Chapter Three: Overview General Information
35
Chapter Three: Overview
General Information
The 247 power supply/readout can be connected to as many as four MFCs through connectors
J1 to J4 on the rear panel (refer to Figure 6, page 43). Communication to and from the unit
occurs through connector P6. Connector P5 is used to join two 247 units or to connect a 247 unit
to an external controller.
The main power supply provides ±15 Volts to power the MFCs. The voltage corresponding to
the flow rate, +5 VDC at full rated flow, is received at the input amplifier where the fine zero
correction is made. The output from this amplifier is referred to as the
transducer output
.
This signal is amplified times two and applied to a scaling control, the output of which is
buffered to become the scaled output. This signal is applied to the Digital Panel Meter on the
front panel (refer to Figure 5, page 40) and to the
scaled output
on the rear panel connectors P5
and P6.
The MFCs set point signal is applied through a switch circuit which is controlled from a front
panel switch or a TTL logic level on connector P6. When the circuit is turned ON, the set point
signal is applied to the MFC and flow begins. When the switch circuit is turned OFF, flow will
stop.
The flow rate is determined by the magnitude of the set point signal with +5 V corresponding to
full flow. The source of this signal is selected by the Set Point Source Switch on the front panel
(refer to
Set Point Signal Source
, page 36, for additional information).
Flow Signal Path
The flow signal from the MFC (0 to 5 V) enters the 247 unit at pin 2 in Connectors J1 to J4. The
signal is buffered and the system injects a zero correction signal, if necessary, using the front
panel ZERO CONTROL. This signal goes to an output pin of the Interface connector P6 and to
the spring loaded READ/SET POINT switch. The
READ
position is the default; the up or
SET
POINT
position is a momentary condition which allows the flow signal to be amplified times
two and scaled by the scaling control. Refer to
Front Panel Controls
, page 40, for more
information.
The zeroed and scaled signal is sent to P6 and the Channel Selector Switch, which routes the
signal to the Digital Panel Meter where it is read directly in flow engineering units (sccm or slm).
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