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19
The analog output signal leads may be run to the host system’s
signal input and power with the following options:
1. Four conductor shielded cable
2. Three conductor shielded cable (over short distances)
3. Two, two conductor shielded cables, one pair for signal
output, one pair for power input.
Ground shield at one end of cable only.
The power f or the FLSC-28 is provided by the Host System. 10-
40 Vdc should be provided and installed with correct polarity.
SECTION 3 OPERATION
Perform any purging of piping with spool piece in place. Once
completed, install the flowmeter and connect cabling to pickup
coil and power to the unit. If false indication occurs turn
SENSITIVITY control counterclockwise until indication stops.
The analog output commences with flow through the flowmeter.
For the analog output, the span is established by either the
factory calibration or field calibration. The range is 0-5 Vdc.
3.1 PRINCIPLE OF OPERATION
A simplified block diagram of the FLSC-28 Frequency to
Current Converter 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 flowmeter is connected to the
FLSC-28 with a twisted shielded pair cable. The signal enters 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 signal entering the frequency to voltage converter is passed
through a combination of a divide by N and a DIP switch
matrix. The ON output is chosen whose pulse rate is between 75
and 150 Hz at the maximum flow rate measured. This scaled
pulse rate is then filtered into an analog voltage. This voltage is
proportional to volumetric flow rate.
The resulting output voltage related to flow is then fed into the
output amplifier. The output amplifier is a voltage to current
amplifier and offers ZERO and SPAN adjustments and is
available in the process range of 0-5 Vdc.
The precision power supply filters and regulates the input
power and generates the internal 7.5 Vdc power for all circuits
as well as providing reverse polarity protection.
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