Controlling crosstalk in multi-axis force measurement systems

In high-precision force measurement, the goal is to isolate mechanical input quantities into independent electrical output signals. Multi-axis sensors However, crosstalk occurs when a load applied exclusively to one axis generates a parasitic signal in another axis.

For interface instrumentation and multi-axis sensor-Systems Mastering this problem requires a dual approach: minimizing the mechanical coupling at the spring body and the application of mathematical compensation through precision electronics.

In this technical discussion, we will examine the causes, considerations, and best practices for managing crosstalk when using multi-axis sensors.

Mechanical and electrical causes of crosstalk

Crosstalk is rarely the result of a single error, but rather the sum of small physical and electrical interactions. Here are examples that illustrate this point with regard to crosstalk sources.

• Spring body geometry and machining – Minimal deviations in the symmetry of a sensor or the alignment of its internal measuring elements can cause a vertical load to generate a slight bending moment.
• DMS alignment – If a strain gauge designed to measure axial strain is slightly twisted during installation, it will detect a proportion of the transverse strain of orthogonal loads.
• Poisson's transverse contraction number – The physical expansion of a material under pressure can be detected by strain gauges in adjacent channels if the Wheatstone bridge circuit is not perfectly balanced.
• Cable interference – In multi-channel systems, capacitive coupling between adjacent conductors in a cable can reflect a signal from one axis to another and appear as mechanical crosstalk.

Mathematical compensation via the sensitivity matrix

To determine the actual forces, we treat the multi-axis sensor as a linear system. For a 6-axis sensor that measures forces and moments, the relationship between raw voltage and applied loads is defined by a sensitivity matrix.

The diagonal elements represent the primary sensitivity, while the off-diagonal elements quantify the crosstalk. To determine the actual loads, the instrumentation must apply the inverse coefficient matrix.

By performing this matrix multiplication in real time, the instrumentation mathematically subtracts the parasitic signals and reduces crosstalk from several percentage points to a fraction of a percent of the full-range output.

Here are four concrete examples that demonstrate possibilities for controlling sensitivity and crosstalk:

• Instrumentation strategies for error reduction, which involves choosing the right one Signal conditioner The initial steps are just as crucial as the sensor design itself. Interface offers tools specifically designed for multi-channel synchronization and matrix calculations. Read more in our Review of the webinar on innovative multi-axis technology and instrumentation.
• The BX8 multi-channel data acquisition system is an instrument designed for multi-axis sensors. It features an integrated matrix calculation function that allows the user to directly input the calibration coefficients. BX8-HD15 BlueDAQ Series Data Acquisition System for Discrete Sensors with Laboratory Housing performs cross-compensation internally and delivers a linearized, corrected digital output.
• 9840 Intelligent Indicator For simpler systems, this is a highly stable indicator that provides the precise excitation voltages required to maintain bridge equilibrium. Any fluctuation in the excitation voltage can be misinterpreted by the system as a change in force on an unloaded axis. See the 9840-400-1-T 4-Channel Intelligent Indicator for full specifications.
• 6-conductor bridge extension Using sense leads ensures that the voltage across the strain gauge bridge remains constant regardless of cable length. This preserves the integrity of the sensitivity matrix, which is based on a stable ratiometric relationship. Read the article. Considerations regarding bridge extension.

Best practices for system integration

Even with sophisticated electronics, the physical installation determines the basic crosstalk of the system.

#1 – Precision of the mounting surface is essential. High-performance sensors require mounting surfaces that are machined to extreme flatness. Any warping in the plate creates prestress on the strain gauges and increases nonlinearity.

#2 – Shielding and grounding can Prevent electrical crosstalk. Use cables where each pair of strain gauge leads is individually shielded. All shields should be grounded to a single star point on the measuring amplifier to avoid ground loops.

#3 – Alignment is the starting point. The use of precision dowel pins or centering aids ensures that the sensor axes are perfectly aligned with the machine axes. This prevents geometric crosstalk, where a load is applied at a slight angle relative to the intended vector.

By combining precision-engineered sensors with matrix-capable instrumentation such as the BX8, engineers can achieve the level of axis isolation required for the most demanding tests in the aerospace and automotive industries.

To learn more about multi-axis technology and crosstalk, watch our webinar for more detailed information.