eDAQ Picostat, Руководство пользователя

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92 eDAQ Potentiostats
When the Picostat is in Standby mode the Working and Reference
electrodes are disconnected by an internal relay. This prevents
unwanted current flowing through your electrochemical cell.
An overload condition is indicated when the error voltage exceeds a
small non-zero value. This indicates that the system could not establish
or sustain a balanced state. The Overload light will be reset when
scanning is stopped or when the Picostat controls are next accessed.
The reference voltage is measured by a high input impedance amplifier
which provides a low impedance output to the
e-corder unit.
The voltage at the working electrode is effectively held at a virtual
ground potential (zero volts) by a voltage-to-current convertor, the
output of which reads directly in current units and is also applied to the
e-corder unit. The Picostat has three gain ranges of 100 pA/V,
1 nA/V, and 10 nA/V. The maximum current output signal (I Out) is
10 V at any gain setting. Secondary amplification of the current signal
is done by the
e-corder . The gain and secondary amplification are set
by the single ‘range’ menu in the software which offers a combined
total of eleven current range settings from ±10 pA to ±100 nA in 1:2:5
steps.
The coaxial shields of the reference and working electrode lead wires
(which carry a high impedance signal) are maintained at the same
potential as the lead wire itself to minimise electrical interference, and
reduce lead capacitance.
QuadStat
The QuadStat is comprised of four subunits which function in
potentiostat mode only — that is the QuadStat cannot be used as a
galvanostat. A block diagram of the QuadStat construction is shown in
Figure A–3 .
Within the QuadStat an ‘error voltage’ is generated from the difference
between the voltage on the Reference electrode and the sum of the
excitation (command) voltage set provided at E In, and the voltage
provided by the E Offset DAC. This error voltage drives a high gain
amplifier (VCVS – voltage controlled voltage source) the output of