The micro-ohmmeter is designed to measure very low resistances such as circuit breaker contacts, transformer and motor windings, wire and cable samples. It is far superior to general purpose 4 1/2 digit multimeters and ohmmeters when measuring very low resistances. It is also battery-powered to eliminate the need for lugging around large power supplies or generators into inaccessible substations. The resistors R1 and R4 along with zener diodes ZD1 and ZD2 protect the ADC input against voltage surges.
Ranges
Milliohm & micro-ohm meters are accurate test instruments equipped for measuring very low resistance values, often down to divisions of the ohm (less than one millionth of an ohm). They’re ideal for tasks that require meticulous resistance measurements in tight spaces or challenging environments. There are also battery-powered micro-ohmmeters available that eliminate the need to carry heavy 100A or 200A mains-powered units on-site. These can be used to measure the contact resistance of circuit breakers, switches and busbar joints.
A micro-ohmmeter can also be used to check the integrity of shunt resistors, coils and transformers. They can be connected to the equipment under test using four-wire Kelvin binding post terminals that accept banana plugs, spade lugs or wires. Some models can even provide logging capability and data storage. This enables a technician to monitor the progress of a job over time and make comparisons between different samples. They can be viewed and printed on-screen or saved in a file for future reference.
Accuracy
A Microohmmeter provides extremely accurate measurements at very low test currents. This is a huge advantage over general purpose meters that rely on 4-terminal connections. The best micro-ohmmeters offer basic accuracy of 0.02% and resolution of 1 mO. Rugged Kelvin measurement connections minimize lead resistance errors and 80 dB of ac noise rejection provide rock-steady readings in noisy environments.
Using a micro-ohmmeter to measure the contact resistance of circuit breakers is essential to prevent arcing between contacts. This arcing creates carbonised layers that increase the contact resistance and cause heating which could lead to the circuit breaker failing to operate when needed. This is a potential safety hazard for transmission and distribution lines that must be avoided.
In addition to preventing arcing, measuring the contact resistance of fuses and weld connections is another important application for a micro-ohmmeter. These tests must be conducted reliably to ensure the highest quality results and product yield. The fastest precision micro-ohmmeters, such as the 1750 Series by TEGAM, are widely used in manufacturing environments to meet the stringent requirements for fuse production and welding points.
Displays
GAO Tek micro ohmmeters are compact and portable, perfect for on-the-go resistance measurements. These handheld units feature easy-to-read displays and automatic ranging for effortless operation. With the press of a button, users can select and activate the desired test current. The micro ohmmeter then automatically calculates and displays the resistance measurement, simplifying operations in tight spaces or challenging environments.
A modern ohmmeter circuit uses a combination of an electronic current passing through the resistance, an analog to digital converter (adc) and a microcontroller or microprocessor that divides the voltage by the current using Ohm’s Law to provide a reading of the resistance value at that moment. This is why ohmmeters quote their accuracy at the center of scale.
Other micro ohmmeters use a continuous measurement current to measure inductive materials (coils, transformers, motor windings). These units require the user to continuously push the test button for a continuous test. To prevent damage to the adc, these devices utilize resistors, capacitors and zener diodes to protect the ADC input against voltage surges.
Batteries
Unlike many other handheld microohmmeters which use alkaline cells, our models utilize high-quality lithium batteries. These provide a regulated test current which allows you to make multiple measurements without having to wait for the battery to recharge. Our bulk purchasing program lets you save money on batteries and get them delivered directly to you.
Many engineers take 10A battery-powered microohmmeters on site to measure low resistance in circuit breakers, however these instruments may not accurately reflect the current produced by a breaker’s contacts. This can lead to false readings and misinterpretation of results.
Megger has developed a handheld, battery-powered 200A micro-ohmmeter which eliminates the need for power supplies and long leads. It also has a CAT IV 600 VAC/500 VDC safety rating making it suitable for harsh environments and substations. It uses a supercapacitor to inject a high current for a short duration, enabling it to achieve class-leading performance. In addition, it has an option to perform tests using a DualGround method, which grounds both sides of the test object during the measurement, improving safety.
More Words
A microohmmeter (also called a digital low resistance ohmmeter or DLRO) is an instrument designed to measure very low resistance values. It is usually used in circuit breakers for checking the contact resistance to prevent arcing between the live contacts and incoming service.
