EP3797408B1 - Device, method, and control module for monitoring a two-wire line - Google Patents

Description

The present invention relates to a device for monitoring a two-wire line, in particular a two-wire line of a fire protection system, and an associated method and an associated control module.

According to the EN54 Part 13 standard, fire protection systems, for example for fire detection and alarm generation, must be certified and, in particular, the compatibility of system components must be assessed. For this purpose, it is necessary, for example, that the resistance of a two-wire line to which devices such as alarm devices and/or triggering devices are connected does not exceed a certain value in order to be able to provide sufficient current or voltage in the event of a trigger and not to jeopardize the triggering. In particular, in the case of two-wire lines, a series resistance R _L in the longitudinal direction of the line and a parallel resistance Rs between the two lines can be described. If the series resistance R _L is too high, the voltage applied between the lines is not sufficient to trigger devices such as valves. At the same time, it must be ensured that the parallel resistance Rs does not become too small, which would correspond to the case of a short circuit between the two lines.

According to the prior art, several possibilities are known for detecting faults on control lines in alarm and control systems, for example in fire protection systems.

EP 2 804 163 for example relates to a method for measuring a line resistance RL and thus for determining faults in control lines in such a hazard warning and control system. However, the system is not able to determine not only a series resistance of the line but also a parallel resistance between the two lines. In other words, the system only allows you to determine one of the two interesting resistance values or a total value resulting from both values.

Other solutions known from the prior art can be found, among others, in EP 2 232 455 , EP 2 093 737 , EP 1 816 619 , DE 2 038 795 , DE 30 36 029 .

EP 2 916 303 A1 proposes a control device and a control method for a fire alarm system, the control device and the control method being able to monitor an on-line impedance or an inter-wire impedance of field wires. The device is connected to a line with a capacitive element terminated at a far end of the line. The method comprises: sampling at least three output voltages (V ₁ , V ₂ , V ₃ ) of the monitoring power supply at at least three different times (t ₁ , t ₂ , t ₃ ), the at least three times being all before the capacitive element dies reaches saturation, and the time points include at least three time points that satisfy: t ₂ = nt ₁ , t ₃ = (2n - 1)t ₁ , where n is an integer greater than 1; and based on the at least three output voltages (V ₁ , V ₂ , V ₃ ) calculating an on-line impedance (R c ) or an inter-wire impedance (Rs) of the line.

EP 3 062 299 A1 provides an apparatus and method for detecting and adapting to end of line resistance in a NAC of a control panel or power amplifier of, for example, an alarm system and for locating ground faults in the alarm system. The apparatus may include a notification device circuit, the notification device circuit including first and second analog input ports, the notification device circuit including first and second external output ports, and the notification device circuit including an end-of-line resistor. Current can be passed through the notification device circuit via the first and second analog input ports, and voltage can be measured at each of the first and second external output ports. The measured voltage can have a value of end-of-line resistance or a condition of the notification device circuit that is open, shorted, faulty, or normal.

What all known systems have in common is that they either require complex, active termination components or cannot differentiate between series and parallel resistance and only detect a combination of series and parallel resistance. Passive terminating components may also be subject to temperature influences from semiconductor components. While the active terminating component has the advantage that it monitors the two-wire lines itself, the component itself and its maintenance is very expensive. Against this background, it was an object of the present invention to provide a device for monitoring a two-wire line, in particular a two-wire line of a fire protection system, as well as a method for monitoring such a two-wire line and an associated control module, which at least partially have the disadvantages known from the prior art avoids.

In a first aspect, the object is achieved according to the invention by a device for monitoring a two-wire line. The two-wire line is in particular a two-wire line of a fire protection system. The device comprises a passive terminating component for terminating the two-wire line, with the passive terminating component having a chargeable energy store, a constant current source for providing a measuring current to the passive terminating component, a voltage detection unit for detecting a voltage curve at output terminals of the two-wire line, a control unit for controlling the constant current source and for Evaluating the detected voltage curve, the control unit being set up to separately determine a series resistance and a parallel resistance of the two-wire line.

