MKS 246C, Instruction Manual

Page: 50 / 92

Front Panel Controls Chapter Three: Overview
40
Zero Control
This 20-turn potentiometer is used for fine zero adjustment. It has a limited range of ±3% of FS;
therefore, larger adjustments must be made with the zero control on the MFC.
Set Point Source Switch
This 3-position toggle switch selects the source of the set point signal to be sent to the MFC.
The FLOW and RATIO positions are driven by the output of the SET POINT CONTROL; the
EXT position is driven by an externally applied voltage level.
FLOW Position: Selects the set point signal from the front panel Set Point Control.
The signal is driven from the +5 V internal reference.
RATIO Position: Selects the set point signal from the front panel Set Point Control.
The signal is driven from an external controller (the external set point input at
pin 7 in Interface connector J9). This setting provides for the set point voltage
to be the ratio of an external source where the ratio is set by the front panel Set
Point Control.
EXT Position: Selects the set point signal from a pin on Interface connector J9, allowing the
flow rate to be controlled directly from an external 0 to +5 V signal.
Set Point Control
This 10-turn potentiometer sets the set point level as a percentage of full scale when the Set
Point Source Switch is in the FLOW or RATIO position.
When the Set Point Source Switch is in the:
FLOW Position: Determines the set point voltage from ± 0.1 to 100% of full rated flow
RATIO Position: Determines the ratio of an incoming set point voltage from ± 0.1 to 100%
of Channel 1 Flow Signal
Note
The Set Point Control is the same type of 10-turn potentiometer used to
set the Scaling Control Factor. For detailed information on how to adjust
the potentiometer, refer to Scaling Control Potentiometer, page 46.
Refer to How To Setup the System, step 8, page 57, for an example Set
Point Control calculation.