eDAQ Picostat, User Manual

Page: 94 / 122

90 eDAQ Potentiostats
The Potentiostat is fitted with an internal 1 MΩ dummy cell for use in
potentiostat or galvanostat mode. The dummy cell is physically
connected whenever the ‘Real cell’ mode is not being used.
The Potentiostat has gain ranges at decade intervals from 1 nA/V to
10 mA/V, provided by an I to V convertor and PGA. 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 21 current range settings
from ±20 nA to ±100 mA in 1:2:5 steps,
page 102 .
The Potentiostat uses an error amplifier to compare the difference in
potential between the reference electrode and the excitation potential
set using the analog output of the
e-corder . The output of this amplifier
provides an error signal the feed back circuit tries to zero.
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.
The Potentiostat is powered by reg17 V, –17 V and +8 V DC
lines from the
e-corder , see Figure 2–3 on page 9 . The use of DC
power allows its use inside Faraday cages.
Working
Auxiliary
Shield
Reference
Shield
Overload
Online
Low Pass
Filter
Overload
detector
Dummy
Cell
+
–
+
–
Front Panel Back Panel
I
2
C Control
Interface
E In
(Command
voltage)
E Out
(Reference
voltage)
I Out
I
2
C Input
I
2
C Output
Ground
∑
×
PGA
x1
x10
Hi Z
x10
I to V
DAC
Ref Amp
1 MΩ
100 kΩ
100 kΩ
10 MΩ
1 Hz Square
Wave
iR Comp
Power Amp
Error
Voltage
Figure A–1
Block diagram of the
Potentiostat.