Chapter 5: Panel Indicators and Connectors--Front Panel
5 - 4
If you need to make changes to your cell leads, do so between experiments, when the Cell On LED is off and
the potentiostat is inactive.
In a typical experimental sequence, the Cell On LED is off between experiments and during any open-circuit
potential measurements. It glows yellow whenever the cell is polarized.
Overload LED
The Overload LED is just below the Cell On LED.
The Overload LED is normally unlit. When it glows red, some circuit in the Interface 1000 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 11 V. This condition is known as an E Overload.
The control amplifier has lost control of the cell. The absolute value of the cell current may be trying to
exceed 1 A, or the absolute value of the counter electrode voltage may be trying to exceed 22 V.
Either condition is a Control Overload.
The absolute value of the cell current has exceeded full scale on the current range presently in use.
This condition is an I Overload.
Transient (temporary) overloads during an experiment in which the cell voltage or current is being stepped or
swept are often normal. In most cases, they do not indicate a system or instrument malfunction.
Consider the case of an infinitely-fast voltage step into a perfect capacitor. In theory, charging a perfect
capacitor requires an infinite current. The current spike seen at each step in a stepped voltage waveform can
easily illuminate the Overload LED. The current spike normally decays to near zero before the actual current
and voltage readings are taken.
Overload indications when the cell is being connected or disconnected are 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.
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