In-circuit measurements are tricky and don’t always yield the results we expect. Through extensive testing, #LcrResearch has developed 5 recommendations on how to effectively use an #LcrPro1 #LcrMeter for in-circuit testing.
1. Be aware of not only the component you are testing, but also surrounding components
The LCR meter measures a complex impedance during in-circuit testing. This means that the result is affected not only by the component you are currently measuring, but also by other components that connect to the component under testing. The measured component can have series and/or parallel connection to other nearby components, which can change the impedance of the measured component. One simple example, two 10K ohm resistors in parallel, measured individually, will display a reading of 5K ohms.
2. Set a proper test voltage on your Pro1 LCR meter when measuring an active component
Active components, such as ICs (Integrated Circuit), usually have diodes built into the input and output pins for ESD (Electro-Static Discharge) protection, as shown by the following schematic:
As you can see, two ESD protection diodes are placed inside the IC’s digital input pin. One is connected to the power line, while the other is connected to the ground. While the IC is powered down, those diodes may be forward biased by an LCR meter’s 0.5V or 1.0V test signal. Therefore, it may yield unexpected results when you use a high test voltage to measure IC pins or a component connected to an IC.
The Pro1 LCR meter provides three test voltage levels: 0.2V, 0.5V and 1.0V. The 0.2V is specially designed for in-circuit testing. It is low enough to prevent active components from being forward biased, allowing for a more accurate and reliable test result.
3. Select proper test tips
Choose precise test tips to reach the component under testing reliably. For testing boards with crowded components, using sharp and thin test tips will help prevent contact with adjacent components during testing. The Pro1 is built with ultra-precise gold-plated test tips, making it an optimal LCR meter for in-circuit testing.
4. Use a good board with known component values as your golden board
Discovering failed components from multiple boards is a much simpler process when you can compare the results from your board to the results from your golden board.
5. Always de-energize the component before testing
Never forget to power down the board and discharge big capacitors before doing in-circuit testing. It will prevent your Pro1 LCR meter from being damaged by energized components.