LS SERIES SERVICE MANUAL
ISSUE 4.0 OVERVIEW 8
A numerical list of PCB's is shown below: -
04/1451 Loadcell Amplifier (contained inside the YLC loadcell plug)
SPK/LS/0005 Main PCB
SPK/LS/0004/A Motor Drive PCB including Power Dump Resistor and Loom
SPK/LS/0045 Hand Held Remote PCB and LCD Display
04/1460 Full Console PCB
SPK/LS/0044 Full Console LCD Display
04/1461 Extensometer Interface PCB
EXP/2258 Extensometer Amplifier (contained inside the extensometer plug)
SPK/LS/0042 Digital and Analogue Switch Mode Power Supply Unit
TNT/0185/00 LS1 and variants transformer
TNT/0186/00 LS2K5E and LS5S transformer
1.9 Load Measuring System
The load measuring system consists of a full bridge strain gauged loadcell, which is physically
connected to the test specimen in the loading frame, a loadcell amplifier and a 16 bit ADC
(effectively increased to 18 Bit by the embedded code). The sample is mounted between
the moving and lower crossheads of the machine and the required load is applied to it by moving
the upper crosshead either upwards or downwards.
The loadcell bridge is energised by a stable 4V DC supply from the Main PCB and will give a
potential difference of 8mV when its rated load is applied to it. This output is amplified by a low
noise DC amplifier that is inside the loadcell 15 pin D plug and this also contains an EEPROM,
which stores the loadcell value and calibration information.
The nominal output of this amplifier is 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 analogue
output of this amplifier is converted into 16 bit data by the ADC on the Main PCB, which is
mounted on the base of the machine.
The load measuring system has 2 overload protection features. The first is a software overload,
which will stop the machine if the displayed load exceeds 115% of the loadcell value. The
second is a hardware overload circuit, which will stop the machine if the absolute loadcell output
exceeds approx. 128% of the loadcell value. Therefore, the maximum rated load can ONLY be
achieved if the absolute loadcell offset and the offset introduced by the grips is less than 28% of
the loadcell value.
Note that each occurrence of a loadcell being overloaded by more than 28% is recorded in the
loadcell EEPROM and may be viewed using the diagnostic mode.
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