Veeco MS40 Operation And Maintenance Manual page 153

Prior to software revision 3.8, the MS-40 would start transmitting data through
its RS-232 port whenever it detected a specific logic level on its DSR pin.
This, however, had to be changed because certain types of computers caused
the MS-40 to transmit data even if the computer was turned off. This would
cause the MS-40 to 'lock-up' after a short period of time. The remote
computer now has to issue a command to the MS-40 before it will transmit any
data (MS-40's that are built as ILDs always transmit data). This command is
made up of 3 ASCII characters. 'S1Z' will command the MS-40 to start
transmitting data. 'S0Z' will command the MS-40 to stop transmitting data.
This method is not to be used for RS-232 hand-shaking.
The remote PC or controller has the ability to send many different commands
to the MS-40. There are two basic types of commands. One command is
equivalent to pressing a key on the MS-40's user panel and the other type is
equivalent to a parameter change. The key press commands allow for remote
control and the parameter changing commands allow the remote computer or
controller to change either the system delay, testing crossover pressures,
indicate ILD automatic or manual mode, or change the REJECT set point.
Most remote commands will be sent to control normal operation/cycling of the
MS-40 leak detector. Normal starting and stopping of test cycles will be
controlled remotely. If the remote computer is making leak test decisions,
such as how long to test a specific part, the software must be aware that
accurate leak rates only occur in the GROSS, REVERSE, DIRECT and
SNIFFER testing states. Roughing states do not test for the presence of
helium and rough close delay states corrupt the flow of helium by pumping
some of the helium away with the rough pump. Leak test decisions should not
be made in these states. Also, during normal test cycles, if the high vacuum
pressure exceeds 5.0 x 10-4 Torr, the filament is turned OFF but the leak test
cycle is not terminated. This is called the PRESSURE BURST CLEANUP
mode. The filament on/off flag sent with the 'L' packet is one method of
monitoring this state. However, if using the old compatible serial stream
format, monitoring the filament current will give the remote computer a faster
response to this situation. Filament on/off status is sent on every third
transmission of the filament current as mentioned above. The filament will be
turned back on every 10 seconds to check the high vacuum pressure. If the
pressure is still too high, the filament will shut itself back off, otherwise it will
remain on and testing will continue.
Vacuum Instrument Corp.
2099 Ninth Avenue
Ronkonkoma, NY 11779
631.737.0900
1109-186-00 Rev. C d-xv