Instructions for Use of LD-3 Dielectric Cell with 7600 Precision LCR Meter for Measurement of Dielectric Constant in accordance with ASTM D 150, IPC-TM-650 and IEC-60250
The 7600 Precision LCR Meterwith the LD-03 Dielectric Cell were designed to make Dielectric Constant and Dissipation Factor measurements in accordance with IEC-60250 and ASTM D 150.
The LD-3 Rigid Dielectric Cell is designed for testing rigid flat materials. Material up to 8cm (3-1/8 inches) with a maximum thickness of 1.1 cm (7/16 inch) can be used in the dielectric cell. The dielectric cell is made up of two electrodes. One electrode is fixed with a grounded guard ring and the other is movable via a micrometer. The micrometer allows precise measurement of electrode spacing. The grounded guard ring reduces fringe effects to improve measurements.
The three terminal electrical connections are made via GR-874 connection on the fixed electrode side (optional BNC to GR-874 adapter, LD-08 is available) and banana connection LD-05, Pomona Electronics 4684, on the movable electrode side. A 1 Meter BNC to BNC-T cable set 1689-9602 is available for connection to the cell.
Parts required for connection are shown below for the LD-3 Dielectric Cell.
Part Number Description
LD-02 BNC Tees
1689-9602 1 Meter BNC Cable Set
LD-05 BNC to Banana Adapter
LD-08 GR874 Adapter
Figure 1 shows the correct connection of the 7600 Plus Precision LCR Meter with a LD-3 Dielectric Cell. It is important to make sure that the shields from all BNC cables are connected at the cell especially for high frequency operation. This is accomplished on the movable electrode side by use of a shielded banana adapter and GR-874 to BNC Adapter on the fixed side.
Figure 1 IET Labs 7600 Plus Precision LCR Meter Connected to an LD-3 Rigid Dielectric Cell Same connection applies to 1920.
Connect the 1689-9602 BNC to BNC cable lead set to the pair of BNC tees on the test fixture. The BNC tees are then connected via an 874 adapter to the specific LD3 cell. Make sure that the PH/IH connectors go to one BNC tee and the PL/IL connectors go to the other BNC tee. See Figure 2 for Connection.
Figure 2 Connection of Adapters to cell for Measurement
Open & Short Compensation
It is very important to perform an OPEN and SHORT circuit zero with the instrument before making measurement. Figure 3 illustrates the preferred method to accomplish short. The BNC Ts should be connected together to perform short compensation. This can be done with another BNC T or barrel connector.
Figure 3: Cable Lead Position for Short Compensation
Figure 4 illustrates the preferred method to accomplish open compensation. Note that the connection to the movable electrode should not be made during open compensation. The movable electrode in the cell should be adjusted for maximum distance between the electrodes.
Figure 4: Cable Lead Position for Open Compensation
To perform measurements reconnect the cell as shown in figure 5.
Figure 5 Connection of Adapters to cell for Measurement
First the sample is inserted in the cell and the electrodes closed with the micrometer until they just touch the sample. Do not force the electrodes against the sample as this can damage the cell. Turn the micrometer with a light finger touch. Record the micrometer setting, or zero the micrometer, as hm. Set the instrument to measure parallel capacitance and measure the capacitance and dissipation factor of the sample as Cxm and Dxm.
Open the electrodes and remove the sample. Then close the electrodes to the same micrometer reading hm, or back to zero if micrometer was zeroed. Measure C (parallel) and D of empty cell as Ca and Da.
Calculate Kx and Dx of the sample from:
Kx = (1.0005) Cxm/Ca and Dx = |Dxm| - |Da|
The factor 1.0005 in the formula for Kx corrects for the dielectric constant of (dry) air. Subtracting Da from Dxm removes any constant phase error in the instrument. For even better D accuracy, adjust the electrode spacing until the measured capacitance is approximately equal to Cxm and then measure Da.
Note is possible to get negative numbers for Df when below 0.0005 due to errors in the LCR meter and open/short compensation. As the accuracy of the 7600 Plus Precision LCR Meter for Df is 0.0005 this is well within the accuracy of the meter.
A Teflon sample TS-100 is available for checking measurements on the LD-3. The TS-100 has a dielectric constant value of 2.0 and dissipation factor of less than 0.0002 over a broad frequency range from 1 kHz to 2 MHz.
Here is an example of a laboratory that uses the 7600 Precision LCR Meter to perform testing on polymer materials to ASTM D 150 and IEC 60250.Intertek Plastics Technology Laboratory ASTM D 150 and IEC 60250