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DHR/AR Rheometer: Setting the Sample Gap

In this topic
Introduction
Using the DHR/AR Gap Control Panel
Zero Gap Routine

Introduction

Zeroing the gap between upper and lower test geometries is a prerequisite to setting the measurement gap for sample testing. Zeroing the sample gap requires lowering the head until the upper and lower geometries touch, then setting the gap value to read zero millimeters. After that, moving the head results in an accurate gap indication as displayed by the gap value. The sample gap should be re-zeroed any time a new geometry is mounted or the test temperature is changed. The DHR Series and AR Series Rheometers can take account for changes due to geometry and sample expansion with temperature during tests, but always begin with the assumption that the sample gap is correct at the start of an experiment. For example, if running a test at 200°C, the geometry should be heated and sufficiently equilibrated at that temperature to ensure the thermal expansion of the tool is accounted for when establishing a zero point. Failure to accurately zero the sample gap can have an adverse effect on the accuracy of the calculated data in certain test geometries.

Using the Gap Control Panel

To access the Gap section of the Control panel, click the Experiment tab > Controls and select Gap. For more information on the Control panel, refer to Understanding the Control Panel.

The table below explains the Gap controls (from left to right on the Gap toolbar).

Gap Control Panel Functions
Item	Function
Stop Head	Stops any head movement.
Go To Geometry Gap	Moves the head to the value specified in the geometry gap\truncation gap field for the current geometry.
Go to Trim Gap	Moves the head to the Trim offset position, which is defined in the Geometry Setup window.
Raise to Loading Gap	Moves the head to the value specified in the loading gap field for the current geometry.
Zero Gap	Runs the zero gap routine.
Zero axial force	Sets axial force to zero.
Tare Gap	Sets the current head position to Zero Gap.
Head up	Moves head up while button remains pushed.
Head down	Moves head down while button remains pushed.
Options	Shortcut to Gap Options.
Set gap	Enter a value and click Apply (the green arrow).

Zero Gap Routine

Clicking on the Zero Gap icon starts the routine and instructional text, and two new buttons appear in the gap section of the Control panel.

NOTE: If your display does not meet the minimum specification for TRIOS, or you are not running with the application maximized, some of the dialog may be obscured.