Since the passive terminating component according to the invention has a chargeable energy store, the control unit makes it possible to charge the chargeable energy store by means of the constant current source. The recorded voltage curve, which is evaluated both during and after the operation of the constant current source, for example, enables both the series resistance and the parallel resistance of the two-wire line to be determined in a simple manner, since the voltage curve depends on these resistances due to fundamental laws.

While the measuring current is being provided, the chargeable energy store is being charged, resulting in an increasing voltage. If the measuring current is not provided, the parallel resistance of the two-wire line will form a closed circuit together with the terminating component and lead to the chargeable energy storage device self-discharging.

In particular, no voltage drops across the series resistance during a time in which the constant current source is not being operated, so that the voltage curve is exclusively indicative of the parallel resistance. Thus, both the parallel resistance and the series resistance can be inferred from the voltage curves, which are recorded while the measurement current is being provided and during a time when no measurement current is being provided.

It is particularly preferred that the passive terminating component is arranged at an end of the two-wire line that is remote from a fire alarm and/or extinguishing control panel. The arrangement at the end makes it possible, in particular, for the complete longitudinal component of the line resistance to be detectable between the output terminals.

In a preferred embodiment, the chargeable energy store of the passive terminating component is designed as a capacitor that can be arranged between the two wires of the two-wire line. A capacitor is a particularly simple and effective form of chargeable energy storage. Other chargeable energy stores, for example accumulators, are also conceivable in other embodiments. In principle, all chargeable energy storage devices that have a differential equation for the charging and discharging process that is equivalent to the capacitor can preferably be used for the method.

In a preferred embodiment, the capacitor has a capacitance which is above 0.1 μF, in particular above 1 μF and particularly preferably in the range from 1 μF to 10 μF. With a capacitance in the preferred range, it is ensured that the charging effected by the measuring current and a self-discharge of the capacitor can take place in a temporal order of magnitude that is sufficient for an effective determination of the line resistances in accordance with EN54 Part 13.

In a preferred embodiment, the control unit is set up to change the voltage profile in response to a change in the measurement current provided evaluate. In particular, when the constant current source is switched on and switched off, there are jumps in the recorded voltage profile. The jumps directly indicate a line resistance. Consequently, the accuracy of the determination initially depends only on the accuracy of the discrete measured values of the voltage profile directly after switching on and off.

In a preferred embodiment, the control unit is set up to charge the chargeable energy store during a predetermined first time period by controlling the constant current source and to evaluate self-discharge of the chargeable energy store during a subsequent second time period after the constant current source has been switched off. A voltage of the chargeable energy store is preferably also evaluated during the first time period. The predetermined first time period is 0.5 ms, for example. Preferably, the predetermined second period of time directly follows the predetermined first period of time and is also 0.5 ms, for example. These exemplary values have proven to be particularly practicable, of course, other durations of the first or second time period are also conceivable, in particular the two time periods can also be different.

In a preferred embodiment, the control unit is set up to determine the series resistance and the parallel resistance of the two-wire line from the time curve of the voltage during the first and second period. Depending on the application, longer or shorter periods of time are of course also possible, and the second period can also have a different duration than the first period.

The predetermined second period of time is preferably followed by a predetermined third period of time before another measurement, beginning with the first period of time, takes place. During the third period of time, the chargeable energy store is preferably completely discharged, so that the renewed determination of the line resistances begins with a voltage of 0 V. Accordingly, the constant current source is preferably also switched off during the third time period.

For this purpose, the chargeable energy store is preferably discharged during the third time period via a discharge resistor that can be switched on, for example.

In a preferred embodiment, the control unit is set up to determine the series resistance of the two-wire line based on a voltage change when the constant current source is switched on and/or switched off. This simple Determination also requires high accuracy and resolution of the recorded measured value over time.

In a preferred embodiment, the control unit is set up to determine the parallel resistance and the series resistance of the two-wire line based on two successive approximations of the voltage profile during the first and second period. In this case, in particular, the second period of time and, based on this, the first period of time are to be evaluated first.

In a preferred embodiment, the control unit is set up to use discrete values of the recorded voltage profile, in particular by means of the least squares method, to calculate constants of two linear equations of the voltage in the first order of a time-dependent variable during the first and second period to approximate.

