Placing Control and Measurement Accelerometers During Shaker Tests

March 25, 2026
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Getting accelerometer placement right is one of the most critical aspects of any vibration test. It directly affects what the controller “sees,” how the shaker responds, and ultimately whether your results are valid or misleading. The challenge is that most test standards do not clearly define where sensors should be placed, so engineers must rely on best practices and experience.

1. Why Placement Matters

The control accelerometer acts as the feedback point for the vibration control system. If it is placed in a low response area, the controller may increase the drive level unnecessarily, potentially overstressing the unit under test or the fixture. On the other hand, placing it in a highly responsive location can lead to undertesting.

Research and industry experience show that poor sensor placement can significantly distort results, sometimes even masking failures or creating false positives.

2. Recommended Placement for Control Accelerometers

As a rule, the control accelerometer should be mounted as close as possible to the interface between the fixture and the unit under test. This ensures that the measured input closely represents what the test item experiences.

On slip tables, the preferred location is on the fixture near the unit under test. While the far end of a small slip table may sometimes be acceptable, controlling from the shaker attachment point should be avoided, as this area can behave like a node and provide misleading feedback.

It is also important to avoid placing the sensor in nodal regions or heavily damped areas, as this can result in artificially low readings and excessive drive levels.

3. When to Use Multiple Control Points

In larger or more complex setups, vibration levels can vary significantly across the structure. In these cases, relying on a single control accelerometer is not sufficient.

Using multiple control sensors and averaging their response provides a more representative input. For larger fixtures or payloads, using at least four control accelerometers is considered good practice. This approach reduces the risk of over testing or undertesting due to localised vibration differences.

4. Best Practices for Measurement Accelerometers

Measurement accelerometers are used to understand how the structure behaves rather than to control the test. These should be placed at key structural locations, such as high strain areas, known modal hot spots, and positions that capture bending or torsional behaviour.

Proper mounting is essential. Poorly mounted accelerometers can produce unreliable data, so it is important to verify mounting integrity before running high-level tests.

Measurement channels can also be used during initial low-level sweeps to confirm that the chosen control location provides a representative response.

5. Special Considerations for Slip Tables and Large Fixtures

Slip tables and large fixtures introduce additional complexity due to their size and flexibility.

For slip tables, the control point should remain close to the unit under test rather than near the shaker interface. Smaller tables may be more forgiving, but larger systems require more careful placement and often benefit from multiple control points.

For large or compliant fixtures, vibration can vary widely across the structure. In these cases, multipoint control is essential to ensure accurate and reliable testing.