The meter sends a current through the unknown resistor and detects the voltage drop to calculate resistance.

Working in Different Modes:

DC Voltage Measurement:
The meter uses a multiplier resistor in series with the galvanometer. The voltage causes a small current to flow through the coil, moving the pointer proportionally.
DC Current Measurement:
The current flows directly through the shunt and galvanometer. The meter uses calibrated shunts to measure various current ranges.
Resistance Measurement:
The internal battery sends a current through the unknown resistor and the meter. The deflection is then translated into a resistance value.
AC Measurement:
For AC, a rectifier is used to convert AC into DC, which the galvanometer can respond to. The meter scale is calibrated accordingly to give RMS values.

Advantages of Analog Multimeter:

Can show continuous changes in signal.
No battery needed for voltage and current measurements.
Simple and inexpensive for basic use.

Limitations of Analog Multimeter:

Less accurate than digital multimeters.
Needle movement is affected by vibration.
Requires manual range selection and scale reading.
Not suitable for low voltage or weak signal detection.

Conclusion

An analog multimeter works on the principle of a moving coil galvanometer, where electric current causes a mechanical movement of a pointer over a calibrated scale. By adding proper resistors and internal circuits, it can measure voltage, current, and resistance. While not as advanced as digital meters, analog multimeters are still useful for observing signal trends and simple electrical testing tasks.