When measuring capacitance of capacitors, two types of meters are available: the multimeter and the LCR meter. Many customers compare the measurement from an LCR meter with the measurement done by a multimeter. There are often significant differences between them. Why is that?
The differences between an LCR meter and a multimeter
The LCR meterThe LCR meter puts an AC voltage on the capacitor and measures the phase and amplitude of the signal. With these 2 parameters, the capacitance can be determined quite accurately. In practice, capacitors are used for AC signals, so this type of measurement best approximates reality. |
The MultimeterThe measurement made by an LCR meter is accurate, but the electronics that make the measurement are relatively expensive. A multimeter often has as many as 10 different measurement functions, and each function should not cost too much. Therefore, a multimeter measures capacitance with a cheaper circuit. This involves applying a DC current and measuring the charging time of the capacitor. This DC measurement gives a good indication of capacitance but is more inaccurate. |
The deviation in practice
To show how large the deviation of the multimeter is in practice, we measured some capacitors with the DER-EE DE-5000 LCR meter and with the Fluke 117 multimeter. The values of our measurements are given below.
| Specified value | FLUKE 117 | DE-5000 |
|---|---|---|
| 2.2 μF | 2.18 μF | 2.08 μF |
| 220 μF | 223 μF | 211 μF |
| 470 μF | 500 μF | 462 μF |
| 2200 μF | 2158 μF | 1865 μF |
| 4700 μF | 4757 μF | 4390 μF |
When analyzing these results, we might initially conclude that the Fluke 117's values are more accurate. Although the Fluke's values are closer to the specified value, this is not necessarily the case.
We need to consider the tolerance of capacitors, which indicates how far the actual value of the capacitor can deviate from the specified value. Typically, this tolerance is 5%, 10%, or 20%. The capacitors in this measurement had a tolerance of 20%, and the measurements from the DE-5000 fall within this range.
Furthermore, we know that the technology of the DE-5000 is much better suited for measuring capacitance, which always gives more accurate results. This means that the results of the DE-5000 are closer to actual capacitor values compared to those of the Fluke 117.
Conclusion
The DMM and LCR meters have different purposes and techniques, so their results cannot be directly compared. The choice of which type of meter to use depends entirely on the application, ease of use, and required accuracy.
