Other Experimental Parameters
There are a number of experimental parameters required for epsilon which are designed to optimize instrument control and experimental data acquisition. However, in most instances, the default values set by the software for these parameters are the optimum values, and typically no user input is required. Indeed, if you are not sure what effect varying a given parameter will have on the experiment, it is best not to change it from the default value!
These parameters are as follows:
Setup / Manual Settings (I/O)
Cell
Filter
Current Sensitivity Gain
Stabilizing Capacitor
In all the dialog boxes described below, the Apply button must be clicked to activate any of the changes entered by the user. If the dialog box is exited without clicking Apply, the changes will not be applied.
Setup / Manual Settings (I/O)
The Setup / Manual Settings (I/O) dialog box is accessed from the Experiment menu (Fig1).
Figure 1. Manual Settings dialog box.
| Cell Stand / Accessories |
The correct option must be selected to control the various Cell Stand operations from the software (i.e., purge and stir for the C3; purge, stir, and knock/dispense for the CGME; and purge and rotate for the RDE-2). Before the Cell Stand can be selected, the Cell Stand must be switched on and connected to the epsilon as described under Interfacing BASi® Accessories with the epsilon. Similarly, the PWR-3 must be connected to the ACCESSORIES
port of the epsilon before it can be selected. |
| Purge / Stir |
The purging and stirring/rotation functions of BASi® Cell Stands can be switched on and off from this dialog box. If one of these functions is enabled, the time for which this function is active must also be entered. The Stop
button is used to stop this function before the specified time. The appropriate Cell Stand from Cell Stand / Accessories
must be selected in order to ensure proper activation of these functions. Note that selection of RDE-2Cell Stand / Accessories
changes Stir
to Rotate
and activates the RDE2 - RPM
option.
|
| Line freq (50/60 Hz) |
This selects the frequency of the line supply, which is used to calculate the time required for one of the current sampling options (1 Line Period) in pulse and square wave experiments. The selected value is stored in the .ini file. Measuring the current over one line cycle is important for noise minimization. |
| Default Display Type |
This selects the default Display Type
- Polarographic or IUPAC. |
| Current Cell Status |
This option specifies whether the electrochemical cell is actively connected (Cell On
is checked) to the instrument at that moment. The default condition is that it is disconnected (Cell On
is not
checked). This is the safest option, since manipulation of the cell lead connections while the cell is connected can cause harm to the user and severe damage to the instrument. If Cell On
is checked, the potential applied to the cell must also be specified (@ Potential (mV)). The Current Cell Status
will be maintained until an experiment is run. During an experiment, the cell is obviously connected; the cell connection at the end of the experiment is defined by the End Of Experiment Cell Condition. |
| External E and I |
These activate the back-panel analog inputs and outputs. |
| Back Panel Events On/Off |
These activate the back-panel Timed Event relays. |
Cell
The Cell dialog box is accessed using the Cell button in the Change Parameters dialog box (Fig2).
Figure 2. Cell dialog box.
| End of Experiment |
This option specifies whether the electrochemical cell remains actively connected at the end of an experiment, and, if so, at what potential. The default condition is Cell Off
(i.e., the electrochemical is not actively connected). If the cell is to remain actively connected, the applied potential can be the initial potential (Cell ON @ initial potential) or the final potential (Cell ON @ final potential) of the experiment specified in the associated Change Parameters
dialog box, or at a user-specified potential (Cell On @ Potential (mV)). HOWEVER, CAUTION SHOULD BE USED IF ANY OF THE CELL ON
OPTIONS ARE USED, SINCE CONNECTING OR DISCONNECTING THE ELECTRODES WHEN THE CELL IS ON CAN RESULT IN DAMAGE TO THE POTENTIOSTAT, THE CELL, AND/OR THE USER! |
| Ext / Internal Cell |
This function allows the user to select between an external cell connection (required for running an experiment on an electrochemical cell) or an internal dummy cell (for troubleshooting). Two choices are available for the internal dummy cell - a 10 KOhm or a 10 MOhm resistor. Note that the internal dummy cell is NOT available for Controlled Potential Electrolysis (CPE). |
| CGME SMDE Mode |
This option is activated only when CGME SMDE Mode
has been activated in the Setup / Manual Settings (I/O)
dialog box, and is required when using the SMDE mode of the BASi® Controlled Growth Mercury Electrode (CGME) for polarography and stripping experiments. It can also be used with voltammetry experiments using a single mercury drop for the entire experiment. Both the number of mercury drops before the experiment (Pre Run Drops) and the drop knock operation (Knock) can be specified in this dialog box. For most potentiostatic experiments, the Pre Run Drops
are formed with the cell on at the Initial Potential
(for stripping experiment, they are formed at the Deposition Potential). Note that the Pre Run Drops
option is NOT available for Controlled Potential Electrolysis (CPE).
|
| RDE2 Rotation |
This option is activated only when RDE-2
has been activated in the Setup / Manual Settings (I/O)
dialog box. It is used to specify the Rotation Rate
used during the experiment, and also allows the option of rotating the electrode during the Quiet Time.
|
Filter
Figure 3. Filter / F.S. dialog box.
The Filter/Full Scale dialog box is accessed through the Change Parameters dialog boxes. Note that the channel selection function is enabled only for techniques that require the optional bipotentiostat board (i.e., MCCV and MCA).
| Current Sensitivity |
There are two gain stages for the current-to-voltage converter which control the current Full Scale. The first stage has values in decades from 100 nA to 10 mA, whereas the second stage is a multiplier with values of 1, 0.1, and 0.01; that is, the lowest Full Scale
is 1 nA. There is more than one combination for intermediate values of the Full Scale, and the default values selected by the software are suitable for most applications. Note that the Automatic
box must be unchecked before a different value can be selected. |
| Noise Filter Value |
Analog filtering is used to remove noise from the experimental data. The filtering in the epsilon consists of a two-pole Bessel filter. The amount of filtering (the cut-off frequency of the filter) must be selected with care, since overfiltering can distort the experimental data. The correct filter frequency depends on the time scale of the experiment, and is selected by the software to be at least 10 time larger than the time scale of the electrochemical experiment. Although an alternative filter can be selected manually, it is generally best to use the default filter. Note that the Automatic
box must be unchecked before a different value can be selected. |
Stabilizing Capacitor
There are some operations of the epsilon that can cause some electronic instability, particularly controlled potential electrolysis experiments and iR compensation. A stabilizing capacitor is therefore used during these operations in order to provide stability. The default selections are generally optimum for virtually all conditions, although the selection can be changed.
