LS SERIES SERVICE MANUAL
ISSUE 4.0 LOAD MEASURING SYSTEM 1
4. LOAD MEASURING SYSTEM
4.1 General
The load is measured by a full bridge strain gauge loadcell (YLC loadcell) whose output signal
is amplified then converted into 16 bit data in a successive approximation ADC. The loadcell is
able to measure both tensile and compressive loads with a through-zero load capability. The
loadcell is supplied with a stable DC voltage and any change of the output signal is an
accurate measure of the specimen loading. The output of the loadcell is amplified by a highly
stable, low noise DC amplifier inside the loadcell plug, whose output is approx. 0 volts with no
load applied, rising to +8.0 volts for maximum tensile load and falling to -8.0 volts for
maximum compressive load.
The loadcell is connected to a 16-way IDC connector, P8, on the Main PCB, via the external
loadcell cable and the internal loadcell cable. Both of these cables use direct connections.
The loadcell output signal is converted into 16 bit data using a capacitor-based successive
approximation Analogue to Digital converter. The ADC contains a built-in clock and a
sample/hold input stage and can measure input voltages in the range of +10V to -10V. The
amplifier output is also fed to an overload detector circuit that will stop the machine if the
loadcell is accidentally overloaded.
4.2 Loadcell
The YLC loadcells are a DC energised full bridge device, which are fitted with an integral 15
pin D plug that contains the low noise loadcell preamplifier and a pre-programmed EEPROM.
During a loadcell calibration, a calibration look-up table is created and stored inside the
EEPROM. This table is used to correct any small offsets and/or non linearity's in the loadcell
transducer and amplifier. The calibration look-up table can only be created or modified by using
the Engineer's Calibration mode using the full control console or NEXYGEN Plus 3.
The loadcells are calibrated in the metric units (Newtons) but the microprocessor can
automatically convert the load readings to either the SI units (kgf) or the English Imperial units
(lbf) if required.
4.3 Loadcell Gradings
The load accuracy of the machine can be classified by various standards authorities dependant
upon the country of use. The British authority is the British Standards Institute and the relevant
standard is BS EN ISO 7500-1. The American authority is the ASTM and the relevant standard
is ASTM E4.
These standards state that the load may not be verified below the Lower Limit of Verification
(even though the loadcell will read below this value), as given by the formula: -
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