Explanation of signal filters in measuring amplifiers
A low-pass filter is usually used for measuring amplifiers with analog output. But also the electronic components, like e.g. Interference suppression or instrumentation amplifiers have the characteristic of a low-pass filter: Signal components of higher frequencies are amplified less than signal components of lower frequencies (the amplification bandwidth product of the instrumentation amplifier is responsible for this).
As a rule, low-pass filters with cut-off frequencies are deliberately used well below the capabilities of an instrument amplifier. Limit frequency means: a signal with this frequency is only transmitted with approx. 70% compared to the expected amplitude. The "order" of the low-pass filter also describes how much the amplitude is reduced (damped) with increasing frequency. The order describes the steepness of the filter characteristic curve. Second order filters are common for amplifiers with analog output. For a second order filter, the attenuation is -40dB per decade: If the frequency increases by a factor of 10, the amplitude decreases by a factor of 100.
The reason for using a filter is that the filter reduces the statistical dispersion of the signals: The noise amplitude is reduced if the "bandwidth", i.e. the range of frequencies that may pass through the filter undamped, is restricted. This improves the resolution of the measuring amplifier. The rule of thumb is: One tenth of the bandwidth reduces the noise amplitude by a factor of 3. This is especially true if the signal contains all the frequencies equally.
Usually, there are some outstanding freuence components within the noise: e.g. 50Hz for interferences from the network.
When selecting the low-pass filter, the cut-off frequency should be at least 5 times higher than the signal frequencies to be measured so that the measurement result is not distorted. The low pass filter should be as low as possible and as high as necessary.
https://www.me-systeme.de/en/technology-first/electronics/basics/filter
https://www.me-systeme.de/en/technology-first/electronics/basics/comparison
https://www.me-systeme.de/en/technology-first/electronics/gsv-6/aufloesung-gsv-6bt