Beatrice Lang
Electrical connectors are a crucial component in power supplies, acting as the interface between the source and load. To ensure optimal performance, it is essential to measure the contact resistance between connectors before use. Contact resistance indicates the difficulty of current flow, and higher resistance leads to increased heat generation and power consumption. To measure contact resistance, a digital multimeter can be used, with the dial set to measure ohms. The probes are then touched to each end of the connector, providing a reading of the resistance between those two points. Multi-sensor CMMs are also used to measure intricate connector components, employing tactile contact probes, optical sensors, and confocal white light non-contact sensors for scanning.
| Characteristics | Values |
|---|---|
| Tool | Analog or digital multimeter |
| Unit | Ohms |
| Setup | Connectors should be detached when checking resistance |
| Process | Touch one probe to each end of a wire to measure wire resistance; touch both to a connector to measure resistance between those two points |
| Factors | Foreign substances (dirt, solder flux, oil), body contact with metal ends of test leads, or parallel circuit paths |
| Contact Resistance | Indicates the difficulty of current flow; smaller is better |
| Insulation Resistance | Indicates that current does not leak between adjacent terminals; higher is better |
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What You'll Learn
Using a digital multimeter
Firstly, make sure all power is off on the circuit you are testing. Then, isolate the component you are testing from the complete circuit. Either remove the component or isolate it with an open switch. Next, set the selector dial to Ω (ohms). Insert the black test lead into the COM jack and connect the test lead and probes to the component terminals. Observe the readout window to obtain the Ω reading. Compare the results to the manufacturer’s Ω specifications. If the readings match the component, then resistance is not a problem. If the component is a load, there should be resistance that matches the manufacturer’s specs. If the reading is infinite (I) or overloaded (OL), then the component is open. If the reading is zero, then the component is closed (if it is a load, this is an internal short).
Digital multimeters support two measurement methods. In most cases, you will use the two-terminal measurement method. This method applies a constant current and measures the resistance value using the instrument’s voltmeter. The display should show OLΩ because, in Resistance mode, even before test leads are connected to a component, a digital multimeter automatically begins taking a resistance measurement. The MΩ symbol may appear in the display because the resistance of open (unattached) test leads is very high. When the leads are connected to a component, a digital multimeter automatically uses the Autorange mode to adjust to the best range. Press the Range button to manually set the range.
Other factors can affect resistance readings, including foreign substances (dirt, solder flux, oil), body contact with the metal ends of the test leads, or parallel circuit paths. The human body becomes a parallel resistance path, lowering total circuit resistance. Thus, avoid touching the metal parts of the test leads. Press the RANGE button to select a fixed measurement range. Press the HOLD button to capture a stable measurement, and the MIN/MAX button to capture the lowest and highest measurement.
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Contact resistance
In power supplies, connectors are an essential component as they lie at the interface between the source and load. It is crucial to have minimal contact resistance between the terminal connector and the pluggable connector to reduce voltage drop and heat dissipation. To measure the contact resistance of electrical connectors, a setup is required, as illustrated by Samir Gautam in his Medium article. The process involves measuring the initial contact resistance, then removing and reconnecting the connector multiple times, and finally evaluating the difference in contact resistance after several cycles.
The contact resistance measurement is an important test, especially for contacts that carry large amounts of current. An increase in contact resistance can lead to a high-voltage drop in the system. Additionally, it helps identify fretting corrosion and allows for the diagnosis and prevention of contact corrosion. Dynamic contact resistance measurements, such as those performed by the CIBANO 500, provide valuable information about wear-related issues with the main and arcing contacts within the interrupter chamber.
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Insulation resistance
The insulation resistance value of connectors is determined by the spatial distance between adjacent terminals, the materials used in the moulding, and the creepage distance of the moulded part. The higher the insulation resistance, the better.
To test insulation resistance, the insulating material must be in good condition. If the material is damaged, dirty, or wet, it will produce a high leakage current. The test voltage will continue to increase, and as the interference current decreases, the insulation resistance measurement will rise. The simplest method of testing is fast measurement or point-reading measurements. A test voltage is applied to the measured object for 30 or 60 seconds, while the resistance value is read. This method is susceptible to temperature and humidity, so the measurement must be made at a normalized reference temperature.
Another method is to use a continuous measurement technique to measure insulation resistance over a specified period. This method is not affected by temperature and can provide a clear assessment of insulation monitoring.
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Pin alignment
Pin connectors play a vital role in electrical power delivery and signalling within electronic devices. Accurate pin alignment is essential to guarantee that each connector adheres to design specifications and functions seamlessly with adjacent connectors. This precision is particularly crucial in preventing issues such as bent or missing pins, which can hinder the interlocking of connectors and lead to potential defects during production.
To achieve precise pin alignment, advanced technologies like KEYENCE's connector pin inspection sensors (including the LJ-X8000 Series) offer an effective solution. These sensors can detect not only bent or misaligned pins but also any missing pins within the connector casing. By integrating such technology into the production line, manufacturers can enhance the accuracy and reliability of their connector pin inspection processes, ensuring that their connectors meet the required standards.
The geometry and pin count of connectors can vary, presenting challenges for standard inspection methods. Modern electronics often feature densely packed and tightly encased components, making access and visibility difficult for traditional inspection techniques. This underscores the importance of employing specialised equipment, such as that offered by KEYENCE, to ensure accurate pin alignment even in intricate designs.
Additionally, it is worth noting that electrical connector resistance can have a significant impact on circuit design. While higher resistance in connectors can lead to increased heat generation and power consumption, lower resistance is desirable in certain contexts, such as RF connectors and audio output. Therefore, when considering pin alignment, it is crucial to factor in the specific application requirements to optimise connector performance and overall circuit functionality.
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Quality assurance
When measuring and inspecting electrical connector components and finished products, it is important to thoroughly analyze housing and contact pin components for wear monitoring and quality assurance. Speed and productivity must be balanced with accuracy and repeatability.
To ensure quality, it is also necessary to measure the contact resistance between the connectors before using them in a product. This can be done using a digital multimeter, which measures resistance, current, voltage, and more. The setup for contact resistance measurement involves a terminal block header (male connector configuration) placed on the PCB of a power supply. A pluggable terminal block (female connector) is then used to power up the load.
To ensure the quality of the connector, it should have minimal contact resistance to lower voltage drop and reduce heat dissipation. Higher insulation resistance is also better as it prevents short-circuit currents between adjacent terminals.
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Frequently asked questions
The first step is to detach the connectors.
After detaching the connectors, use a digital multimeter to measure the resistance.
Turn the dial to the resistance mode (ohms) and touch the probes to each end of the connector.
Remove and reconnect the connector 10 times. Repeat this step for 10 cycles and evaluate the difference in contact resistance after the 100th cycle.
A high insulation resistance value is desirable as it indicates that there is no leakage of current between adjacent terminals.
