Dual Canopy Mechanic Electrical Engineering Co., Ltd. is one of the leading manufacturers and suppliers of Loop Resistance Tester in China. Please feel free to wholesale discount products for sale here and get quotation from our factory. Customized orders are welcome.
Core technical selling points
The Loop Resistance Tester (also known as a Contact Resistance Tester or Micro-Ohmmeter) is a specialized instrument designed to measure the electrical resistance of switching devices and their connections. Unlike general-purpose ohmmeters or winding resistance testers, this device is specifically engineered to test the contact resistance of high-voltage circuit breakers, disconnectors (isolators), and busbar joints.
The measurement of contact resistance is critical because excessive resistance at contact points leads to localized overheating (hot spots), accelerated aging, and potential catastrophic failure of switchgear. To accurately measure these very low resistances (often in the micro-ohm range) and to break through surface oxidation films on contacts, the tester injects a high DC test current, typically ranging from 100A to 600A (or higher), in accordance with international standards such as IEC 62271-1.
Our Loop Resistance Tester utilizes the four-wire Kelvin method to eliminate lead resistance errors, providing accurate, repeatable measurements essential for preventive maintenance and quality control in power utilities and industrial plants
What is Technical data?
| Measuring Current | 50A 100A 200A |
| Measuring Range | 0~100mΩ(50A) 0~50mΩ(100A) |
| Minimum Resolution | 0.1μΩ |
| Accuracy | ± (0.5% +2μΩ) |
| Power | 1000W |
| Power supply | AC220V±10% 50Hz |
| Working Temperature | 0~40ºC |
| Humidity | ≤90%RH, no condensation |
| Dimensions(mm) | 355*275*147 |
| Instrument weight | 9.5 Kg |
How do I operate it?
Electrical Loop Tester High Precision Loop Measurement Meter
Working principle of the loop resistance tester
During the measurement process of the loop resistance tester, a high-frequency switching power supply outputs a current of 100A or more, which is applied between the two terminals of the measured resistor. The voltage drop generated by the current flowing through the measured resistor is sampled by the sampling circuit. After being amplified by the preamplifier, the analog signal is converted into a digital signal by the A/D converter. Then, the data is filtered, processed and handled by the microprocessor. According to the principle that the current in a series circuit is equal everywhere, and using Ohm's law R = U/I, the DC resistance value of the measured body can be obtained by calculating the ratio of the voltage drop U at the load terminals to the current I in the circuit.
Electrical Loop Tester High Precision Loop Measurement Meter
The wiring method of the loop resistance tester
According to the four-wire measurement method, connect the test sample to the instrument panel using the dedicated test wires. Pay attention that the voltage measurement wire should be placed inside the current output wire.
Connect the AC 220V power supply (note: the third wire of the power inlet, which is the protective ground, must be connected to the earth). Press the power switch. At this time, the ammeter and ohmmeter display "000" (no limit on the number of decimal places is allowed).
Press the measurement switch, adjust the current output knob (clockwise direction) until the current meter display shows "100.0", then read the number on the resistance meter head to obtain the resistance value of the tested item and make a record. (If it shows "1", it indicates that the measured circuit is beyond the measurement range.)
After the test is completed, turn the current output adjustment knob (clockwise) to the minimum, reset the measurement switch, and then turn off the power switch. If you want to repeat the test, simply reset the measurement switch, reattach the test clamp, and then press the measurement switch.
**Model Selection Consultation:** Based on your specific test object (circuit breaker rated current, contact material) and required accuracy levels, we recommend the most suitable current range (100A is suitable for general maintenance; 200A/400A is suitable for large-scale circuit breakers or factory type testing).
**Standards Interpretation:** We provide clarifications regarding the requirements for loop resistance test currents and acceptance criteria as stipulated in standards such as IEC 62271-1 and DL/T 845.3.
**Customized Technical Solutions:** For switchgear with specialized structures (e.g., fully enclosed GIS), we provide dedicated test cables and customized wiring schemes.
**Comparative Analysis:** We outline the key distinctions between "Loop Resistance Testers" and "DC Resistance Testers," clearly specifying that the former is designed for measuring "contact resistance" while the latter is used for "winding resistance," thereby helping you avoid errors during equipment selection.
FAQ
Q1: Why is it necessary to use a high current (e.g., over 100A) when measuring switch contact resistance, rather than a standard multimeter or a low-current resistance tester?
A: The surfaces of switch contacts often harbor oxide films, oil films, or minute impurities. Low currents (e.g., in the milliampere range) are unable to break down these insulating layers; consequently, the measured resistance values tend to be artificially high and unstable, failing to reflect the true contact condition. **High currents (over 100A)** generate sufficient thermal effects and electric field strength to break through these surface oxide films, thereby enabling the measurement of the true metallic contact resistance. Furthermore, national standards (such as IEC 62271-1) explicitly stipulate that the test current must not be less than 100A.
Q2: What is the difference between a loop resistance tester and a DC resistance tester?
A: Although both devices operate on similar principles (utilizing the four-wire method), they are designed for different applications and parameters:
Loop Resistance Tester: Specifically designed for switch contacts; it outputs high currents (100A–600A) and typically features a measurement range in the micro-ohm level, used for assessing contact resistance.
DC Resistance Tester: Specifically designed for **inductive loads (such as transformer windings and motor coils)**; it outputs lower currents (typically 1A–20A) and features a wider measurement range, used for assessing the DC resistance of coils. Never use a DC resistance tester to measure switch contacts, as the insufficient current will lead to severe data distortion.
Q3: Are measurement results significantly affected by temperature? How should this be addressed?
A: The impact is significant. The resistance of copper and aluminum conductors increases as the temperature rises (copper has a temperature coefficient of approximately 0.393%/°C). Without temperature correction, data measured in the summer cannot be meaningfully compared with data measured in the winter. Our testers feature a built-in temperature correction function: by inputting the ambient temperature or the temperature of the test specimen, the instrument automatically converts the measured value to the corresponding value at a standard reference temperature (e.g., 20°C), thereby facilitating the comparison of historical data.
Hot Tags: Loop Resistance Tester, China Loop Resistance Tester manufacturers, suppliers, factory, Loop Resistance Testers LRT , Contact Resistance tester, Contact Resistance Meters, Contact Resistance test kit
