Document Ref 903158-001 Page 11
Component Technical Manual MA26 MP-T1 Meter for Fuel Dispensers
Magnetic disk
The disc contains one outer ring, divided into 20 north and 20 south polarised
magnetic parts and one inner ring divided into 10 north and 10 south polarised
magnetic parts. The disc will be driven by, as mentioned before, the volume
meter. A liquid flow in forward direction (this liquid has left the measurement
transducer) results in a counter-clockwise movement of the disc. If the liquid is
going backwards the disc will rotate clockwise.
The disc can have small movements in both directions, this will be caused by
vibrations of the MP-T1 pulser. These movements are called “oscillations of
the disc”. The oscillations will never result in centilitre pulses on the output of
the MP-T1 pulser.
Hall effect sensors (direction)
Two sensors (sensor A and sensor B) are placed above the outer ring of the disc.
They are used to indicate the direction of the disc. Every transition on the
signal coming from sensor B represents a half centilitre.
Hall effect sensor (fault detection)
A third sensor (sensor C) is placed above the inner ring of the disc. Due to the
fact that this ring contains 10 north and 10 south polarised magnetic parts, the
output frequency of this sensor will be the half of the frequency coming from
the two other sensors. This difference in frequency makes it possible to
distinguish between normal operation, sensor defects or disc oscillations.
Digital filter
This part will remove glitches shorter then 8µs from the sensor signals.
Sequence detector
The sequence detector distinguishes the different movements of the disc by
evaluating the three sensor signals.
Backward flow count (centilitres)
When the disc turns clockwise the sequence detector generates backward count
pulses. The backward flow count buffer keeps up with the amount of backwards
count pulses. When the buffer reaches 20 cl (40 pulses) it will generate an
overflow message. If the disc turns counter-clockwise the sequence detector
generates forward count pulses. The backward flow count buffer will decrease
with the amount of forward count pulses until it reaches the 0 cl. At this point
the buffer will not decrease anymore and the switch will be closed so that the
timer receives forward count pulses on its trigger input.
Timer (400µs)
A pulse on the trigger input of the timer will start this one shot 400µs timer.
During this 400µs, the timer will activate the output driver for line A (or B).
Every half cl the timer alternates between line A and B. So, if there was a pulse
on output line A, a half cl later it will be followed by a pulse on output line B.
A pulse on output line B will be followed by a pulse on output line A, etc.
Issue A
To Next Page
Loading...