Both linear equations thus lead to two parameters each, one constant and one dependent on time in the first order. To put it bluntly, a graph of the linear equations corresponds to a straight line in each case, with the two parameters then specifying the ordinate intercept and the slope of the straight line. The time-dependent variable may be a linear function of time, i.e., for example, directly time, or, preferably, an exponential functional function of time. The exponential dependence on time corresponds to the exponential course of charging and discharging, in particular of capacitors. The series resistance and the parallel resistance can then be derived with high accuracy from the two parameters obtained for each equation.

In addition, due to the approximations, it is not necessary to calibrate or measure a capacity of the chargeable energy store in order to infer the resistances from the time profile of the voltage. This capacity also results from the approximations and can be derived from the parameters of the two equations.

In a preferred embodiment, the control unit is designed to monitor a number of two-wire lines. This simplifies the overall structure of the device in that a number of control units for monitoring a number of two-wire lines, for example for fire protection systems which regularly include a larger number of two-wire lines, are not required. Likewise, the constant current source can be set up, and several of the two-wire lines with one to supply constant current. Of course, combinations of several control units and/or constant current sources are also conceivable for monitoring.

In a further aspect, the object mentioned at the outset is achieved by a method for monitoring a two-wire line. The two-wire line is in particular a two-wire line of a fire protection system. The method includes: providing a measurement current to a passive terminating component for terminating the two-wire line, the passive terminating component having a chargeable energy store, detecting a voltage curve at output terminals of the two-wire line, and evaluating the detected voltage curve to determine a series resistance and a parallel resistance of the two-wire line to determine.

The method according to the invention makes it possible to obtain the same advantages as can be achieved with the device according to the invention for monitoring a two-wire line. Furthermore, all of the configurations of the device described as being preferred can be combined in an analogous manner with the method according to the invention.

In a preferred embodiment, the measurement current is provided in a first period for charging the chargeable energy store and is not provided in a subsequent second period, with a voltage profile at output terminals being recorded and evaluated during the first period and the second period.

In a preferred embodiment, the parallel resistance and the series resistance of the two-wire line are determined using two successive approximations of the voltage profile during the first and second period.

In a preferred embodiment, discrete values of the sensed voltage waveform are used to determine the shunt resistance and series resistance from approximate constants of two linear equations of first order voltage of a time dependent variable during the first and second periods.

In a further aspect, the object mentioned at the outset is achieved by a control module of a fire alarm and/or extinguishing control center for monitoring a two-wire line of a fire protection system, the control module being set up to carry out the method according to the invention.

In a further aspect, the object mentioned at the outset is achieved by using a capacitor as a passive terminating component for terminating a two-wire line of a fire protection system.

Fig. 1:

schematisch und exemplarisch ein Beispiel einer erfindungsgemäßen Einrichtung zur Überwachung einer Zweidrahtleitung und

Fig. 2.

schematisch und exemplarisch Spannungsverläufe bei verschiedenen Widerständen.

Further advantages and refinements are described below with reference to the accompanying drawings. Here show:

Figure 1:

schematically and by way of example an example of a device according to the invention for monitoring a two-wire line and

2

schematic and exemplary voltage curves for different resistances.

1 shows a schematic and exemplary first example of a device 1 according to the invention for monitoring a two-wire line 2. The two-wire line 2 is connected at two output terminals 4, 6, for example, to a control panel 100 of a fire protection system, such as a fire alarm and/or extinguishing control panel. It is important to ensure that the resistances occurring across the line are within the permissible range, so that, for example, in the event of a trip there is sufficient voltage dropping or being present.

A termination component 10 with reverse polarity protection configured as a diode 52 and a consumer represented as a resistor 54 is typically provided at a termination 8 of the two-wire line. This avoids a short circuit via the two-wire line and simultaneously creates the possibility of monitoring with a current flowing through the terminating component 10 . In particular, due to the reverse polarity protection, a monitoring current never goes through the terminating component 10.

The two-wire line, to which several participants such as detectors, alarm devices, etc. are connected, can be modeled as a combination of series resistance R _L and parallel resistance Rs. One aim of the present invention is to be able to determine or monitor the series resistance R _L and the parallel resistance Rs separately. For this purpose, the invention proposes a particularly simple passive terminating component 10 which is connected to the termination 8 of the two-wire line 2 . In contrast to the conventional terminating component 50, which only determines the overall line resistance, it is therefore possible to determine R _L and Rs separately.

