Advanced Measurement Technology 273A, User Manual

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Model 273A Potentiostat/Galvanostat User’s Manual
Fig. 9. Electrometer.
Warning! This switch provides no protection against the possibility of dangerous
potentials being present at the cell cable leads. These leads can be handled
safely only when the front-panel cell enable switch is in the off position.
1. REFERENCE ELECTRODE JACK: The reference electrode plugs directly into this white
jack. Several suitable electrodes are available from Princeton Applied Research.
2. CELL SWITCH: This switch has two positions, DUMMY and EXT. Normal operation occurs
in the EXT position. In the DUMMY position, a 100 k , 1% resistor inside the Electrometer
Housing is substituted for the cell. The feature is useful for determining that the Model 273A
is functioning correctly.
Note that this is a locking-type toggle switch. To change the setting, it is necessary to grasp
the "bat" and pull it outwards a millimeter or two to release the catch.
3. SENSE and WORKING ELECTRODE JACKS: These two jacks are used together to give
the operator control of the sense function. The upper "gray" jack is internally connected
directly to the reference input of the Electrometer Amplifier. The lower "green" jack is
connected internally to the adjacent Working Electrode lead, which ends in a clip having a
green insulating boot.
In operation, the working electrode of the cell must be returned to the reference input of the
Electrometer Amplifier. The user can do this in either of two ways. If error due to IR drop in
the working electrode lead is not a consideration, simply connect the jumper (shorting plug)
from the Sense jack (gray) to the Working Electrode jack (green) immediately below it.
When working at high currents, it may well be important to eliminate IR drop error resulting
from the resistance of the working electrode lead and alligator clip. To do so, connect a lead
from the Sense jack (gray) directly to the Working Electrode at the cell. Be sure to clip to the
electrode and not to the clip at the end of the working electrode lead. Attaching the sense
lead to the clip at the end of the working electrode lead will still leave the IR drop in the clip
itself as a source of error. Sensing at the cell also prevents errors due to inductance in the
working electrode lead. This inductance can cause significant phase shifts.
Sensing at the electrometer is convenient and yields good results in many applications.
Sensing at the cell gives faster speed and freedom from errors due to IR drop in the working
electrode lead. As a general rule, sensing at the cell is recommended in applications where
the current will exceed 100 mA or where the equivalent cell impedance is less than 5
.