Advanced Measurement Technology 273A, User Manual

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Model 273A Potentiostat/Galvanostat User’s Manual
2. This technique corrects for any changes in the uncompensated resistance as the scan
progresses.
3. No adjustment is required on the part of the user. The only action required is the simple
press of a button to enable the correction. (The default values of Functions 13, 17, 18, and
19 will give good results in many applications.)
Disadvantages of the technique include:
1. The correction occurs at finite times. Thus the technique is not suitable for scan rates greater
than 500 mV/s and may, in fact, not work properly at scan rates greater than 100 mV/s.
2. If the correction isn't updated frequently enough, the applied correction can be in error.
3. In some cases, this technique can cause the entire system to oscillate.
The procedure for establishing Current Interrupt IR Compensation is very simple. Simply press
the CURRENT INTERRUPT key. The associated indicator will light and the iR drop will be
automatically compensated in subsequent measurements. To turn the technique OFF, simply
press the CURRENT INTERRUPT key again (the indicator light will extinguish). Note: If the cell
is turned OFF while current interrupt is selected, the current interrupt routine is skipped and no
correction occurs. When the cell is turned back on, the current-interrupt routine resumes.
Once Current Interrupt Compensation is running, the user may wish to monitor the waveform at
the rear-panel ELECTROMETER MONITOR connector with an oscilloscope with the goal of
optimizing the Current Interrupt Parameters as established by Functions 13, 17, 18, and 19. The
selection of the extrapolation points and the % Correction setting determine the accuracy of the
applied correction. Bear in mind that the waveform width (interval between disconnect and
reconnect) is
190 µs. The thirty-two samples (spaced at 5 µs intervals) are located, equally
spaced, in the first 160 µs of the waveform. Note that the waveform depicted in Fig. 7 is
idealized; actually encountered waveforms may not be so easy to analyze.
5.2.12. E Monitor
The potential of the working electrode with respect to the reference electrode is continuously
provided at this connector. This same signal is provided to the Recorder X Drive signal line at
the rear-panel RECORDER INTERFACE connector. A meaningful E MONITOR output is
provided as long as there is a reference electrode. If there is no reference electrode, such as
would normally be the case in Galvanostatic operation, the E MONITOR output is undefined. In
Potentiostatic operation, if IR COMPENSATION is on (either technique), the compensation
corrects the E MONITOR output level for the IR drop.
Note: This is not the case for the rear-panel ELECTROMETER MONITOR output, which is not
compensated.
The E MONITOR signal is analog and quite clean, free of the steps, spikes, and similar
interference common to digitally produced signals. The output impedance is 1 k
. It is inverted
with respect to the applied potential. For example, if the applied potential is + 1 V, the potential
at the E MONITOR connector will be -1 V. Note that the potential at the rear-panel
ELECTROMETER MONITOR connector is also inverted with respect to the applied potential.
5.2.13. CURRENT RANGE Group
There are three keys, nine indicators, and one BNC connector in this group. Their function is to
set and monitor the Model 273A's full-scale current range. One of the eight available current
ranges is always selected, and the corresponding indicator lit. A cell current equal to the selected
current range gives 1 V at the I MONITOR connector. A current of two times the current range
generates an I OVERLOAD condition, except on the 1 A range where the limit is 1 A.