Adjustable
setpoints SP 1
andSP2
3-12
Operation
The two user adjustable setpoints, SPl and SP2, operate identically,
but are completely independent. Their purpose is to open or close
relay contacts as a function of calculated system pressure in units that
are selected for display on the front panel or by actual pump current.
Using ion pump current to control setpoints is convenient if the
DIGITEL is switched between different pressure measurement units.
The relay can control valves, heaters, chart recorders, interlocks,
alarms, or other system functions. For example, you may want to open
a valve and start a chart recorder when the pressure falls below 1 x 1
o-
8
torr, and sound an alarm and shut down an electron gun if the
pressure exceeds 5 x 1
o-
6
torr. The rule for the control of the relay is
that C is switched to NC except when pressure is less than the setpoint,
at which time C switches to NO and the red lamp immediately to the
right of the appropriate setpoint key lights. When this happens, the
setpoint is on. Note that the setpoint is off if power is off, if high
voltage is off (see Subsection 3.9.3 for the exception), if the pressure is
higher than the setpoint, or if the setpoint is not active.
Note
There is a difference between the terms
on
and
active. On
refers
to the state of the relay.
Active
refers to whether the setpoint is
enabled or not. If a setpoint is not active, it cannot be on.
Before a setpoint is operational it must be programmed with a setpoint
value (parameter 1 ). Until this first parameter is programmed, or if its
mantissa is zero, the setpoint is not active. Each setpoint consists of
three parameters. The parameters are set using the numeric mode of
the keypad as described for Parameter 1.
Parameters 1 and 2 have two digits that can be adjusted: the mantissa
and the exponent. Each parameter has a range of 9. 0 x 10-
0
to 1. 0 x
10-
9
.
If parameter 1 is set to 0.0 x 10-
0
,
the setpoint is not active. The
third parameter consists of four digits, which may be set to O or 1.
Note
When programming the DIGITEL, if you are not sure what
something is for, set it to zero.