Ohmmeters

An ohmmeter is a device used to measure electrical resistance and continuity of electrical circuits and components. It is available in a range of sizes, voltages and types, each with varying levels of accuracy. Ohmmeters (or ohm meters) are available in three main variations including micro-ohmmeter (for measuring low resistance), standard ohmmeters for general purposes, and megohmmeters (for measuring high resistance), all of which measure electrical resistance in ohms. There are various types of meters available with different sensitivity levels which include micro, mega and milliohm meters.

Types of Ohmmeters

Ohmmeters come in various types designed for specific measurement needs.

Milli-Ohm Meter

A milli-ohm meter measures very low resistance values, typically in the milliohm (mΩ) range. It offers high accuracy and resolution, making it suitable for applications such as:

• Measuring the resistance of wires and cables.
• Testing the continuity of electrical connections.
• Characterising low-value resistors.
• Evaluating the quality of electrical contacts.

Micro Ohm Meter (Low Resistance Ohmmeter)

A micro ohm meter, also known as a low resistance ohmmeter or low ohm meter, specialises in measuring extremely low resistance values in the micro-ohm (µΩ) range. Low ohm resistance testers are used in applications such as:

• Measuring contact resistance in switches and relays.
• Testing the resistance of PCB traces and connectors.
• Analysing the resistance of motor windings and transformers.
• Verifying the integrity of grounding systems.

Due to their specialised nature and the technology required for such precise measurements, the price of micro ohm meters tends to be more expensive than standard ohmmeters.

Standard Ohm Meter

A standard ohm meter is a general-purpose instrument used to measure resistance values within a typical range, usually from ohms to kilohms. These meters are commonly found in multimeters and are suitable for a wide range of applications, including:

• Testing resistors in electronic circuits.
• Checking the continuity of fuses and circuit breakers.
• Measuring the resistance of sensors and transducers.
• Troubleshooting electrical wiring and components.

Mega Ohm Meter

A mega ohm meter is designed to measure very high resistance values in the megohm (MΩ) range. These meters are often used for insulation testing and other applications involving high resistance, such as:

• Testing the insulation resistance of cables and wiring.
• Measuring the resistance of insulators and dielectrics.
• Assessing the quality of electrical isolation.
• Checking for leakage currents in electrical systems.

Analogue & Digital Ohm Meters

Ohmmeters are available as analogue or digital.

**Analogue Ohmmeters **

Analogue ohmmeters use a moving needle to indicate the measured resistance value on a graduated scale. They are generally simpler and less expensive than digital ohmmeters. However, they may be less accurate and as such are often preferred for quick checks and basic troubleshooting where high precision is not critical.

Digital Ohmmeters

Digital ohmmeters display the measured resistance value directly as a numerical readout on an LCD or LED screen. They offer higher accuracy, resolution, and are easier to read compared to analogue ohmmeters. Digital meters are preferred for applications requiring precise measurements and where clear, unambiguous readings are essential.

How Does an Ohmmeter Work?

Ohmmeters work by passing a small current through a sample, allowing the instrument to measure the voltage drop across it. This measurement indicates how much an object resists allowing current to flow through it, highlighting the resistance in ohms. Ohmmeters must be calibrated prior to ensure accurate measurements. RS offers an in-house calibration service to RSCAL standards.

Key Features of an Ohmmeter or Resistance Meter

When choosing an ohmmeter or resistance meter, consider these key features to ensure you select the right one for your needs:

• Measurement Range: Indicates the span of resistance values the ohmmeter can measure, from low micro ohm values to high mega ohm values. Select a meter with a range that encompasses the resistances you typically encounter in your work.
• Accuracy and Resolution: Accuracy refers to how close the measured value is to the true resistance value. Resolution refers to the smallest difference in resistance the meter can detect. Higher accuracy and resolution are essential for precise measurements, especially in applications where even small variations in resistance can be significant.
• Test Current: Ohmmeters apply a small current to measure resistance. The magnitude of this test current can influence the measurement accuracy and the potential impact on the component being tested. Some meters offer adjustable test currents to optimise for different applications.
• Display Interface: Digital ohmmeters offer a clear numerical display for easy reading, while analogue meters use a needle and scale. Consider the clarity and readability of the display, as well as the ease of use of the interface and controls.
• Special Functions: Some ohmmeters include additional features that enhance their functionality and versatility. These may include:
  • Continuity testing (with audible alerts) for quickly checking electrical connections.
  • Diode testing for verifying the operation of diodes.
  • Temperature compensation to account for the effect of temperature on resistance measurements.
  • Data logging capabilities for recording measurements over time.
• Safety Features: Some ohmmeters come with additional safety features like over-current protection and overload protection to prevent damage to the meter or the circuit being tested. These features are crucial for ensuring safe operation and preventing accidents.

