Question 1

How to measure capacitors/Test a Capacitors (1): How do I correctly measure capacitance and dissipation factor?

Accepted Answer

A. The key to measure the capacitance and dissipation factor correctly is the meter settings (see Table 1).

Class Type	Capacitance	Frequency	Voltage
Class I	1ꯠpF and under	1MHz ± 10%	0.5 ～ 5 Vrms
Class I	Over 1ꯠpF	1kHz ± 10%	0.5 ～ 5 Vrms
Class II	10uF and under	1kHz ± 10%	1.0 ± 0.2 Vrms
Class II	Over 10uF	120Hz ± 20%	0.5 ± 0.2 Vrms

Table 1: Frequency and voltage settings for different capacitance range and class types.

The voltage settings are very critical for high capacitance capacitors. For some cap meters, the applied voltage to the test component is insufficient and thus the capacitance reads low.

The frequency settings are also important. Since capacitance changes with frequency, industry standards specify the test frequency at 1MHz, 1kHz, or 120Hz (see Table 1).

The recognition of the aging phenomenon for EIA class II capacitors is also important. For class II materials, capacitance decreases with Time1. Therefore, an industry convention has been accepted that states the capacitance shall be within tolerance at 1000 hours since the time of the last heat (TOLH)2.

TDK MLCC Application Note, “What is the Capacitance of this Capacitor?”, S. Maloy. (1999)
IEC-384-9 (1988), Appendix A

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Question 2

How to measure capacitors/Test a Capacitors  (2): Why is it necessary to measure capacitance at different test frequency/voltages depending on the capacitance range?

Accepted Answer

A. The frequency settings for the meter are mainly depended on the parasitic of the component. In order to achieve more accurate reading of the component, measuring frequencies are directed away from the Self-Resonance Frequency (SRF) of the component. Industry users set the standards at different frequency points depending on the capacitance value (see Table 1). The capacitance over 10uF was considered in the range of Tantalum capacitors. Therefore, as the ceramic capacitance range began to increase into the Tantalum capacitor range, the industry adopted the frequency standard for Tantalum measurements into ceramic capacitors.

The applied voltage is also depended on the capacitance of the capacitor. Generally, the 10uF and under have applied voltage of 1.0 ± 0.2 Vrms. But over 10uF, the applied voltage is 0.5 ± 0.1 Vrms. High capacitance capacitors have very low impedance, therefore to supply enough current to make the measurement, the power supply needs more current than that supplied at 1.0 ± 0.2 Vrms. Therefore, by lowering the applied voltage, the power supply will be able to supply enough current to measure the high capacitance capacitor accurately.

Class Type	Capacitance	Frequency	Voltage
Class I	1ꯠpF and under	1MHz ± 10%	0.5 ～ 5 Vrms
Class I	Over 1ꯠpF	1kHz ± 10%	0.5 ～ 5 Vrms
Class II	10uF and under	1kHz ± 10%	1.0 ± 0.2 Vrms
Class II	Over 10uF	120Hz ± 20%	0.5 ± 0.2 Vrms

Table 1: Frequency and voltage settings for different capacitance range and class types.

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Question 3

How to measure capacitors/Test a Capacitors  (3): What is the difference between Cp and Cs of capacitance?

Accepted Answer

A. An impedance analyzer can measure the capacitance in parallel known as Cp or in series known as Cs. The circuit model will be depending on the value of capacitance of the capacitor (see Figure 1).

When C is small and impedance is high, parallel impedance between C and Rp will become significantly higher than Rs. Thus the meter setting for measuring capacitance should be Cp. When C is large and impedance is small, parallel impedance for C and Rp is not as significant. Therefore, Cs should be used for the meter setting to measure capacitance. A good rule of thumb to select the impedance setting is to use Cp for capacitor impedance values greater than 10kΩ and Cs for less than 10Ω.

Figure1: Impedance equivalment circuit

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Question 4

How to measure capacitors/Test a Capacitors  (5): What is “stray capacitance” of a meter?

Accepted Answer

A. Stray capacitance is a type of measurement error defined as capacitance between the connections of a fixture and/or tip of the tweezers. When the fixture is open, there is some stray capacitance added to the measurement of the capacitor. However, if open compensation is properly performed, the stray capacitance generated by the fixture can be accurately compensated.

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Question 5

How to measure capacitors/Test a Capacitors  (6): What is compensation of measurement errors&#44 and why is it necessary?

Accepted Answer

A. Compensation is a technique used to compensate for error added during measurement, such as the residual parasitic from the fixture, tweezers, etc.
When measuring the capacitor, a fixture or tweezers is needed to make electrical contact. However, the fixture has some parasitic impedance and admittance, which can add unwanted impedance or admittance to the measurement value. Therefore, compensation of the parasitic is necessary.
Compensation usually consists of three steps. These steps are open, short, and load compensation. When performing the open compensation, the parasitic admittance is compensated. When performing the short, the parasitic impedance is compensated. Load compensation sets the reference point for a 50Ω load measurement.
Obviously compensation is paramount for low capacitance (<1000pF) measurements, where any additional measurement error could significantly effect the displayed value.

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Question 6

How to measure capacitors/Test a Capacitors  (7): How can I accurately measure the quality factor (Q)?

Accepted Answer

A. The quality factor is a measure of the extent to which a capacitor acts like a theoretically pure capacitor6. It is the inverse of the dissipation factor (DF). Q is typically reported for capacitance values ≦ 330pF, DF > 330pF.

An accurate Q value can be obtained from Q-meter that utilizes precise inductance coils that correspond to a specific capacitance range. Often multiple coils are necessary to adequately measure across the 0.5 ～ 330pF range. For capacitors > 330pF, the quality factor can be calculated by take the inverse of the dissipation factor (see Formula 1).

*1 "Glossary of Capacitor Terms", Ray Ostlie （1989）

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Question 7

Measurements to SRF (1): What meter do I need in order to measure SRF (Self Resonance Frequency) of a capacitor?

Accepted Answer

A. The HP4291A (RF Impedance/Material Analyzer) has an operating frequency range from 1MHz to 1.8GHz and impedance range from 0.1Ω to 50kΩ. The HP4194A (Impedance/Gain-Phase Analyzer) has a frequency range from 100Hz to 40Mhz and impedance range from 0.1Ω to 1MΩ. Therefore, HP4291A is recommended for measuring small capacitance (1 pF) in RF Range1. Since, only the SRF measurement for small capacitance capacitors will be discuss in this paper, the HP4291A will be main example for most of the frequent asked questions. There are 3 fixtures that are compatible with HP4291A. These fixtures are HP16191A, HP16192A, and HP16193A.

* New Technologies for Wide Impedance Range Measurements to 1.8 GHz, Product Note 4291-1 P/N 5966-2046E

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Question 8

Measurements to SRF (2): Why should I use HP4291A to measure low capacitance capacitor’s SRF (Self Resonance Frequency)?

Accepted Answer

A. When measuring low capacitance capacitor, the SRF is very high. The SRF can easily be calculated (see Formula 1).

Where
C : Nominal capacitance
L : Equivalent series inductance

As the result from formula 1, the smaller the C value is, the larger the SRF value will be. Therefore, the wide range of frequency is necessary. HP4291A has the operating frequency from 1MHz to 1.8GHz, which will cover most of the SRF for low capacitance capacitors.

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