13
Notes for Figure 3-1
• Only Potentiostat Mode circuitry is shown in this figure. In this mode the voltage difference
between the Reference and Working Sense leads (called Esig) is feedback into the control
amplifier.
In Galvanostat Mode, the feedback is from Isig.
In ZRA mode, the feedback is from a differential amplifier measuring the difference between the
Counter Sense and Working Sense leads of the cell cable. The counter sense circuitry is not
shown. It is conceptually similar to the voltage-sensing circuit that generates Esig.
• The Bias DAC and PFIR (Positive Feedback IR compensation) DAC are set using a computer bus
that is not shown.
• Switches are either reed relays or MOS switches as appropriate. All switches are under computer
control (obviously, because the Reference 600+ does not have a knob-and-dial front panel).
• All components shown as being variable (resistance Rm, capacitor IEStab and capacitor CASpeed)
are actually several fixed-value components switched into the circuit. They are not continuously
variable as implied in the figure.
• The monitor BNC connectors for Isig and Esig are lightly filtered using an RLC circuit.
• The programmable attenuator on Esig prior to the ADC channel scales Esig so that it is compatible
with the A/D channel’s 3 V input range. The 0.25 gain setting allows the Reference 600+ to
measure potential signals slightly in excess of 10 V (on a 12 V full-scale range). Isig is gained to be
3 V full-scale so it does not require a similar attenuation function.
• All the resistors summing voltages into the Control Amplifier input do not have values shown; their
values depend on scaling factors too complex to discuss in this simplified diagram.
• Calibration components are not shown.
• Gamry’s software can disconnect the signal generator from the Potentiostat. Once disconnected it
can be used for other experimental control tasks.
• Overload protection and overload detection are not shown. Good engineering practice demands
that any possible misconnection of the cell leads will not damage the instrument. This practice has
been followed in the Reference 600+ design.
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