This chapter takes you step by step through the operations required to collect and analyse charge decay data using the JCI155v4 Charge Decay Test Unit and the software supplied.
Figure 2.1 - Main Menu Screen
Place the JCI155v4 on a sample of a material with a fairly short charge decay time, e.g.: paper.
After pressing at the preliminary screen display the main menu will appear, more or less as shown in figure 2.1. However be careful to read the information in the status panel before proceeding. If this indicates that drive A has many kBytes free and "Port 1" has no "bad link" message appended to it, then all is well.
Otherwise, please see the chapter 13 "Trouble Shooting", which has sections on Disc Drive Problems and Serial Link Problems before proceeding further.
Please ensure your instrument is not set to "Computer control". The selections available on the main menu will then start with "Run under manual control". To select this (if the selector bar is not already in this position), use the up arrow key until the selector bar is on this selection, then press .
Figure 2.2 - Run Parameters Menu Screen.
You will be presented with the Run Parameters menu. The run parameters are discussed fully in chapter 10 "Software Operation for Data Collection". All run parameters default to a set of sensible values (the temperature and humidity are set to evidently wrong values so it will be seen when these have been set), so press once again to pass on to the Sample Identity Menu.
Figure 2.3 - Sample Identity Entry Screen
You are responsible for providing sample identity information at the start of each run. Type over the default sample identity, and try modifying and correcting your entry as required by using the following keys:
(Backspace), ,,,+,, , +,
Then press once to complete your entry. The selection bar will move up to proceed.
Set the JCI155v4 Polarity to -ve, for better corona discharge. Move the JCI155v4 Plate Control switch to the Charging position. Listen for the charging plate drive motion to be completed. Set the Corona switch to Continuous, and adjust the potentiometer to give some 7-8kV. Then the Corona switch can be set to Pulse on discharge.
Press again, and after a short pause while any instrument zero drift is corrected, a set of graph axes will appear, and the computer will beep once.
Figure 2.4 - Initial Graph Screen - ready to run.
When this graph a ppears move the JCI155v4 Charging Switch to discharge position.
Figure 2.5 - Initial Graph Screen - Discharge in progress
If there is sufficient char ge on the sample to trigger the software, the RUN message will change to RUNNING and an initial graph of the charge decay will be drawn on the screen. The graph may appear to be a bit small, but the scale needs to be large enough to allow for the large signals obtained from good insulators. If the decay time constant exceeds 15 seconds, the graph will be replaced by a screen showing the surface voltage values as a column of figures. This numerical display may last a long time. You may press at any time after the first 3 seconds to bypass further data collection.
If the discharge does not start, please see Chapter 13 (Trouble Shooting, §Charge Decay Run Starting Problems).
Figure 2.6 Analysis Preparation Menu Screen
A short while after the initial graph display (or the numerical display) disappears, the data is saved to disc, and a message appears on screen to show this. The program will then show the Analysis Preparation Menu. If there is a problem with the disc a different menu will appear offering you courses of action to o vercome the problem: see the chapter 13 "Troubleshooting", section on Disc Drive Problems. On the Analysis Preparation Menu, select Analyse with DEFAULT parameters and press to proceed with on screen analysis of the charge decay.
Figure 2.7 On Screen Analysis (completed).
After a pause while the discharge peak value is located, the analysis screen shown above will rapidly fill with numbers. The right hand dark panel shows time, surface voltage and "local" time constant. If it overflows, early values scroll away, but can be recalled when the display is complete, using the following keys:
+, , , , , +
The top left area shows various operational parameters recorded at the time of the run, while the two small dark panels left of centre show results computed "on the fly" during the run using integer arithmetic for speed and the same figures computed using real arithmetic during analysis of the results. On an analysis using default parameters values should correspond, but note that analysis zero shift should read 0.000 as this is a difference value. Vs and Ve are user settable values between which a decay time has been requested (see screen figure 2.2). If a decay time is estimated by projection to a time beyond the end of the run, the percentage or time of estimation are indicated, otherwise a "measured" indicator appears. When you have finished examining this analysis, press to advance to the Graph Preparation menu.
Before showing the Graph Preparation menu, there is a brief pause while the analysis results are saved. If there happens to be insufficient space, a warning screen will show. This will clear within 10 seconds, or at once if is pressed again. (No special action is taken, as the information is easily regenerated).
Figure 2.8 - Graph Preparation Menu Screen
From the Graph Preparation Menu, select the option marked Graph with DEFAULT Parameters and press . A graph of the surface voltage versus time for the charge decay will be seen, together with a stepped display of variation of time constant, corresponding to the local time constants shown in the on-screen analysis.
Figure 2.9 - Graphical Display of Surface Voltage and Local Time Constant
When you are finished with the graph, press to return to the Graph Preparation Menu. (There may be be a pause while the graph is saved to disc for printing as part of a batch later). From the Graph Preparation Menu you can select a repeat of the graph, a repeat of the analysis or a further run, then press ; or you may select Quit, then press to return to the main menu.
If you have a printer connected, then pressingwill cause the screen to be printed. If it does not work, see Chapter 13 ("Trouble shooting", §Printing from screen).
You have now completed the basic operations for running the JCI155v4 in conjunction with DECAY18 and recording, displaying and analysing the observations.
In chapters 9-12 "Software Operation ..", you will find sections devoted to the use of the menus, entering and editing your own parameters, initialising the program with your own default settings, and many aspects of the software designed to simplify tasks associated with the collection and management of Charge Decay Data files.