Gamry ECM8, Operator'S Manual

Page: 21 / 46

Chapter 2 -- Introduction--Switching and Inactive Cell Control
2 - 5
Switching and Inactive Cell Control
In the Operation Overview, we said you can think of the ECM8 as a complex switch. This section of the
manual describes the ECM8 switching in some detail. In addition, control modes for inactive cells are
discussed.
Each of the eight ECM8 channels is
made up from an independent set of
switches and control circuits. Figure 2-2
is a simplified schematic diagram for
one channel of the ECM8. Switches
connected with dotted lines are always
switched together and are therefore
treated as one multi-pole switch. All the
switches are under control of the system
computer. Shield relays are not shown.
The cell cable from the system
potentiostat is connected at the left side
of the schematic. The system
potentiostat cell cable is also connected
to all of the other channels. The system
computer must insure that only one cell
at a time is connected to the system
potentiostat.
Figure 2-2
Simplified Schematic of One ECM8 Channel
Switch S1 controls which cell is active. S3 and S4 control the inactive mode of the cell on this channel.
Looking at the schematic, you can see that switch S1 connects this channel's cell to the system potentiostat.
An active channel always has S3 and S4 open. The relays in S1 are rated to carry 2 Amps and switch 1
Amp. You can normally use the ECM8 with potentiostats rated at up to 100 volts of output compliance
and 2 Amps of output current.
To avoid transients, you should always turn off the cell at the system potentiostat prior to switching S1. The
ECM8 switches all its relays nearly simultaneously (even those in different channels), but there is still about
1 millisecond in which the relay pattern in the ECM8 is in neither the initial or final configuration.
Switching transients as the ECM8 switches channels with a "live" potentiostat can be particularly severe
because the system potentiostat's feedback goes through one of the S1 relays. To avoid the problem, turn
off the cell at the system potentiostat before switching channels.
The switch labeled S2 is part of the Aux A/D option. It connects one of 8 pairs of uncommitted contacts
to a common input/output connector. The most common use for this set of contacts is to multiplex 8
signals to the one auxiliary A/D input on a system potentiostat. The BNC connectors for this function are
therefore labeled "Auxiliary A/D Input" on the ECM8 rear panel. The holes for these BNC connectors are
filled with plugs if the Aux A/D option is not installed. The system computer must make sure that S2 is
closed for only one channel at a time.
Switch S2 is controlled independently of S1, although they are often switched together. It is possible to
connect your system potentiostat to the cell on Channel 3 and simultaneously select the Auxiliary A/D
connection for Channel 6.