DE2262939C3 - Circuit for evaluating pulse-modulated alternating voltages, in particular pilot voltages in carrier frequency systems - Google Patents

Description

30th

The invention relates to a circuit for evaluating pulse-modulated alternating voltages, in particular pilot voltages in carrier frequency systems with a rectifier forming the input of the overall circuit.

Primary group amplifiers in carrier frequency systems are monitored by means of pilot voltages. Included becomes the pilot voltage on the transmission side of the one transmission direction in a certain duty cycle switched on and off (pulse modulated) if the transmission in the other direction is disturbed.

From DE-AS 11 33 822 a circuit arrangement is for displaying deviations in the amplitude of an alternating voltage from a nominal value, in particular for pilot level monitoring in carrier frequency systems, known. The AC voltage received is Pilot voltage, rectified. With the difference between the resulting directional voltage and a comparison voltage is used to control a transistor generator. The oscillations of the transistor generator are displayed and are a measure of compliance with the specified setpoint. If the pilot voltage is sampled, this method is not very suitable because the transistor generator delays oscillates and has a hysteresis, d. H. the level values when tearing off and reinserting the Vibration are not the same.

From DE-AS 12 74 195 Next Schaltungsanord- _b o voltage is known for selectively receiving a sinusoidal measuring or pilot signal in a power-line communication. In two receiving channels working in parallel, the pilot signal is modulated with two carrier voltages of the same frequency and shifted in phase by 90 °, and then rectified in a phase-sensitive manner. The resulting useful signal is freed from the frequency deviation between the carrier voltage and the pilot signal. This circuit arrangement has the disadvantage that it responds to changes in the amplitude of the pilot signal that occur between the ring modulator and the evaluation device.

The object of the invention is to provide a circuit which, in the case of the keying of the Pilot AC voltage supplies a signal in the event of any other change in the amplitude of the pilot AC voltage does not emit a signal

This object is achieved in that the circuit a first voltage-dividing low-pass filter that has a time constant with a value between the reciprocal values the alternating voltage and the sampling frequency has a second voltage-dividing low-pass filter, whose Division factor is greater than that of the first low-pass and has a time constant with a value above which has the reciprocal values of the alternating voltage and the sampling frequency and contains a differential amplifier, whereby the low-pass outputs each have a differential amplifier input and the low-pass inputs jointly the rectifier are made, the input of the Overall circuit forms

A further development has a rectifier with connected smoothing capacitor for content, the is connected to the output of the differential amplifier.

The mode of operation of the circuit according to the invention is explained with reference to the figure. The input, point E, is preceded by a first rectifier DX , not shown here. DV is the differential amplifier with the non- inverting input Eni and the inverting input Ei; RX, R 2 and CX form a first low-pass filter; /? 3, R 4 and C2 form a second low-pass filter.

It is

RXjRl <R3 / R4 Ci (RiWR2) <C2 (R3 || R4)

Eq. 1
Eq. 2

and with the pilot frequency Fp and the sampling frequency ft results

~ < C \ {R \\\ Rl \ < -J-
JP / '

<C2 (R $ \ R4)

Gl. 3

GI. 4th

The rectified pilot voltage flies at the point at. It is in the form of half sine waves. This tension is smoothed out by the low-pass filters.

In the steady, steady state, according to Eq. 1 the DC voltage at Ei is higher than that at Eni; the output of the differential amplifier DV has a negative potential.

Both low-pass filters can follow a slow, steady change in the pilot voltage; the DC voltage at Ei remains higher than that at Eni; the output of the differential amplifier remains at negative potential.

When the pilot voltage is sampled as described above, it follows according to Eq. 3 and Eq. 4 the voltage at Ei at the sampling frequency is much higher than the voltage at Eni; the sign of the input voltage difference changes periodically with the sampling frequency and a square wave is produced at the output of the differential amplifier.

With the help of the voltage divider R 5, D, C3 this output square-wave voltage is rectified and smoothed. When the input AC voltage is not sampled, the capacitor C3 is charged. If the keying starts, the capacitor C3 is periodically fully discharged via the diode D and only slightly charged via the resistor R 5; the capacitor remains practically discharged, the output of the circuit is at negative potential.

1 sheet of drawings

Claims (2)

Patent claims: 1. Circuit for evaluating pulse-modulated AC voltages, in particular pilot voltages in carrier frequency systems with a rectifier forming the input of the overall circuit, characterized in that the circuit has a first voltage-dividing low-pass filter which has a time constant with a value between the reciprocal values of the AC voltage and the sampling frequency, a second voltage-dividing low-pass filter, the division factor of which is greater than that of the first low-pass filter and which has a time constant with a value above the reciprocal values of the AC voltage and the sampling frequency and contains a differential amplifier (DV) , the low-pass output being shared by a differential amplifier input and the low-pass inputs are connected to the rectifier, which forms the input of the overall circuit. 2. A circuit according to claim 1, characterized in that a rectifier (R 5, D) with the smoothing capacitor (C 3) connected is connected to the output of the differential amplifier (DV).