Advanced Measurement Technology 273A, User Manual

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Model 273A Potentiostat/Galvanostat User’s Manual
In galvanostatic operation, making the applied current more positive by any means except
applying a potential to the EXTERNAL INPUT connector will tend to make the current more
cathodic; making the applied current more negative will tend to make the current more anodic.
This sense is reversed at the external input connector. There, making the input more positive will
make the cell current more anodic. Making the input more negative will make the cell current
more cathodic. Bear in mind that the EXTERNAL INPUT is a high-impedance potential input in
both potentiostatic and galvanostatic operation. In potentiostatic operation, a volt at the External
Input results in a volt at the working electrode (other control sources zero). In galvanostatic
operation, a volt at the External Input results in full-scale cell current (other control sources zero).
The EXTERNAL INPUT is controlled by the EXT ON key. When pressed, the associated
indicator lights and the Model 273A becomes responsive to potentials applied to the EXT INPUT
connector. If pressed again, the indicator goes out, indicating that potentials applied to this input
will be ignored.
5.2.10. FILTER Group
This group contains two indicators and a key. The key allows the user to select OFF (no filter) or
LOW PASS (low-pass filter selected). The indicator corresponding to the filter status will always
be lighted.
The low-pass filter has a sharp cutoff at 5.3 Hz. (A 590 Hz low-pass filter is also available under
software control from the back panel.) It is often helpful when making low-current measurements
on large electrodes because it reduces the noise at the OUTPUT connector. The disadvantage of
using the filter is that the Output response time is degraded. The filter has no effect on I
MONITOR output. Use of the filter for galvanostatic operation is not recommended.
It may be advantageous to synchronize data acquisition with the power line frequency when
filtering. This can be done using Override 14, if desired. The use of Override 14 is described in
Section 5.2.4.
5.2.11. IR COMPENSATION Group
Introduction
There are three keys and two indicators in this group. Positive-Feedback IR Compensation is
selected by pressing the POSITIVE FEEDBACK key. Current Interrupt IR Compensation is
selected by pressing the CURRENT INTERRUPT key. Both keys are toggles for the
corresponding function. However, only one IR Compensation mode can be active at a time. If
one of the two is active and the other is selected, the one previously active will drop out and the
newly selected mode will become active. The associated indicators indicate the status of the IR
Compensation modes. The SET IR key is used in establishing Positive Feedback IR
Compensation. Note: Positive feedback is not available when the Model 273A is operating
in the galvanostatic mode.
The voltage at the front-panel E MONITOR connector and at the rear-panel RECORDER
INTERFACE connector is corrected when either technique is employed, in contrast to the voltage
output at the rear-panel ELECTROMETER MONITOR connector, which is not corrected for the
iR drop.
The two IR Compensation techniques are performed in entirely different ways. Because the
techniques each have strengths and weaknesses, some situations will call for one technique and
some for the other. Table 2 briefly lists the relative strengths of the two techniques. Both
techniques are discussed in the following paragraphs.