METHOD AND APPARATUS FOR DETECTING SLOW AND SMALL CHANGES OF ELECTRICAL SIGNALS INCLUDING THE SIGN OF THE CHANGES, AND CIRCUIT ARRANGEMENT FOR THE EXACT DETECTION OF THE PEAK VALUE OF AN ALTERNATING VOLTAGE

DETAILED DESCRIPTION I claim: 1.
Apparatus for detecting slow and small changes of electrical signals including the sign of the changes, comprising: a controlled switch (2) connected in the path of the signal to be detected; a capacitor (3) connected with a first terminal to the switch and charged to the voltage of said signal; an amplifier (5) with an input connected to second terminal of the capacitor (3) and generating a pulse signal corresponding to the charge or discharge current of the capacitor having corresponding proper sign; a window comparator (7) having first and second reference voltages (+U.
sub.
K, -U.
sub.
K) determining a window, and a signal input connected to output of the amplifier (5) for indicating whether the output signal of the amplifier lies in the range defined by the window or it has been crossed in negative or positive directions; storage and logical units each having first and second storage means (8, 11); and a pulse generator (9) connected to control input of the controlled switch (2) to make it closed for periodically repeated sampling periods, and also connected to the storage and logical units, wherein said first storage means storing the logical state of the window comparator (7) taken during said pulse signal with proper sign, and a predetermined section of each pulse of said pulse generator reading such stored values of said first storage means into said second storage means.
2.
The apparatus as claimed in claim 1, wherein said pulse generator (9) has pulses with variable period time.
3.
The apparatus as claimed in claim 1, wherein the amplifier (5) comprises RC feedback elements complementing each of said charging or discharging pulse with a respective pulse of opposite sign, and the time of these pulses being in the same order of magnitude.
4.
The apparatus as claimed in claim 1, wherein the voltage window of said window comparator (7) being adjustable to be symmetric relative to the base level of the output signal of the amplifier (5).
5.
The apparatus as claimed in claim 1, wherein said first storage means being a pair of bistables (8a, 8b), having inputs gated by the inverted output of the other one in the pair, furthermore said bistables being reset by the leading edges of the sampling pulses of the pulse generator (9)