SECTION 6 - LSS (LOAD SENSING SYSTEM) SERVICE
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6-1
SECTION 6. LSS (LOAD SENSING SYSTEM) SERVICE
6.1
LSS (LOAD SENSING SYSTEM)
Theory of Operation
The Load Sensing System (LSS) is designed to measure
platform load and prevent overload situations. The sys-
tem consists of pressure sensors on the lift cylinder, an
elevation angle sensor, and the control module.
For vehicles with a single lift cylinder, a dual-channel
pressure sensor with current output is mounted on the
lift cylinder to measure head pressure. The primary
feedback is scaled 0-3626 PSI as 4-20 mA. The backup
feedback is scaled 0-3626 PSI as 20-4 mA. A single chan-
nel pressure with voltage output is mounted on the lift
cylinder to measure rod pressure. The rod feedback is
scaled 0-1450PSI as 0.5-4.5V. The pressures are com-
bined with geometric information about the lift cylinder
to calculate the net lift cylinder force. The primary and
backup channels of the lift cylinder head pressure trans-
ducer are continuously compared to detect sensor
integrity issues.
The elevation angle sensor is used to estimate platform
height based on lower arm angle. The calibration pro-
cess teaches the control system the feedback voltage for
the stowed and fully elevated positions. The feedback
voltage and calibration information are combine with
geometric information to calculate the platform height.
The LSS can be calibrated in the field without test
weights using the procedure within the CALIBRATIONS '
LOAD 0% menu. The procedure allows the control sys-
tem to measure net lift cylinder force at a variety of plat-
form heights while lifting up and down with an empty
platform. Once the force profile is validated, the control
system uses geometric information to calculate the
remaining calibration information for a loaded platform.
Vehicles calibrated with this method may experience a
slight capacity reduction (10% to 20%) but remain regu-
latory compliant. The control system will flash the
Ground Overload Indicator twice at power-up to indi-
cate LSS has been calibrated without test weights (refer
to DIAGNOSTICS ' LOAD ' 110% CAL).
The LSS can be calibrated to maximum accuracy in the
service center with test weights using the procedure
within the CALIBRATIONS ' LOAD 110% menu. This pro-
cedure should be executed after CALIBRATIONS ' LOAD
0%. The procedure allows the control system to replace
the calculated calibration information with measured
net lift cylinder forces while lifting up and down with a
loaded platform.
If the vehicle must be calibrated in a situation with
restrictive ceiling height, the LSS will accept a partial
height calibration. The platform should be lifted as close
as practical to the ceiling when prompted to LIFT TO
MAX ELEV. The control system will automatically restrict
lift up to the demonstrated platform height until the
system is re-calibrated to full height in the future.
The LSS can be periodically verified without test weights
to extend calibration intervals. The procedure within the
CALIBRATIONS ' VERIFY LOAD menu allows the control
system to confirm net lift cylinder forces against calibra-
tion information at a variety of platform heights while
lifting up and down with an empty platform. The control
system will indicate PASS if the measured forces com-
pare within a tight tolerance to the calibration informa-
tion, and FAIL otherwise. Verification automatically
restricts lift up if the vehicle is calibrated in a situation
with restrictive ceiling height.
During operation, the control system measures platform
load while platform height is 10% to 90% of maximum
height. The system functions in this manner to avoid
abnormalities caused by deployment of the Pot-Hole
system and maximum extension of the lift cylinder.
The control system provides a mechanism to ignore
instantaneous changes in friction and avoid spurious
overloads. Measured platform load must be greater
than the capacity limit for a period that exceeds the
PERSONALITIES ' LOAD ' OVR DBNCE (seconds) setting
before the LSS indicates an overload. Once an overload
has occurred, measured platform load must be less than
the capacity limits for a period that exceeds the PER-
SONALITIES ' LOAD ' OVR HOLD (seconds) setting before
the LSS indicates no overload.
Accessories mounted in the platform have an impact on
the LSS capacity limit. The PERSONALITY ' LOAD ' ACC'Y
(KG) setting is used to account for accessories by reduc-
ing the capacity limit. The control system will manage
accessories properly when the LOAD ' ACC'Y setting is
adjusted prior to LSS calibration according to the docu-
mentation furnished with the factory-provided accesso-
ries. Light-weight accessories like optional lighting or
foot-switches do not impact the LSS capacity limit and
the LOAD ' ACC'Y setting should be set to zero. Accesso-
ries like the Electrician's Tree reduce the LSS capacity
limit according to their weight and the LOAD ' ACC'Y set-
ting must be set to account for their total weight.
Finally, accessories like the Panel Carrier induce wind
loading on the vehicle and reduce the LSS capacity limit
by more than their weight and the LOAD ' ACC'Y setting
must be to the values recommended by JLG. Follow the
documentation furnished with factory-provided acces-
sories when fitting more than one accessory to a vehicle
or consult JLG.
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