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66 T i m i n g

S c r e e n

Time of Flight

Use this timer with a projectile launcher, two photogates, and a

Time-of-Flight Accessory.

The constant, Photogate Spacing, is the distance (in

meters) between the centers of the photogates.

The measurements are Initial Velocity and Time Of Flight.

•

Initial Velocity is the Photogate Spacing divided by the time-between-gates.

•

Time Of Flight is the elapsed time starting when the projectile blocks the
first photogate and ending when it hits the Time-of-Flight Accessory.

Photogate Timing

Use this timer for general measurements made with one or

two photogates.

The constants are Flag Length and Photogate Spacing.

•

Flag Length is the length (in meters) of the object that passes through the
photogates.

•

Photogate Spacing is the distance (in meters) between the centers of the pho-
togates. This constant is not relevant if you are using only one photogate.

There are four measurements: Time In Gate, Velocity In Gate, Time Between
Gates, and Velocity Between Gates.

•

Time In Gate is the time that the flag spends inside either gate each time it
passes through. A data point is recorded every time either photogate detects
a blocked-unblocked sequence.

•

Velocity In Gate equals Flag Length divided by Time In Gate.

•

Time Between Gates is the time elapsed between successive interruptions of
either gate. A data point is recorded every time one of the photogates is
blocked (except the first time).

•

Velocity Between Gates equals Photogate Spacing divided by Time
Between Gates.

General Counting

Use this timer with nuclear sensors, drop counters, and

other counting-type digital sensors. The constant, Count Time Interval, is the
period over which the timer counts pulses for each data point. It is also the time
between successive data points.

The measurement, Pulse Count, is the number of pulses (nuclear events or drops)
detected during the Count Time Interval. Pulse Count data points are recorded at
a constant rate, one data point at the conclusion of every Count Time Interval.

Collision Timer

Use this timer to measure the velocities of two carts before

and after they collide. The constant is Flag Length, which is the length (in
meters) of the objects that pass through the photogates. The flags attached to both
carts must be the same length.

The measurements, Velocity 1 and Velocity 2, are the velocities measured by
each photogate. Velocity 1 is Flag Length divided by the time-in-gate of the first
photogate. Velocity 2 is Flag Length divided by the time-in-gate of the second
photogate.

Arrange the photogates so that the collision occurs between the photogates.

The Time-of-Flight Accessory is

PASCO part ME-6810. Projectile
Launchers include ME-6800 and
ME-6801. A Photogate Bracket, part
ME-6821, is necessary to attach the
photogates to the launcher.

Photogate Timing works best for mea-

suring the velocity of a single object that
blocks only one photogate at a time. To
measure the separate velocities of two
objects, use Collision Timer.