Bypass Assembly; Electronics Assembly; Valve Assembly - Advanced Energy FC-77 Series User Manual

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Advanced Energy
As a result of the techniques of thermal mass flow measurement, gas flow can be
measured independently of factors which affect volume and density, such as
temperature and pressure.

Bypass Assembly

The bypass assembly diverts a small stream of incoming gas through the flow sensor
and channels the rest through the bypass and toward the valve assembly of the MFC.
The bypass assembly design ensures a constant flow ratio between the flow sensor and
the larger flow passing through the instrument, making the output signal of the flow
sensor proportional to the total (or mass) gas flow. A comparator circuit in the
electronics assembly compares the output signal from the flow sensor and the flow set
point. The signal created from this comparison drives the control valve until the
difference between the set point and the sensor output signal decreases to zero.

Electronics Assembly

The electronics assembly consists of a bridge circuit, a high resolution analog
converter, a valve drive circuit, and an analog I/O. The signal generated by the bridge
circuit is amplified and fed into the analog converter which outputs this signal into the
CPU (central processing unit). The CPU compares the set point signal to the sensor
reading to generate a signal to drive the control valve.

Valve Assembly

The valve assembly consists of a normally closed or normally open, solenoid control
valve.
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