DE2322068B2 - CIRCUIT ARRANGEMENT FOR OBTAINING A DC VOLTAGE AS A MEASURE OF THE CHANGE OF ATTENUATION IN LEVEL-CONTROLLED MESSAGE TRANSMISSION SYSTEMS - Google Patents

Description

ί ^; 0

a Bode-network is used as a cushioning member, the variable resistor (R 3) is decoupled direct current by a capacitor (Ci) from Hilfsvierpol (HV) of the Bode network, and that the resistor (R opposite to the choke (Dr) in row 4 ), at which the DC voltage can be removed, is selected in its size equal to the characteristic impedance (R 0) of the auxiliary quadrupole (Fig.l).

2. A circuit arrangement according to claim 1, characterized in that the DC voltage is supplied (at the resistor A4 ') via a resistor (R5) of a display device (A), the other terminal on a through which a further auxiliary direct current (1 2) resistance (R 6), and that these resistors (R 4 ', R5, R6) satisfy the condition that their total resistance effective in terms of direct current is equal to the characteristic impedance (RO) of the auxiliary quadrupole (FIG. 2, equation 6).

3. Circuit arrangement according to claim 1 or 2, characterized in that when using a Bode-Netiwerkes with transformer (V) the transformer output winding via the parallel connection of a resistor (R 4 ") with a capacitor (Ci) with the variable resistor (R 3) is connected that the first auxiliary direct current (Ji) is also fed to this connection point and that the display device (A) is switched on via screen means (Rs, C 2) , the resistors (RA ", Rs, R5 ', R6) being so dimensioned that their total resistance effective in terms of direct current is equal to the characteristic impedance (RO) of the auxiliary quadrupole (Fig. 3, equation 7).

55

The invention relates to a circuit arrangement for obtaining a DC voltage as a measure of the Change of attenuation in level-regulated communication systems, with the DC voltage as Voltage drop across a variable resistor of the attenuator through which an auxiliary current flows the level device is created and the variable resistor is connected in series a choke and a resistor in parallel. In such communication systems it is necessary to continuously monitor the condition of the transmission lines and amplifiers. That also includes Findings about the current setting of the regulated amplifiers contained in the transmission system or regulated attenuators.

There is already a method known (DT-AS 17 62 373), in which the display of the monitoring system Pill resistance of a thermistor is used as an actuator in a regulated attenuator is used. The known method provides a DC voltage that is proportional to the ratio of the AC output voltage to AC input voltage of the attenuator.

However, in some applications it is desirable to keep the display size non-proportional to the Ratio of alternating voltages, but proportional to the logarithm of this ratio, d. i.e., it should e.g. B. with a linear meter for direct current or direct voltage a Statements about the gain in logarithmic measure can be obtained. One in Neper or The decibel scale on the direct current instrument is unsatisfactory because of the accuracy of the reading due to the non-linear graduation is very different over the entire range of the scale. The measured one Rather, the direct voltage or direct current value would have to be converted into a logarithmically changing display variable be converted, which is complex and technically difficult. Otherwise the known solution is only for an attenuator in Γ circuit specified, which is not can be transferred to a Bode network that is widely used today.

The object of the invention is to use simple means to obtain a display size that corresponds to the logarithm is proportional to the voltage ratio.

The object is achieved according to the invention in that in order to achieve a linear relationship between the DC voltage and the change in attenuation in a logarithmic measure

t / l

a Bode network is used as an attenuator, its variable resistance by a capacitor is DC-decoupled from the auxiliary quadrupole of the Bode network, and that the to the choke in Resistance lying in series, at which the direct voltage can be removed, in its size equal to the characteristic impedance of the auxiliary quadrupole is selected.

The invention, its configuration and mode of operation will be described below with reference to the figures for some Exemplary embodiments explained in more detail:

F i g. 1 shows an embodiment of the invention in the simplest form;

F i g. 2 shows a variant of the invention in which the polarity of the display current is reversed compared to the first embodiment and the display is adapted to the measuring range of the instrument in a certain way;

F i g. 3 shows another variant of the invention, in which a transformer, which is present anyway, instead of the Throttle is also used.

In Fig. 1, the components Al, R2, R3 and the auxiliary quadrupole HV represent an example of a known network according to Bode. The capacitor C1 still contained in the Bode network is used for DC isolation and is irrelevant for the AC transmission properties of the network.

tion. With the variable resistor A3 can change the attenuation of the Bode network in a known manner. It applies to Bode-Ne; zwerke in general the equation

It / =

k.

(1)

where Δ a denotes the change in attenuation of the network, starting from an average attenuation; k is a constant that characterizes the dimensioning of the network; the reflection factor ρ is according to the equation

R3 - R ₁ , R 3 + ~ R "

(2)

/ <3 - R ₁ ,

k + \ a
k- \ ci '

(3)

^R »

2k "

(4)

2 k

(4a)

U = JX

R4

Ia-Jl

R4

2k

(S)

'5

a measure of the change in the variable resistance A3, where RO represents the real wave resistance of the quadrupole.