Industrial Applications for Ohmmeters

Ohmmeters are used in a wide range of applications where the measurement of electrical resistance is required.

Laboratory and Research Environments

In laboratories and research settings, ohmmeters are essential for characterising materials and testing electronic components with high precision. Researchers rely on ohmmeters to analyse the electrical properties of new materials and conduct experiments that require accurate resistance measurements.

Production

Ohmmeters are vital tools in production environments for quality control and testing during the manufacturing process. Manufacturers use ohmmeters to verify the resistance of components like resistors, cables, and connectors, ensuring they meet specifications and identifying faulty components to prevent defective products.

Household Troubleshooting

Homeowners and DIY enthusiasts can use an ohm meter for basic electrical troubleshooting around the house. A digital ohmmeter can help diagnose common electrical problems, such as checking the continuity of fuses, whether a safety relay is working, and identifying broken wires in appliances.

Automotive Industry

The automotive industry relies heavily on ohmmeters for testing various electrical components in vehicles, including wiring harnesses, sensors, and starter motors. By measuring resistance, technicians can identify faulty components and ensure proper electrical flow within the vehicle's systems.

Telecommunications

In telecommunications, a resistance meter is essential for testing the resistance of cables, connectors, and antennas to ensure signal integrity and prevent data loss. Technicians use ohmmeters to troubleshoot faults in telecommunications equipment and maintain the quality of communication networks.

How to Use an Ohm Meter

Using an ohm meter correctly and safely is essential for obtaining accurate measurements and preventing damage to the meter or the circuit being tested. Follow these steps to use an ohm meter effectively:

1. Select Range: Choose the resistance range on the ohm meter that is most suitable for the component or circuit you are testing. Start with a higher range and then switch to a low ohm meter for lower ranges if necessary to obtain a more precise reading.
2. Zero the Ohm Meter: Before taking any measurements, short the test leads together and adjust the zero-adjust knob (if available) until the meter reads zero. This calibrates the meter and ensures accurate readings.
3. Isolate Component: If you are testing a component within a circuit, disconnect it from the circuit to avoid interference from other components. This ensures that you are measuring only the resistance of the component in question.
4. Connect Leads: Connect the red test lead to the positive terminal of the component and the black test lead to the negative terminal. If you are unsure of the polarity, it is generally safe to connect the leads in either direction when measuring resistance.
5. Read Measurement: Observe the reading on the ohm meter display. If the reading is outside the selected range, adjust the range switch accordingly.
6. Record Value: Note down the measured resistance value, including the units (ohms, kilohms, megohms, etc.).
7. Turn Off the Ohm Meter: After completing the measurement, turn off the ohm meter to conserve battery power.

How to Select a Suitable Ohm Meter

Here’s how to choose the correct ohm meter for your application

Measurement Range and Accuracy

• Determine the range of resistance values you need to measure. This will help you choose an ohm meter with an appropriate measurement range, from low resistance micro ohms to mega ohms.
• Consider the accuracy requirements of your application. If you need precise measurements, choose a resistance meter with high accuracy and resolution.

Application and Features

• Think about the types of components and circuits you will be testing. This will help you determine whether you need a general-purpose ohm meter or a specialised meter like a low ohm resistance tester or a mega ohm meter.
• Consider any additional features that might be useful for your applications. These may include continuity testing, diode testing, temperature compensation, or data logging capabilities.

Type and Display

• Choose between an analogue or digital ohm meter. Analogue meters are generally simpler and less expensive, while digital meters offer higher accuracy and ease of use.
• Consider the display type and size. Ensure the display is clear, easy to read, and provides the necessary information.

Safety and Durability

• Look for an ohm meter with safety features like over-current protection and overload protection. These features help prevent damage to the meter and ensure safe operation.
• Consider the durability and build quality of the ohm meter. Choose a meter that can withstand the demands of your work environment.

Trusted Ohmmeters Manufacturer, Supplier & Distributor in Malaysia

RS has a large range of ohmmeters from leading brands such as Megger, Chauvin Arnoux and from our very own brand RS PRO. Our wide range of products have been selected to meet high industry standards, so you are ensured reliable and robust solutions. RS has on hand technical advisors to offer advice on specific requests and offering our in-house calibration service.

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