MKS 246C, Instruction Manual

Page: 47 / 92

Chapter Three: Overview General Information
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Chapter Three: Overview
General Information
The 246 readout can be connected to a single MFC or MFM through MFC connector J8 on the
rear panel of the unit (refer to Figure 8, page 41). Communication to and from the unit occurs
through Interface connector J9. The microjack connectors are used to join multiple 246 units or
to connect a 246 unit to an external controller.
Flow Signal Path
The main power supply provides ±15 Volts to power the MFC. 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 flow signal from the MFC (0 to 5 V) enters the 246 unit at pin 2 of the J8 connector. The
signal is buffered and the system injects a zero correction signal, if necessary, using the front
panel ZERO CONTROL. This signal is sent to three places:
1. To an output pin on Interface connector J9.
This is a 0 to 5 Volt, non-gas-corrected output. This output is zero-corrected
and is wired to microjack J10 (flow output). The zero and scaled signal is
sent to J9.
2. To the MFC connector J8.
This zero-corrected signal is used by MKS flow controllers for comparison
against incoming set point voltages.
3. To a second amplifier stage.
The second amplifier stage amplifies the incoming 0 to 5 V signal times two, making it a 0 to 10
V signal which is applied to the scaling control, the output of which is buffered to become the
scaled output. The output is labeled as a "0 to 1 V corrected output" but in fact, the output voltage
range is 0 to 1 V only when the Gauge Factor Scaling Control potentiometer is set to 1.00 (refer to
Gauge Factor Scaling Control, page 44, for more information). Otherwise it is possible for the
output to be as high as 0 to 10 V.