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45
SECTION 3 OPERATION
Perform any purging of piping with spool piece in place. Once
completed, install the flowmeter and connect cabling to pickup coil.
If false counting action occurs turn Sensitivity control clockwise.
The pulse output and analog output commence with flow through
the flowmeter.
For the analog output, the span is that established by either the
factory calibration or field calibration. The range is 05 Vdc into a
maximum of 1000 ohms of loop resistance.
3.1 PRINCIPLE OF OPERATION
A simplified block diagram of the FLSC-36B Frequency/Voltage
Flow Converter Subsystem is shown in Figure 3-1. Key
functional blocks as well as flow information are designated.
The basic operation of the system is as follows.
The frequency signal from the turbine flowmeter is connected to
the FLSC-35B 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 flow meter signal is then passed through a signal
conditioning chain where it is amplified and shaped into a train
of digital pulses whose frequency is related to the volume flow
rate
The signal entering the frequency to analog converter is passed
through a combination of a divide by IN and a DIP switch
MATRIX. The ON output is chosen whose pulse rate is between
75 and 150 Hz at the maximum flow rate to be measured. This
scaled pulse rate is then fed to a precision monostable circuit.
The output of the monostable is then filtered into an analog
voltage that is proportional to volumetric flow rate.
The output amplifier is a voltage to voltage amplifier. It offers
zero and span available in a process range of 0 to 5 Vdc.
The Power Supply provides for operating bias voltage for all
internal circuitry.
The pulse output amplifier provides a TTL/CMOS compatible
square pulse of 5 volt amplitude. The output amplifier is
buffered from the signal driving the analog output.
3.2 CONTROLS AND ADJUSTMENTS (See Figure 3-2.)
FUSE, A circuit protection device located inside of case (see
paragraph 3.2.1)
SENS. A multiple turn control used to set the threshold
sensitivity level above the ambient noise pickup.
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