Mounting LowProfile Load Cells Without an Interface Base

Achieving precise and reliable force measurements with your Interface LowProfile Load Cell hinges on replicating the conditions under which it was meticulously calibrated.

When integrating a LowProfile cell directly onto a customer-supplied mounting surface without utilizing a factory-supplied base, strict adherence to specific criteria is recommended and essential for maintaining the sensor’s inherent accuracy. Deviations from these guidelines can compromise crucial performance characteristics, such as linearity, repeatability, and hysteresis, leading to unreliable data.

Interface load cells respond to forces that act in the axis perpendicular to the mounting surface. The response of the load cell to a non-axial force is proportional to that force multiplied by the cosine of the angle it forms with the loading axis.

Tip: Interface strongly recommends using a factory-supplied base with your LowProfile. We offer bases with most LowProfile universal, tension, and compression-only sensors. Interface also offers load cell base kits as part of our accessories.

The following reference, as outlined in our Load Cell Field Guide, outlines how to mount a LowProfile Load Cell without a base properly. It blends instruction with the underlying benefits and crucial references derived from Interface’s expert recommendations.

The Golden Rule is Reproducing Calibration Conditions

One fundamental principle is central to accurate load cell installation: directly mounting a LowProfile cell onto a structure should precisely reproduce the mounting used during its calibration. This ensures that the sensor operates under the same mechanical constraints and material interactions for which its performance specifications were validated.

Five Pillars of Proper Direct Mounting

When incorporating your LowProfile directly onto your mounting surface, observe the following five critical criteria:

#1 – Material and Hardness Harmony: Matching Thermal Expansion and Hardness

• Instruction: Select a mounting surface material that mirrors the coefficient of thermal expansion and hardness of your specific LowProfile.
• Benefits: This crucial step minimizes stress and potential measurement errors from differential expansion or contraction due to temperature fluctuations. A surface with similar hardness ensures proper load transfer and prevents localized deformation of the direct mounting interface.
• Reference: For LowProfiles with capacities up to 2000 lbf, utilize 2024 aluminum. The mounting surface should be 4041 steel for all larger-capacity cells, hardened to a Rockwell C (RC) hardness of 33 to 37. This ensures compatibility with the load cell material in your direct mounting configuration.

#2 – Thickness Matters: Ensuring Dimensional Stability of Your Interface

• Instruction: Your mounting surface should be at least as thick as the factory-supplied base commonly used with your specific Interface LowProfile Load Cells.
• Benefits: Although the cell may physically function with a thinner direct mounting, doing so can compromise its dimensional stability under load. This can directly impact the sensor’s ability to maintain linearity, repeatability, and hysteresis specifications. Sufficient thickness provides the necessary rigidity for optimal direct connection performance.
• Reference: Remember, adhering to this thickness guideline helps ensure your LowProfile® cell meets its stated performance benchmarks when mounted directly to your structure.

#3 – The Imperative of Flatness: Achieving Optimal Contact in Direct Mounting

• Instruction: The mounting surface must be ground to a flatness of 0.0002″ T.I.R. (Total Indicator Reading).
• Benefits: A flat surface ensures uniform contact between the load cell and your mounting structure. This even distribution of force prevents stress concentrations that can distort readings and negatively affect the cell’s accuracy and longevity in a direct mount.
• Reference: If your mounting plate undergoes heat treatment after the initial grinding, it’s prudent to perform a final light grind to guarantee the required level of flatness for the direct interface.

#4 – The Strength of Mounting Bolts: Selecting the Right Fasteners for Direct Attachment

• Instruction: Employ Grade 8 mounting bolts to secure your LowProfile directly.
• Benefits: Grade 8 bolts offer the high tensile strength necessary to securely fasten the load cell without yielding or loosening under load. This ensures a stable and reliable direct connection, which is crucial for accurate measurements.
• Reference: Interface offers these high-quality bolts for direct order, eliminating the need for local sourcing and guaranteeing the correct specification for your direct mounting. For cells with counterbored mounting holes, use socket head cap screws for a flush fit. For all other LowProfile cells, hex head bolts are the recommended choice for direct attachment. Do not use washers under the bolt heads in this direct mounting scenario.

#5 – The Art of Torque: A Gradual and Sequential Approach for Direct Mounting

• Instruction: Employ a three-step sequential torquing procedure for the mounting bolts when attaching the load cell directly.
• Benefits: This methodical approach ensures even distribution of clamping force across the direct mounting interface, preventing distortion of the load cell and guaranteeing a secure and stable installation.
• Reference: The recommended torquing sequence is as follows:
  • Initially, tighten all bolts to 60% of the specified torque.
  • Next, increase the torque to 90% of the specified value.
  • Finally, apply the full 100% of the specified torque. For Interface LowProfile Load Cells featuring four mounting holes, follow the tightening pattern designated for the first four holes in a standard 8-hole pattern when performing your direct mount.

By meticulously adhering to these five critical mounting criteria, you can ensure that your LowProfile Load Cell operates at its optimal performance level, delivering the accurate and reliable measurements you depend on, even when integrated directly into your system without a base. Remember, replicating the calibration conditions on your mounting surface is the cornerstone of precision force measurement.