This application note is for instances where you want to overplot the results of multiple test runs on a single plot. To accomplish this, there are two alternate approaches. The easiest way to
overplot multiple test runs, or frames of data, is to turn off the check box for Auto Clear in the X-Axis settings. This method has some disadvantages because you can’t place cursors on previous frames and you can only use the low resolution print mode. This is because the data from the previous frames are not kept in memory.

The second approach is a little more involved, but you get to use cursors and high resolution printing for multiple test runs. The remainder of this application note describes this second approach.

The overall process is broken into two distinct steps: data acquisition and post-processing. The data acquisition step adds a Disk Out to the instrument and stores the data to disk. For the post-process step, you will have an instrument with multiple Disk In elements (up to 10) and a single Display element.

Data Acquisition Step

Your data acquisition instrument probably looks something like this:

This application note assumes that you are acquiring the data all into one file (a single file, multiple frame approach). This works best when you have a trigger set up in your acquisition element (the A/D in this case) to tell Snap-Master when a new frame begins. (The trigger is not required to make this method work.)

In most cases, you are probably not interested in keeping the data around after you make the printout of the runs. To always use the same data file, turn on the Auto Overwrite check box in the Disk Out element. This cuts down the number of steps required in the Post Process step because you will not have to define the Disk In file name for each new set of runs.

Post-Process Step

For replay, your instrument will look like this:

The number of Disk In elements in your instrument depends on how many tests you want to overplot. The maximum number of Disk In elements allowed by the configuration we will use is 10, which is also the maximum number of channels that can be overplotted.

Each Disk In element has a sequence of steps to follow. When you use the single file method described here with Auto Overwrite turned on, you can set up this instrument once and save it, which saves a great deal of time when doing the actual testing.

When setting up the post-process instrument, perform the following steps for each Disk In:

1. Open the Disk In element.

2. Select the data file where the raw data is stored.

3. Press the Replay Options button.

4. Select the Frame Range radio button.

5. Enter the same frame number for the Start At and Stop At settings. For the first Disk In element this is 1, for the second disk in this is 2, etc.

6. In the Letter Re-Mapping table, find the element letter used by the A/D element in your acquisition instrument (it was B in our example). For the first Disk In map element B to Z, for the second Disk In map element B to Y, for the third Disk In map element B to X, and so on. Using this method frame 1 appears as channels Z0, Z1, Z2, frame 2 appears as channels Y0, Y1, Y2, and so on.

7. Close the Replay Options dialog by pressing the OK button.

8. Close the Disk In Settings dialog by pressing the OK button.

9. Repeat for each Disk In element.

The next step in the post-process instrument is to set the Display element layout. Remember that each element letter (starting at letter Z and going backwards) represents a separate frame, and the channel numbers are the same for each frame.

Hint: To set up your Display quickly, try changing the Default Settings dialog to enable Auto Layout. The Overplot Same Channel Number setting automatically overplots like channels on the same Y-T plot. If you are using another plot type such as Y-X, this step is not important.

Running The Test

Each time you run the test, you will perform the following steps:

1. Acquire up to 10 frames of data using the Data Acquisition step.

2. When done acquiring data, switch to the Post-Process step instrument.

3. Start the Post-Process step instrument.

Because we are using the same data file repeatedly during acquisition, there are relatively few steps once the instruments are set up. The only limitation to this method is that it deletes previous data by overwriting the data file. That is why this method is best when the end user is interacting directly with Snap-Master and you are only interested in high resolution printouts of the data.

Alternate Method

If you want to save the raw data files after each run, you can adapt this application note to use a multiple file approach. This approach also works best when you have a Front Panel which sequences the events, keeps track of the data file names, and automatically writes them to the Disk In elements.

In the data acquisition step, use the File Seed naming method in the Disk Out to keep a consistent file name for each run. After each frame, you need to restart the instrument manually or with a DDE command from the Front Panel. In the post-process step, you need to set the file name in each Disk In element each time you want to run the instrument (omit steps 4 and 5 when setting up the post-process instrument).