How Fast can Strain Gages Respond?
For sinusoidal inputs, research has shown that strain gages with an average gage length (approximately .250 inch) can respond up to 300 kHz with very little degradation of the sensitivity (Dynamic Response of Strain Gages up to 300 kHz, K. Udea and A. Umeda, Experimental Mechanics, June 1998). For transient or impact events, the length of the strain gage will certainly influence the ability of the gage to go from 0 or no strain, to a maximum value. To minimize this averaging effect of the gage, we suggest using shorter gage lengths for transient (step type) inputs, on the order of 0.125 inch (or smaller).
For most applications, the instrumentation will be limiting factor. The two main components to evaluate will be the frequency response of the amplifier, and the digital sampling speed, assuming that an A/D converter is being used. Oftentimes, the frequency response will be specified at the -3dB point, which means you are attenuating the signal by approximately 30% at that particular frequency! You may find that keeping the frequencies below the -0.5 dB point of the amplifier is preferred because the output is then attenuated by less than 5%.
Digital sampling can open a Pandora’s box. In general, a minimum of 10X oversampling for sinusoidal inputs is recommended, and more is better. For transient inputs, we suggest setting your digital sampling to the maximum rate and then evaluating the peaks once the data is recorded. Ideally you would have at least three data points to construct the peak signal – one data point at the peaks suggests that you need to sample faster!