Alicat MC Series Mass Flow Controller - Manual (Page 19)

19
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CONTROL SETUP (conti nued)
LOOP VAR—The selecti on of what variable
to close the loop on is a feature unique to
Alicat mass fl ow controllers.
Pressing the LOOP VAR butt on on the
Control Setup screen will allow you to
change what variable is controlled.
Use the line-up and line-down butt ons
to move the arrow in front of the desired
opti on.
When the mass fl ow controller is supplied
with the control valve upstream of the
electronics porti on of the system, the unit
can be set to control on outlet pressure
(absolute pressures only) or volumetric
fl ow rate, instead of mass fl ow rate.
The change from mass to volume can
usually be accomplished without much, if
any, change in the P and D setti ngs.
When you change from controlling
fl ow to controlling pressure,
someti mes fairly radical changes
must be made to the P & D variables. See
page 20 – PID TUNING.
Contact Alicat if you are having diffi culti es
with this procedure.
ON AUTO / OFF AUTO—refers to the standard auto-tare or “auto-zero” feature.
The auto-tare feature automati cally tares (takes the detected signal as zero) the
unit when it receives a zero set-point for more than two seconds.
A zero set-point results in the closing of the valve and a known “no fl ow”
conditi on. This feature makes the device more accurate by periodically
removing any cumulati ve errors associated with drift .
It is recommended that the controller be left in the default auto-tare ON
mode unless your specifi c applicati on requires that it be turned off .
LN-DN
CANCEL SET
LN-UP
>Mass Flow
Volumetric Flow
Pressure
LOOP
VAR
ON
AUTO PID MAIN
SETPT
SOURCE
SETPT
+0.0