LS SERIES SERVICE MANUAL
ISSUE 4.0 OVERVIEW 9
1.10 Extension Measuring System
The machine is fitted with a digital encoder and this is used to provide the crosshead extension
measurement and also to control the motor speed. The encoder is connected directly to the
motor shaft. The encoder pulses are counted in an up/down counter to provide the high-
resolution extension measurement.
The crosshead movement is normally used to calculate the sample elongation but an external
extensometer may be required when testing dumbbell samples etc.
Note that the LS Series use the same type of extensometers as the Plus Series but the
external connector is different. Therefore, either an adaptor cable or an external
extensometer interface box is required before ANY extensometer can be connected to the
machine.
A single ANALOGUE external extensometer may be connected to the machine by using an
adaptor cable, part number 09/1047 (37 way female to 25 way female).
A single DIGITAL external extensometer (e.g. single encoder or twin/differential encoders) may
be connected to the machine by using an adaptor cable, part number 09/1047 (37 way female
to 25 way female).
One, two or three ANALOGUE external extensometers can be connected simultaneously to
the machine by using an extensometer interface box, part number 01/3905. This interface
box is powered from the LS series machine and requires no external power supply. It is
supplied with a 37 way to 37 way cable that goes from the rear of the LS series test machine
to the rear of the interface box.
The front of the interface box is fitted with three 25 way D sockets which are used to connect
one, two or three extensometers to the LS series test machine. The sockets can be used in
any order because each extensometer has a unique identity and is selected either using the
LS series control console or the NEXYGEN Plus 3 software console.
In addition to an ANALOGUE external extensometer, a single DIGITAL external extensometer
(encoder - single or twin/differential) may also be connected to the extensometer interface box,
i.e. only ONE DIGITAL external extensometer can be connected and used. The DIGITAL
external extensometer can be connected to any of the three sockets on the front of the box.
The 25 way D plug on the end of the extensometer lead contains a small PCB which is fitted with
an EEPROM which stores the extensometer calibration information. The PCB also contains a
DC amplifier with 4 fixed ranges and a stable strain gauge excitation voltage so is suitable for
use with a self-powered extensometer, a strain gauge extensometer, an LVDT or an encoder.
Note that the signal from an Analogue External Extensometer is converted into data using a 16
Bit ADC.
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