OM6009 8/11 Payload Meter III - Section 60
Page 60-9
Loading Conditions
The final load calculation of the PLMIII system is not
sensitive to loading conditions. The final load is
calculated as the truck travels away from the shovel.
Variations in road conditions and slope are
compensated for in the complex calculations
performed by the payload meter.
Pressure Sensors
Small variations in pressure sensors can also
contribute to payload calculation error. Every
pressure sensor is slightly different. The accuracy
differences of individual sensors along the range
from 0 - 281 kg/cm
2
(0 to 4000 psi) can add or
subtract from payload measurements. This is also
true of the sensor input circuitry within individual
payload meters. These differences can stack up 7%
in extreme cases. These errors will be consistent and
repeatable for specific combinations of payload
meters and sensors on a particular truck.
Swingloads
Swingload calculations can be affected by conditions
at the loading site. Parking the truck against the berm
or large debris can cause the payload meter to
inaccurately calculate individual swingloads. While
the PLMIII system uses an advanced calculation
algorithms to determine swingloads, loading site
conditions can affect the accuracy.
Speed and Distance
The payload meter receives the same speed signal
as the speedometer. This signal is a frequency that
represents the speed of the truck. The payload meter
uses this frequency to calculate speeds and
distances. The meter assumes a single value for the
rolling radius of the tire. The rolling radius may
change at difference speeds by growing larger at
higher speeds. The actual rolling radius of the tire will
also change between a loaded and empty truck. The
payload meter does not compensate for these
changes.
HAUL CYCLE DATA
PLMIII records and stores data in its on-board flash
memory. This memory does not require a separate
battery. The data is available through the download
software.
PLMIII can store 5208 payload records. When the
memory is full, the payload meter will erase the
oldest 745 payload records and continue recording.
PLMIII can store 512 alarm records. When the
memory is full, the payload meter will erase the
oldest 312 alarm records and continue recording.
All data is calculated and stored in metric units within
the payload meter. The data is downloaded and
stored in metric units within the Paradox database on
the PC. The analysis program converts units for
displays, graphs and reports.
The units noted in the Table 1 are the actual units
stored in the data file. The value for the haul cycle
start time is the number of seconds since January 1,
1970 to the start of the haul cycle. All other event
times are referenced in seconds since the haul cycle
start time. The PC download and analysis program
converts these numbers into dates and times for
graphs and reports.
Haul Cycle Warning Flags
The payload meter expects haul cycles to progress in
a particular way. When something unexpected takes
place, the system records a warning flag. Several
events within the haul cycle can cause a warning flag
to be generated. Each one indicates an unusual
occurrence during the haul cycle. They do not
necessarily indicate a problem with the payload
meter or payload calculation.
A: Continuous Loading
This message is generated when the truck is loaded
over 50% full without the payload meter sensing
swingloads. This indicates that a continuous loading
operation was used to load the truck. It may also
indicate that the payload meter did not receive the
brake lock input while the truck was being loaded.
There may be a problem with the wiring or the brake
lock was not used. The payload meter will not
measure swingloads unless the brake lock is used
during the loading process.
B: Loading to Dumping Transition
This message is generated when the payload meter
senses a body up input during the loading process.
This message is usually accompanied by a
no_final_load flag.
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