Ransburg RF1 FiberOptic Meter 77786-XX, A11516-XX - Manual (Page 10)

FM-00-02.5
THEOR THEOR THEOR THEOR THEORY Y Y Y Y OF OPERA OF OPERA OF OPERA OF OPERA OF OPERATION TION TION TION TION
Fluid flowing through the flow meter causes the
spur gears within the meter to rotate at a speed,
which is proportional to the rate of flow through
the meter. The total number of gear rotations is
proportional to the total amount of fluid that flowed
through the meter during these gear rotations.
When fluid flows through the meter in a given di-
rection the gears rotate in one direction. When
the direction of flow is reversed the gears rotate
in the opposite direction. Measurement of the gear
rotation and direction provides the information that
the control system requires.
The fiber transmitter is located on top of the flow
meter. Two variable reluctance type pickups ex-
tend from the transmitter enclosure and into the
flow meter. These pickups are positioned over the
teeth of the rotating gears. As the ferrous (mag-
netic) gear teeth rotate past each sensor it causes
the pickup to see a changing magnetic field. This
changing magnetic field is converted into an elec-
trical signal by the coil inside each pickup.
Two pickups are used such that that rotation di-
rection information can be determined. The pick-
ups are located such that the signals that they
produce are in quadrature or 90 degrees out of
phase to each other. In one direction pickup “A”
is high while pickup “B” goes high. In the other
direction pickup “B” is high while pickup “A” goes
high. The electronics detects these two conditions
to determine the direction of rotation and hence
fluid flow.
The signals from the pickups are fed into the elec-
tronics module. The electronics module first con-
ditions the signals from the pickups to turn them
into logic level digital signals. The flow rate and
direction information is then extracted. This infor-
mation is then encoded into a form that can be
used to modulate an LED. The encoded informa-
tion is then fed to a driver circuit that drives the
LED.
A self-contained non-replaceable battery powers
the transmitter. This battery is designed to pro-
vide power for several years of use under normal
operating conditions. The signal encoding method
is designed to use the minimum amount of bat-
tery power while fluid is flowing in the forward di-
rection. Power consumption goes up significantly
if the meter is run in the reverse direction.
The encoded optical pulse stream is conveyed
through the fiber cable to the receiver. The re-
ceiver first converts the encoded light pulses back
into electrical signals. These pulses are then fed
into a microcontroller that decodes them. The de-
coded outputs consist of channel “A” and chan-
nel “B” quadrature signals. These signals are then
fed to the output section where they are converted
into one of four different formats for driving the
attached control equipment
TRANSMITTER TRANSMITTER TRANSMITTER TRANSMITTER TRANSMITTER
The transmitter is contained in a plastic enclosure
and was designed to be mounted to the top of the
flow meter. The meter and transmitter are de-
signed to be intrinsically safe. Thus they can be
mounted in hazardous (classified) locations con-
taining potentially explosive atmospheres.
INTRODUCTION INTRODUCTION INTRODUCTION INTRODUCTION INTRODUCTION
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RF 1 Fiber Optic - Safety
Figure 1: Transmitter Figure 1: Transmitter Figure 1: Transmitter Figure 1: Transmitter Figure 1: Transmitter
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