Question: Can I use FlexiForce™ sensors to measure dynamic loads?

Answer: If testing involves dynamic forces (impacts briefer than 0.1 - 0.3 seconds) instead of static forces which are applied to the sensor for longer than that, this brief time interval must be accounted for in the Calibration process. This is because there is a rise time associated with the sensor's output.

Rise time refers to how long it takes the sensor to settle at the appropriate value within our error limits, which for FlexiForce sensors is between 0.1 - 0.3 seconds. This differs from the response time of the sensor which is ~5µs. If your application involves an impact which is briefer than 0.1-0.3ms, the recommended method is to calibrate the sensor dynamically against a load cell with a quicker rise time. This allows you to match the responses of both the sensor and the load cell at given forces and impact time intervals, providing a more appropriate Calibration than a static one.

For instance, if the impact force takes place in 50ms, then the sensor should be calibrated against a load cell with dynamic forces that last only 50ms (hitting the sensor/load cell sandwich with a hammer in the same time interval and force range that is expected in the experiment). The load cell and the FlexiForce sensor outputs then need to be analyzed. Only the data points that take place within the specified time interval and force range should be used to construct a calibration curve for the FlexiForce sensor. If the dynamic event could be within a range of time intervals, say anywhere from 20-50ms, it would be best to have a few different Calibration curves (for instance, one for 20ms, another one for 35ms and a final one for 50ms) as an impact force lasting 50ms versus the same force which lasts only 20ms will produce two different outputs from the sensor. It will be necessary to conduct some testing to determine how many dynamic Calibration curves are needed for your application and accuracy requirements.

If a load cell is not available, the next best option is to use the sensor for comparative studies.

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