PASCO ME-8930 SMART TIMER User Manual

Page 15

012–06734A

Smart Timer

timing interval. If you wish to stop the count during a timing interval, press Start/

Stop. The display will freeze the current count and the “*” will disappear from the

first column. At this time you may select a new measurement or start a new timing

interval. The maximum counting rate for any of the counting modes is 5,000 counts

per second and the maximum count is 9,999,999.

60 Seconds: Other than timing the count interval for 60 seconds, the 60-second count

mode is the same as the 30-second mode.

5 Minutes: Other than timing the count interval for 5 minutes, the 5-minute count mode

is the same as the 30-second mode

Manual: Manual mode will count high-to-low voltage transitions on either input and

display them on the second line of the liquid crystal display. There is no time limit for

counting, however the upper limit on the number of total counts is still 9,999,999. Each

count will be accompanied by a short beep. Used with a PASCO SN-7927 G-M Tube/

Power Supply, this mode is useful for group demonstrations to show the random nature

of atomic disintegration and the inverse-square relationship between number of

disintegration’s detected and distance from the radioactive source.

Test Mode

Gates: In the Test:Gates measurement, the external measuring accessory is powered as

long as the top line of the display reads Test:Gates. This mode is useful for experiment

setup or for testing accessory photogates, G-M tubes, or other Smart Timer accessories.

Pressing the Select Measurement key will exit the test mode and remove power to the

external device. The display graphics depict a blocked photogate as a vertical line and an

unblocked photogate as an arrow.

Timing Diagrams

The timing diagrams on pages 8 and 9 show the interval, t, that is measured in each

timing mode. In each diagram, an elevated line corresponds to the photogate being

blocked, and a depressed line corresponds to the photogate being unblocked. The

calculation modes assume the use of a fence of fixed width (1 cm or 5 cm) or a pulley

having a diameter (groove to groove) of 4.8 cm and 10 spokes, such as the Super Pulley

or Smart Pulley.

LOCK Switch

The internal LOCK switch provides a way to temporarily lock

out speed and acceleration modes. To access the LOCK

switch, turn the power off, and remove the bottom half of the

Smart Timer case as if you were going to replace the batteries.

Look along the lower edge of the printed circuit board, and

note the LOCK switch button at the edge (Figure 3). The circuit

board also has the words “LOCK” and “UNLOCK” printed

along the same edge. Moving the switch to the LOCK position

will cause the display to read MODE UNAVAILABLE

whenever speed or acceleration modes are selected.

LOCK switch

circuit board

Figure 3

Location of the LOCK switch on the circuit
board.