If equation 2 is inserted into equation 1 and solved for R 3, the result is

The relationship according to equation 3 is non-linear.

This gives a statement about the relationship between the size of the variable resistance R 3 and the change in attenuation of the Bode network in neper or decibel.

According to the invention, a resistor R 4 of the magnitude RO of the wave resistance of the auxiliary four-pole is connected in parallel to the resistor R 3. Equation 3 gives the equation for this parallel connection

because of the condition /? 4 = RO , the equation changes to

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Equation 4a shows that apart from an additive component - ^ - there is a proportional relationship between the quantity /? 3 || /? 4 and the change in attenuation Δ a in neper or decibel.

If a constant direct current / 1 flows through the parallel connection of R 3 and R 4, a direct voltage is obtained at these resistors according to equation 4a

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and thus for the desired DC voltage to the linear relationship with the logarithmic mentioned ^ ₀ mix amount of attenuation.

The resistor R 4 must not be connected directly in parallel with the variable resistor R 3 in terms of alternating current, in order not to change the alternating current properties of the Bode network. <, ₅ A throttle Dr is therefore provided in series flit R 4 for decoupling. In addition, a capacitor CI is required for DC decoupling,

if the auxiliary quadrupole should have a DC current path to the reference point of the circuit. The direct voltage occurring at the resistor RA can be displayed with a conventional voltage indicator or other display device A, the resistance inherent in these instruments having to be taken into account when dimensioning R 4.

In general, it is desirable that an increasing display correspond with an increasing level. In the Circuit arrangement according to FIG. 1, this is the case when the Bode network acts as an attenuator in If the Bode network is used in the negative feedback path of an amplifier the polarity of the display is reversed, which is canceled by additional measures can be.

In FIG. 2, a further constant auxiliary direct current / 2 is used for this purpose, which generates a voltage across a resistor R 6 which is directed in the opposite direction to the voltage applied to the display device A. The voltage at R 6 can be dimensioned so that the current through the display device A increases with increasing attenuation of the Bode network. Resistor R5 in FIG. 2 represents an additional resistance, which can also be the instrument internal resistance itself or to which the instrument internal resistance is added for the calculation. The three resistors R 4 ', RS and R 6 must then be dimensioned so that the condition

RA '[RS + R6)
RA '+ R5 + R6

16)

is satisfied.

In addition to this condition, there is still the possibility of dimensioning these three resistors R 4 ', RS and R 6 so that the display device A has half the deflection at medium attenuation of the Bode network and the full or at the limits of the control range of the Bode network shows a zero deflection. This enables the monitoring operating personnel to be given simple instructions to initiate appropriate measures when the display limits are reached.

In Fig. 3, the display is essentially similar to the circuit according to FIG. 2, but the original resistor R 5 is divided here into the resistors Rs and RS 'in order to be able to insert a filter capacitor C1; this prevents AC voltages from the AC circuit in the display circuit or z. B. Interference voltages from the display circuit get into the AC circuit. Furthermore, in FIG. 3 the choke Dr realized with hooves of one winding of the transformer Ü; the original resistor R 4 is now in the order interchanged in series with the transformer Ü. This circuit is advantageous if the auxiliary quadrupole of the Bode network is already terminated with a transformer. In this case, the otherwise necessary choke can be saved by using the transformer. The condition according to the invention for the resistor to be connected in parallel with the variable resistor R 3 in terms of direct current is now i.

RA "■ (Rx 4- R5 '+ R6)

R 4 '-I RS + R5' + R 6 ~ "
The capacitor Cl must in this case in parallel

R 4 "lie in order to avoid undesirable influence on the AC behavior of the network. The resistance Rs and the AC internal resistance of the DC power source / 1 must be large compared to the largest value of the variable resistor R 3 in order not to influence the original control range.

In the exemplary embodiments, the supply of a constant auxiliary DC current is shown and explained. Of course, the circuit can also be used in a dual version with a constant DC voltage infeed can be realized; It is also possible to use auxiliary voltage sources with almost any interior Resistance to be used if the corresponding internal resistance is effective in the overall shell device are included and the condition according to the invention is met again in each case, d. i.e., dat the total resistance of the measuring arrangement is equal to the characteristic impedance AO of the auxiliary quadrupole.

1 sheet of drawings

Claims (1)

Patent claims: 1. Circuit arrangement for obtaining a DC voltage as a measure of the change in attenuation in level-regulated communication systems, with the DC voltage as a voltage drop a variable resistance of the attenuator of the attenuator through which an auxiliary current flows Level device is created and the variable resistor is a series circuit of a choke and a resistor is parallel, characterized in that to achieve a linear relationship between the DC voltage and the change in attenuation in the logarithm! - $ che: n measure