Chapter 6 -- Panel Indicators and Connectors--Rear Panel
6 - 3
Overload LED
The Overload LED is normally unlighted. When it glows red, this indicates that some circuit in the Reference
3000 has exceeded its normal operating limit. Conditions that generate Overloads include:
• The absolute value of the differential electrometer output voltage (the difference in voltage between
the Working and Reference leads) exceeds 10 volts. This condition is known as an E Overload.
• The control amplifier has lost control of the cell.
Remember that the Reference 3000 can be operating with compliance limits of ± 1.5 Amps at ± 30
Volts or with compliance limits of ± 3.0 Amps at ± 15 Volts.
The absolute value of the cell current may be trying to exceed the compliance current or the absolute
value of the counter electrode voltage may be trying to exceed the compliance voltage setting. Either
condition will be called a Control Overload.
• The absolute value of the cell current has exceeded full scale on the current range presently in use.
This condition is known as an I Overload.
An Overload indication does not indicate an instrument failure or system malfunction. Many normal conditions
can light the Overload indicator.
For example, transient (temporary) overloads during an experiment in which the cell voltage or current is being
stepped or swept are often normal. Consider the case of an infinitely fast voltage step into a perfect capacitor.
In theory, charging the capacitor requires an infinite current. The current spike seen at each step in a stepped
voltage waveform can easily light the Overload LED. The current spike will normally decay to near zero before
the actual current and voltage readings are taken.
Overload indications when the cell is being connected or disconnected are also common and usually do not
indicate a problem. Overloads can also be seen when one of the cell leads is disconnected from the other cell
leads, even though the cell is off. Again, this does not indicate a problem.
A steadily glowing Overload LED during an experiment most likely indicates a problem is occurring. Possible
causes include:
• One of the cell leads is disconnected (this is the most common cause),
• a gas bubble in the cell is blocking one of the electrodes,
• the potentiostat could be oscillating (see the next chapter).
NOTE
As described above, a glowing red Overload LED does not necessarily indicate a system
malfunction. The Overload LED can light when one or more cell leads are disconnected,
without indicating a problem with the system. The Overload LED can often light
momentarily during a swept or stepped experiment. The only Overload LED indication
that definitely points towards a problem is a continuously glowing Overload LED during
an experiment.
Rear Panel
The rear panel contains one switch and a large number of connectors. A picture of the Reference 3000 rear
panel can be seen in Figure 4 - 2.
Power In Jack
The Reference 3000 derives all its power from a +24 volts DC supply connected to the Power In jack on the
lower right side of the rear panel. The input current is less than 5 amps.
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