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Chapter 9 -- Measurement of Small Current Signals--Hints for System and Cell Design
Only connect the Reference 3000 ground to earth ground if all conductive cell
components are well isolated from earth ground. A glass cell is usually well isolated. An
autoclave is generally not well isolated.
Avoid External Noise Sources
Try to keep your system away from electrical noise sources. Some of the worst are:
Fluorescent lights
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Motors
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Radio transmitters
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Computers and computer monitors
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Try to avoid AC powered or computerized apparatus within your Faraday shield.
Cell Cable Length and Construction
The Reference 3000 is shipped with 60 cm shielded cell cables. We also offer extended length cables and
unshielded cables as extra cost options.
Cell cables longer than 1 meter will result in degraded instrument performance. Increased noise and decreased
stability both can occur. However, with most cells, the instrument will work acceptably with an extended cell
cable, so our advice is go-ahead and try it. As a rule, you should not attempt to use current interrupt IR
compensation with cell cables longer than 5 meters.
We do not recommend that you use the Reference 3000 with any cables not supplied by Gamry Instruments.
The Reference 3000 cable is not a simple cable like a typical computer cable. The Reference 3000 cable
includes a number of individually shielded wires contained within an overall shield. The Counter/Working
cable contains fuses. We pay careful attention to issues such as shield isolation, isolation resistance, and
capacitance.
If you do need a special cable, contact us with your requirements.
Lead Placement
Many experiments with the Reference 3000 involve cells with small capacitances, the value of which may be
important.
In these cases, the capacitance between the Reference 3000's cell leads can result in an error. The Reference
3000 alligator clips can have 10 pF or more of mutual capacitance if they are run alongside each other.
If you wish to avoid excessive capacitance:
Place the leads as far apart as possible. Pay special attention to physical separation between the
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working electrode/ working sense leads and the counter/ counter sense/ reference electrode leads.
Have the leads approach the cell from different directions.
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Remove the alligator clips from the leads. In extreme cases you can replace the banana plugs and
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pin jack with smaller connectors. If you do so, be careful not to compromise the isolation between
the center conductor and the shield.
The cell leads must not be moved during an experiment measuring small currents. Both microphonic and
triboelectric effects can create spurious results when the cell cables are moved.
NOTE
9 - 6
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