Difference Between Analog and Digital Multimeter

Analog vs Digital Multimeter

Multimeter or a multitester is a measurement instrument used in electronics, which is designed to perform tasks of several measuring instruments. The voltage, current, and resistance measurements can be made using different options available in a common Multimeter; therefore, it is also called VOM (Volt Ohm meter). In more expensive and advanced models, capacitance and inductance can also be measured and can be used to detect pins of semiconductor elements like transistors and diodes.

More about Analog Multimeter

Analog Multimeter is the older type of the two multimeters, and it is actually an ammeter. Its operation is based on a spring loaded moving coil mechanism positioned inside a magnet. When a current flows through the coil, interaction between the induced magnetic field in the coil and the fixed magnet create a force to move the coil. The needle connected to the coil moves proportional to the force produced, where the force is proportional to the current flowing through the coil. The moving needle points to the numbers marked on a dial, indicating the amount of current passing through the coil.

To measure voltage and resistance, the internal circuit is attached to additional circuits such that current through the coil represent the voltage or the resistance. This additional circuitry also gives multimeter the ability to operate on different value ranges. For example, with a multimeter it is possible to measure 20mV and 200V, but the scale has to be set accordingly.

The output (display) of the analog multimeter is a real time continuous output, where theoretically the needle indicates the value at that instant. Therefore, analog multimeters are preferred still by some professionals due to its real time response which is important when measuring capacitor or inductor circuits. Disadvantages of the analog meters are the parallax error they cause in the readings and the delay in response due to the inertia of the needle and the mechanism. This inertia become advantageous when there is noise present in the measurement; that is the needle would not move for small changes when the voltage or current is measured.

The Analog multimeters have to be supplied a voltage for measuring resistance; usually a AAA battery is used. Depending on the output voltage of the battery at the time (which decrease with time, not 1.5 V always), the scale for resistance has to be manually adjusted to zero.

More About Digital Multimeter (DMM)

Digital Multimeter, which is the newer type of the two multimeters, is completely electronic in operation, and no mechanical components are involved in the measurements. The whole operation of the device is based on electronic components.

In contrast to the operation of the analog multimeter, digital multimeter uses voltage to detect the input signal. All the other measurements such as current and resistance are derived from the voltage across the test leads.

Digital multimeters obtain several samples of the signal during a short period of time and average the signals to provide better accuracy. The analog signal is converted into a digital signal by the analog to digital converter, which is the most important component of the multimeter circuit, inside the multimeter. To improve precision further, most DMM models use a method called successive approximation register (SAR) in the analog to digital conversion step.

Digital multimeters display a numerical value as the output which has a higher accuracy than the analog multimeters. Also, advanced digital multimeters offer automatic ranging features so that the user do not have to select the range of the measurement manually. Additionally, this becomes a safety feature too. Since no moving parts are inside, the digital multimeters are unaffected by shocks such as the impact with a solid surface.

What is the difference between Analog and Digital Multimeter?

• Analog multimeters give the output as a reading on a scale against a pointer, while digital multimeter output is in numerical form displayed on a LCD.

• Analog multimeters give a continuous output and carry a greater uncertainty in the measurement (about 3%), while digital multimeter measurements have a far less uncertainty (about 0.5% or less). Digital multimeters are more accurate than analog multimeters.

• Digital multimeters have a better range of measurements than analog multimeters.

• Digital multimeters offer additional features such as capacitance, temperature, frequency, sound level measurements and detection of semiconductor device pins (transistor / diode).

• Analog multimeters have to be calibrated manually, while most digital multimeters are calibrated automatically before every measurement.

• Analog multimeters have to be set for the specific range of measurement manually, while some must digital multimeters have auto ranging feature.

• Analog multimeters require practice to take good measurements, while digital multimeters can be operated even by an untrained person.

• Analog multimeters are less costly while digital multimeters are expensive.