The EC Detector Schedule contains all the information for control of the EC detectors in their constant-potential mode (see the PAD section for the Pulsed Amperometric mode). The Detector Schedule contains instructions used during programmed runs, and also allows manual control of the detectors. Note that the EC detectors must be enabled in the Detector Channel Options section before this detector schedule can be accessed.
The schedule also can be reached by clicking the <<OK or OK>> buttons from other Method screens.
The schedule consists of time lines, edit boxes, and pushbuttons. For every time line there will be a subline for each EC detector enabled under Detector Channel Options. These will be labeled 1-4, corresponding to detectors W1-W4.
TIME is set in minutes, with a minimum interval of 0.1 minutes between lines. Every detector schedule must have at least two time lines: a 0.0 line and an end line. The length of a run is determined by the longest time line in any of the following modules in the Method: Pump, EC Detector, External Detector, PAD, or Switch Schedule. (Click here for a review of the Method modules.) At the end of the run, the detectors revert to the time 0.0 conditions.
DET. is the detector number, corresponding to detectors W1-W4.
POTENTIAL is set by entering the voltage, in millivolts, in the edit box provided. Potentials must be in 10 mV increments. Use a minus sign (-) to indicate negative potentials.
+/- is the sign for the Range. Use a minus sign (-) for reductions, to make the peaks positive-going on the screen.
RANGE is the full-scale sensitivity of the detector, in Amperes full scale. Large values are less sensitive than small values. When in doubt, use a less-sensitive value, as small peaks can still be quantitated by ChromGraph Report. If you use a sensitive range and the peaks go offscale, that run is useless. Range is set via a drop-down listbox:
FILTERis the noise-filtering setting for the detector, in Hertz. Large values give less filtering than small values. A value of 0.1 Hz is common. For determinations at or near the detection limits of the detector you should determine which filter setting provides the greatest signal-to-noise ratio (peak height / baseline noise) for your particular conditions. Filter is set via a drop-down listbox.
OFF. is an offset (in % of full scale) that can be applied to raise the baseline on the graph. Its most common use is to separate the traces of different detectors on the screen. Offset takes effect after a manual or programmed rezero.
POL. is the polarity of the analog signal that's available from the back-panel connectors. It's most common use is to change the pen direction on an external chart recorder. Changes here have no effect on the screen or on the data.
ZERO allows you to program an automatic rezero as each time line is reached during a programmed run. To rezero manually, use the Zero button in the Detector Status box.
The pushbuttons have their usual meanings as explained in the Using The Method Screens section. Two additional pushbuttons, Warmup and Stop, are explained below.
Manual control is needed when setting up, equilibrating, or performing maintenance on the detectors. The following functions are available:
WARMUP turns on the detectors at the insensitive range of 1 uAfs. ALWAYS turn on the detectors using the WARMUP mode, as this range can handle the surge of current at initial startup. The detectors will equilibrate faster if you use WARMUP.
When the Warmup button is pressed, a dialog opens that allows you to choose which detectors to turn on:
NOTE: No detector can be turned on unless its predecessor also is on (e.g., you can't turn on W2 unless W1 is turned on at the same time or already is on).
As always, the Detector Status box displays the current condition of the detectors.
EXEC. Once the detectors are equilibrated, then use EXEC to send the final conditions (line 1 of the detector schedule) to the detectors.
ZERO To rezero manually, use the Zero button in the Detector Status box.
STOP opens a dialog to turn off the detectors:
NOTE: No detector can be turned off unless subsequent detectors also are turned off (e.g., you can't turn off W1 unless W2 is turned off at the same time or is already off).
ALWAYS TURN OFF THE DETECTORS BEFORE TOUCHING THE CELL LEADS OR DISASSEMBLING THE ELECTRODES. STATIC DISCHARGES FROM YOUR FINGERS CAN DAMAGE THE UNIT'S AMPLIFIERS.