Chapter 8 -- Measurement of Small Signals--Floating Operation
8 - 7
• 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 Interface 1000 to measure 10
10
ohm impedances at 1 kHz. Many of the factors
listed above limit the performance.
As a rule of thumb, the product of Impedance, Z, times frequency, f, should be less than 10
9
ΩHz for good
EIS measurements with an Interface 1000.
Z · f < 10
9
ΩHz
Ancillary Apparatus
Do not use the Interface 1000 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 Interface 1000 cell leads.
Floating Operation
The Interface 1000 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 Interface 1000 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 Interface 1000 is operated in a floating
mode. The instrument specifications only apply on isolated cells with the Interface 1000 earth ground
referenced (not floating).
Special precautions must be taken with the cell connections when the Interface 1000 must float. Make
sure that all the cell connections are isolated from earth ground. In this case, you must disconnect the
chassis ground terminal of the Interface 1000 from earth ground.
Finally, ancillary apparatus connected to the Interface 1000 must be isolated. External voltmeters,
ammeters, FRA's etc. must be isolated. This includes devices connected to the monitor connector located
on the Interface 1000 front panel.
Cables used with the User I/O Connector must be carefully constructed. We do not recommend
connection to the User I/O connector using a 15 conductor shielded cable. The shield will generally be
connected to the metal shell of the User I/O connector on the Interface 1000 end of the cable. The shield
will often be connected to an earth ground on the other end of the cable. Connecting the grounds in this
way destroys the Interface 1000's ability to float and to make measurements on earth grounded cells. In
extreme cases, this connection can cause damage to the Interface 1000.
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