Product category:
Mechanical testing equipment
News Release from: Instron | Subject: Dynacell
Edited by the Laboratorytalk Editorial
Team on 23 June 2003
Eliminating load cell errors
System placesas the accelerometer right at the heart of the load cell, allowing error correction for both amplitude and phase and eliminating the possibility of errors due to off-centre loading
Instron has developed the Dynacell to eliminate the load measurement errors that are introduced due to acceleration of load string components during any fatigue or high-speed test During tests carried out on servohydraulic machines, elements of the load string are subjected to acceleration
This article was originally published on Laboratorytalk on 3 Jul 2002 at 8.00am (UK)
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Consequently, the load cell reads the forces resulting from its own movement and the mass of the fixtures attached to it, in addition to the true force applied to the specimen.
The error that is introduced due to inertial mass is proportional to the acceleration of the load cell, and the mass of the grips or fixtures attached to it.
A load error in the order of several percent can be introduced at typical test frequencies, and the effect is present in both actuator-mounted and crosshead-mounted load cell configurations.
This problem has been recognised by the international standards organisations.
The American Society for Testing and Materials (ASTM) states in ASTM E467-98a: "It is well understood how to measure forces applied to a specimen under static conditions.
During dynamic operation however, additional errors may manifest themselves in a testing machine." Researchers have known for years that inertial load errors can be compensated by measuring the acceleration of the load cell using an accelerometer.
The inertial force can be continuously measured by multiplying the acceleration by the moving mass.
This can then be subtracted from the total load reading to obtain an accurate determination of load applied to the specimen.
Dynacell is said to be the only load measurement system available with the accelerometer right at the heart of the load cell, allowing error correction for both amplitude and phase, and eliminating the possibility of errors due to off-centre loading.
As the accelerometer is integral to the testing system, set-up is consistent and reliable between operators.
Instron's advanced digital control system, the FastTrack 8800 features a fully automated set-up routine that takes less than a minute.
The Dynacell is supplied with all new Instron servohydraulic systems, and can be used to improve the performance of existing servohydraulic machines from most manufacturers with the addition of an Instron Extend upgrade.
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