The invention relates to a filter module for a fuel conveying unit comprising a fuel pump with two pump chambers which are independent of each other. An inverting gain stage includes an input terminal connected to the output terminal of the input stage, an output terminal for delivering an amplified signal, and a variable feedback resistor connected between the output terminal and input terminal thereof. The heater can be configured as a resistive heater, and the humidity sensor can be configured from one or more humidity-sensing die. The unclassified document theme score and the theme scores for the various classes are compared and the unclassified document is classified into the classification having the nearest theme score.