The termination component 10 according to the invention has a chargeable energy store 12, which is designed as a capacitor with a capacitance C in the example shown. Furthermore, the passive terminating component 10 does not show any temperature dependence of the determination, so that the capacitance C can be determined automatically, which is why no configuration/calibration of the terminating component 10 is necessary.

According to the invention, the parallel resistance Rs and the series resistance R _L together with the capacitance C are now determined by a control unit 40 using a voltage profile U(t), the function of which is referred to in FIG 2 is described.

A constant current source 20 is arranged between the output terminals 4, 6 in order to provide a constant but preferably adjustable measurement current I1 via the chargeable energy store 12 of the passive termination component 10.

A voltage detection unit 30 for detecting a voltage curve U(t) between the output terminals 4, 6 is also provided. The control unit 40 is set up to control the constant current source 20 and to evaluate the voltage curve U(t) detected by the voltage detection unit 30 . In this case, the control unit 40 enables the series resistance R _L and the parallel resistance Rs of the two-wire line 2 to be determined in a skilful manner, as will be explained below.

In summary, the control unit 40 should therefore be able to make a reliable statement as to whether the line resistances R _L , Rs that are present allow a sufficient voltage at the load in the event of activation.

The control unit 40 is either designed as a separate module, for example within the fire alarm and/or extinguishing control panel 100 , or can be designed as an integral part of the fire alarm and/or extinguishing control panel 100 . In a preferred case, all of the components of the device 1 provided on the control panel side for monitoring a two-wire line are in the form of a monitoring module that is 1 shown with dashed lines. In this case, for example, a further control unit 45 of the fire alarm and/or extinguishing control center 100 will take over the additional functions for fire monitoring and/or extinguishing control.

The voltage curve U(t) at the module terminals 4, 6 is measured continuously. In this case, the chargeable energy store 12 is initially charged with the current I1 via the constant current source 20 for a specific period of time T1. The constant current source 20 is then switched off and the self-discharge of the capacitance C via the parallel resistance Rs is observed over a period of time T2. Finally, the chargeable energy store 12 is completely discharged via a discharge resistor of a discharge unit 60 during a subsequent time period T3.

2 FIG. 3 schematically shows a diagram 300 in which the recorded voltage U(t) is shown over time. In particular, the subdivision into the periods T1, T2 and T3 has been made and four different voltage curves 310, 312, 320, 322 for two different values of the series resistance R _L and two different values of the parallel resistance Rs were recorded. During the second time period T2, these four voltage curves 310, 312, 320, 322 coincide with two voltage curves 314, 324, since the time behavior of the self-discharge is independent of the series resistance R _L .

The switch-on and switch-off moments of the constant current source 20 are particularly interesting and important for the calculation. The line resistance can be determined directly from the jumps 330, 340 that can be seen in the voltage profile U1. The time behavior of the self-discharge is only characterized by a time constant that depends on the capacitance C and the parallel resistance Rs.

The following differential equation of the voltage U applies to the charging process in the period T1: $$u={\mathit{IR}}_L+R_S\left(I-C\frac{\partial u}{\partial t}\right)$$

It is assumed that the capacitor is completely discharged at the beginning of each measurement, i.e. before the time period T1. With U(t=0) =0, a solution to equation (1) is given by $$\begin{array}{l}u\left(t\right)=I\left[R_L+R_S\left(1-e^{-\frac{t-T_S}{R_{S}C}}\right)\right]\\ u\left(0-\right)=0\\ u\left(0+\right)={\mathit{IR}}_L\end{array}$$

During the self-discharge, ie during the time period T2, no voltage drops across the series resistance R _L . Therefore, the standard capacitor discharge equation can be used $$\begin{array}{l}u\left(t\right)=u\left(T_L+\right)e^{-\frac{t-T_L}{R_{S}C}}\\ u\left(T_L+\right)=u_C\left(T_L-\right)\end{array}$$

The forced discharge during the third period T3 is not considered. The discharge time only has to be long enough for the chargeable energy store 12 to be completely discharged at the start of the next measurement.

