Advertisement
Reference electrodes often develop high impedances as they see use. Anything that can clog the isolation frit
can raise the electrode impedance. Avoid using saturated KCL based references in perchlorate ion solutions
Instrument Settings
There are several things to remember in setting up a very sensitive experiment.
In EIS, use the largest practical excitation. Don't use a 10 mV excitation on a coated specimen that
•
can handle 100 mV without damage.
Avoid potentials where large DC currents flow. You cannot measure 1pA of AC current on top of
•
1 mA of DC current.
EIS Speed
In EIS, do not expect the PCI4 to measure 10
limit the performance.
As a rule of thumb, the product of Impedance, Z, times frequency, f, must be less than 10
measurements with a PCI4.
Z · f < 10
Ancillary Apparatus
Do not use the PCI4 with ancillary apparatus connected directly to any of the cell leads. Ammeters and
voltmeters, regardless of their specifications, almost always create problems when connected to the PCI4 cell
leads.
Floating Operation
The PCI4 is capable of operation with cells where one of the electrodes or a cell surface is at earth ground.
Examples of earth grounded cells include: autoclaves, stress apparatus, pipelines, storage tanks and battleships.
The PCI4's internal ground is allowed to float with respect to earth ground when it works with these cells, hence
the name floating operation.
Instrument performance can be substantially degraded when the PCI4 is operated in a floating mode. The
instrument specifications only apply on isolated cells with the PCI4 earth ground referenced (not floating).
Special precautions must be taken with the cell connections when the PCI4 must float. Make sure that all the
cell connections are isolated from earth ground. In this case, even the floating ground terminal of the PCI4
must be kept isolated.
Finally, most ancillary apparatus connected to the cell of the PCI4 must be isolated. External voltmeters,
ammeters, FRA's etc. must be isolated. This includes devices connected to the monitor connectors located on
the PCI4 Controller board mini-panel.
Chapter 5 -- Measurement of Small Signals -- Floating Operation
10
ohm impedances at 1 kHz. Many of the factors listed above
9
ΩHz
5-7
9
ΩHz for good EIS
Advertisement
