4.6 Data Entry

Data entry is the process of recording the current measured values into the database – saving them for future reference.

· By pressing the Data Entry button on the instrument measuring the current feature – or the button of one of the instruments measuring a feature in the current set.

· By pressing the F4 key – the shortcut to the Enter item on the Measure menu.

What Happens When You Enter Data?

ATS SPC effectively takes a snapshot of the instrument measurements for the current feature – or the features in the current set – and records it in the database. Each measurement is filed under the batch and feature name to which it belongs.

If you are using data tags in the current batch ATS SPC marks each data value with your selected tag set.

If you are working in a signed database ATS SPC records your User ID along with the data and then signs it by calculating a hash value from the data and storing that as well.

When the data has been safely recorded ATS SPC updates any chart controls attached to the current feature(s). Histograms and scatter charts, along with basic statistics controls, update immediately but process charts and statistics controls do not change until you have entered a complete subgroup of measured data.

Data Rejection

As data is entered ATS SPC checks it for feasibility. If the data is wildly too big or too small ATS SPC refuses to enter it on the assumption that it was probably due to instrument errors or mishandling.

You can configure what ATS SPC considers to be feasible data in the Configuration Options property page Data Entry Options.

Data Entry Sound Events

If so configured, ATS SPC will play a sound when any one of three events occurs: Data Entry, Data Rejection, Data Out of Control. In relatively quiet environments this additional feedback, that data has in fact been entered, can be useful.

When ATS SPC runs for the first time it registers the sound events with Windows and you can use the Control Panel ‘Sounds’ applet to set up sounds for these events just as you would for Windows events.

Serial Numbers

If your batch is configured to collect serial numbers then, before you enter data, you must type the serial number for the part being measured into the serial number control. This may contain letters, numbers, and dots, dashes, squiggles - almost any printable character. ATS SPC checks the serial number to ensure it is unique within the batch and will show a warning message if you try to enter data for two parts with the same serial number.

In multi-feature/set batches you only need to enter the serial number once, while you are measuring the first feature/set.

If you are measuring parts with consecutive serial numbers you can click on the up or down buttons in the serial number control to increment or decrement the previous serial number quickly and easily.

What Happens at the End of a Subgroup?

When you have entered a complete subgroup of data, ATS SPC checks the new subgroup for control violations. It checks the subgroup mean against the mean control limits and looks for new trends in the mean chart. It checks the spread, i.e. the range or sigma, against the spread limits and looks for trends in the spread chart. And finally it checks each measured value in the subgroup for violations of the individual control limits and tolerance limits.

When this is done ATS SPC shows a summary of the violations, if there were any, or gives an all clear message if there weren’t. Either of these messages can be suppressed.

Batches, and in fact, individual features can be configured to ignore certain types of violations or perhaps to show the violation as a message on screen but not to record it in the charts. This is the default behaviour for tolerance violations since, strictly speaking, these have no statistical significance.

Deleting Data

Since it is easy to enter erroneous data by accident, instrument mis-handling etc. ATS SPC provides the means to delete the last data entered. You can’t select data from anywhere in the batch to delete but you can carry on deleting the last data item until you have reached the beginning of the batch!

With the batch open in Data Entry mode choose Measurement+Delete Last, or press the shortcut key, F3, to delete the last data entered.

ATS SPC steps back through your features or measurement sets and removes the last entered data. Note that you can’t delete data from features or sets that have no data!

Note that, if you are working in a signed database ATS SPC simply marks the data as deleted but retains it in the database for future reference.

Eliminating Data

Sometimes you need to delete data from statistical calculations but it would be useful if they remained in the chart as a record of process performance. When a process goes out of control, for example, as long as you have found and eliminated the cause of the problem, you should exclude any affected subgroups from future calculations of control limits, capability studies etc. ATS SPC provides the means to do this by 'eliminating' subgroups or individual measurements. This leaves them visible in the chart controls but marked so that they are not included in future statistical calculations.

Eliminated data is excluded from the following calculations: control limits, capability indices, mean, grand mean and mean range/sigma. It is also excluded from the histogram control and from capability studies. Eliminated data is included in control charts and scatter charts although it is marked as eliminated.

Once a subgroup or measurement has been eliminated you can un-eliminate it by repeating the elimination process.

Eliminate a subgroup

You cannot eliminate single measurements from process control features – only complete subgroups. So you need to be able to select a subgroup, or range of subgroups to eliminate. This requires a process chart, mean range or mean sigma.

If you eliminate a subgroup that is already eliminated, you will un-eliminate it.

1. Select the subgroup to eliminate by right clicking it. You can select a range of subgroups to eliminate by right clicking and dragging over them.

You can select the subgroup, or range of subgroups, with the left mouse button if you wish and then right click any of the selected subgroups to open the context menu.

1. If necessary press CTRL+TAB to select the scene containing a control chart showing the data you want to eliminate.

3. Press LEFT or RIGHT to select the subgroup to eliminate. You can select a range of subgroups by holding down the SHIFT key while pressing the cursor keys.

Eliminate a single measurement

You cannot eliminate single measurements from process control features – only from basic features. You need to be able to select a measurement, or range of measurements to eliminate. This requires a scatter chart or a data grid control.

If you eliminate a measurement that is already eliminated, you will un-eliminate it.

1. Select the measurement to eliminate by right clicking it. You can select a range of measurements to eliminate by right clicking and dragging over them.

You can select the measurement, or range of measurements, with the left mouse button if you wish and then right click any of the selected points to open the context menu.

1. If necessary press CTRL+TAB to select the scene containing a scatter chart or grid showing the data you want to eliminate.

3. Press LEFT or RIGHT to select the chart point to eliminate (or Up or Down to select a grid line). You can select a range of measurements by holding down the SHIFT key while pressing the cursor keys.

Viewing Data

After you have entered data into a chart you can look at the numerical values again using the Subgroup Readings function in the View menu or from the chart's context menu (opened when you right click in the chart).

This dialog shows the value of the chart point and the time and date it was entered. If the chart is subgroup based it shows the individual values making up the subgroup as well as the subgroup mean and sigma or range. There are four tabs which show, additionally, logbook messages, tolerance and control status, serial numbers, and data tags.

While the Subgroup/Readings dialog is open you can click on another chart point, or press ALT+F6 and scroll through the charts, and see the details of other subgroups or readings

View Chart Data

ATS SPC opens a dialog to show you the value of the reading or the values of all the readings in the subgroup if you selected a process feature. Also shown are any logbook messages and, for subgroups, the subgroup statistics – i.e. mean and sigma or range.

3. To see details of other subgroups or readings click on a chart point and the dialog will update. Using the keyboard press ALT+F6 and then TAB and/or scroll thru the charts as normal.

4. Click on the dialog or press ALT+F6 again to move the focus back to the dialog.

5. When you have seen enough, click the Close button at the top right of the dialog or press ALT+F4 when the dialog has the focus.