The above explained and in 2 The 3-part measurement curve outlined is preferably repeated periodically to determine the resistance values. Discrete voltage values are available for each measurement, which can be divided into charging and self-discharging processes. An advantage of the solution according to the invention lies in the short time required for detecting a fault, which is in the range of a few milliseconds.

The voltage profile U(t) is subsequently divided into corresponding measurement value profiles U1, U2 and U3 for further processing in the time periods T1, T2 and T3. In particular, therefore, measured value vectors U1 and U2 are available from the voltage detection unit 30, which are detected during the time periods T1 and T2. The aim of the following calculations is to determine the parameters R _L and Ps and, incidentally, C from U1 and U2 as precisely as possible.

Equations (2) and (3), in which these parameters occur, are considered for this purpose. It is noticeable that there are two unknowns in Equation (3): The time constant τ = R _S * C and the starting value U ( T _L +) . The control unit 40 preferably first determines these constants before determining the remaining unknowns in a separate subsequent step using equation (2).

As mentioned, the goal is to make statements about the parameters based on the recorded series of measurements of the voltage curves U1 and U2. Equations (2) and (3) define the course of the voltage values over time, with the parameters that best simulate the course of the curve being determined via an estimation or approximation. In this example, the least squares method is used for this, with which N observed measured values are reduced to a

function are projected, in this case onto a first-order linear equation of time t: $$y\left(t\right)=a+\mathit{\beta t}$$

$$Q\left(\alpha ,\beta \right)={\displaystyle \sum _{i=1}^N{\epsilon }_i}={\displaystyle \sum _{i=1}^N{\left(y_i-\alpha -{\mathit{\beta t}}_i\right)}^2}\stackrel{!}{=}\mathit{min}$$

$$\widehat{\alpha }=\bar{y}-\widehat{\beta }\bar{t}$$

$$\widehat{\beta }=\frac{{\displaystyle {\sum }_{i=1}^N\left(t_i-\bar{t}\right)\left(y_i-\bar{y}\right)}}{{\displaystyle {\sum }_{i=1}^N{\left(t_i-\bar{t}\right)}^2}}=\frac{\mathit{cov}\left(t,y\right)}{\mathit{var}\left(t\right)}$$

With the least squares method, an associated measurement error ε _i is added to the measurement values y _i recorded at the respective associated times t _i , which describes a deviation from the ideal measurement curve: $$y_i=a+{\mathit{\beta t}}_i+e_i$$

$$Q\left(a,\beta \right)={\displaystyle \sum _{i=1}^N{e}_i}={\displaystyle \sum _{i=1}^N{\left(y_i-a<figure-callout\; id="2"\; label="-\; \beta t\; i"\; filenames="imgf0001.png"\; state="\{\{state\}\}">-</figure-callout>{\mathit{\beta t}}_i{}_{}\right)}^2}\stackrel{!}{=}\mathit{at\; least}$$

$$\widehat{a}=\bar{y}-\widehat{\beta }\bar{t}$$

$$\widehat{\beta }=\frac{{\displaystyle {\sum }_{i=1}^N\left(t_i-\bar{t}\right)\left(y_i-\bar{y}\right)}}{{\displaystyle {\sum }_{i=1}^N{\left(t_i-\bar{t}\right)}^2}}=\frac{\mathit{cov}\left(t,y\right)}{\mathit{var}\left(t\right)}$$

The least squares method first adds the squares of the individual measurement errors ε _i to a sum Q that depends on the two parameters α and β . Subsequent minimization of this sum leads to the best estimates α̂ β̂ for the parameters α and β .

As mentioned, Equation (3) is first used for the self-discharge process during the time period T2, since this is only influenced by two of the three parameters. For the sake of simplicity, the point in time at which the constant current source 20 is switched off is shifted to the zero point in time: $$\begin{array}{c}u\left(t\right)=u\left(T_L+\right)e^{-\frac{t}{R_{S}C}}\\ \tau =R_{S}C\\ u\left(t\right)=u\left(T_L+\right)e^{-\frac{t}{\tau }}\end{array}$$

This equation does not depend linearly but exponentially on the time t. The equation is therefore exponential and therefore not linear and must be logarithmized on both sides in the first order of the time t in order to convert it into a linear equation.

