You are here: Using the DHR/AR > Introducing the DMA Mode for the DHR Rheometer

Introducing the DMA Mode for the DHR Rheometer

In this topic
Overview
DMA Testing
Loading the Sample in DMA Mode

Overview

The DMA is an integrated feature of the DHR available with the software version 3.2 and above. Earlier rheometers have to be upgraded to the firmware version 9.27 in order to use the DMA feature. In the DMA mode, the magnetic bearing operates as an actuator applying a small sinusoidal linear deformation to the sample while recording the force at the same time.

NOTE: When operating the magnetic bearing as a motor, bearing inertia contributions have to be accounted for as well as the non-linearity in the linear displacements. After loading a new geometry, an linear (axial) mapping of the geometry must be done.

DMA Mode

DMA refers to the dynamic mechanical analysis in tension, compression and bending of solid samples. In this mode the rotary motion is locked and only an oscillating linear motion is applied to the sample.

In the DMA mode, the test procedure has to include an Option step with the Axial force control set to active or inherit for automatic adjustment of the static force. Refer to Axial Force Control Guidelines for additional information. The DMA feature uses the standard Oscillation test modes. The selected geometry controls the deformation mode, either rotational or axial.

Loading the Sample in DMA Mode

In DMA mode the rotational motion has to be locked in order to keep the sample aligned.

After installing and aligning the geometry using the alignment tool (see also Available Test Geometries for details), run the axial mapping calibration from the File Manager > Geometries > Calibration.

The upper geometry is now locked in the position required for sample loading. When the test fixture is unlocked, it can easily be realigned and locked using the Move to alignment position button on the Motor Instrument panel.

NOTE: Because the upper geometry can be tightened in any angular position, the alignment position is different every time the upper geometry is installed. Therefore, axial mapping and locking in a new home position is always required when installing a DMA geometry.

Next, load the sample; the procedure depends on the selected DMA geometry. Refer to the selected geometry's help topic for sample loading details (see also Available Test Geometries).