Analogue filters

This technique is of high accuracy and is meant to be used in precision measurement instrumentation, for it is inherently insensitive to the DC-offset and the AC-noise in the sinusoidal signal which can be substantially reduced by a great variety of electronic devices ranging from various electronic analogue filters, and digital filters to the most effective lock-in amplifiers. 

Figure 3.12. Eliminating noise with analogue filters. Spectra were recorded over a spectral width of 5 kHz with no sample in the probe. The analogue filter window was set to (a) 6 kHz, (b) 3 kHz and (c) 1 kHz and the associated noise attenuation is apparent, although the cut-off point is ill defined.

Figure 3.13. The effect of analogue filters on signal-to-noise. Spectrum (a) was recorded with the correct filter width (1.25 times the spectral width), and (b) and (c) with it increased 10- and 100-fold respectively.

Within the BMS, the measured values are used for state determination and for system control. Therefore, it is important that the measured values are correct, failures are detected, and substitute functions are available in case of measurement failures. Thus, the following processing should be carried out (i) analogue filtering ... 

In the circuit, the analogue stage replaces the passive filter, which is often required by switching amplifiers. That is, it performs the tasks of an analogue filter at the power level. The ripple of the output signal of the switching amplifier can be dampened by more than 20 dB. A passive coil filter usually... 

Examples of analogue processing include anti-aliasing filters for the conversion stage. In situations where real-time processing power is limited, there may also be benefits in implementing analogue filters. 

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