Most signals are composed of AC and DC components. The DC component is at 0Hz and acts as an offset in the time domain, and the AC component consists of all other frequencies. Coupling is the way the transducer transfers the information.
AC Coupled sensors will only transfer AC signals and thus removes the DC offset, this is done by making use of DC blocking capacitor in series with the output of the transducer. The blocking capacitor (C) and input impedance (R) of the sensor signal conditioning block will form a high-pass filter with cut-off frequency: 1/(2πRC)
DC Coupled sensors allow both the AC and DC components through, the DC component is a 0Hz signal and is an offset around which the AC component is superimposed.
