MKS 651C, Instruction Manual, Page: 43 / 172

Chapter Three: Overview Front Panel
29
Local and Remote Operation
The Key Lock switch is used to select front panel control (Local) or rear panel control (Remote).
When set to Local, control command input and set point parameter modification must be entered
via the front panel. Information requests (not commands) and 651 unit responses, however, may
still be sent through the Serial Interface connector on the rear panel. Refer to Table 26, page 128,
and Table 27, page 134, for a listing of the request and return message protocol.
When the Key Lock switch is set to Remote, the front panel becomes locked out. This is a useful
feature for preventing accidental command entries. It is still possible, however, to scroll through
the displays to view existing parameters using the [
] and [ ] keys. When in Remote
mode, control command input and set point parameter modification must be entered via the rear
panel either by RS-232 command protocol at the Serial Interface connector or through digital
logic levels at the I/O connector. Refer to Figure 4, page 31, for the location of the connectors,
to Table 8, page 32, for the Serial RS-232 Interface connector pinout, and to Table 10, page 34,
for the I/O connector pinout. Chapter Six: Remote Operation, page 61, contains more detailed
information about RS-232 control and digital logic operation.
Command Priority
The 651 pressure controller responds to the most recent command, whether it is issued in Local
mode or Remote mode. In switching from Remote to Local, the 651 instrument will respond to
the last command issued in Remote until a new command is issued in Local. In switching from
Local to Remote, the 651 instrument will continue to respond to the last command issued in
Local until a new command is issued in Remote.
Control Mode: Self-Tuning or PID Control
The 651 instrument can control a vacuum system in one of two ways. When used in the Self-
Tuning control mode, the 651 instrument determines control parameters based upon the system’s
characteristics using a unique control algorithm, and does not require the input of lead or gain
values. To activate this feature from the front panel, be sure the Key Lock switch is set to Local,
and hold down both scrolling keys simultaneously for approximately three seconds, to enter the
Setup menu. Scroll through the Setup menu until the Control mode entry appears. The Control
mode screen is shown on page 41. To change from PID to Self-Tuning, turn the Adjust knob
counterclockwise. Then press the [Learn] key for about three seconds. Once the unit has
learned the system characteristics, it can operate with the Key Lock switch set to either Local or
Remote. Refer to How To Activate the Learn Function, page 70, for more information about the
[Learn] key.