Set Up an Experiment

In Fathom, there are several ways to set up an experiment. Dragging a meter or slider to a collection will create an experiment, as will selecting a collection and choosing the Create Experiment menu item. Dragging a meter or slider to an existing experiment will add it to the experiment. To configure the experiment parameters, use the Experiment panel in the inspector.

Experiments can also be set up without the sensors physically present; for example, by the instructor at home to facilitate data collection in the classroom, or as homework in preparation for a lab period.

•To collect data at regular timed intervals, click Collect By Time. You can specify how many cases you want to collect, at what rate, and for what duration. If you specify any two of these then Fathom calculates the third quantity, for example, 100 cases per second for 3000 cases, or 100 cases per second for 30 seconds. If you collect by timed intervals, time is automatically an attribute of the experiment.

If you are trying to collect data at a very fast rate (faster than 100 cases/second) from a LabPro sensor, for example, 10,000 cases/second from a microphone, then data collection proceeds in batch mode. This means that no cases will be visible in the experiment collection until the experiment is over. The meters will update during this duration and the experiment progress bar will indicate that the experiment is in progress. The LabPro buffers the data in batch mode, so there is a limit on the total number of cases collected. The LabPro buffer can only store 12,287 points, and this is divided by the number of attached sensors to give the limit on number of cases. For instance, if you have three sensors attached, the LabPro will store about 4000 cases.

If you are collecting faster than 10,000 cases/second (especially with triggering) then collection proceeds in a Fast Mode. This mode may have some channel limitations. If you experience problems, make sure your sensor is attached to channel 1 of the LabPro.

•To collect data based on keyboard events, click Collect By Keypress. If you collect by keypress, Fathom always collects the value of the key pressed.

•To collect data from a photogate, create a photogate meter and attach it to the collection. An experiment inspector will appear. A photogate does not have to be present to create the experiment. (see Collect from Photogates).

•Click Turn Experiment On to begin collecting. You can defer the start of the collecting based on some external condition (see Triggering below).

Triggering: To trigger the start of an experiment based on external conditions, check the Trigger checkbox. This will open up a panel that allows you to specify when to begin collecting data. You can trigger collection when a meter value falls or rises through a threshold.

trigger