3.
MEASUREMENT OF SMALL CURRENT SIGNALS
This chapter describes the issues surrounding the measurement of small current signals to include proper
shielding and cell design recommendations.
3.1. Faraday Shield
The LCI and corresponding potentiostat system operate near the limits of current measurement. The LCI
system can resolve current in the attoamp (10-18) range. For perspective, 100aA represents the flow of
around 600 electrons per second!
A Faraday shield for low current measurements is mandatory. A Faraday shield is a conductive enclosure
that surrounds the cell. The materials can vary from a metal box or fine wire mesh, to a plastic case
covered in conductive paint. The conductive coating should be continuous on all sides of the cell
(including the bottom), and all parts operate as a single, conductive unit.
For the LCI, the best shielding will occur if the LCI main body and the cell leads are all placed inside the
Faraday shield, as the shield must be connected to the LCI ground. Note the photos below of the
Princeton Applied Research K0269B Faraday box. The box is made of steel with a few small openings for
cell cables or other leads. The box can be used in a vertical or horizontal position. In the photo to the
right, the LCI Main body has been attached to the wall of the K0269B using Velcro tape (not supplied).
Also note in the upper left corner above the cell is a grounding point to connect the ground lead from the
LCI to the Faraday shield (not connected in photo).
Figure 15. K0269B Faraday Box
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