This chapter describes the Data Collection Software accessed from Selection 1 of the main menu, by reference to the sub-menu entries by which further features may be accessed. It is prescribed reading for a new user of the software, so that he may grasp the range of its capability, but need not be learnt, as it is referenced in the index.
Data collection involves the following steps:
The Run Parameters Menu is shown at figure 10.1 below (also figure 2.2 above). It has a Proceed action, seven editable items, Default / Cancel and Quit actions.
Figure 10.1 - Run Parameters Menu Screen.
Leads to the Enter Identity Screen if the JCI155v4 instrument is in manual control mode, or the Instrument Parameters Menu if in computer control mode. Use this action to proceed with a charge decay run.
These are voltage levels which the surface potential must exceed at the start of a charge decay run in order to trigger the system into data logging. They are best set at at a bit below half the minimum peak surface potential expected, but are not very critical. If they are too low (less than 20V) the data logging may be triggered by instrument noise or interference. It may be appropriate to set one of these levels high to inhibit triggering on spikes of the wrong polarity. It will be found that these are limited to the range ±5 to ±1000 Volt, and that appropriate polarity is enforced.
These should be entered as externally measured values at least at the start of every session, and when appropriate thereafter. They appear on screens and screen print out during the analysis. If they are both at the default silly values of 99°C, 99%R.H., it is likely that this step has been ignored! It will be found that these values are limited to the ranges -55 to +155°C and 0.0 to 100.0 %R.H. respectively.
These values may be edited to facilitate the logging of the time for surface potential to decay from a fixed value (Analysis Period Start) to a fixed percentage of that value (Analysis Period End). These show up on the Analysis Screen (figure 2.7) and the Graph Screen (figure 2.9) as Vs and Ve start and end voltages. The settings automatically assume the correct polarity for the discharge. If the surface potential at the start of the charge decay is less than Vs, then Vs is taken as the surface potential at the start of the charge decay. The range of the Analysis Period Start is ± 15 to ±10,000 Volts, while the range of Analysis Period End is ±5 Volts (as a percentage) to 100%
There are two selections available:
Recording will also stop at the end of a data collection phase in which the signal becomes too low to be very reliable (~5V).
The latter setting is useful for obtaining quick readings on materials with long time constants. If Analysis Period Start is set at 10,000V, which effectively forces the true analysis period start to be the start of the charge decay, and Analysis Period End is set to say 90%, then the recording will terminate in 1/10th of the time constant.
Note also that the logging is divided into phases, and the stopping times are affected as shown in Table 10.2 below:
| Nº of|
|Peak||3 secs||3 secs||0.0025||1||Recording stopped & Phase complete|
|Decay1||12 secs||15 secs||0.01||3-4||(Recording stopped & Phase Complete)|
|Decay3||20 mins||22.2mins||1.0||100||- ditto -||- ditto -|
|Decay4||3.33hrs||3.7hrs||10.0||100||- ditto -||- ditto -|
|Decay5||33.3hrs||37hrs||100.0||100||- ditto -||- ditto -|
|Decay6||2 weeks||2.2 weeks||1k||100||- ditto -||- ditto -|
|Decay7||4.5 mths||5 mths||10 k||100||- ditto -||- ditto -|
Figure 10.2 Table of Data Logging Phases
Use this selection for cancelling all changes and / or restoring all defaults. See Chapter 9 ("Menus", §Restoring defaults / cancelling changes), and / or read the instruction line carefully before you press when this line is selected.
This selection returns to the main menu.
This menu is shown in figure 10.3 below (also at figure 2.3) and is encountered in manual control mode when proceeding from the Run Parameters menu (figure 10.1 above) or having selected the Repeat Run option in the Analysis / Graph Preparation Menus. It offers a Proceed action, entry / edit of the sample identity, a Default / Cancel line, and a Quit action.
Figure 10.3 - Sample Identity Entry Screen
Use this action to proceed with a charge decay run.
Enter or edit this item with a note of up to 50 characters (including spaces), peculiar to the particular sample. Note that it is more convenient to categorize groups of samples using the hierarchical directories of the computer's filing system. This identity will appear on screens and screen print out during the analysis.
This selection may be used for cancelling any changes and / or restoring the defaults. See Chapter 9 ("Menus", §Restoring defaults / cancelling changes) and / or read the instruction line before you press press when this line is selected.
