Pasco Science WorkshopTM

The Photogate

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BHS -> Staff -> Mr. Stanbrough ->Pasco Interface Notes-> this page

The photogate operates sends an infrared beam from one "leg" to the other. As long as the beam is not broken, the photogate sends a 5 volt signal to the interface. When some object breaks the beam, the signal drops to 0 volts. You can tell that the photogate is operating by observing the small red LED on top, which lights when the photogate beam is blocked.

It is somewhat difficult for us to independently determine the precision of a photogate. According to the technical documentation for the Pasco photogates and Science WorkshopTM software, the photogate has a resolution of 0.1 ms (1 x 10-4s). This means that the photogate (and software) can distinguish 2 events that occur 0.1 ms apart as separate events. So, suppose that we consider the uncertainty of a photogate event as 0.1 ms.

However, when you use a photogate to measure the time it takes a solid object to pass through, you are actually measuring a time interval tf - to = the difference of two times. In this mode, the uncertainty of the time interval measurement would be 0.1 ms + 0.1 ms = 0.2 ms (or, if you want to be fancy, photogate resolution calculation ).

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BHS -> Staff -> Mr. Stanbrough ->Pasco Interface Notes-> this page
last update July 10, 2000 by JL Stanbrough