Ohmmeter, components, types, design, uses

What is ohmmeter?

An ohmmeter can be defined as a type of electronic device mainly used to calculate the electrical resistance of a circuit. Resistance is a fundamental property of electrical components and materials and is measured in ohms (symbol Ω). Electrical resistance is a calculation of how strongly an object resists current flowing through it.

Components:

It usually consists of the following parts:

Test Leads: These are leads or probes used to connect an ohmmeter to the part under test. They usually have insulated handles for safety and have lugs or clips for a secure connection.

Power Source: The ohmmeter has an internal power source that supplies a known current to the part under test. The power source can be a battery or an electronic circuit that generates direct current.

Meter: The meter is an ohmmeter display unit that gives resistance measurements. This can be an analog meter with a pointer or a digital display such as an LCD or LED display. The meter is calibrated to display a resistance value based on current and voltage measurements.

Selector switch: Many ohmmeters have a selector switch that allows the user to select different resistance ranges. This switch selects the correct circuit and current levels for accurate measurements.

Zeroing: Some ohmmeters have a knob or button for zeroing. This feature allows the user to calibrate the ohmmeter to compensate for any residual resistance in the test leads or internal circuitry. This allows for more accurate measurements by setting each offset to zero.

Power: Ohmmeters require a power supply to operate. This can be a battery for handheld portable ohmmeters or an AC adapter for desktop models.

These are the major components commonly found in an ohmmeter. However, the specific design and additional features may vary depending on the model and manufacturer. Advanced ohmmeters may include additional features such as autoranging, data logging, or connectivity to transfer data to a computer or other devices.

Types:

Two types of ohmmeters are commonly used:

Analog Ohmmeter: Analog ohmmeters use a moving needle or pointer on a scale to indicate the resistance value. They usually have a round dial with different resistance values marked around the circle. As the test current passes through the part or material under test, the pointer deflects to indicate the resistance value on the scale. Analog ohmmeters require visual interpretation and may be less accurate than digital ohmmeters. However, they can be useful in situations where a quick resistance measurement is needed.

Digital ohmmeter: Digital ohmmeters have a digital display that directly shows the resistance value. They use digital circuits to measure resistance and display it in numbers or alphanumeric characters. Digital ohmmeters provide more accurate and accurate readings than analog ohmmeters. They often have additional features such as autoranging (automatically selecting the correct range for the resistance being measured), data hold (retaining the reading on the display), and backlighting for better visibility. Digital ohmmeters can also perform other measurements such as continuity tests and diode tests.

Ohmmeter Design:

The construction of an ohmmeter circuit is a combination of a milliohmmeter with a set of resistors connected in series and a DC battery. The following parts of the analog ohmmeter are included.

Display: Different scales are displayed to measure different electrical quantities. At the top is a non-linear ohmmeter scale.
Pointer: The reading on this scale varies depending on the resistance principle.
Range Selector Knob: There is a knob in the middle for selecting different functions.
Milliammeter or microammeter: At a constant voltage, the current through the ammeter changes as the Resistance changes:This gives the output impedance in ohms (Ω).
Multimeter dial: The dial is located around the dial with the different series selectors.
Slots/Ports: Two inputs are available for connecting sensors.
Sensors/Outputs: Comes with two sensors: a black sensor and a red sensor.

How to calculate ohms?

Ohm's law and force
To find the voltage, (V) [V = I x R] V (volts) = I (amps) x R (ohms).
To find the current, (I) [I = V ÷ R] I (amps) = V (volts) ÷ R (ohms).
To find the resistance, (R) [R = V ÷ I] R (ohms) = V (volts) ÷ I (amps).

To calculate (P), use [P = V x I]. V (volts) x I (amps) = P (watts). 

Applications:

Ohmmeters have various uses in electrical and electronic applications. Here are some common uses for ohmmeters:

Resistance measurement. The primary purpose of an ohmmeter is to measure the resistance of electrical components, conductors, and circuits. It allows you to determine the resistance value of resistors, potentiometers, coils, windings and other passive components.

Continuity Testing: Ohmmeters are often used for continuity testing to see if a circuit or connection is continuous or has interruptions. When an ohmmeter measures very low or near zero resistance, it indicates that the circuit is closed and has continuity.

Troubleshooting: Ohmmeters are invaluable tools for troubleshooting electrical circuits. By measuring resistance at various points in a circuit, it is possible to identify an open circuit (high resistance or infinite resistance), a short circuit (very low resistance), or faulty components.

Quality Control: Ohmmeters are used in the manufacturing and quality control processes to ensure that components and products meet resistance specifications. They help verify the integrity and durability of resistive components during production.

Testing Wires and Cables: Ohmmeters are used to measure the resistance of wires and cables, which can help determine the length, gauge, and overall quality of the conductors. This can be useful for checking wiring continuity or looking for bad connections.

Earth Tests: Ohmmeters can be used to test the resistance between an electrical system or equipment and the earth. This ensures proper grounding, which is essential for safety and to prevent electric shock.

Component Sorting: Ohmmeters are used to sort and classify resistors or other components based on their resistance values. This is common in electronic component manufacturing, where resistors are ordered with a certain tolerance range for proper use in circuits.