This selection returns to the main menu.
This menu is shown in figure 10.4 below (also at figure 3.2) and is encountered in computer control mode when proceeding from the Run Parameters menu (figure 10.1 above) or having selected the Repeat Run option in the Analysis / Graph Preparation Menus. It offers a Proceed action, five editable instrument parameters, entry / edit of the sample identity, a Default / Cancel line, and a Quit action.
Figure 10.4 - Instrument Parameters Menu Screen
Use this action to proceed with a charge decay run. Remote start from the JCI155v4 instrument may also be achieved when this is selected.
Limits of 0 to 9600 volts are indicated. There are only 31 equal steps from 0 upwards available, and the displayed value adjusts to the nearest step after confirmation. Recall that polarity is c ontrolled by the setting of the JCI155v4 Polarity switch.
Limits of 0.02 to 1000 secs are indicated, and are obtainable in steps of 0.01 secs to 1.0 secs, 0.1 secs to 10 secs, then 1 sec.
Compensation for dead time between initiation of plate release and the event itself, so that the effective plate release coincides with the removal of the corona charging voltage. Should not be adjusted without reference to the handbook and / or consultation with JCI.
In Computer Control mode it is possible to specify that a charge decay run be repeated with identical Run and Instrument parameters up to 99 times. Serious use of this feature requires some thought to be given to data storage. The Drive List Menu described in Chapter 12 ("Software operation for Charge Decay file management", §Drive Lists Menu) allows the best use to be made of your computer's floppy, hard and ram discs. At the end of each run, provision is made for an inter-run holdoff time to allow sample to lose its charge prior to the next run, and the analysis and graph are omitted, so that the multiple runs may be performed unattended.
Applies after runs when the number of runs is set greater than one. Range is 0 to 10,000 secs in whole seconds. A hold-off screen appears for this length of time between the runs with visual indication of the progress of the hold off time, and an audible beep every 3 seconds. While the holdoff screen appears, pressing and holding key will terminate the hold off time at once.
Enter or edit this item with a note of up to 50 characters (including spaces), peculiar to the particular sample. Note that it is more convenient to categorize groups of samples using the hierarchical directories of the computer's filing system. Both the directories and this identity will appear on screens and screen print out during the analysis.
Use this selection for cancelling all changes and / or restoring all defaults. See See Chapter 9 ("Menus", §Restoring defaults / cancelling changes), and / or read the instruction line before you press when this line is selected.
This selection returns to the main menu.
This screen is shown in figure 10.5 below, (also at figures 2.4, 2.5). The only possible keyboard action is to terminate the display by pressing .
Figure 10.5 - Initial Graph Screen - Discharge in progress
Terminating at this point returns directly to the main menu. Use this to recover from a situation when the decay will not start, due e.g. to low charge and insufficient surface potential, or recognition of some error in physical or operational set up..
Terminating will take effect only after the first three seconds of the run has elapsed. Termination leads to saving of data up to the point of termination, then entry to the Analysis Preparation Menu. Use this to abort a run that is not wanted, or has yielded enough data.
The screen terminates naturally after 3 or 15 seconds as indicated above. If the recording is complete, then termination leads to saving of data up to the point of termination, then entry to the Analysis Preparation Menu (Chapter 11); otherwise the Numerical Screen (figure 10.6 below) is entered.
If data collection lasts for more than 15 seconds, the initial graph screen is replaced by a screen in which the surface potential data is written in numeric form to the screen, 1200 times per decay phase, using a page of 200 numbers overwritten 6 times per phase.
Figure 10.6 Numerical Screen
This screen is shown in figure 10.6. The only possible keyboard action is to terminate the display by pressing .
As shown above, indicators show the phase number, and the time into the r un. The target indicators are shown regardless of recording mode: in manual mode these are a convenient indication of when the run may be terminated without losing useful data. In any case the screen terminates on completion of recording as indicated in table 5.1 above, leading to data save and the Analysis Preparation Menu (Figures 2. 6, 11.1).
Premature termination has the same effect as for the initial Graph Screen above with the Running indicator showing, i.e. abandon further data collection, save data and bring up the Analysis Preparation Menu.
If there is a problem saving the data e.g. disc fills up, then a menu will appear offering information and solutions. This is discussed in Chapter 13 ("Trouble shooting", §Drive Operations Menu).