$$\log \left(e^x\right)=x$$

$$\log \left(U\left(t\right)\right)=\log (U\left(T_L+\right)-\frac{t}{\tau }$$

$$\log \left(U\left(t\right)\right)={\alpha }_2+{\beta }_{2}t$$

$${\alpha }_2=\log \left(U\left(T_L+\right)\right)$$

$${\beta }_2=-\frac{1}{\tau }$$

The usual arithmetic laws for the natural logarithm are used here: $$\log \left(x\ast y\right)=\log \left(x\right)+\log \left(y\right)$$

$$\log \left(e^x\right)=x$$

$$\log \left(u\left(t\right)\right)=\log (u\left(T_L+\right)-\frac{t}{\tau }$$

$$\log \left(u\left(t\right)\right)=a_2+{\beta }_{2}t$$

$$a_2=\log \left(u\left(T_L+\right)\right)$$

$${\mathrm{<figure-callout\; id="2"\; label="\beta "\; filenames="imgf0001.png"\; state="\{\{state\}\}">\beta </figure-callout>}}_2=-\frac{1}{\tau }$$

Equation (4) shows the now linear form with respect to t. This means that all recorded voltages U2 are first logarithmized. The least squares approach can then be applied to these values in a simple manner, see equation (4).

The parameters α ₂ and β ₂ follow from the application of the least squares approach to all measured values during the self-discharge from U2. The time constant τ can then be determined using equation (6): $$\tau =-\frac{1}{{\mathrm{<figure-callout\; id="2"\; label="\beta "\; filenames="imgf0001.png"\; state="\{\{state\}\}">\beta </figure-callout>}}_2}$$

The desired parameters R _S , R _L and C are therefore still unknown. However, they can now be determined by looking at the loading process.

Equation (2) already described the voltage curve of the charging process. Shifted to zero in time and using the time constant τ , it can be written as $$u\left(t\right)=I\left[R_L+R_S\left(1-e^{-\frac{t}{\tau }}\right)\right]$$

In contrast to the discharge curve, this exponential curve also has an offset. It cannot therefore be calculated directly using the least squares approach.

$$U\left(t\right)={\alpha }_1+{\beta }_1{e}^{-\frac{t}{\tau }}$$

$${\alpha }_1=I\left(R_L+R_S\right)$$

$${\beta }_1=-{\mathit{IR}}_S$$

However, the time constant τ is already determined. Equation (7) can therefore be rewritten in a linear form, cf. Equation (8): $$u\left(t\right)=I\left(R_L+R_S\right)-{\mathit{IR}}_S{e}^{-\frac{t}{\tau }}$$

$$u\left(t\right)=a_1+{\beta }_1{e}^{-\frac{t}{\tau }}$$

$$a_1=I\left(R_L+R_S\right)$$

$${\beta }_1=-{\mathit{IR}}_S$$

All that is required is to calculate the corresponding exponential function for each time value using the known time constant τ .

$$R_L=\frac{{\alpha }_1}{I}-R_S$$

$$C=\frac{\tau }{R_S}$$

The parameters α ₁ and β ₁ follow from the application of the least squares approach to all measured values U1, ie from the period T1. Finally, the desired parameters R _S , R _L and C can be calculated directly using equations (10, 9, 3a): $$R_S=-\frac{{\beta }_1}{I}$$

$$R_L=\frac{a_1}{I}-R_S$$

$$C=\frac{\tau }{R_S}$$

As a result, this means that after each charging-self-discharging curve, the required values can be specified precisely using only two least-squares estimates to be carried out.

The time durations T1, T2 and T3 can be, for example, in the range of fractions of a millisecond, in particular 0.1-1 ms, and particularly preferably 0.5 ms, or a few milliseconds. Due to the short measurement duration, an appropriately high rate of repetition of the measurement is possible.

