Vernier Tech Info Library TIL #1623

Question

How do I set Logger Pro to use a photogate?

Answer

To answer this question you must know what time interval you plan to measure with the photogate(s).

Each time interval mode has a name. Start with what it is you are trying to measure:

If you need to know how long a gate is blocked by a single object, which you'll then use to find a speed using the ratio of the object length and the blocking time, you'll need "gate timing."

If you need to know the time between successive blocks of one or two gates, you'll need some variant of "pulse timing." For example, projectile motion experiments work best with pulse timing with two gates.

If you need to know timing information from a pulley or a picket fence object, you'll need "motion timing."

If you need to measure the period of a pendulum, which is the time from the first to the third block of a photogate, you need "pendulum timing."

There are also other, less common timing modes.

Each of these timing modes is a different setup in Logger Pro. The default timing mode is motion timing, which is perfect if you're going to do the picket fence freefall experiment, but it is not what you need for all other activities.

Once you know which timing mode you need, the easiest thing to do is to use a prepared experiment file that comes with Logger Pro.

Choose File / Open, then go to the folder Experiment Files/Probes and Sensors/Photogates. Browse through those files. The files in this folder handle most common photogate timing situations.

The terminology used in naming the files corresponds to the timing mode in each. Here is a complete list of the terms:

"Gate" timing means timing how long a photogate is blocked.

"Pulse" timing means timing from the blocking of a photogate until the next blocking of a photogate.

"Motion Timer" means timing from leading edge to leading edge of a picket fence like object (object with a series of opaque bars, evenly spaced)

"Bounce" timing is meant for studying the bounce of a ball using a photogate mounted one ball diameter above the floor.

"Flash" timing measures how long a photogate is unblocked. It can be used to measure how long a camera shutter is open.

"Strobe" timing measures the time between unblocking events of the photogate. It can be used to check the timing of a strobe light, if the light replaces the IR source of the photogate.

"Collision" timing is like gate timing, but assumes two photogates are used to measure speeds before and after a collision. The moving objects are assumed to have "flags" of known length on them that go through the photogates.

"Pulley" timing assumes you have a Smart Pulley or a Supper Pulley mounted so that it blocks the photogate with its spokes as it turns.

"Pendulum" timing measures the period of a pendulum if mounted at the bottom of the swing.

"Jump" is set up to use with a laser beam along the floor pointed into one of our newer photogates which allows you to use the laser beam as the photogate beam. It measures the hang time of someone jumping.

We have a few labs using photogates in our Physics with Vernier book. There are experiment files for these labs.

If you are using photogates with calculators, you will need to use the DataGate program, which is a free download from:
http://www.vernier.com/calc/software/datagate.html

Created by: dvernier on February 07 2007
Last updated by: jhopkins on June 02 2009