1403 Air Capacitor and 7660 LCR Meter Calibration

Model 1403 Air Capacitor for calibration of the 7660 Precision LCR Meters and other LCR meters

This application note demonstrates how the 7660 Precision LCR Meters performs frequency-dependent measurements on the 1403 Air Capacitor Standards . The performance of the 7660 exceeds expectations for accuracy when measuring low value capacitors.

The 7660 Precision LCR Meter performs precision impedance measurements over a frequency range of 10 Hz to 2 MHz. The LCR Meter can measure 14 different impedance parameters with 0.05% accuracy, meeting today’s requirements for component and material testing. The ease of use and user-friendly menu programming makes the 7660 ideal for applications in metrology, product development, incoming inspections, or production line testing.

The IET Labs/GenRad 1403 Air Capacitor Standards are stable, three-terminal standards in decimal values from 0.005 pF to 1000 pF. The capacitance change is less than 0.01% at frequencies up to 2 MHz for 1 pF and 200 kHz for 1000 pF standard making the standard ideal for verifying LCR meters and bridges at frequencies other than 1 kHz. There are also a number of papers and articles on the frequency response of the 1403.

Summary

The combination of the 7660 and 1403 will be used in this application note to show the performance of the 7660 Precision LCR Meter at 1 kHz. The 7660 Precision LCR Meter can sweep across frequency and show the data in both tabular and graphical formats to characterize a variety of components or in this case the 1403 Air Capacitance Standard.

The 1403 Standard Air Capacitor was used as it has a flat response across frequency as long as f << fr, where f is the desired frequency and fr is the resonance frequency of the 1403 which is greater than several MHz.

The typical series resonance frequency of the 1403-1pF and 1403-1000 pF is 174 MHz and 21 MHz respectively. More information on resonant frequency and frequency response can be found in reference 1 and reference 2.

The frequency sweep from the 7660 will be compared with the calculated frequency response shown in reference 1.

The setup for testing is very similar to what was done in reference 1 using an AH2500A to calibrate the 1403 Standard at 1 kHz. The frequency response of the 1403 is then based upon the change in capacitance for the given resonant frequency of the standard. See the formula below.

Detail

1403-10 pF-BNC

The 1403-10 pF-BNC was calibrated using an AH2500A at 1 kHz, 1.5 Vac and using a standard 1 meter cable. The AH2500A was zeroed prior to measurements.

The calibrated value of the 1403-10pF standard was 9.982864 pF with a MU of 7.0 ppm.

The 7660 Precision LCR Meter was then used to measure the 1403 at 1 kHz and 1 VAC. A 250 point frequency sweep from 100 Hz to 1 MHz was then performed to show the 1403 frequency characteristics.

The accuracy specification for the 7660 is 1.7% for 10 pF under the following conditions: slow, 1 VAC and 1 kHz.

Table 1: Comparison at 1 kHz
Component	Calibrated Value AH2500A	AH2700A MU (ppm)	Measured Value 7660	7660 MU (ppm)	Difference (ppm)
1403-10 pF-BNC	9.982864	7.0	9.984735	17,000	187
1403-1000 pF-BNC	1000.3975	6.0	1000.539	700	141

The difference between the calibrated value of 9.982864pF and the measured value of 9.984735 pF is +0.02% or +187 ppm. This is significantly better than the accuracy specification for the 7660.

The measured change in capacitance from 1 kHz to 100 kHz is +0.01%.

The measured capacitance at 1 MHz is 10.01041 pF, an increase of 0.26%.

Graph 1: Sweep from 100 Hz to 1 MHz of a 1403-10pF-BNC Standard using the 7660

Graph 2: Expected Capacitance Graph of a 1403-10 pF from Reference 1

1403-1000 pF-BNC Performance Across Frequency

Graph 3: Sweep from 100 Hz to 1 MHz of a 1403-1000pF-BNC Standard using the 7660

The 1403-1000 pF was calibrated using an AH2500A at 1 kHz. The calibrated value of the standard is 1000.3975 pF with a MU of 5.5 ppm.

1kHz: 1000.539 pF
100 kHz: 1000.751 pF

The difference is +0.014% or 141 ppm—again better than the stated accuracy.

Change in capacitance from 1 kHz to 100 kHz is +0.02%. The frequency response increases with frequency and approaches resonance. Graph 3 and Graph 4 show similar responses.

Graph 4: Expected Capacitance Graph of a 1403-1000 pF from Reference 1

Conclusion

The accuracy of the 7660 Precision LCR Meter exceeds its specification at 1 kHz. Sweep and table functions simplify evaluating components. Measured results of the 10 pF and 1000 pF capacitors match theoretical expectations.

The flat frequency response of the 1403 Standard Air Capacitor facilitates calibration at various frequencies.

The 2TP air-dielectric capacitance standard development by NIMT confirms the frequency behavior of the 1403 capacitors (Reference 1).

For full specifications, visit IET Labs or email sales@ietlabs.com.

References

Establishment of 2TP air-dielectric capacitance standard by Monthol Homklintian
The paper "The Measurement and Uncertainty of Air Dielectric Capacitors from 1 kHz to 10 MHz" discusses environmental effects on the 1403 Series Air Capacitors.