Gamry Instruments PCI4/300 Potentiostat/Galvanostat/ZRA Operator's Manual page 33

Chapter 4 -- Stability in Potentiostat Mode -- Improving Potentiostat Stability
Provide a high frequency shunt around the cell. A small capacitor between the red and white cell
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leads allows high frequency feedback to bypass the cell. See Figure 4-2. The capacitor value is
generally determined by trial and error. One nanofarad is a good starting point.
In a sense, this is another form of an AC coupled low impedance reference electrode. The counter
electrode is the low impedance electrode, eliminating the need for an additional electrode in the
solution.
Red
White
Green
Figure 4-2
High Frequency Shunt
100 pF to 10 nF
Reference
Working
4-3
Counter