| 摘要 |
A triangle-wave generator (33) generates a triangle signal which has a high frequency with respect to the system frequency and which is conducted to an input of a comparison device (29). An analog signal proportional to the sampled voltage in the electrical system is conducted to the other input terminal of the comparison device (29). The output variable of the comparison device is a pulse-width-modulated signal, the pulse width being proportional to the magnitude of the voltage in the electrical system. This signal is multiplicatively combined with a signal which is proportional to the amplitude of the current in the system and is conducted to an integrator (63) in order to derive a signal which is proportional to the power consumption in the system. This signal is converted in a pulse generator (73) into a pulse chain, the frequency of which is proportional to the power consumption. For error correction, the polarity of the input terminals of the comparison device to which the signals proportional to the triangular and analog voltage are connected is changed by means of a switching device (17, 19). The switching device (17, 19) is operated whenever an output pulse occurs in the pulse chain of the counter. The integrator (63) then tends to integrate and as a result compensates for displacement errors. The invention is suitable for measuring kilowatt-hours by electrical means. <IMAGE> |
