Description
The DC Corrosion combined with a Multiplexer is a system for cost-effective electrochemical-corrosion monitoring. You can use a multiplexed system to sequentially test eight electrochemical cells using only one high-performance potentiostat/galvanostat/ZRA. Multiplexed tests include corrosion rate versus time (via repeated polarization resistance scans), galvanic corrosion versus time, and potentiodynamic and galvanodynamic scans.
Applications for a multiplexed system include inhibitor and materials screening, on-line corrosion monitoring, and quality-control of corrosion-control products.
Definitions of Important Terms
The following important terms are used throughout this help section.
Term |
Description |
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The cell (if any) currently connected to the system potentiostat. Any electrochemical measurements are made on the active cell. |
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An independent switch in each Multiplexer channel. It need not be switched along with the cell connections. This switch is only used in galvanic corrosion tests. It is used to multiplex the reference-electrode signals from each cell to the single Auxiliary A/D input on the system potentiostat. |
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Either an electrochemical cell, or the switches needed to connect an electrochemical cell to the system potentiostat. |
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One of the eight Multiplexer channels. A channel includes cell switching, an Aux A/D switch, a local potentiostat, and a D/A converter. The term cell is used when only the cell-switching portion of a channel is discussed. |
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Any cell not currently connected to the system potentiostat. "Inactive" is a slightly misleading term, for an inactive cell can still be "actively" controlled by the Multiplexer. |
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The computer responsible for coordinating operation of a Multiplexed DC Corrosion system. |
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The potentiostat responsible for making electrochemical measurements on the cells used in the experiment. The system potentiostat in a Multiplexed DC Corrosion system is a Gamry Instruments' Reference™ or Interface™ family instrument. |
The figure below shows the block diagram for a Multiplexed DC Corrosion system connected to eight electrochemical cells.
A Potentiostat/Galvanostat/ZRA, the so-called System potentiostat, is installed inside the System computer. Unlike in a DC Corrosion system, the System potentiostat's cell connector is not attached directly to an electrochemical cell. Instead, the potentiostat is attached to an Electrochemical Multiplexer (IMX8). The Multiplexer has eight cell ports, each of which can be connected to an electrochemical cell. Each port and its associated support circuitry is referred to as a channel.
You can think of the Multiplexer as a sophisticated multi-pole switch. It can connect the potentiostat’s cell leads to any one of its cell ports. The cell that is currently connected to the system potentiostat is called the active cell. A LED on the front panel of the Multiplexer indicates which channel is currently active. Cells that are not connected to the System potentiostat are referred to as inactive cells.
Unlike a simple switch, the Multiplexer can potentiostatically control each inactive cell by a low-current potentiostat built into each channel. If you are switching galvanic corrosion cells, the inactive cells can also be shorted. This allows galvanic corrosion to continue between measurements, minimizing the effect of multiplexing on the system. See the corresponding Multiplexer's Operator's manual for more information concerning inactive-cell control modes.
The Multiplexed DC Corrosion software controls the IMX8 via USB whereas the now retired ECM8 is controlled via an RS-232 serial connection.
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