19
CAUTION! Never leave a Controller with a non-zero setpoint if
no pressure is available to make flow. The controller will apply
full power to the valve in an attempt to reach the setpoint.
When there is no flow, this can make the valve very HOT!
CONTROL (continued)
LOOP VAR
—The selection of what variable
to close the loop on is a feature unique to
Alicat mass flow controllers.
Pressing the
LOOP VAR
button on the
Control Setup screen will allow you to
change what variable is controlled.
Use the Up and Down buttons to move the
arrow in front of the desired option.
When the mass flow controller is supplied
with the
control valve upstream
of the
electronics portion of the system, the unit
can be set to control on outlet pressure or
volumetric flow rate, instead of mass flow
rate.
The change from mass to volume can
usually be accomplished without much, if
any, change in the P and D settings.
When you change from controlling
flow to controlling pressure,
sometimes fairly radical changes
must be made to the P & D variables.
See
page 20 –
PID TUNING
.
Contact Alicat if you are having difficulties
with this procedure.
DOWN
CANCEL
SET
UP
>Mass Flow
Volumetric Flow
Abs Pressure
Gauge Pressure
LOOP
VAR
BACK
PID
MAIN
SETPT
SOURCE
SETPT
+0.0
