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switch to the ON position. An auto-zero event is initiated by moving the toggle switch mo-
mentarily to the ZERO position. The Output display (and the output to the chart recorder)
will be set to zero, and whatever current there was will be added to the Offset
mote-control connector to AUTO ZERO is provided on the terminal strip of the back panel
(see Figure 4.2).
A control knob is provided below the AUTO ZERO toggle switch on the front panel to enable
a small amount of voltage to be added to the output. This may be necessary for integrators
that work best with a slightly positive "zero" baseline. The effect of this control knob is not
apparent on the LC-4C display: it only affects output to the recording device. An adjustment
is needed if 1) the baseline on your integrator is zero or negative, or 2) your chart-recorder
pen does not go to the "zero" position when the LC-4C output display reads zero. To use
this control, zero both the LC-4C and the recording device independently, then turn the con-
trol knob until the baseline on the recording device is at the desired location. This control is
only active when AUTO ZERO is on.
The MANUAL OFFSET knob can be turned to null out background currents from 0–10 nA,
0–100 nA, or 0–1000 nA, depending on the range chosen. The range and sign of the offset
are determined by two toggle switches located above the adjusting knob. When set on [+],
the circuit will null anodic (oxidative) currents; on [–], it will null cathodic (reductive) cur-
rents. As with auto-offset, the circuitry is disabled when OFF is selected.
When both AUTO- and MANUAL OFFSETS are off, the detector continues to function nor-
mally, and the OUTPUT display shows the true current output of the detector. When both off-
sets are on, the true current output of the detector is the sum of the Output, Offset
set
displays.
M
MARKER
This front-panel push button will produce a momentary pen deflection on your chart re-
corder to mark events. A remote-control connection to MARKER is provided on the terminal
strip on the back panel (see Figure 4.2).
CELL
The CELL switch controls the function of the working electrode. In the STBY mode, the work-
ing electrode is off. In the ON mode, the working electrode is on and the selected potential
is applied. The TEST mode is used only for troubleshooting the controller for electronic
problems (see Appendix I, page 41).
WARNING: The CELL switch must be in the STBY position when the
LC-4C is turned on or off, and for any electrode servicing. Disas-
sembling a "live" cell can permanently damage the working elec-
trode and the electronic circuits.
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Section 4. Operating the Electrochemical Detector
display. A re-
A
, and Off-
A
25
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