Methods of capacitance calibration and test equipment measurement

Capacitance is a parameter of electrical measurement devices that needs to be accurate in order to ensure the safety of equipment and the quality of outcomes. As it is a measure of a component or devices’ ability to store charge, it is particularly critical in circuits, sensors and many other electronic devices.

Accurate capacitance calibration ensures the accuracy and precision of these devices through reliable measurement equipment. In this article, we will explore capacitance calibration, the various methods used and highlight the importance of a UKAS accredited service. 

What exactly is capacitance calibration? 

Capacitance describes a component’s ability to store an electric charge, with capacitors being energy-storing devices that play an important role in electric circuits. They come in a variety of forms, playing roles in filtering, energy storage and signal processing. As such, any inaccurate measurements of these components can lead to the critical failure of equipment. 

Capacitance calibration involves comparing the capacitance value of a device under test (DUT) with a reference standard. The goal is to determine and correct any deviation from the known standard, ensuring the DUT's readings are accurate. This process is crucial for maintaining the integrity of electronic systems and is commonly performed in laboratories accredited by standards such as UKAS (United Kingdom Accreditation Service).

Methods of capacitance calibration

1. Direct comparison method

The direct comparison method involves comparing the capacitance of the DUT with a reference capacitor of known value. This is achieved by connecting both capacitors in parallel or series and measuring the combined capacitance. The difference between the measured value and the known reference value indicates the calibration error.

Steps: 

• Connect the DUT and the reference capacitor in parallel or series.
• Measure the combined capacitance using a precision LCR (inductance, capacitance, resistance) meter.
• Calculate the deviation from the reference value.
• Adjust the DUT accordingly to match the reference standard.

2. Bridge method

The bridge method is a more precise technique involving a capacitance bridge, such as the Schering Bridge. These bridges compare the unknown capacitance with a known standard by balancing the bridge circuit. When balanced, the bridge provides an accurate measurement of the unknown capacitance.

Steps: 

• Set up the bridge circuit with the DUT and the reference standard.
• Adjust the bridge until it reaches a balanced state (no voltage difference across the bridge).
• Read the capacitance value directly from the bridge's calibrated scale.

3. Substitution method

In the substitution method, the DUT is replaced by a known reference capacitor in the measurement circuit. The capacitance value of the reference capacitor is then adjusted until it matches the measurement previously obtained with the DUT. This method is particularly useful for calibrating capacitors with non-standard values.

Steps:

• Measure the capacitance of the DUT using a precise instrument.
• Replace the DUT with a reference capacitor in the same measurement setup.
• Adjust the reference capacitor until the measurement matches the DUT's value.
• Record the reference capacitor's value as the accurate capacitance of the DUT.

Test equipment for capacitance measurement

Accurate capacitance measurement requires specialised test equipment, each offering varying levels of precision and functionality.

LCR meters measure inductance (L), capacitance (C), and resistance (R) with high accuracy. They are commonly used in capacitance calibration due to their precision and ease of use. Modern LCR meters come with advanced features such as automatic range selection and digital displays.

Capacitance bridges, such as the Schering Bridge and Wien Bridge, are used for high-precision capacitance measurements. These devices offer excellent stability and accuracy, making them ideal for laboratory use.

Impedance analysers provide detailed information about a component's impedance over a range of frequencies. They are valuable for characterising capacitors' performance under different conditions and are used in advanced calibration processes.

High-precision digital multimeters can measure capacitance in addition to voltage, current, and resistance. While not as precise as LCR meters or capacitance bridges, DMMs are versatile tools suitable for general-purpose capacitance measurements.

The value of accredited capacitance calibration with DM

Capacitance calibration ensures the accuracy and reliability of electronic components, using methods such as direct comparison, bridge, substitution and ratio transformer techniques. Each method offers varying levels of precision and is supported by specialised test equipment like LCR meters, capacitance bridges, impedance analyzers and digital multimeters.

Using UKAS-accredited calibration services is crucial for precision engineering industries. This is because it ensures adherence to the highest standards of accuracy, reliability and traceability. UKAS accreditation signifies that a laboratory meets rigorous international standards, providing confidence in the precision of measurements and reducing

DM stands out as an industry leader in providing electrical calibration services, fully backed by UKAS accreditation. Our expertise, state-of-the-art facilities and commitment to quality make us the ideal partner for your calibration needs. We offer both on-site and lab-based calibration services, ensuring minimal disruption to your operations while maintaining the highest levels of accuracy and compliance. For dependable and precise calibration, contact our team today and ensure your equipment meets the highest standards.