Filter for obtaining a useful signal, constant with respect to time, from a noisy measuring signal

A filter apparatus for providing a useful signal constant with respect to time from a measuring signal including measuring noise, comprising:

• (a) means for integrating a measuring signal with respect to time and thereby providing an integrated measuring signal;
• (aa) said means for integrating the measuring signal including
• (1) a voltage-to-frequency converter,
• (2) clock means for generating clock intervals,
• (3) an accumulator to which the output signals from the voltage-to-frequency converter are applied and which is resettable at predetermined clock intervals,
• (4) a first memory for storing the integrated measuring signal,
• (5) adding means to which, in said predetermined clock intervals, the content of the accumulator is applied as one summand, and the contents of said first memory is applied as another summand with a delay of one clock interval, and
• (6) the output of the adding means being read into the first memory and constituting the digitized integrated measuring signal;
• (b) said integrated measuring signal containing a component varying substantially linearly with time with a predetermined coefficient which represents the useful signal;
• (c) filtering means for generating output signals indicative of a preselected, variable model which represents an estimate of said integrated measuring signal and an estimate of a first order coefficient of the linearly time-variable component of the estimate of said integrated measuring signal corresponding to the time-constant useful signal;
• (d) said filtering means including
• means for multiplying the difference of the integrated measuring signal and the estimate of the integrated measuring signal by a first time-variant factor and the time of a concerned clock interval,
• means for multiplying the difference of the integrated measuring signal and the estimate of the integrated measuring signal by a second time-variant factor,
• means for adding the two products thus obtained and for forming a zero variation signal representing a variation of a zero order coefficient of the model,
• a second memory for storing the zero order coefficient of the model,
• zero adding means to which the zero variation signal thus obtained is applied as one summand, and the contents of the second memory is applied as an other summand with a delay of one clock interval, in order to thereby obtain the zero order coefficient of the model, and
• the output of the zero adding means being read into the second memory for storing in the second memory the zero order coefficient of the model;
• (e) said filtering means further including
• means for multiplying the difference of the integrated measuring signal and the estimate of the integrated measuring signal by a third time-variant factor and the time of said concerned clock interval,
• means for multiplying the difference of the integrated measuring signal and the estimate of the integrated measuring signal by a fourth time-variant factor,
• means for adding the two products thus obtained and forming a first variation signal representing a variation of a first order coefficient of the model,
• a third memory for storing the first order coefficient of the model,
• first adding means to which the first variation signal thus obtained is applied as one summand and the contents of the third memory is applied as another summand with a delay of one clock interval, in order to thereby obtain the first order coefficient of the model,
• the output of the first adding means being read into said third memory, the contents of the third memory delayed by one clock interval forming the first coefficient of a model, and
• means for multiplying said first order coefficient by the time of said concerned clock interval;
• (f) means for adding the zero order coefficient and the first order coefficient multiplied by the time of said concerned clock interval for forming the estimate of said integrated measuring signal;
• and
• (g) said first order coefficient providing the estimate of the time-constant useful signal.