SHIMPO 933 - Manual (Page 13)

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directly affect the results of bounce testing. The maximum air pressure used to actuate
the air cylinder and the adjustment of the air flow restrictors (optional and not part of the
basic LCTS) will affect bounce measurements as well as overall test speed. Consider
these variables when making bounce measurements. Slower test speed results in
longer bounce values.
Figure 7 illustrates the voltage measured across a typical normally open contact as it is
actuated. The open circuit voltage is 5.0 volts for the LCTS since the contact has a 1.0
KOhm pullup load to a 5 volt source. When actuated, the voltage will typically drop to
near 0.0 volts. The ASTM designation calls out 2 threshold voltages, the
specified upper
transition voltage (SUTV) and the specified lower transition voltage (SLTV). The bounce
time is measured from the initial point where the measured voltage (V
m
) falls below SLTV
until the last time V
m
transitions below SLTV after exceeding SUTV. The LCTS allows
the adjustment of SLTV and SUTV to meet the requirements of the device being tested.
The allowable range is 0 to 5 volts. SUTV can not be set below SLTV. The LCTS
application software displays these thresholds as voltage, resistance and a percentage
of the open circuit voltage.
Bounce
Open
Closed
Contact
Voltage
SUTV
SLTV
Figure 7.
Bounce Timing
The LCTS is a software controlled system. It uses a tight timing loop to monitor the
contact during the testing. This loop time is slightly less than 25 usec. Thus the
sampling resolution is this same time, even though the counters used to record the time
event have approximately a 1 usec resolution. Bounce events that are less than 25 usec
in duration are likely to be missed. If extremely short duration bounce events must be
measured, TRICOR Systems offers a hardware bounce module with 1.6 usec resolution.
The maximum bounce time measurable is 0.104856 seconds. The application software
limits maximum bounce tolerances to 0.1 seconds.
The bounce time measurements are symmetrical for both the opening and closing
contact states. The transition directions are, of coarse, reversed. The threshold
tolerances are the same for both the opening and closing conditions. It is not possible to
separate tolerance for the two conditions.
The bounce threshold tolerances are also used to determine the initial state of the switch
contact prior to each half cycle of the test. If the contact condition should be “open”, the