SHIMPO 933 - Manual (Page 17)

17
Maximum Down Time
Cylinder
Contact
Minimum Down Time Reduced Time
Figure 9.
Testing Speed-Up
Without knowledge of the contact closure, the user is forced to configure the LCTS so
that the
Maximum Test Time has enough padding to allow for variations in the plunger
travel time to get to the switch, the switch travel time, the bounce and stabilize times of
the switch as well as the variations that may result from temperature and pressure
uncertainties. The
Maximum Test Time value is set to encompass all these times plus
any worst case padding. The Maximum Test Time is a limit case to prevent the system
from locking up should the device being tested fail to actuate. Typical settings for this
configuration parameter might be 0.5 seconds. This value keeps the LCTS running, but
is long enough to encompass most system failures such as lost air pressure or a failed
switch. The test half cycle is always guaranteed to complete in no more than the
Maximum Test Time value.
The Minimum Test Time is set according to the characteristics of the device under test.
This time should be set to provide a minimum delay from the point where the switch is
first detected crossing the SLTV threshold. Typically the value assigned to this
configuration parameter should be adjusted to guarantee that the contact has stabilized
so that the final contact resistance can be read. As a switch wears, the amount of
bounce and stabilization time increase. This
Minimum Test Time should included
padding to allow for device approved wear.
By setting the Minimum Test Time to an appropriate value, the LCTS can make the final
contact resistance measurement based on the time from the contact transition, not the air
cylinder command. This allows an improvement in test time because the travel times of
the cylinder and switch can be ignored. This results in a reduced test time. The travel
times are, of coarse, still important, but by positioning the switch appropriately, these
times can be minimized without concern for their actual values. See Section 8 on Force
and Speed for suggestions on increasing the test rate.
It is important to set the Minimum Test Time greater than the Maximum Bounce Time
Tolerance. If not, the testing will end and the last bounce transition will become the
bounce measurement. This value may be incorrectly small. The application software
does not validate the relationship between
Maximum Bounce Time and Minimum Test
Time . Be sure to set both of these test limits according to the properties of the device
under test.