List of References

1

Device for monitoring a two-wire line

2

two-wire line

4, 6

Output terminal of the two-wire line

8th

Termination of the two-wire line

10

closing component

12

chargeable energy storage

20

constant current source

30

voltage detection unit

40

control unit

45

control unit

50

consumers with reverse polarity protection

52

diode

54

Resistance

60

unloading unit

100

Fire alarm and/or extinguishing control panel

RL

series resistance

Rs

parallel resistor

C

capacity

I1

measuring current

U(t)

voltage curve

T1

first period

T2

second period

T3

third period

300

diagram

310, 312, 314, 320, 322, 324, 326

voltage curve

330

voltage jump

340

voltage jump

Claims (12)

1. A device (1) for monitoring a two-wire line (2), in particular a two-wire line (2) of a fire protection system, comprising

   a passive terminating component (10) for terminating the two-wire line (2), wherein the passive terminating component has a chargeable energy storage (12),

   a constant current source (20) for providing a measuring current (11) to the passive terminating component,

   a voltage detection unit (30) for detecting a voltage curve (U(t)) at output terminals (4, 6) of the two-wire line (2),

   a control unit (40) for controlling the constant current source (20) and for evaluating the detected voltage curve (U(t)), the control unit (40) being configured to determine a series resistance (R_L) and a parallel resistance (Rs) of the two-wire line (2), the control unit being configured to evaluate the voltage curve (U(t)) in response to a change in the provided measuring current (11) and to charge the chargeable energy storage (12) during a predetermined first period (T1) by controlling the constant current source (20) and to evaluate a self-discharging of the chargeable energy storage (12) during a subsequent second period (T2) after the switching off of the constant current source (20).
2. The device (1) according to claim 1, wherein
   the chargeable energy storage (12) of the passive terminating component (10) is designed as a capacitor that is arrangeable between the two wires of the two-wire line (2).
3. The device (1) according to claim 2, wherein
   the capacitor has a capacitance (C) that is above 0.1 µF, particularly above 1 µF, and particularly preferred in the range from 1 µF to 10 µF.
4. The device (1) according to claim 1, wherein
   the control unit is configured to determine the series resistance (R_L) and the parallel resistance (Rs) of the two-wire line (2) from the voltage curve (U(t)) over time during the first (T1) and second (T2) period.
5. The device (1) according to claim 4, wherein
   the control unit is configured to determine the parallel resistance (Rs) and the series resistance (R_L) of the two-wire line (2) on the basis of two approximations, based on one another, of the voltage curve (U(t)) during the first (T1) and second (T2) period.
6. The device (1) according to claim 5, wherein
   the control unit is configured to use discrete values of the detected voltage curve (U(t)), in particular by means of the least squares method, to approximate constants of two linear equations of the voltage in the first order of a time-dependent variable during the first (T1) and second (T2) period.
7. The device (1) according to one of the preceding claims, wherein
   the control unit is designed to monitor multiple two-wire lines (2).
8. A method for monitoring a two-wire line (2), in particular of a fire protection system, the method including

   providing a measuring current (11) to a passive terminating component (10) for terminating the two-wire line (2), wherein the passive terminating component (10) comprises a chargeable energy storage (12),

   detecting a voltage curve (U(t)) at output terminals (4, 6) of the two-wire line (2),

   evaluating the detected voltage curve (U(t)) in order to determine a series resistance (R_L) and a parallel resistance (Rs) of the two-wire line (2),

   wherein the measuring current (11) is provided in a first period (T1) for charging the chargeable energy storage (12) and is not provided in a subsequent second period (T2), wherein a voltage curve (U(t)) at the output terminals (4, 6) is detected and evaluated during the first period (T1) and the second period (T2).
9. The method according to claim 8, wherein the parallel resistance (Rs) and the series resistance (R_L) of the two-wire line (2) are determined on the basis of two approximations, based on one another, of the voltage curve (U(t)) during the first (T1) and second (T2) period.
10. The method according to claim 9, wherein
    discrete values of the detected voltage curve (U(t)) are used to determine the parallel resistance (Rs) and the series resistance (R_L) from approximated constants of two linear equations of the voltage in the first order of a time-dependent variable during the first (T1) and second (T2) period.
11. A control module of a fire alarm and/or extinguishing control center for monitoring a two-wire line (2) of a fire protection system, wherein the control module is configured to carry out the method according to one of claims 8 to 10.
12. The use of a capacitor as a passive terminating component (10) for terminating a two-wire line (2) of a fire protection system in a device for monitoring the two-wire line (2) according to one of claims 1 to 7.

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