Komatsu 830E-AC Shop Manual page 841

Load Calculation
The final load calculation is different from the last
swingload calculation. The accuracy of the swing
load calculation depends on loading conditions and
the position of the truck during loading. The last swin-
gload calculation is not the value recorded in memory
as the final load. The final load is determined by a
series of calculations made while the truck is travel-
ing to the dump site.
Carry Back
Carry back is calculated as the difference between
the current truck tare and the clean truck tare. The
clean truck tare is calculated using the PC software.
When the suspensions are serviced or changes are
made that may affect the sprung weight of the truck,
a new clean truck tare should be calculated.
Measurement Accuracy
Payload measurements are typically repeatable
within 1%. Accuracy for a particular scale test
depends on specific combinations of pressure sen-
sors and payload meters as well as the specifics of
each scale test. Comparisons from different scale
tests are often made without considering the differ-
ences introduced by the specific installation and
operation of the scales for each test. In addition,
each pressure sensor and payload meter introduces
it's own non-linearity. Each truck becomes an individ-
ual combination of sensors and payload meter.
Errors from these sources can introduce up to a ±7%
bias in the payload meter calculations for a specific
scale test, for an individual truck.
Because the PLMIII calculates a new empty tare for
each payload, a detailed scale test must weigh the
trucks empty and loaded for each haul cycle. Using a
simple average of 2 or 3 empty truck weights as an
empty tare for the entire scale test will introduce sig-
nificant error when comparing scale weights to
PLMIII weights.
M20008 02/05
SOURCES FOR PAYLOAD ERROR
Payload Error
The number one source of error in payload calcula-
tion is improperly serviced suspensions. The payload
meter calculates payload by measuring differences in
the sprung weight of the truck when it is empty and
when it is loaded. The sprung weight is the weight of
the truck supported by the suspensions. The only
method for determining sprung weight is by measur-
ing the pressure of the nitrogen gas in the suspen-
sions. If the
maintained, the payload meter cannot determine an
accurate value for payload. The two critical factors
are proper oil height and proper nitrogen charge.
If the suspensions are overcharged, the payload
meter will not be able to determine the empty sprung
weight of the truck. The suspension cylinder must be
able to travel up and down as the truck drives empty.
The pressure in an overcharged suspension can
push the suspension rod to full extension. In this
case, the pressure inside the cylinder does not accu-
rately represent the force necessary to support that
portion of the truck.
If the suspensions are undercharged, the payload
meter will not be able to determine the loaded sprung
weight of the truck. The suspension cylinder must be
able to travel up and down as the truck drives loaded.
If the pressure in an undercharged suspension can-
not support the load, the suspension will collapse
and make metal-to-metal contact. In this case, the
pressure inside the cylinder does not accurately rep-
resent the force necessary to support that portion of
the truck.
Low oil height can also introduce errors by not cor-
rectly supporting a loaded truck. This is why the cor-
rect oil height and nitrogen charge are the most
critical factors in the measurement of payload. If the
suspensions are not properly maintained, accurate
payload measurement is not possible. In addition,
suspension maintenance is very important to the life
of the truck.
Payload Meter III
suspensions are not properly
M20-13