Advanced Measurement Technology 273A, Руководство пользователя

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Chapter 5—Operating Instructions 39
Warning! When working with the cell, including making and breaking connections, the
CELL ENABLE switch must be in the off position. The ±100 V output and high
current capability of the 273A make it a dangerous device, one capable of
causing severe injury or even death. The connections should be handled only
switch. Whenever it is in the OFF position, there is no possible way, including commands from an
external computer, for voltage to be applied to the counter electrode. This switch is provided to
assure operator safety when working on the cell.
The upper Cell key provides the normal Cell ON/OFF control during operation. Unlike the CELL
ENABLE switch, this key is subject to software override. For example, the ON state must be
selected before starting a scan. However, a scan may contain delay intervals to be carried out in
the Cell OFF state. If this is the case, the cell is turned off automatically at the appropriate points
in the measurement sequence.
The Cell indicator light gives the cell status at all times. This red indicator has three states, OFF,
HALF BRIGHT, and FULL BRIGHT. The significance of each state is:
OFF: Both the CELL key and the CELL ENABLE switch are OFF, or the CELL key is OFF and
the CELL ENABLE switch is ON.
HALF BRIGHT: CELL key is ON but the CELL ENABLE switch is OFF.
FULL BRIGHT: Both the CELL key and the CELL ENABLE switch are ON. The cell is ON only
when the light is at full brightness.
The Model 273A is controlled even when the cell isn't ON, that is, having the Cell OFF does not
cause an overload condition.
In the context of this discussion, CELL ON and CELL OFF refer to the path from the Control
Amplifier output to the Counter Electrode cable lead. The red indicator does not respond to the
status of the actual counterelectrode connection. That connection could be secure or faulty and it
would have no effect on the red indicator, which responds only to the CELL ON switch, the CELL
ENABLE switch, and on the governing software. However, if the Cell is ON and there is no
connection to the counter electrode, the effect will be the same as if the cell had infinite
resistance and an E OVERLOAD indication will occur.
5.2.9. INPUT Group
This group contains one indicator, one key, and one BNC connector. Together they provide the
means for summing external control potentials with those generated in the instrument or
transmitted to it from an external computer via the rear-panel RS-232C or GPIB port. The
external control potential is applied to the EXTERNAL INPUT connector. In potentiostat
operation, voltages from -10 V to + 10 V can be applied. In galvanostat operation, the range is
-2 V to +2 V (corresponding to ±2 times the full-scale current), except on the 1 A Current Range
where the range is restricted to ± 1 V. The input impedance is 100 k
.
In potentiostatic operation, all of the control potentials add algebraically. For example, if the
voltage applied to the EXTERNAL INPUT is +0.5 V, at a time when a programmed potential of
+0.5 V is applied, the net potential seen by the Model 273A will be + 1.0 V, and the working
electrode would be controlled at + 1.0 V with respect to the reference electrode. A positive
applied potential will make the current tend to be more anodic. A negative applied potential will
make the current tend to be more cathodic.