Introduction

The F329 exploits a very delicate and soft strain system that makes it possible to resolve forces down to 4µN with standard loadcell instrumentation such as our TR150 loadmeter and the DSCUSB loadcell digitiser.

Technical Limitations

Self Mass

The self mass of the active strain system will create a repeatable zero output change with change in orientation in a gravitational field. If the loadcell is to be used in different orientations a table of corrections can be created by replicating the changes and recording the changes in zero output. It is important to replicate the different positions accurately to obtain repeatable results.

Acceleration of the loadcell will create a measurement error whereby the self mass is accelerated and a reactive fore is generated.

Tare Mass

Any tare mass attached to the input boss will add the effects described above by adding to the self mass of the strain system. A maximum tare mass of 25% of the rated load is recommended. For a 0.1N range this is approximately 2.5g.

Stiffness

A standard F329 with a 0.1N rated load has a measurement axis stiffness of 1.3 x 103N/m. A full range force of 0.1N creates a deflection of approximately 0.08mm. The loadcell input boss must be permitted to deflect by this amount for accurate measurement of the applied force. This means that some force measurements whereby micron magnitude deflections result will not be suitable.

We recommend that force transmission systems are analysed using a simple linear spring to model the loadcell. Some micro engineered machines may be affected by the reaction force, please consult our engineering department for assistance with your application.

Moment and Torque

Input torque to the live force input boss must be minimal, normal frictional torques achieving thread insertion should not be exceeded i.e. thread locking by adhesive is suggested. Bending moments and torsional loadings are severely restricted so we recommend consulting our engineering department to achieve a viable loadcell solution.

Vacuum Process Applications

These will require different material specifications so the loadcell dimensions are likely to increase to permit the same low force measurement.

Real World Interface

The F329 design can be adapted to your specific needs to permit the use of specialist probes or hardware.

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