PASCO ME-8930 SMART TIMER - Manual (Page 14)

Smart Timer 012–06734A
10
Pulley (rad/s): The Smart Timer will measure the speed of a pulley passing through a
photogate in units of radians/second. One measurement will be taken each time the Start/
Stop switch is pressed. The Smart Timer cannot differentiate between clockwise and
counterclockwise directions. Note that, as in many other modes, if a “*” shows in the first
character position of the second line, the Smart Timer is actively waiting for an external
timing event to occur. If the “*” is not showing, the Timer measurement mode may be
changed. This mode has a minimum speed requirement. The photogate must be blocked
twice within two seconds to obtain a valid reading, translating to a minimum speed of
0.31 rad/s.
Pulley (rev/s): Besides displaying in different units, this mode uses the display differently
than in the radians/second measurement. The display provides a real-time measurement of
the speed of the pulley by updating once per second. Once a speed is displayed, press the
Start/Stop key to freeze the display. The Smart Timer indicates that the measurement is
frozen by displaying a “!” in the first column. Press Start/Stop to erase the “!” and start
collecting new measurements. Any time the first column is blank or has a “!” displayed,
the type of measurement being done can be changed by pressing the Select
Measurement or Select Mode keys. To move to a different measurement, press Start/
Stop again. Like the radians/second measurement, there is a two-second maximum time
for two photogate blocks, translating to a minimum speed of 0.05 rev/s. Also note that
accuracy decreases rapidly as pulley speeds increase above 600 rpm. At 600 rpm,
accuracy is 1%.
Acceleration Modes
One Gate: The Smart Timer uses the time measurement between two equally spaced (5
cm) block/unblock/block sequences to calculate average acceleration. In activities using
the Smart Timer Picket Fence, the Picket Fence must be positioned so that the photogate
blocks only the 3-bar segment (5cm fence) of the Picket Fence. Note that the Smart Timer
is able to discern between acceleration (positive number) and deceleration (negative
number).
Linear Pulley: In this mode, the Smart Timer converts rotary motion of a PASCO pulley
to an equivalent linear acceleration in cm/s
2
.
Angular Pulley: In this mode, the Smart Timer converts rotary motion of a PASCO
pulley to an equivalent angular acceleration in rad/s
2
.
Two Gates: When two photogates are placed an arbitrary distance apart, the average
acceleration between the two can be calculated. In this mode, the inputs used are not
arbitrary. The first photogate to be encountered must be connected to input #1 and the
second to input #2.
Count Modes:
30 Seconds: The timed 30-second count mode will count high-to-low voltage transitions
on either input and display them on the second line of the liquid crystal display. After the
counting period is over, the Smart Timer will beep once, remove the power to the external
device, and freeze the display. Pressing Start/Stop erases the old count and begins a new