The BDS 1314 is an extension for the Novocontrol sample cells BDS 1200 and Alpha-A Active Sample
Cell ZGS. Its main purpose is to add a grounded guard ring to suppress edge field and surface
current contributions, see below.
The BDS 1314 is designed for being mounted into the Novocontrol Dielectric Sample Cells, BDS 1200
and ZGS.
In the Novocontrol sample cells BDS 1200 and ZGS (Alpha-A Active Sample Cell), the generator voltage
is applied to the bottom electrode, while the current signal is measured at the top electrode. The
latter is connected to the virtual ground of the current measurement electronics.
Measurements without guard electrodes may suffer from two effects:
Influence of electric fringe fields developing at the outer rim of the electrodes. These add to
the measured capacity and thus tend to lead to increased values for the measured capacity (real
part, Cp’) and permittivity ε’.
Currents flowing over the sample surface. This tends to increase the measured conduction and
may
lead to increased tan δ values.
Both effects can be reduced or even suppressed using a grounded extra electrode in a concentric
configuration around the top (current collecting) electrode, see Figure 1. Ideally, both edge
fields
and surface currents are blocked by the grounded guard electrode.