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Appendix D -- I/O Connections for the PCI4 -- CE Compliance, EMI and Cable Shielding
Appendix D -- I/O Connections for the PCI4
The PCI4 Potentiostat has a number of connectors that allow it to communicate electronically with the world
outside of the computer. This appendix describes these connectors and the signals available on their pins.
CE Compliance, EMI and Cable Shielding
The European Community has instituted standards limiting radio frequency interference (EMI) from electronic
devices. Compliance with these standards requires that special shielded cell cable connections are used in all
CE compliant systems.
The PCI4 is electrically floating. Its connections to the electrochemical cell under test are not connected in any
way to earth ground. While this is advantageous for testing many types of electrochemical systems, it can result
in significant radio frequency (RF) interference.
The interior of a personal computer is filled with RF energy. The computer's earth grounded enclosure
prevents the escape of this energy.
Now consider the case of the PCI4. It is a floating potentiostat built on a board that mounts inside the
computer. The floating circuits inside the computer act as an antenna, picking up RF energy. The
potentiostat's cables can then radiate this energy outside of the enclosure, generating RF emissions.
The cell cable supplied with your PCI4 has an overall shield that is connected to the computer's chassis ground.
This shield acts as an extension of the computer's chassis, keeping the RF emission level lower than the limits in
the regulations. Note that use of cell cables not designed and sold by Gamry Instruments can result in
excessive RF radiation.
Grounds and the PCI4 Potentiostat
The PCI4 has been specially designed for operation with cells in which one of the electrodes is connected to
earth ground. Earthed electrodes often occur in field experiments, because metal pipelines and structures are
generally earth grounded. In the lab, experiments involving either autoclaves or stress apparatus often have
earth grounded electrodes. Conventional potentiostats do not work properly or safely in these experiments. In
the typical glass or plastic test cell, none of the electrodes are earth grounded, so no grounding problems arise.
The PCI4 analog circuits are electrically isolated from the computer's chassis which is at earth ground. Another
name for circuits that are isolated is "floating". The isolation is accomplished by means of optical isolators and
transformers.
Extraordinary measures were taken in the design of the PCI4 to maximize the degree of isolation. However,
you can still measure higher impedances and smaller currents on cells that are not earth grounded than you
can on earth grounded cells.
If you are working with earth grounded electrodes, ground connections for your potentiostat are critical. You
must be careful that the floating ground connection on all PCI4 connectors does not get connected to earth
ground.
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