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58
SECTION 3 OPERATION
3.1 PRINCIPLE OF OPERATION
A simplified block diagram of the FLSC-51151B is shown in Figure
3-1. Key functional blocks as well as information flow are
designated. The basic operation of the system is as follows.
The frequency signal from the turbine flowmeter is connected to
the FLSC-51/51B with a twisted pair shielded cable. The signal
enters through the SENSITIVITY control which is used to reject
unwanted noise by raising the trigger threshold above the
background noise present.
The low level flowmeter signal is then passed through a signal
conditioning chain where it is filtered, amplified and shaped into a
train of digital pulses whose frequency is related to the volume
flow rate and where each pulse represents a discrete volume of
fluid.
The linear signal in the form of a pulse train is then passed to the
System Factor which scales the signal for totalization.
The pulse scaling circuitry composing the System Factor
affectively multiplies the pulse rate by a number set into the digital
thumbwheel switch array on the PCA-62 printed circuit card.
At the output of the System Factor, each pulse represents a
decimal multiple of the desired flow measurement units.
The pulse train is fed to the System Factor Multiplier which
effectively multiplies the pulse rate by either 1, .1, .01, .001 or .0001
depending on the position selected on the corresponding switch.
At the output of the System Factor Multiplier block, each pulse
represents one unit of flow in the desired measurement units.
The pulse train is then passed through an output drive stage
which is connected to a host system. A pulse is output each time a
discrete volume of fluid, represented in the desired units, passes
through the flowmeter.
3.2 START-UP OPERATION
Perform any purging of piping with spool piece in place. Once
completed, install the flowmeter and connect cabling to pickup
coil
With the Flow Measurement System properly installed and
calibrated, verify the following performance checks before
placing the system into active service.
The signal conditioner is normally shipped with the
SENSITIVITY pot fully counterclockwise. At start-up, turn this
pot gradually clockwise until input signal is sensed.
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